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Selective and Divergent Synthesis of Naphthalene- and Phenanthrene-Fused Azahelicenes by Turning Rearrangement On or Off

Chihiro Maeda, Sayaka Michishita, Tadashi Ema

Chemistry - A European Journal 2025年

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

The Scholl reaction has been used to synthesize a variety of polycyclic aromatic hydrocarbons, where 1,2-aryl shifts have sometimes occurred to yield unique rearrangement products. However, such 1,2-aryl shifts are often uncontrollable, and the selective and divergent synthesis with or without rearrangement is desired. Here, we achieved the control of the rearrangement in the Scholl reaction of carbazoles by changing the N-substituents. The Scholl reaction of 3,6-bis{2-(2-naphthyl)phenyl}carbazoles and 3,6-bis{2-(9-phenanthrenyl)phenyl}carbazoles with an N-benzyl group gave multiple azahelicenes via double rearrangement, while those with an N-benzoyl group gave aza[9]helicene and quadruple [4]helicene in the former and latter cases, respectively. The reaction mechanisms on the divergent reaction pathways were investigated by DFT calculations, which well supported the experimental results.

DOI： 10.1002/chem.202404325

B,N-Embedded Helical Nanographenes Showing an Ion-Triggered Chiroptical Switching Function 査読

Chihiro Maeda, Sayaka Michishita, Issa Yasutomo, Tadashi Ema

Angewandte Chemie - International Edition 2025年

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

Intramolecular oxidative aromatic coupling of 3,6-bis(m-terphenyl-2’-yl)carbazole provided a bis(m-terphenyl)-fused carbazole, while that of 3,6-bis(m-terphenyl-2’-yl)-1,8-diphenylcarbazole afforded a bis(quaterphenyl)-fused carbazole. Borylation of the latter furnished a B,N-embedded helical nanographene binding a fluoride anion via a structural change from the three-coordinate boron to the four-coordinate boron. The anionic charge derived from the fluoride anion is stabilized over the expanded π-framework, which leads to the high binding constant (Ka) of 1×105 M−1. The four-coordinate boron species was converted back to the parent three-coordinate boron species with Ag+, and the chiroptical switch between the three-coordinate boron and four-coordinate boron species has been achieved via the ion recognition with the change in the color and glum values.

DOI： 10.1002/anie.202418546

Terpolymerization reactions of epoxides, CO<inf>2</inf>, and the third monomers toward sustainable CO<inf>2</inf>-based polymers with controllable chemical and physical properties 招待査読

Koichi Nakaoka, Tadashi Ema

Chemical Communications 61 ( 1 ) 46 - 60 2025年

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

Carbon dioxide (CO2) serves as a cheap, abundant, and renewable C1 building block for the synthesis of organic compounds and polymers. Selective and efficient CO2 fixation processes are still challenging because of the kinetic and thermodynamic stability of CO2. Among various CO2 fixation processes, the ring-opening copolymerization (ROCOP) of epoxides and CO2 gives aliphatic polycarbonates with high atom economy, although the chemical and physical properties of the resulting polycarbonates are not necessarily satisfactory. Introducing the third monomers into this ROCOP system provides new terpolymers, and the thermal, optical, mechanical or degradation properties can be added or tuned by incorporating new polymer backbones derived from the third monomers at the expense of the CO2 content. Here we review the terpolymerization reactions of epoxides, CO2, and the third monomers such as cyclic anhydrides, lactones, lactides, heteroallenes, and olefins. The development of catalysts and the control of the polymer structures are described together with the chemical and physical properties of the resulting polymers.

DOI： 10.1039/d4cc04615c

Synthesis and Postfunctionalization of Acrylate-Appended Poly(cyclohexene carbonate)s: Modulation of Properties of CO<inf>2</inf>-Based Polymers 査読

Chihiro Maeda, Hina Inoue, Tadashi Ema

Macromolecules 58 ( 3 ) 1571 - 1577 2025年

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

Functional CO2-based polycarbonates are expected to be sustainable materials. Herein, a bifunctional aluminum porphyrin catalyzed the terpolymerization of cyclohexene oxide (CHO), acrylate-appended CHO, and CO2 to provide poly(cyclohexene carbonate)s (PCHCs) with acrylate groups. Postfunctionalization of PCHCs via Michael addition or Heck reaction enabled the incorporation of thiol, amine, and aromatics into PCHCs with high selectivity and efficiency. PCHCs with the flexible long alkyl chains showed a glass-transition temperature (Tg) of down to 52 °C, which was much lower than that of PCHC (127 °C). In sharp contrast, PCHCs with rigid pyrenyl groups showed Tg values of up to 152 °C and fluorescence emission. Thus, a wide range of polymers were obtained by robust and sustainable synthetic methods, and the functional groups modulated the properties of the CO2-based polycarbonates.

DOI： 10.1021/acs.macromol.4c02881

Recent development of azahelicenes showing circularly polarized luminescence 招待査読

Chihiro Maeda, Tadashi Ema

Chemical Communications 61 ( 25 ) 4757 - 4773 2025年

Terpolymerization of Propylene Oxide, CO<inf>2</inf>, and p-Toluenesulfonyl Isocyanate for the Synthesis of Poly(urethane-carbonate): p-Toluenesulfonyl Isocyanate Acts as a Backbiting Suppressor

Satoshi Muranaka, Io Yamamoto, Tadashi Ema

ACS Applied Polymer Materials 6 ( 24 ) 15366 - 15374 2024年12月

掲載種別：研究論文（学術雑誌）

Terpolymerization of propylene oxide, CO2, and p-toluenesulfonyl isocyanate (TsNCO) was catalyzed by bifunctional AlIII porphyrin catalysts to afford polyurethane-poly(propylene carbonate), PU-PPC, with high CO2 contents of up to 39 wt %. TsNCO acted as a backbiting suppressor at the initial stage of the terpolymerization, contributing to the selective formation of PU-PPC. In contrast to the high electrophilicity of TsNCO, the carbamate anion generated by the reaction of TsNCO with the alkoxide intermediate has modest nucleophilicity owing to the tosyl group, which allows for the smooth formation of the PU units and the subsequent elongation of the PPC units on the catalyst to selectively produce PU-PPC. Terpolymers having the PU and PPC units in a 1:1 ratio had glass transition temperature (Tg) of 86-104 °C, while those with higher PPC contents had Tg values of 39-40 °C. Block copolymer PU-b-PPC, which was synthesized in a one-pot two-step manner, showed two Tg values at 45 and 76 °C. Pure PU showed 10% weight loss temperature (Td10) at 230 °C, while PU-PPC with high PPC contents showed Td10 at 236-254 °C. They were degradable upon UV light irradiation and heat treatment, while they were resistant to acid. The terpolymerization strategy using TsNCO as a backbiting suppressor potentially enables one to create CO2-based polymers such as plastics and elastomers with degradability controlled by UV light or heat.

DOI： 10.1021/acsapm.4c03431

Cyclic Azahelicene Dimers Showing Bright Circularly Polarized Luminescence and Selective Fluoride Recognition 査読

Chihiro Maeda, Issa Yasutomo, Tadashi Ema

Angewandte Chemie - International Edition 63 ( 30 ) e202404149 2024年7月

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed-aza[7]helicenes with (1R)-menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid π-frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region.

DOI： 10.1002/anie.202404149

Temperature-Induced Sign Inversion of Circularly Polarized Luminescence of Binaphthyl-Bridged Tetrathiapyrenophanes 査読

Kazuto Takaishi, Fumiya Yoshinami, Yoshihiro Sato, Tadashi Ema

Chemistry - A European Journal 30 ( 32 ) e202400866 2024年6月

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

D2-symmetric (R)-binaphthyl-bridged pyrenophanes containing thioether bonds were synthesized. The pyrenophanes exhibited the temperature-induced sign inversion of circularly polarized luminescence (CPL) while maintaining the emission wavelength and reversibility. The Δglum value reached 0.02, and the FL quenching by heat was negligible. The sign inversion of CPL originates from the inversion of intramolecular excimer chirality associated with excitation dynamics. The two pyrenes form a kinetically trapped left-handed twist excimer at low temperatures, while they form a thermodynamically favored right-handed twist excimer at high temperatures. The thioether linkers can impart flexibility suitable for the inversion of chirality of the excimers.

DOI： 10.1002/chem.202400866

Skeletal Formation of Carbocycles with CO<inf>2</inf>: Selective Synthesis of Indolo[3,2-b]carbazoles or Cyclophanes from Indoles, CO<inf>2</inf>, and Phenylsilane 査読

Sha Li, Shoko Nakahara, Taishin Adachi, Takumi Murata, Kazuto Takaishi, Tadashi Ema

Journal of the American Chemical Society 146 ( 22 ) 14935 - 14941 2024年6月

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

The catalytic reactions of indoles with CO2 and phenylsilane afforded indolo[3,2-b]carbazoles, where the fused benzene ring was constructed by forming two C-H bonds and four C-C bonds with two CO2 molecules via deoxygenative conversions. Nine-membered cyclophanes made up of three indoles and three CO2 molecules were also obtained, where the cyclophane framework was constructed by forming six C-H bonds and six C-C bonds. These multicomponent cascade reactions giving completely different carbocycles were switched simply by choosing the solvent, acetonitrile or ethyl acetate.

DOI： 10.1021/jacs.4c04097

Synthesis of hydroxy acids via the light-driven carboxylation of epoxides with CO<inf>2</inf> 査読

Chihiro Maeda, Ren Kumemoto, Rio Tanaka, Tadashi Ema

Chemistry Letters 53 ( 5 ) upae086 2024年5月

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

Light-driven ring-opening carboxylation of epoxides with CO2 provided β-hydroxy acids via sequential single electron transfer (SET), followed by reaction with CO2. This reaction condition was applicable to aryl epoxides and oxetanes with (hetero)polycyclic aromatics to give the corresponding β- and γ-hydroxy acids, respectively, with high chemoselectivity.

DOI： 10.1093/chemle/upae086

Terpolymerizations of cyclohexene oxide, CO<inf>2</inf>, and isocyanates or isothiocyanates for the synthesis of poly(carbonate-urethane)s or poly(carbonate-thioimidocarbonate)s 査読

Koichi Nakaoka, Satoshi Muranaka, Io Yamamoto, Tadashi Ema

Polymer Chemistry 15 ( 8 ) 707 - 713 2024年1月

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

Terpolymerization of cyclohexene oxide (CHO), CO2, and aryl isothiocyanates produced poly(carbonate-thioimidocarbonate)s with gradient character, while that of CHO, CO2, and aryl isocyanates furnished poly(carbonate-urethane)s with random sequences. The former underwent partial degradation upon acid treatment or UV irradiation, while the latter was stable under the same conditions.

DOI： 10.1039/d3py01165h

Selective Conversions of CO<inf>2</inf> into Value-Added Chemicals via Cooperative Catalysis Using Multifunctional Catalysts 査読

Tadashi Ema

Bulletin of the Chemical Society of Japan 96 ( 7 ) 693 - 701 2023年7月

担当区分：筆頭著者,　責任著者掲載種別：研究論文（学術雑誌）

Carbon dioxide (CO2) is not only a greenhouse gas but also a renewable carbon source for organic synthesis. Here we have summarized our studies on the conversions of CO2 into value-added chemicals via cooperative catalysis using multifunctional catalysts. For example, bifunctional metalloporphyrin catalysts with quaternary ammonium halides were developed for the selective synthesis of cyclic carbonates or polycarbonates from epoxides and CO2. Bifunctional MgII and ZnII porphyrins showed high catalytic activity for the synthesis of cyclic carbonates, while bifunctional AlIII porphyrins catalyzed the copolymerization of cyclohexene oxide and CO2 to give poly(cyclohexene carbonate). The high catalytic activities resulted from the cooperative action of the central metal ion and the quaternary ammonium salts. Chiral catalysts for the kinetic resolution of terminal or internal epoxides with CO2 were also developed. In addition, macrocyclic multinuclear metal complex Zn5L3, which was synthesized by the self-assembly of Zn(OAc)2 and a BINOL derivative (L), catalyzed the reduction of CO2 with phenylsilane to produce various useful synthetic intermediates and organic compounds.

DOI： 10.1246/bcsj.20230099

Synthesis and Photophysical Properties of Dihetero[8]circulenes 査読

Chihiro Maeda, Koki Akiyama, Tadashi Ema

Organic Letters 25 ( 21 ) 3932 - 3935 2023年6月

One‐Pot Synthesis of Aldehydes or Alcohols from CO 2 via Formamides or Silyl Formates 査読

Fan Yang, Yuta Saiki, Koichi Nakaoka, Tadashi Ema

Advanced Synthesis & Catalysis 365 ( 6 ) 877 - 883 2023年3月

One-Pot Synthesis of Dihydropyrans via CO2 Reduction and Domino Knoevenagel/oxa-Diels–Alder Reactions 査読

Kazuto Takaishi, Ritsuki Nishimura, Yuha Toda, Hajime Morishita, Tadashi Ema

Organic Letters 25 ( 9 ) 1370 - 1374 2023年3月

Circularly polarized luminescence from porphyrin-containing (supra)molecular systems 招待査読

Chihiro Maeda, Issa Yasutomo, Kazuto Takaishi, Tadashi Ema

Journal of Porphyrins and Phthalocyanines 27 ( 07n10 ) 903 - 911 2023年2月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：World Scientific Pub Co Pte Ltd

Functional dyes showing circularly polarized luminescence (CPL) have attracted considerable attention. Porphyrins and porphyrinoids have characteristic properties useful for the development of CPL materials, although the examples of CPL-active porphyrins and porphyrinoids are still limited. Here we have summarized recent progress in CPL-active systems containing porphyrins or phthalocyanines, which are classified into the following four categories: (i) porphyrins with chiral sources; (ii) axially chiral porphyrin dimers; (iii) self-assembled porphyrins; (iv) porphyrin-sensitized CPL dyes.

DOI： 10.1142/s108842462330001x

Circularly polarized luminescence in molecular recognition systems: Recent achievements 招待査読

Kazuto Takaishi, Chihiro Maeda, Tadashi Ema

Chirality 35 ( 2 ) 92 - 103 2023年2月

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）出版者・発行元：Wiley

Abstract

Circularly polarized luminescence (CPL) dyes are recognized to be new generation materials and have been actively developed. Molecular recognition systems provide nice approaches to novel CPL materials, such as stimuli‐responsive switches and chemical sensing materials. CPL may be induced simply by mixing chiral or achiral, luminescent or nonluminescent host and guest; there are several combinations. Molecular recognition can potentially save time and effort to construct well‐ordered chiral structures with noncovalent attractive interactions as compared with the multi‐step synthesis of covalently bonded dyes. It is a challenging subject to engage molecular recognition events with CPL, and it is important and interesting to see how it is achieved. In fact, simple molecular recognition systems can even enable the fine adjustment of CPL performance and detailed conformational/configurational analysis of the excited state. Here we overview the recent achievements of simple host–guest complexes capable of exhibiting CPL, summarizing concisely the host/guest structures, CPL intensities, and characteristics.

DOI： 10.1002/chir.23522

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/chir.23522

Cu-catalyzed carboxylation of organoboronic acid pinacol esters with CO2 査読

Chihiro Maeda, Takumi Cho, Ren Kumemoto, Tadashi Ema

Organic & Biomolecular Chemistry 21 ( 32 ) 6565 - 6571 2023年

Catalytic synthesis and physical properties of CO2-based cross-linked poly(cyclohexene carbonate)s 査読

Chihiro Maeda, Kenta Kawabata, Kaito Niki, Yuma Sako, Takumi Okihara, Tadashi Ema

Polymer Chemistry 14 ( 37 ) 4338 - 4343 2023年

Synthesis of Enamines, Aldehydes, and Nitriles from CO₂: Scope of the One-Pot Strategy via Formamides 査読

Nakaoka, K., Guo, C., Saiki, Y., Furukawa, S., Ema, T.

Journal of Organic Chemistry 88 ( 21 ) 15444 - 15451 2023年

Synthesis of Trimethylene Carbonates and Polycarbonates from Oxetanes and CO2 Using Bifunctional Aluminum Porphyrin Catalysts 査読

Chihiro Maeda, Hina Inoue, Ayano Ichiki, Takumi Okihara, Tadashi Ema

ACS Catalysis 12 ( 22 ) 13042 - 13049 2022年10月

Mechanism of BPh3‐Catalyzed N‐Methylation of Amines with CO2 and Phenylsilane: Cooperative Activation of Hydrosilane 査読

Manussada Ratanasak, Takumi Murata, Taishin Adachi, Jun‐ya Hasegawa, Tadashi Ema

Chemistry – A European Journal 28 ( 58 ) e202202210 2022年10月

Binaphthyl‐Bridged Pyrenophanes: Intense Circularly Polarized Luminescence Based on a D 2 Symmetry Strategy 査読

Kazuto Takaishi, Sho Murakami, Fumiya Yoshinami, Tadashi Ema

Angewandte Chemie International Edition 61 ( 26 ) e202204609 2022年7月

Ruthenium Complexes Bearing Axially Chiral Bipyridyls: The Mismatched Diastereomer Showed Red Circularly Polarized Phosphorescence 査読

Kazuto Takaishi, Yusuke Nakatsuka, Hitomi Asano, Yuya Yamada, Tadashi Ema

Chemistry – A European Journal 28 ( 6 ) e202104212 2022年1月

Deoxygenative CO2 conversions with triphenylborane and phenylsilane in the presence of secondary amines or nitrogen-containing aromatics 査読

Takumi Murata, Mahoko Hiyoshi, Shinsuke Maekawa, Yuta Saiki, Manussada Ratanasak, Jun-ya Hasegawa, Tadashi Ema

Green Chemistry 24 ( 6 ) 2385 - 2390 2022年

Enhancement of protein thermostability by three consecutive mutations using loop-walking method and machine learning 査読

Kazunori Yoshida, Shun Kawai, Masaya Fujitani, Satoshi Koikeda, Ryuji Kato, Tadashi Ema

Scientific Reports 11 ( 1 ) 2021年12月

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）

We developed a method to improve protein thermostability, “loop-walking method”. Three consecutive positions in 12 loops of Burkholderia cepacia lipase were subjected to random mutagenesis to make 12 libraries. Screening allowed us to identify L7 as a hot-spot loop having an impact on thermostability, and the P233G/L234E/V235M mutant was found from 214 variants in the L7 library. Although a more excellent mutant might be discovered by screening all the 8000 P233X/L234X/V235X mutants, it was difficult to assay all of them. We therefore employed machine learning. Using thermostability data of the 214 mutants, a computational discrimination model was constructed to predict thermostability potentials. Among 7786 combinations ranked in silico, 20 promising candidates were selected and assayed. The P233D/L234P/V235S mutant retained 66% activity after heat treatment at 60 °C for 30 min, which was higher than those of the wild-type enzyme (5%) and the P233G/L234E/V235M mutant (35%).

DOI： 10.1038/s41598-021-91339-4

Chiral exciplex dyes showing circularly polarized luminescence: Extension of the excimer chirality rule

Kazuto Takaishi, Sho Murakami, Kazuhiro Iwachido, Tadashi Ema

Chemical Science 12 ( 43 ) 14570 - 14576 2021年11月

掲載種別：研究論文（学術雑誌）

A series of axially chiral binaphthyls and quaternaphthyls possessing two kinds of aromatic fluorophores, such as pyrenyl, perylenyl, and 4-(dimethylamino)phenyl groups, arranged alternately were synthesized by a divergent method. In the excited state, the fluorophores selectively formed a unidirectionally twisted exciplex (excited heterodimer) by a cumulative steric effect and exhibited circularly polarized luminescence (CPL). They are the first examples of a monomolecular exciplex CPL dye. This versatile method for producing exciplex CPL dyes also improved fluorescence intensity, and the CPL properties were not very sensitive to the solvent or to the temperature owing to the conformationally rigid exciplex. This systematic study allowed us to confirm that the excimer chirality rule can be applied to the exciplex dyes: left- and right-handed exciplexes with a twist angle of less than 90° exhibit (-)- and (+)-CPL, respectively. This journal is

DOI： 10.1039/d1sc04403f

Facile Synthesis of Azahelicenes and Diaza[8]circulenes through the Intramolecular Scholl Reaction

Chihiro Maeda, Shuichi Nomoto, Koki Akiyama, Takayuki Tanaka, Tadashi Ema

Chemistry - A European Journal 27 ( 63 ) 15699 - 15705 2021年11月

掲載種別：研究論文（学術雑誌）

Carbazole-based aza[7]helicenes and hetero[9]helicenes were successfully obtained via the intramolecular Scholl reaction of 3,6-bis(biphenyl-2-yl)carbazole congeners, while the reaction of 3,6-bis(naphthylphenyl)-appended carbazole gave a triple helicene via an unexpected simultaneous double aryl rearrangement. DFT calculations suggested that the rearrangement proceeded via an arenium cation intermediate. In addition, the reaction of methoxy-appended substrate gave an azahepta[8]circulene via the concurrent C−C bond formation. These helical dyes showed circularly polarized luminescence. The azahepta[8]circulene was further transformed into deeply saddle-distorted dibenzodiaza[8]circulenes as the first example of its solution-based synthesis and unambiguous structural determination.

DOI： 10.1002/chem.202102269

C-Methylenation of anilines and indoles with CO<inf>2</inf>and hydrosilane using a pentanuclear zinc complex catalyst

Kazuto Takaishi, Hiroyasu Kosugi, Ritsuki Nishimura, Yuya Yamada, Tadashi Ema

Chemical Communications 57 ( 65 ) 8083 - 8086 2021年8月

掲載種別：研究論文（学術雑誌）

The one-stepC-methylenation of anilines and indoles with CO2and phenylsilane was catalyzed by a pentanuclear ZnIIcomplex to give diarylmethanesviageminal C-H and C-C bond formation. It is proposed that the zinc-hydride complex generatedin situis a catalytically active species and that bis(silyl)acetal is a key intermediate. When aniline was used as a substrate, both theC-methylenation andN-methylation proceeded.

DOI： 10.1039/d1cc03675k

Circularly Polarized Luminescence Liquids Based on Siloxybinaphthyls: Best Binaphthyl Dihedral Angle in the Excited State

Kazuto Takaishi, Tomoki Matsumoto, Miyu Kawataka, Tadashi Ema

Angewandte Chemie - International Edition 60 ( 18 ) 9968 - 9972 2021年4月

掲載種別：研究論文（学術雑誌）

A series of axially chiral 1,1′-binaphthyls with trialkylsiloxy (OSiR3) groups were synthesized. Among them, 1 a–c possessing OSiR3 groups at the 7,7′-positions and methyl groups at the 2,2′-positions were liquids at room temperature, and the neat liquids showed circularly polarized luminescence (CPL) (R=Bu; Φfl,liquid=0.21, |glum,liquid|=1.6×10−3). The |glum,liquid| value is the highest of pure liquids. These compounds remained liquid over a broad range of temperatures, down to −50 °C. Time-dependent DFT calculations indicated that in the excited state, the binaphthyls adopt a transoid conformation with a small angle between the electric and magnetic transition dipole moments (θμ,m=77°), which is a key factor in their CPL activity. The best binaphthyl dihedral angle in the excited state is approximately 110°.

DOI： 10.1002/anie.202101226

Synthesis and electronic properties of carbazole-based core-modified diporphyrins showing near infrared absorption

Chihiro Maeda, Takuma Shirakawa, Tadashi Ema

Chemical Communications 56 ( 95 ) 15048 - 15051 2020年12月

掲載種別：研究論文（学術雑誌）

Directly linked carbazole-based core-modified diporphyrin D2 and fused diporphyrin F2 were synthesized. These diporphyrins showed significant electronic interactions and conjugation allowing for redshifted near infrared (NIR) absorption and small HOMO-LUMO gaps as confirmed by NIR absorption spectroscopy, cyclic voltammetry (CV) measurements, and DFT calculations. This journal is

DOI： 10.1039/d0cc06289h

Aggregation-Induced Circularly Polarized Luminescence from Boron Complexes with a Carbazolyl Schiff Base

Chihiro Maeda, Shuichi Nomoto, Kazuto Takaishi, Tadashi Ema

Chemistry - A European Journal 26 ( 57 ) 13016 - 13021 2020年10月

掲載種別：研究論文（学術雑誌）

A variety of carbazolyl-appended Schiff bases were readily synthesized from 1-formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole-based BODIPY analogues showing solid-state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et2AlCl-mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation-induced fluorescence and circularly polarized luminescence (CPL) with the ΦF and glum of up to 0.22 and −3.5×10−3, respectively, in the solid state. The solid-state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations.

DOI： 10.1002/chem.202001463

Tetrameric and Hexameric Porphyrin Nanorings: Template Synthesis and Photophysical Properties

Chihiro Maeda, Shoki Toyama, Naoki Okada, Kazuto Takaishi, Seongsoo Kang, Dongho Kim, Tadashi Ema

Journal of the American Chemical Society 142 ( 37 ) 15661 - 15666 2020年9月

掲載種別：研究論文（学術雑誌）

Hexameric and tetrameric porphyrin nanorings, Z6T6 and Z4T4, were synthesized in 53% and 14% yields, respectively, by the Sonogashira-type self-oligomerization of porphyrin monomer 1 using hexadentate template T6 and tetrapyridylporphyrin template T4. Template-free nanorings Z6 and Z4 were also prepared. The femtosecond transient absorption measurements revealed fast excitation energy hopping (EEH) along these nanorings with hopping rates of 2-5 ps. Treatment of Z6 with chiral template CT6 gave Z6CT6 showing circular dichroism (CD) and circularly polarized luminescence (CPL) in the absorption and fluorescence regions of Z6, respectively, which indicates chirality transfer from CT6 to Z6.

DOI： 10.1021/jacs.0c07707

Aluminum porphyrins with quaternary ammonium halides as catalysts for copolymerization of cyclohexene oxide and CO<inf>2</inf>: metal-ligand cooperative catalysis

Jingyuan Deng, Manussada Ratanasak, Yuma Sako, Hideki Tokuda, Chihiro Maeda, Jun Ya Hasegawa, Kyoko Nozaki, Tadashi Ema

Chemical Science 11 ( 22 ) 5669 - 5675 2020年6月

掲載種別：研究論文（学術雑誌）

Bifunctional AlIIIporphyrins with quaternary ammonium halides,2-Cland2-Br, worked as excellent catalysts for the copolymerization of cyclohexene oxide (CHO) and CO2at 120 °C. Turnover frequency (TOF) and turnover number (TON) reached 10 000 h−1and 55 000, respectively, and poly(cyclohexene carbonate) (PCHC) with molecular weight of up to 281 000 was obtained with a catalyst loading of 0.001 mol%. In contrast, bifunctional MgIIand ZnIIcounterparts,3-Cland4-Cl, as well as a binary catalyst system,1-Clwith bis(triphenylphosphine)iminium chloride (PPNCl), showed poor catalytic performances. Kinetic studies revealed that the reaction rate was first-order in [CHO] and [2-Br] and zero-order in [CO2], and the activation parameters were determined: ΔH‡= 12.4 kcal mol−1, ΔS‡= −26.1 cal mol−1K−1, and ΔG‡= 21.6 kcal mol−1at 80 °C. Comparative DFT calculations on two model catalysts, AlIIIcomplex2′and MgIIcomplex3′, allowed us to extract key factors in the catalytic behavior of the bifunctional AlIIIcatalyst. The high polymerization activity and carbonate-linkage selectivity originate from the cooperative actions of the metal center and the quaternary ammonium cation, both of which facilitate the epoxide-ring opening by the carbonate anion to form the carbonate linkage in the key transition state such asTS3b(ΔH‡= 13.3 kcal mol−1, ΔS‡= −3.1 cal mol−1K−1, and ΔG‡= 14.4 kcal mol−1at 80 °C).

DOI： 10.1039/d0sc01609h

Synthesis of silyl formates, formamides, and aldehydesviasolvent-free organocatalytic hydrosilylation of CO<inf>2</inf>

Takumi Murata, Mahoko Hiyoshi, Manussada Ratanasak, Jun Ya Hasegawa, Tadashi Ema

Chemical Communications 56 ( 43 ) 5783 - 5786 2020年5月

掲載種別：研究論文（学術雑誌）

Carbon dioxide (CO2) was used as a C1 source to prepare silyl formates, formamides, and aldehydes. Tetrabutylammonium acetate (TBAA) catalyzed the solvent-freeN-formylation of amines with CO2and hydrosilane to give formamides including Weinreb formamide, Me(MeO)NCHO, which was successively converted into aldehydes by one-pot reactions with Grignard reagents.

DOI： 10.1039/d0cc01371d

Azahelicene-Fused BODIPY Analogues Showing Circularly Polarized Luminescence

Chihiro Maeda, Keiji Nagahata, Takuma Shirakawa, Tadashi Ema

Angewandte Chemie - International Edition 59 ( 20 ) 7813 - 7817 2020年5月

掲載種別：研究論文（学術雑誌）

Helical carbazole-based BODIPY analogues were readily synthesized via aza[7]helicenes. The structures of azahelicene-incorporated BF2 dyes were elucidated by x-ray diffraction analysis. DFT calculations revealed that the π-conjugated system expanded from the helicene moiety to the BODIPY framework. The azahelicene-fused boron complexes showed the Cotton effects and the circularly polarized luminescence (CPL) in the visible region. Furthermore, an axially chiral binaphthyl group was attached to the helically chiral dyes, which enhanced the chiroptical properties.

DOI： 10.1002/anie.202001186

Minimization of Amounts of Catalyst and Solvent in NHC-Catalyzed Benzoin Reactions of Solid Aldehydes: Mechanistic Consideration of Solid-to-Solid Conversion and Total Synthesis of Isodarparvinol B

Kenta Iwai, Masakazu Ono, Yoshiko Nanjo, Tadashi Ema

ACS Omega 5 ( 17 ) 10207 - 10216 2020年5月

掲載種別：研究論文（学術雑誌）

Attempts were made to minimize the amounts of catalyst and solvent in the NHC-catalyzed benzoin reactions of solid aldehydes. In some case, solid-to-solid conversions proceeded in the solvent-free NHC-catalyzed benzoin reactions. Even if a mixture of the substrate, N-heterocyclic carbene (NHC) precursor, and inorganic base was initially a powdery solid, the reaction did proceed at reaction temperature lower than the melting points of each compound. The solid mixture partially melted or became a slurry or suspension in the meantime. We call this solid/liquid mixture a semisolid state. The reaction giving an optically active product was faster than that giving a racemic mixture of the same product. Melting-point depression was observed for a series of mixtures of the substrate and product in different substrate/product ratios. Solvent-free solid-to-solid conversions were accelerated by the formation of a semisolid state resulting from the melting-point depression of the solid substrate accompanied by the product formation. In the case of solid substrates with high melting points, melting-point depression was useless, and the addition of a small amount of solvent was needed. The first total synthesis of isodarparvinol B was achieved via the NHC-catalyzed intramolecular benzoin reaction using a small amount of solvent as an additive.

DOI： 10.1021/acsomega.0c01141

Synthesis and Chiroptical Properties of Chiral Carbazole-Based BODIPYs

Chihiro Maeda, Keita Suka, Keiji Nagahata, Kazuto Takaishi, Tadashi Ema

Chemistry - A European Journal 26 ( 19 ) 4261 - 4268 2020年4月

掲載種別：研究論文（学術雑誌）

A series of carbazole-based boron dipyrromethenes (BODIPYs) 2 a–g bearing binaphthyl units have been synthesized by the Et2AlCl-mediated reaction of the corresponding BODIPY difluorides 1 a–g with 1,1′-binaphthalene-2,2′-diol. Substituents such as halogen, nitrile, and amino groups were tolerated under the reaction conditions, and the reaction of the phenylethynyl-substituted 1 h gave (R,R)-3 h bearing two binaphthyl units. The chiroptical properties of these dyes with different substituents were investigated by UV/Vis, CD, fluorescence, and circularly polarized luminescence (CPL) spectroscopy. The CD spectra showed Cotton effects in the absorption region of the BODIPY moieties. In addition, they showed CPL both in solution and in the solid state. Interestingly, several dyes recorded higher glum values in the solid state, probably due to intermolecular interactions. Because (R,R)-3 h recorded relatively low glum values, the diastereomer (R,S)-3 h was prepared. The (R,S) diastereomer showed intense CPL, which suggests a synergetic effect of the two binaphthyl groups. Finally, chiral carbazole-based BODIPY dimers have been synthesized for the first time and their chiroptical properties were investigated. They showed redshifted fluorescence and CPL, which reached the near-IR (NIR) region in the solid state.

DOI： 10.1002/chem.201904954

Solvent-Induced Sign Inversion of Circularly Polarized Luminescence: Control of Excimer Chirality by Hydrogen Bonding

Kazuto Takaishi, Kazuhiro Iwachido, Tadashi Ema

Journal of the American Chemical Society 142 ( 4 ) 1774 - 1779 2020年1月

掲載種別：研究論文（学術雑誌）

A series of pyrenes sandwiched by axially chiral 1,1′-binaphthyls were synthesized. Among them, (R,R)-3 possessing 2-hydroxy-3,3′-dimethylbinaphthyls exhibited solvent-dependent inversion of the sign of circularly polarized luminescence (CPL) without a change in emission wavelength. The (-)- and (+)-CPL were detected in nonpolar and polar solvents, respectively, with glum values of -0.012 and +0.012. This switching property originates from the inversion of excimer chirality caused by the presence or absence of intermolecular hydrogen bonds in the excited state. The CPL intensity was also changed by variation of the temperature and concentration.

DOI： 10.1021/jacs.9b13184

Chiral carbazole-based porphyrins showing absorption and circular dichroism in the near-infrared region

Chihiro Maeda, Tadashi Ema

Journal of Porphyrins and Phthalocyanines 24 ( 1-3 ) 247 - 251 2020年1月

Macrocyclic multinuclear metal complexes acting as catalysts for organic synthesis 査読

Bikash Dev Nath, Kazuto Takaishi, Tadashi Ema

Catalysis Science and Technology 10 ( 1 ) 12 - 34 2020年

担当区分：最終著者,　責任著者

Metal clusters in nature and artificial systems are known to exhibit excellent catalytic activities. Among various coordination systems, macrocyclic multinuclear metal complexes have unique structural features and great potential in organic synthesis. The multiple metal centers in a macrocyclic framework act as specific sites for the binding and activation of substrates, showing high catalytic activity and selectivity as a result of the cooperative effect of the multiple metal centers and robustness originating from macrocyclic skeletons. Most of them are precisely designed and synthesized, while occasionally, nice complexes also emerge from a fortuitous combination of metal ions and ligands. Here we overview the recent achievements of (i) multinuclear metal complexes with a covalently-linked macrocyclic ligand (category A), (ii) multinuclear metal complexes forming a macrocyclic skeleton (category B), and (iii) self-assembled supramolecular coordination complexes (category C). Various organic reactions catalyzed by these coordination systems are summarized here.

DOI： 10.1039/c9cy01894h

Axially Chiral peri-Xanthenoxanthenes as a Circularly Polarized Luminophore

Kazuto Takaishi, Sakiko Hinoide, Tomoki Matsumoto, Tadashi Ema

Journal of the American Chemical Society 141 ( 30 ) 11852 - 11857 2019年7月

掲載種別：研究論文（学術雑誌）

A series of axially chiral peri-xanthenoxanthenes (PXXs) were synthesized from 1,1′-bi-2-naphthol without optical resolution. These are the first examples of chiral PXXs. Among them, PXX 5 with two naphthalene rings connected via a methylenedioxy bridge and a chiral axis displayed intense fluorescence (FL) and circularly polarized luminescence (CPL) both in solution (φFL of 0.72 and |glum| of 1.4 × 10-3) and in the solid state (φFL of 0.13 and |glum| of 4.8 × 10-3). The bridged structure of PXX 5 adjusts the angle between the vectors of the electric and magnetic transition dipole moments, which is essential for showing intense CPL activity.

DOI： 10.1021/jacs.9b06240

Unexpected Macrocyclic Multinuclear Zinc and Nickel Complexes that Function as Multitasking Catalysts for CO<inf>2</inf> Fixations

Kazuto Takaishi, Bikash Dev Nath, Yuya Yamada, Hiroyasu Kosugi, Tadashi Ema

Angewandte Chemie - International Edition 58 ( 29 ) 9984 - 9988 2019年7月

掲載種別：研究論文（学術雑誌）

Unique self-assembled macrocyclic multinuclear ZnII and NiII complexes with binaphthyl-bipyridyl ligands (L) were synthesized. X-ray analysis revealed that these complexes consisted of an outer ring (Zn3L3 or Ni3L3) and an inner core (Zn2 or Ni). In the ZnII complex, the inner Zn2 part rotated rapidly inside the outer ring in solution on an NMR timescale. These complexes exhibited dual catalytic activities for CO2 fixations: synthesis of cyclic carbonates from epoxides and CO2 and temperature-switched N-formylation/N-methylation of amines with CO2 and hydrosilane.

DOI： 10.1002/anie.201904224

Evolving Fluorophores into Circularly Polarized Luminophores with a Chiral Naphthalene Tetramer: Proposal of Excimer Chirality Rule for Circularly Polarized Luminescence

Kazuto Takaishi, Kazuhiro Iwachido, Ryosuke Takehana, Masanobu Uchiyama, Tadashi Ema

Journal of the American Chemical Society 141 ( 15 ) 6185 - 6190 2019年4月

掲載種別：研究論文（学術雑誌）

A versatile method for converting various fluorescent polycyclic aromatic hydrocarbons into circularly polarized luminescence (CPL) excimer dyes with high glum and φFL values is reported. This method involves the functionalization of a chiral quaternaphthyl with six fluorophores via ester linkages in the last step of the synthesis. The usefulness of this approach was demonstrated for 1-, 2-, and 4-pyrenyl, 2- and 3-perylenyl, and 2-anthryl dyes. Most of them are the first or rare examples of CPL dyes. In the ground state, the fluorophores are tightly arranged by cumulative steric and electronic effects. In the excited state, the fluorophores form a twist excimer that maintains the ground-state conformations. The local chiral excimer directly affected the CPL properties. The systematic study on the signs of the CPLs allowed us to find a rule called the excimer chirality rule: right- and left-handed excimers exhibit (+)- and (-)-CPL, respectively.

DOI： 10.1021/jacs.9b02582

Chiral Bifunctional Metalloporphyrin Catalysts for Kinetic Resolution of Epoxides with Carbon Dioxide

Chihiro Maeda, Mayato Mitsuzane, Tadashi Ema

Organic Letters 21 ( 6 ) 1853 - 1856 2019年3月

掲載種別：研究論文（学術雑誌）

Chiral binaphthyl-strapped Zn(II) porphyrins with triazolium halide units were synthesized as bifunctional catalysts for kinetic resolution of epoxides with CO 2 . Several catalysts were screened by changing the linker length and nucleophilic counteranions, and the optimized catalyst accelerated the enantioselective reaction at ambient temperature to produce optically active cyclic carbonates and epoxides.

DOI： 10.1021/acs.orglett.9b00447

Hemisquaramide Tweezers as Organocatalysts: Synthesis of Cyclic Carbonates from Epoxides and CO <inf>2</inf>

Kazuto Takaishi, Takafumi Okuyama, Shota Kadosaki, Masanobu Uchiyama, Tadashi Ema

Organic Letters 21 ( 5 ) 1397 - 1401 2019年3月

掲載種別：研究論文（学術雑誌）

Hemisquaramide tweezers, a new family of H-bond donor organocatalysts, are reported. The catalysts could be synthesized within two steps. Among them, H 8 -binaphthyl-linked hemisquaramide 7 markedly accelerated the synthesis of cyclic carbonates from epoxides and CO 2 . The reactions proceeded well under mild and solvent-free conditions. Kinetic resolution was also achieved at -20 °C (s = 3.0). The adjustable bite angle and orientation of the two NH groups of the catalysts are important for the high activity.

DOI： 10.1021/acs.orglett.9b00117

Chiroptical and catalytic properties of doubly binaphthyl-strapped chiral porphyrins

Chihiro Maeda, Kanae Ogawa, Kosuke Sadanaga, Kazuto Takaishi, Tadashi Ema

Chemical Communications 55 ( 8 ) 1064 - 1067 2019年

Synthesis of chiral carbazole-based BODIPYs showing circularly polarized luminescence

Chihiro Maeda, Keiji Nagahata, Kazuto Takaishi, Tadashi Ema

Chemical Communications 55 ( 21 ) 3136 - 3139 2019年

掲載種別：研究論文（学術雑誌）

Chiral carbazole-based BODIPYs with a binaphthyl unit were synthesized via an Al-mediated reaction. Et2AlCl was found to be a convenient reagent for the reaction to give the chiral BODIPYs in high yields. It has been shown for the first time that these chiral carbazole-based BODIPYs show circularly polarized luminescence (CPL) both in solution and in the solid state.

DOI： 10.1039/c9cc00894b

Synthesis and electronic properties of π-expanded carbazole-based porphyrins

Chihiro Maeda, Yumi Tanaka, Takuma Shirakawa, Tadashi Ema

Chemical Communications 55 ( 68 ) 10162 - 10165 2019年

掲載種別：研究論文（学術雑誌）

Peripheral π-expansion of carbazole-based porphyrins was achieved for the first time by the Pt-catalyzed cyclization and the incorporation of a benzocarbazole unit. These two types of fused porphyrins showed red-shifted and broad NIR absorption due to the expanded π-conjugation as confirmed by NIR absorption spectroscopy and DFT calculations.

DOI： 10.1039/c9cc05079e

Cross-Coupling Approach to an Array of Macrocyclic Receptors Functioning as Chiral Solvating Agents

Tadashi Ema, Takayuki Yamasaki, Sagiri Watanabe, Mahoko Hiyoshi, Kazuto Takaishi

Journal of Organic Chemistry 83 ( 18 ) 10762 - 10769 2018年9月

掲載種別：研究論文（学術雑誌）

Chiral macrocyclic receptors 1 with multiple hydrogen-bonding sites in the cavity were synthesized and used as NMR chiral solvating agents (CSAs). The Suzuki-Miyaura cross-coupling reaction gave rapid access to a series of variants 1b-p of unsubstituted parent compound 1a. Among them, 1d with the 4-cyanophenyl group at the 3,3′-positions of the binaphthyl moiety was the most excellent CSA for a benchmark analyte compound, 2-chloropropionic acid (CPA); both of the quartet and doublet signals of CPA were split most completely in CDCl3. Binding constants (Ka) determined in CDCl3 by NMR titrations indicated that (R)-1d was the most enantioselective (Ka(S)/Ka(R) = 5.4). Interestingly, the Ka value of (R)-1d for (S)-CPA (5900) was greater than that of (R)-1a for (S)-CPA (3080), which strongly suggests an attractive interaction between the 4-cyanophenyl group of (R)-1d and (S)-CPA. The X-ray crystal structure of 1d indicates that one of the two H atoms meta to the cyano group is directed toward the cavity. DFT calculations suggested that this H atom of the 4-cyanophenyl group of (R)-1d forms a weak hydrogen bond with the Cl atom of (S)-CPA (C-H···Cl-C hydrogen bond).

DOI： 10.1021/acs.joc.8b01327

Binaphthyl-Bipyridyl cyclic dyads as a chiroptical switch

Kazuto Takaishi, Makoto Yasui, Tadashi Ema

Journal of the American Chemical Society 140 ( 16 ) 5334 - 5338 2018年4月

掲載種別：研究論文（学術雑誌）

A series of chiral cyclic dyads, axially chiral binaphthyls linked to a 3,3′-bipyridyl, was synthesized. The dyad 2 bearing methoxy groups exhibited ON/OFF properties in circularly polarized luminescence (CPL), yielding a |glum| of 1.6 × 10-3 or 0 without any change in fluorescence. This type of CPL switch is unprecedented. Regioisomer 4 exhibited a dextro/levo rotation switching ability in [α]D. X-ray structures as well as experimental and theoretical analyses suggested that the switching properties depended on conformational changes.

DOI： 10.1021/jacs.8b01860

Calix[4]pyrroles as macrocyclic organocatalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide

Chihiro Maeda, Sota Sasaki, Kazuto Takaishi, Tadashi Ema

Catalysis Science and Technology 8 ( 16 ) 4193 - 4198 2018年

掲載種別：研究論文（学術雑誌）

Calix[4]pyrrole 1, calix[4]arene 2, or porphyrin 3 together with tetrabutylammonium iodide (TBAI) catalyzed the conversion of epoxides and CO2 into cyclic carbonates. Among them, meso-octamethylcalix[4]pyrrole 1a, which was synthesized easily in one step by the acid-catalyzed condensation of pyrrole with acetone, was found to be a very active and robust organocatalyst. DFT calculations suggested that 1a adopts a 1,3-alternate conformation to stabilize the anionic species generated during the catalysis. In the key transition state of the epoxide ring-opening step, one pyrrolic NH group and the tetrabutylammonium (TBA) cation activate the epoxide by hydrogen bonding while another NH group on the opposite side guides the I- anion, which is located away from the TBA cation, to the backside attack on the epoxide.

DOI： 10.1039/c8cy00941d

Intense excimer CPL of pyrenes linked to a quaternaphthyl

Kazuto Takaishi, Ryosuke Takehana, Tadashi Ema

Chemical Communications 54 ( 12 ) 1449 - 1452 2018年

掲載種別：研究論文（学術雑誌）

(R,R,R)-Quaternaphthyls possessing eight and six pyrenes (compounds 4 and 3) displayed intense excimer-CPL. The glum values in solution and in the solid state were +0.034-0.037 and +0.0053-0.0056, respectively. The glum values of 3 and 4 were indistinguishable, indicating that the pyrenes of 3 and 4 assumed the same conformation, even in excited states. The intense CPL was caused by conformationally rigid pyrenes arranged via the cumulative steric effects along the quaternaphthyl axis.

DOI： 10.1039/c7cc09187g

Palladium Complexes of Carbazole-Based Chalcogenaisophlorins: Synthesis, Structure, and Solid-State NIR Absorption Spectra

Chihiro Maeda, Kazuto Takaishi, Tadashi Ema

ChemPlusChem 82 ( 12 ) 1368 - 1371 2017年12月

掲載種別：研究論文（学術雑誌）

Annulation reactions of the butadiyne-bridged carbazole dimer 1 produced carbazole-based chalcogenaisophlorins 2–4, which were transformed into the corresponding palladium complexes 2Pd–4Pd. The structures were characterized by NMR spectroscopy and X-ray diffraction analysis. Metallation fixed the structures which displayed weak antiaromatic character derived from the 20π isophlorin framework. These complexes showed weak near-infrared (NIR) absorption typical for antiaromatic porphyrinoids in solution. In addition, 2Pd and 3Pd showed relatively strong solid-state NIR absorption. X-ray diffraction analyses of 2Pd and 3Pd revealed trimeric and dimeric stacked layered structures, respectively, and DFT calculations suggest that the solid-state NIR absorption is ascribed to intermolecular charge transfer.

DOI： 10.1002/cplu.201700430

Spectroscopic Discrimination of Diastereomeric Complexes Involving an Axially Chiral Receptor

Antonello Filippi, Caterina Fraschetti, Laura Guarcini, Costantino Zazza, Tadashi Ema, Maurizio Speranza

ChemPhysChem 18 ( 18 ) 2475 - 2481 2017年9月

掲載種別：研究論文（学術雑誌）

The infrared multiphoton dissociation (IRMPD) spectra of electrospray ionization (ESI)-formed proton-bound complexes between the axially chiral multifunctional macrocycle MaR and d- and l-phenylalanine (PD and PL) or d- and l-3,4-dihydroxyphenylalanine (DD and DL) are recorded in the (Formula presented.) =2800–3700 cm−1 region. Whereas the diastereomeric [MaR⋅H⋅PD]+ and [MaR⋅H⋅PL]+ complexes do not show any significant spectral differences, the spectrum of [MaR⋅H⋅DD]+ clearly diverges from that of its [MaR⋅H⋅DL]+ diastereomer. A comparison of the experimental spectra with the B3LYP/6-31G**-calculated harmonic vibrational frequencies of a number of stable structures indicates the formation, in the ESI source, of very similar spectroscopically active structures, with the protonated amino acid placed outside the flat cavity of the macrocycle and hydrogen-bonded at its O2 center. Different spectral signatures of the [MaR⋅H⋅DD]+ and [MaR⋅H⋅DL]+ complexes are attributed to the coexistence of several stable rotamers in the ESI source.

DOI： 10.1002/cphc.201700732

Chiral Macrocyclic Organocatalysts for Kinetic Resolution of Disubstituted Epoxides with Carbon Dioxide

Tadashi Ema, Maki Yokoyama, Sagiri Watanabe, Sota Sasaki, Hiromi Ota, Kazuto Takaishi

Organic Letters 19 ( 15 ) 4070 - 4073 2017年8月

掲載種別：研究論文（学術雑誌）

Among chiral macrocycles 1 synthesized, 1m with the 3,5-bis(trifluoromethyl)phenylethynyl group was the best organocatalyst for the enantioselective synthesis of cyclic carbonates from disubstituted or monosubstituted epoxides and CO2. The X-ray crystal structure of 1m revealed a well-defined chiral cavity with multiple hydrogen-bonding sites that is suitable for the enantioselective activation of epoxides. A catalytic cycle proposed was supported by DFT calculations.

DOI： 10.1021/acs.orglett.7b01838

Helical Oligonaphthodioxepins Showing Intense Circularly Polarized Luminescence (CPL) in Solution and in the Solid State

Kazuto Takaishi, Takahiro Yamamoto, Sakiko Hinoide, Tadashi Ema

Chemistry - A European Journal 23 ( 39 ) 9249 - 9252 2017年7月

掲載種別：研究論文（学術雑誌）

A series of oligonaphthodioxepins was synthesized, revealing a helically arranged octamer, (R,R,R,R,R,R,R)-3, which showed intense circularly polarized luminescence (CPL) both in solution and in the solid state. The fluorescence quantum yields (ΦFL) in solution and in the solid state were 0.90 and 0.22, respectively, and the glum values in solution and in the solid state were +2.2×10−3 and +7.0×10−3, respectively. This is one of the highest solid-state CPL glum values yet reported. The high ΦFL and glum values were due to the rigidity, as well as to the fact that (R,R,R,R,R,R,R)-3 was a non-planar molecule. Moreover, (R,R,R,R,R,R,R)-3 was highly stable both chemically and stereochemically.

DOI： 10.1002/chem.201702143

Magnetic Attachment of Lipase Immobilized on Bacteriogenic Iron Oxide Inside a Microtube Reactor for the Kinetic Resolution of Secondary Alcohols

Kyoko Mandai, Takehiro Fukuda, Yuki Miyazaki, Hideki Hashimoto, Hiroki Mandai, Tadashi Ema, Jun Takada, Seiji Suga

Synlett 28 ( 7 ) 805 - 810 2017年4月

掲載種別：研究論文（学術雑誌）

A PTFE microtube reactor was constructed with lipase immobilized on magnetized bacteriogenic iron oxide, which was retained inside of the tube by attraction to an external magnet. The reactor was used for the lipase-promoted kinetic resolution of secondary alcohols and gave sufficient catalytic activity, which was maintained during long-term flow over 14 days.

DOI： 10.1055/s-0036-1589953

Electronic Tuning of Zinc Porphyrin Catalysts for the Conversion of Epoxides and Carbon Dioxide into Cyclic Carbonates

Chihiro Maeda, Sota Sasaki, Tadashi Ema

ChemCatChem 9 ( 6 ) 946 - 949 2017年3月

掲載種別：研究論文（学術雑誌）

Bifunctional ZnII porphyrin catalysts bearing tributylammonium bromide groups at the meta positions of the meso-phenyl groups showed high catalytic activity for the synthesis of cyclic carbonates from epoxides and CO2. Herein, several substituents with different electronic properties were introduced at the para positions. Introduction of electron-donating groups decreased the catalytic activity, whereas the introduction of electron-withdrawing groups increased the activity. The substituents modulated the Lewis acidity of the zinc center, which was confirmed by binding constant experiments. The bifunctional catalyst bearing cyano groups showed the highest catalytic activity with a turnover frequency of up to 42 000 h−1.

DOI： 10.1002/cctc.201601690

Synthetically useful variants of industrial lipases from: Burkholderia cepacia and Pseudomonas fluorescens

Kazunori Yoshida, Masakazu Ono, Takahiro Yamamoto, Takashi Utsumi, Satoshi Koikeda, Tadashi Ema

Organic and Biomolecular Chemistry 15 ( 41 ) 8713 - 8719 2017年

掲載種別：研究論文（学術雑誌）

Industrial enzymes lipase PS (LPS) and lipase AK (LAK), which originate from Burkholderia cepacia and Pseudomonas fluorescens, respectively, are synthetically useful biocatalysts. To strengthen their catalytic performances, we introduced two mutations into hot spots of the active sites (residues 287 and 290). The LPS-L287F/I290A double mutant showed high catalytic activity and enantioselectivity for poor substrates for which the wild-type enzyme showed very low activity. The LAK-V287F/I290A double mutant was also an excellent biocatalyst with expanded substrate scope, which was comparable to the LPS-L287F/I290A double mutant. Thermodynamic parameters were determined to address the origin of the high enantioselectivity of the double mutant. The ΔΔH‡ term, but not the ΔΔS‡ term, was predominant, which suggests that the enantioselectivity is driven by a differential energy associated with intermolecular interactions around Phe287 and Ala290. A remarkable solvent effect was observed, giving a bell-shaped profile between the E values and the log&P or ϵ values of solvents with the highest E value in i-Pr2O. This suggests that an organic solvent with appropriate hydrophobicity and polarity provides the double mutant with some flexibility that is essential for excellent catalytic performance.

DOI： 10.1039/c7ob01823a

Synthesis of carbazole-based BODIPY dimers showing red fluorescence in the solid state

Chihiro Maeda, Takumi Todaka, Tomomi Ueda, Tadashi Ema

Organic and Biomolecular Chemistry 15 ( 44 ) 9283 - 9287 2017年

掲載種別：研究論文（学術雑誌）

Carbazole-based BODIPY dimers 2a-g were synthesized via direct arylation. They showed red-shifted solid-state fluorescence spectra as compared with the corresponding monomer. In addition, unsymmetrical dimers 2d, 2f, and 2g with two different substituents showed red fluorescence with improved quantum yields in the solid state.

DOI： 10.1039/c7ob02419c

Carbazole-based BODIPYs with ethynyl substituents at the boron center: Solid-state excimer fluorescence in the VIS/NIR region

Chihiro Maeda, Keiji Nagahata, Tadashi Ema

Organic and Biomolecular Chemistry 15 ( 37 ) 7783 - 7788 2017年

掲載種別：研究論文（学術雑誌）

Carbazole-based BODIPYs 1-6 with several different substituents at the boron atom site were synthesized. These dyes fluoresced in the solid state, and 3a with phenylethynyl groups exhibited a red-shifted and broad fluorescence spectrum, which suggested an excimer emission. Its derivatives 3b-n were synthesized, and the relationship between the solid-state emission and crystal packing was investigated. The X-ray crystal structures revealed cofacial dimers that might form excimers. From the structural optimization results, we found that the introduction of mesityl groups hindered intermolecular access and led to reduced interactions between the dimers. In addition, the red-shifted excimer fluorescence suppressed self-absorption, and dyes with ethynyl groups showed solid-state fluorescence in the vis/NIR region.

DOI： 10.1039/c7ob01473b

Intramolecular Electronic Coupling in the Thiophene-Bridged Carbazole-Based Diporphyrin

Chihiro Maeda, Mototsugu Takata, Asami Honsho, Tadashi Ema

Organic Letters 18 ( 23 ) 6070 - 6073 2016年12月

掲載種別：研究論文（学術雑誌）

The Glaser coupling reaction of ethynyl-substituted carbazole-based isophlorins provided butadiyne-bridged dimers, which were transformed into the thiophene-bridged dimers via the annulation reaction. Oxidation of these isophlorin dimers afforded carbazole-based diporphyrins. Notable electronic interactions in the diporphyrins have been confirmed by means of UV/vis-near-infrared (NIR) absorption spectroscopy, cyclic voltammetry (CV) measurements, and density functional theory (DFT) calculations.

DOI： 10.1021/acs.orglett.6b03054

Solvent-Free Benzoin and Stetter Reactions with a Small Amount of NHC Catalyst in the Liquid or Semisolid State

Tadashi Ema, Yoshiko Nanjo, Sho Shiratori, Yuta Terao, Ryo Kimura

Organic Letters 18 ( 21 ) 5764 - 5767 2016年11月

掲載種別：研究論文（学術雑誌）

The intermolecular or intramolecular asymmetric benzoin reaction was catalyzed by a small amount of N-heterocyclic carbene (NHC) (0.2-1 mol %) under solvent-free conditions. The solvent-free intramolecular asymmetric Stetter reaction also proceeded efficiently with NHC (0.2-1 mol %). In some cases, even solid-to-solid or solid-to-liquid conversions took place with low catalyst loading (0.2-1 mol %).

DOI： 10.1021/acs.orglett.6b03115

Theoretical Study on Highly Active Bifunctional Metalloporphyrin Catalysts for the Coupling Reaction of Epoxides with Carbon Dioxide

Jun ya Hasegawa, Ray Miyazaki, Chihiro Maeda, Tadashi Ema

Chemical Record 16 ( 5 ) 2260 - 2267 2016年10月

掲載種別：研究論文（学術雑誌）

Highly active bifunctional metalloporphyrin catalysts were developed for the coupling reaction of epoxides with CO2 to produce cyclic carbonates. The bifunctional catalysts have both quaternary ammonium halide groups and a metal center. To elucidate the roles of these catalytic groups, DFT calculations were performed. Control reactions using tetrabutylammonium halide as a catalyst were also investigated for comparison. In the present article, the results of our computational studies are overviewed. The computational results are consistent with the experimental data and are useful for elucidating the structure–activity relationship. The key features responsible for the high catalytic activity of the bifunctional catalysts are as follows: 1) the cooperative action of the halide anion (nucleophile) and the metal center (Lewis acid); 2) the near-attack conformation, leading to the efficient opening of the epoxide ring in the rate-determining step; and 3) the conformational change of the quaternary ammonium cation to stabilize various anionic species generated during catalysis, in addition to the robustness (thermostability) of the catalysts.

DOI： 10.1002/tcr.201600053

Color-Tunable Solid-State Fluorescence Emission from Carbazole-Based BODIPYs

Chihiro Maeda, Takumi Todaka, Tomomi Ueda, Tadashi Ema

Chemistry - A European Journal 22 ( 22 ) 7508 - 7513 2016年5月

掲載種別：研究論文（学術雑誌）

Several carbazole-based boron dipyrromethene (BODIPY) dyes were synthesized by organometallic approaches. Thiazole, benzothiazole, imidazole, benzimidazole, triazole, and indolone substituents were introduced at the 1-position of the carbazole moiety, and boron complexation of each dipyrrin generated the corresponding compounds 1, 2 a, and 3-6. The properties of these products were investigated by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X-ray crystallography, and DFT calculations. These compounds exhibited large Stokes shifts, and compounds 1, 2 a, and 3-5 fluoresced both in solution and in the solid state. Complex 2 a showed the highest fluorescence quantum yield (ΦF) in the solid state, therefore boron complexes of the carbazole-benzothiazole hybrids 2 b-f, which had several different substituents, were prepared and the effects of the substituents on the photophysical properties of the compounds were examined. The fluorescence properties showed good correlation with the results of crystal-packing analyses, and the dyes exhibited color-tunable solid-state fluorescence.

DOI： 10.1002/chem.201505150

Highly Active and Robust Metalloporphyrin Catalysts for the Synthesis of Cyclic Carbonates from a Broad Range of Epoxides and Carbon Dioxide

Chihiro Maeda, Junta Shimonishi, Ray Miyazaki, Jun Ya Hasegawa, Tadashi Ema

Chemistry - A European Journal 22 ( 19 ) 6556 - 6563 2016年5月

掲載種別：研究論文（学術雑誌）

Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso-phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent-free conditions. The meta-substituted catalysts exhibited high catalytic performance, whereas the para- and ortho-substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta-substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500h-1 at 170°C) at an initial CO2 pressure of 1.7MPa; catalyzed the reaction even at atmospheric CO2 pressure (balloon) at ambient temperature (20°C); and was applicable to a broad range of substrates, including terminal and internal epoxides. In a fix! Bifunctional metalloporphyrins act as catalysts for the formation of cyclic carbonates from epoxides and CO2 (see scheme). A comparison of the catalytic activities shows the superior performance of meta-substituted catalysts. A robust zinc(II) porphyrin with eight nucleophiles at the meta positions shows the highest catalytic activity and a broad substrate scope, including terminal and internal epoxides.

DOI： 10.1002/chem.201600164

Determination of enantiomeric excess of carboxylates by fluorescent macrocyclic sensors

Ali Akdeniz, Tsuyoshi Minami, Sagiri Watanabe, Maki Yokoyama, Tadashi Ema, Pavel Anzenbacher

Chemical Science 7 ( 3 ) 2016 - 2022 2016年3月

掲載種別：研究論文（学術雑誌）

Chiral fluorescent chemosensors featuring macrocycles comprising BINOL auxiliary and an array of hydrogen bond donors were synthesized. To enhance fluorescence of the chemosensors, conjugated moieties were attached to the 3,3′-positions of the BINOL auxiliary. The resulting chemosensors recognize a number of carboxylates, namely, enantiomers of ibuprofen, ketoprofen, 2-phenylpropanoate, mandelate, and phenylalanine in a stereoselective fashion. Depending on the structure of the chemosensor, the presence of carboxylate yields fluorescence quenching or amplification. This information-rich signal can be used to determine the identity of the analyte including the sense of chirality. Quantitative experiments were performed aimed at analysis of enantiomeric excess of chiral carboxylates. The quantitative analysis of enantiomeric composition of ibuprofen, ketoprofen, and phenylalanine shows that the sensors correctly identify mixtures with varying enantiomeric excess and correctly predict the enantiomeric excess of unknown samples with error of prediction <1.6%.

DOI： 10.1039/c5sc04235f

Carbazole-Based Boron Dipyrromethenes (BODIPYs): Facile Synthesis, Structures, and Fine-Tunable Optical Properties

Chihiro Maeda, Takumi Todaka, Tadashi Ema

Organic Letters 17 ( 12 ) 3090 - 3093 2015年6月

掲載種別：研究論文（学術雑誌）

Carbazole-based BODIPYs were synthesized in three steps using an organometallic approach consisting of sequential Ir-catalyzed borylation, Suzuki-Miyaura coupling, and boron complexation. Various substituents were introduced into the carbazole moiety, and large substituent effects were confirmed by means of absorption spectroscopy, cyclic voltammetry, and DFT calculations. Dibenzocarbazoles were also converted into the corresponding BODIPYs.

DOI： 10.1021/acs.orglett.5b01363

Quaternary ammonium hydroxide as a metal-free and halogen-free catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide

Tadashi Ema, Kazuki Fukuhara, Takashi Sakai, Masaki Ohbo, Fu Quan Bai, Jun Ya Hasegawa

Catalysis Science and Technology 5 ( 4 ) 2314 - 2321 2015年4月

掲載種別：研究論文（学術雑誌）

Tetrabutylammonium hydroxide (TBAH) and other quaternary ammonium hydroxides catalyzed the cycloaddition of CO2 to epoxides under solvent-free conditions to give cyclic carbonates. When TBAH was exposed to CO2, TBAH was converted into tetrabutylammonium bicarbonate (TBABC), which was a catalytically active species. A D-labeled epoxide and an optically active epoxide were used to study the reaction mechanism, which invoked three plausible pathways. Among them, path A seemed to be predominant; the bicarbonate ion of TBABC attacks the less hindered C atom of the epoxide to generate a ring-opened alkoxide intermediate, which adds to CO2 to give a carbonate ion, and the subsequent cyclization yields a cyclic carbonate. Density functional theory (DFT) calculations successfully delineated the potential energy profile for each reaction pathway, among which path A was the lowest-energy pathway in accordance with the experimental results. The tetrabutylammonium (TBA) cation carries the positive charges on the H atoms, but not on the central N atom, and the positively charged H atoms close to the central N atom form an anion-binding site capable of stabilizing various anionic transition states and intermediates.

DOI： 10.1039/c5cy00020c

Bifunctional catalysts based on m-phenylene-bridged porphyrin dimer and trimer platforms: Synthesis of cyclic carbonates from carbon dioxide and epoxides

Chihiro Maeda, Tomoya Taniguchi, Kanae Ogawa, Tadashi Ema

Angewandte Chemie - International Edition 54 ( 1 ) 134 - 138 2015年1月

掲載種別：研究論文（学術雑誌）

Highly active bifunctional diporphyrin and triporphyrin catalysts were synthesized through Stille coupling reactions. As compared with a porphyrin monomer, both exhibited improved catalytic activities for the reaction of CO2 with epoxides to form cyclic carbonates, because of the multiple catalytic sites which cooperatively activate the epoxide. Catalytic activities were carefully investigated by controlling temperature, reaction time, and catalyst loading, and very high turnover number and turnover frequency were obtained: 220000 and 46000 h-1, respectively, for the magnesium catalyst, and 310000 and 40000 h-1, respectively, for the zinc catalyst. Results obtained with a zinc/free-base hybrid diporphyrin catalyst demonstrated that the Br- ions on the adjacent porphyrin moiety also function as nucleophiles.

DOI： 10.1002/anie.201409729

Chemical modification of lipase for rational enhancement of enantioselectivity

Tadashi Ema, Hiroki Inoue

Chemistry Letters 44 ( 10 ) 1374 - 1376 2015年

掲載種別：研究論文（学術雑誌）

Chemical modifications of the I287C mutant of a Burkholderia cepacia lipase afforded various I287C-X conjugates, among which I287C-PAA bearing an N-phenylacetamide (PAA) moiety showed excellent enantioselectivity and catalytic activity for secondary alcohols. Site-directed chemical modifications are powerful tools to control enantioselective biocatalysis.

DOI： 10.1246/cl.150667

Bifunctional porphyrin catalysts for the synthesis of cyclic carbonates from epoxides and CO <inf>2</inf> : Structural optimization and mechanistic study

Tadashi Ema, Yuki Miyazaki, Junta Shimonishi, Chihiro Maeda, Jun Ya Hasegawa

Journal of the American Chemical Society 136 ( 43 ) 15270 - 15279 2014年10月

掲載種別：研究論文（学術雑誌）

We prepared bifunctional Mg II porphyrin catalysts 1 for the solvent-free synthesis of cyclic carbonates from epoxides and CO 2 . The activities of 1d, 1h, and 1i, which have Br - , Cl - , and I - counteranions, respectively, increased in the order 1i < 1h < 1d. Catalysts 1d and 1j-m, which bear four tetraalkylammonium bromide groups with different alkyl chain lengths, showed comparable but slightly different activities. Based on the excellent catalyst 1d, we synthesized Mg II porphyrin 1o with eight tetraalkylammonium bromide groups, which showed even higher catalytic activity (turnover number, 138,000; turnover frequency, 19,000 h -1 ). The catalytic mechanism was studied by using 1d. The yields were nearly constant at initial CO 2 pressures in the 1-6 MPa range, suggesting that CO 2 was not involved in the rate-determining step in this pressure range. No reaction proceeded in supercritical CO 2 , probably because the epoxide (into which the catalyst dissolved) dissolved in and was diluted by the supercritical CO 2 . Experiments with 18 O-labeled CO 2 and D-labeled epoxide suggested that the catalytic cycle involved initial nucleophilic attack of Br - on the less hindered side of the epoxide to generate an oxyanion, which underwent CO 2 insertion to afford a CO 2 adduct; subsequent intramolecular ring closure formed the cyclic carbonate and regenerated the catalyst. Density functional theory calculations gave results consistent with the experimental results, revealing that the quaternary ammonium cation underwent conformational changes that stabilized various anionic species generated during the catalytic cycle. The high activity of 1d and 1o was due to the cooperative action of the Mg II and Br - and a conformational change (induced-fit) of the quaternary ammonium cation.

DOI： 10.1021/ja507665a

Recent progress in catalytic conversions of carbon dioxide

Chihiro Maeda, Yuki Miyazaki, Tadashi Ema

Catalysis Science and Technology 4 ( 6 ) 1482 - 1497 2014年6月

Chemical fixation of carbon dioxide (CO2), which is an inexpensive and renewable carbon source, is becoming more and more important. The development of both new reactions and new catalysts is needed to overcome the kinetic and thermodynamic stability of CO2. Organic and metal catalysts with unique and excellent activity and selectivity have been developed for various chemical conversions of CO2. In this perspective, we provide an overview of the recent progress in this field, classifying it into several categories, where each research is concisely summarized one by one using a single reaction scheme, a representative catalyst structure, and/or a catalytic cycle. This journal is © the Partner Organisations 2014.

DOI： 10.1039/c3cy00993a

Selective anion sensing by chiral macrocyclic receptors with multiple hydrogen-bonding sites

Tadashi Ema, Keiichi Okuda, Sagiri Watanabe, Takayuki Yamasaki, Tsuyoshi Minami, Nina A. Esipenko, Pavel Anzenbacher

Organic Letters 16 ( 5 ) 1302 - 1305 2014年3月

掲載種別：研究論文（学術雑誌）

Chiral macrocycles featuring sulfonamide and/or amide groups as anion-binding sites were synthesized. X-ray crystal structures and DFT calculations have shown that they adopt different conformations that may lead to unique binding behavior. Indeed, various anions could be sensed by their colorimetric and/or fluorescence signal output. The chiral macrocycles showed chiral recognition for chiral anions. Furthermore, a multisensor array with two or four chiral receptors discriminated seven phosphate anions (AMP, ADP, ATP, CMP, GMP, Pi, and PPi) with 100% classification accuracy. © 2014 American Chemical Society.

DOI： 10.1021/ol403643d

Synergistic effect of quaternary ammonium hydroxide and crown ether on the rapid and clear dissolution of cellulose at room temperature

Tadashi Ema, Takuzo Komiyama, Satomi Sunami, Takashi Sakai

RSC Advances 4 ( 5 ) 2523 - 2525 2014年

Multifunctional macrocyclic receptors as templates for aromatic amino acids: A rare example of a highly selective multi-input multi-output chemo-"Logic Gate"

Caterina Fraschetti, Antonello Filippi, Maria Elisa Crestoni, Tadashi Ema, Maurizio Speranza

ChemPlusChem 78 ( 9 ) 979 - 987 2013年9月

掲載種別：研究論文（学術雑誌）

Proton-bound [M×H×G]+ diastereomeric complexes between some chiral aromatic amino acids or dipeptides(G) and a chiral multifunctional macrocyclic receptor (M=Chirabite-A) undergo, in the gas phase, highly selective substitution and addition reactions by amines, such as 2-aminobutane and piperidine. All the [M×H×G]+ complexes follow time-dependent monoexponential decays. In some cases, the kinetic curves exhibit a plateau revealing the presence of unreactive [M×H×G] + structures. In them, the amino acid is accommodated in the macrocycle cavity in the zwitterionic form by sharing its acidic hydrogen atoms with the pyridine nitrogen atoms of the host. The same interactions are structurally inaccessible to G=dipeptides or monofunctional amines, which then can be readily released from [M×H×G]+. When the amino acid interacts with the amidocarbonyl oxygen atoms pointing outside the macrocycle cavity, it saves the canonical structure and can be readily displaced by the amine. The Chirabite-A may act as an efficient template for aromatic amino acids by releasing them or not depending upon the amino acid configuration and the basicity of the amine. These unique properties confer to the gas-phase diastereomeric [M×H×G]+ complexes the features of multi-input multi-output chemo-"logic gates". © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/cplu.201300086

Robust porphyrin catalysts immobilized on biogenous iron oxide for the repetitive conversions of epoxides and CO<inf>2</inf> into cyclic carbonates

Tadashi Ema, Yuki Miyazaki, Tomoya Taniguchi, Jun Takada

Green Chemistry 15 ( 9 ) 2485 - 2492 2013年9月

掲載種別：研究論文（学術雑誌）

Metalloporphyrins were immobilized on biogenous iron oxide (BIO) produced by iron-oxidizing bacteria, Leptothrix ochracea. These organic-inorganic hybrid materials were used as immobilized catalysts for the synthesis of cyclic carbonates from epoxides and CO2 under solvent-free conditions. ZnII porphyrin immobilized via four tetraalkylammonium bromide groups showed high catalytic activity and reusability at a catalyst loading of 0.1 mol%. The product was obtained in 99% yield after nine times reuse, and the substrate scope was broad. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c3gc41055b

Unexpected behavior of diastereomeric ions in the GasPhase: A stimulus for pondering on ee measurements by ESI-MS

Caterina Fraschetti, Antonello Filippi, Maria Elisa Crestoni, Tadashi Ema, Maurizio Speranza

Journal of the American Society for Mass Spectrometry 24 ( 4 ) 573 - 578 2013年4月

掲載種別：研究論文（学術雑誌）

The most common protocols for the quantitative determination of the enantiomeric excess (ee) of raw mixtures by ESI-MS reveal inadequate in cases where the distribution of diastereomeric derivatives diverges from the ee of original solutions. This phenomenon is attributable to a matrix effect, i.e.; to the stereospecific formation of high order noncovalent adducts in the ESI droplets, which alters the actual availability of the diastereomeric species under MS analysis. In this frame, the assumption of classic protocols that the ionization correction factor q is independent on the composition of the mixture submitted to analysis is questionable. An alternative methodology is presented in this paper, which is aimed at circumventing the problem by excluding any chemical derivatization of the original raw mixture. It is based on the measurement of the actual distribution of ESI-formed proton-bound diastereomeric complexes from the enantiomeric mixture through a careful analysis of their reaction kinetics with a suitable reactant. [Figure not available: see fulltext.] © 2013 American Society for Mass Spectrometry.

DOI： 10.1007/s13361-012-0575-8

Synthetic macrocyclic receptors in chiral analysis and separation

Tadashi Ema

Journal of Inclusion Phenomena and Macrocyclic Chemistry 74 ( 1-4 ) 41 - 55 2012年12月

掲載種別：研究論文（学術雑誌）

Chiral synthetic macrocyclic receptors that can achieve chiral discrimination by NMR spectroscopy and/or chiral separation by HPLC are overviewed. Synthetic macrocycles introduced here include crown ethers, calixarenes/calixresorcinarenes/calixpyrroles, macrocyclic amides/amines, and porphyrins. These macrocyclic frameworks are advantageous because intermolecular interactions can take place effectively, such as the ion-dipole interactions in crown ethers, the CH/π and π-π interactions in calixarenes, hydrogen bonding and salt formation in macrocyclic amides and amines, and π-π stacking and metal coordination in porphyrins. Additional functional groups on the periphery of the macrocyclic platforms not only make the whole molecule chiral but also act as the interaction sites. Chiral macrocyclic receptors can show a high degree of chiral recognition/discrimination by using the peripheral functional groups as well as the macrocyclic skeletons (preorganization). Both hosts and guests are shown in the figures to quickly overview the molecular recognition scope of synthetic macrocyclic receptors in chiral analysis and separation. © 2012 Springer Science+Business Media B.V.

DOI： 10.1007/s10847-012-0136-6

Construction of contiguous tetrasubstituted carbon stereocenters by intramolecular crossed benzoin reactions catalyzed by N-heterocyclic carbene (NHC) organocatalyst

Tadashi Ema, Kumiko Akihara, Ryoko Obayashi, Takashi Sakai

Advanced Synthesis and Catalysis 354 ( 17 ) 3283 - 3290 2012年11月

掲載種別：研究論文（学術雑誌）

Bicyclic compounds with two contiguous tetrasubstituted carbon stereocenters at bridgehead positions were synthesized by N-heterocyclic carbene (NHC)-catalyzed intramolecular crossed benzoin reactions of symmetrical compounds. This desymmetrization strategy was applied to asymmetric synthesis with chiral NHC organocatalysts. Transition-state models were proposed to explain the enantioselectivity. A tricyclic compound with three contiguous tetrasubstituted carbon stereocenters was synthesized by a stepwise strategy. The molecular structure and absolute configuration of the (+)-enantiomer of this tricyclic compound were determined by X-ray crystallographic analysis. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/adsc.201200499

Redesign of enzyme for improving catalytic activity and enantioselectivity toward poor substrates: Manipulation of the transition state

Tadashi Ema, Yasuko Nakano, Daiki Yoshida, Shusuke Kamata, Takashi Sakai

Organic and Biomolecular Chemistry 10 ( 31 ) 6299 - 6308 2012年8月

掲載種別：研究論文（学術雑誌）

Secondary alcohols having bulky substituents on both sides of the hydroxy group are inherently poor substrates for most lipases. In view of this weakness, we redesigned a Burkholderia cepacia lipase to create a variant with improved enzymatic characteristics. The I287F/I290A double mutant showed a high conversion and a high E value (>200) for a poor substrate for which the wild-type enzyme showed a low conversion and a low E value (5). This enhancement of catalytic activity and enantioselectivity of the variant resulted from the cooperative action of two mutations: Phe287 contributed to both enhancement of the (R)-enantiomer reactivity and suppression of the (S)-enantiomer reactivity, while Ala290 created a space to facilitate the acylation of the (R)-enantiomer. The kinetic constants indicated that the mutations effectively altered the transition state. Substrate mapping analysis strongly suggested that the CH/π interaction partly enhanced the (R)-enantiomer reactivity, the estimated energy of the CH/π interaction being -0.4 kcal mol^-1. The substrate scope of the I287F/I290A double mutant was broad. This biocatalyst was useful for the dynamic kinetic resolution of a variety of bulky secondary alcohols for which the wild-type enzyme shows little or no activity. © The Royal Society of Chemistry 2012.

DOI： 10.1039/c2ob25614b

A bifunctional catalyst for carbon dioxide fixation: Cooperative double activation of epoxides for the synthesis of cyclic carbonates

Tadashi Ema, Yuki Miyazaki, Shohei Koyama, Yuya Yano, Takashi Sakai

Chemical Communications 48 ( 37 ) 4489 - 4491 2012年4月

Biogenous iron oxide-immobilized palladium catalyst for the solvent-free Suzuki-Miyaura coupling reaction

Kyoko Mandai, Toshinobu Korenaga, Tadashi Ema, Takashi Sakai, Mitsuaki Furutani, Hideki Hashimoto, Jun Takada

Tetrahedron Letters 53 ( 3 ) 329 - 332 2012年1月

掲載種別：研究論文（学術雑誌）

Iron oxide produced by iron-oxidizing bacteria, Leptothrix ochracea, (biogenous iron oxide: BIO) was used as a support for immobilized palladium catalysts with organic cross-linkers. Palladium immobilized on BIO bearing imidazolium chloride delivered the desired biaryl products in sufficient yields in the Suzuki-Miyaura coupling reactions under solvent-free conditions and could be reused several times without significant loss of catalytic activity. It is shown that BIO can be exploited as a useful support for immobilization of palladium and the BIO-immobilized palladium catalyst effectively promotes the solvent-free Suzuki-Miyaura coupling reactions. © 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetlet.2011.11.044

Molecular recognition of chiral diporphyrin receptor with a macrocyclic cavity for intercalation of aromatic compounds

Tadashi Ema, Norichika Ura, Katsuya Eguchi, Takashi Sakai

Bulletin of the Chemical Society of Japan 85 ( 1 ) 101 - 109 2012年

掲載種別：研究論文（学術雑誌）

Chiral diporphyrin receptor 1, which has a macrocyclic cavity for the intercalation of aromatic guest molecules, was designed and synthesized from pyrrole in five steps. The binding constants (Ka) revealed the greater affinity of 1 for more electron-deficient aromatic guests. The complexation between 1 and 1,3,5-trinitrobenzene (G8) (Ka = 1850M -1) was much stronger than that between porphyrin monomer 3 and G8 (Ka = 50M -1). This result strongly suggests that G8 was intercalated into the cavity of 1 via cooperative double π-π stacking. Interestingly, 1 enabled the naked-eye detection of an aromatic explosive G8; a dark-red solution of 1 in CHCl3 turned into a colloidal suspension upon addition of G8, and the light was scattered. Fluorescence spectroscopy was also useful for the selective detection of G8; fluorescence of 1 was quenched by complexation with G8, which was visible with the naked eye. Despite modest binding constants for dinitrobenzene derivatives, 1 showed a good ability to discriminate the enantiomers of twelve chiral compounds bearing a dinitrophenyl group by NMR spectroscopy. The MM calculations with the MM3 force field reproduced inclusion complexes between 1 and nitroaromatic compounds. The mechanism of chiral discrimination is proposed. © 2012 The Chemical Society of Japan.

DOI： 10.1246/bcsj.20110230

Chiral porphyrin dimer with a macrocyclic cavity for intercalation of aromatic guests

Tadashi Ema, Norichika Ura, Katsuya Eguchi, Yuhei Ise, Takashi Sakai

Chemical Communications 47 ( 21 ) 6090 - 6092 2011年5月

Highly active lipase immobilized on biogenous iron oxide via an organic bridging group: The dramatic effect of the immobilization support on enzymatic function

Tadashi Ema, Yuki Miyazaki, Izumi Kozuki, Takashi Sakai, Hideki Hashimoto, Jun Takada

Green Chemistry 13 ( 11 ) 3187 - 3195 2011年1月

掲載種別：研究論文（学術雑誌）

Iron-oxidizing bacteria, Leptothrix ochracea, produce biogenous iron oxide (BIO), while the heat treatment of BIO gives its magnetized material (m-BIO). In this study, they were chemically modified with silane coupling agents to give organic–inorganic hybrid materials, which were then used as immobilization supports for enzymes. BIO-M, which was prepared by modifying BIO with 3-methacryloxypropyltrimethoxysilane, was found to be the best immobilization support. The immobilized lipases showed remarkably high catalytic activity; for example, Burkholderia cepacia lipase (BCL) immobilized on BIO-M showed a turnover frequency of 33 000 h−1 for 1-phenylethanol (1a). m-BIO-M, which was prepared by modifying m-BIO with 3-methacryloxypropyltrimethoxysilane, was also used as an immobilization support. Although the lipases immobilized on m-BIO-M showed lower catalytic activity than those immobilized on BIO-M, the former could be separated and reused easily by using a magnet. These immobilized enzymes could be recycled at least five times and are environmentally benign biocatalysts. © 2011 The Royal Society of Chemistry.

DOI： 10.1039/c1gc15877e

Bifunctional organocatalyst for activation of carbon dioxide and epoxide to produce cyclic carbonate: Betaine as a new catalytic motif

Yoshihiro Tsutsumi, Kyohei Yamakawa, Masahiko Yoshida, Tadashi Ema, Takashi Sakai

Organic Letters 12 ( 24 ) 5728 - 5731 2010年12月

Chemoenzymatic synthesis of optically active alcohol and β-amino-acid derivative containing the difluoromethylene group

Tadashi Ema, Taro Kadoya, Kumiko Akihara, Takashi Sakai

Journal of Molecular Catalysis B: Enzymatic 66 ( 1-2 ) 198 - 202 2010年9月

掲載種別：研究論文（学術雑誌）

The bioreduction of α,α-difluorinated ketones, ethyl 2,2-difluoro-3-oxobutanoate (2a) and 2,2-difluoro-1-phenyl-1,3-butanedione (2b), with cells of recombinant Escherichia coli overproducing SCR (Saccharomyces cerevisiae carbonyl reductase from bakers' yeast) and GDH (glucose dehydrogenase from Bacillus megaterium) gave enantiomerically pure alcohols, ethyl (S)-2,2-difluoro-3-hydroxybutanoate ((S)-1a) and (S)-2,2-difluoro-3-hydroxy-1- phenyl-1-butanone ((S)-1b), respectively, in the presence of NADP+ and glucose in buffer. The reductions of 2a and 2b proceeded completely at the substrate concentrations of 0.4 M (67 g/L) and 1.0 M (200 g/L), respectively. The opposite enantiomers (R)-1a and (R)-1b were also produced by enzyme E039 (a mixture of carbonyl reductase and formate dehydrogenase) contained in Chiralscreen OH (Daicel Chemical Industries) in the presence of NADH and sodium formate in buffer. Enantiomerically pure (S)-1a was converted by organic synthetic methods into an α,α-difluorinated derivative of (R)-β-aminobutyric acid (BABA) in three steps. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.molcatb.2010.05.009

Rational creation of mutant enzyme showing remarkable enhancement of catalytic activity and enantioselectivity toward poor substrates

Tadashi Ema, Shusuke Kamata, Masahiro Takeda, Yasuko Nakano, Takashi Sakai

Chemical Communications 46 ( 30 ) 5440 - 5442 2010年8月

掲載種別：研究論文（学術雑誌）

Catalytic activity and enantioselectivity of lipase toward poor substrates bearing bulky substituents on both sides have been dramatically improved by rational design; the E value for a poor substrate was increased from 5 (wild-type enzyme) to >200 (I287F/I290A double mutant) with an acceleration of the reaction rate. © The Royal Society of Chemistry 2010.

DOI： 10.1039/c001561j

Synthesis and evaluation of chiral selectors with multiple hydrogen-bonding sites in the macrocyclic cavities

Tadashi Ema, Kazuki Hamada, Kyoko Sugita, Yohei Nagata, Takashi Sakai, Atsushi Ohnishi

Journal of Organic Chemistry 75 ( 13 ) 4492 - 4500 2010年7月

掲載種別：研究論文（学術雑誌）

(Figure presented) Chiral macrocycles with the hydrogen bond donor/acceptor sites in the cavity were synthesized and covalently bonded to silica gel to give chiral stationary phases (CSPs), which showed excellent abilities to resolve various chiral compounds including ketones, esters, carboxylic acids, sulfoxides, amines, amino acid derivatives, and metal complexes. The effect of the linker connecting the macrocyclic moiety to silica was examined, and a more electronegative substituent was found to be better. Various organic solvents could be used as the mobile phase to optimize the resolution efficiency of the CSPs. Although the separation factors (α) tended to decrease with an increase in the solvent polarity, remarkable solvent tolerance was also observed. In some cases, even MeCN and MeOH could be used for the complete resolution of enantiomers. The MM calculations suggested that the chiral recognition of Co(acac)3 is achieved by a combination of steric interactions and hydrogen bonds between the carbonyl O atom coordinated to the Co atom and the macrocyclic amide NH groups. The attachment of substituents to the 3,3′-positions of the binaphthyl moiety improved chiral HPLC performance in some cases. In particular, CSP-1d, having the Br atoms, showed the best performance for several analytes. © 2010 American Chemical Society.

DOI： 10.1021/jo1006587

Chemical modification of biogenous iron oxide to create an excellent enzyme scaffold

Takashi Sakai, Yuki Miyazaki, Ai Murakami, Noriko Sakamoto, Tadashi Ema, Hideki Hashimoto, Mitsuaki Furutani, Makoto Nakanishi, Tatsuo Fujii, Jun Takada

Organic and Biomolecular Chemistry 8 ( 2 ) 336 - 338 2010年

Empirical method for predicting enantioselectivity in catalytic reactions: demonstration with lipase and oxazaborolidine

Tadashi Ema, Norichika Ura, Masataka Yoshii, Toshinobu Korenaga, Takashi Sakai

Tetrahedron 65 ( 46 ) 9583 - 9591 2009年11月

掲載種別：研究論文（学術雑誌）

We derived a novel equation capable of predicting the degree of enantioselectivity in a catalytic reaction without any knowledge of the reaction mechanism and/or the transition-state structure, and tested the validity of this equation by changing substrates systematically in the lipase or oxazaborolidine-catalyzed reactions. A good correlation was observed between the predicted and observed E values, and the stereochemistry of the products could be predicted correctly in most cases (28 out of 30). © 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2009.09.058

Stereoselective synthesis of bicyclic tertiary alcohols with quaternary stereocenters via intramolecular crossed benzoin reactions catalyzed by n-heterocyclic carbenes

Tadashi Ema, Yoshitaka Oue, Kumiko Akihara, Yuki Miyazaki, Takashi Sakai

Organic Letters 11 ( 21 ) 4866 - 4869 2009年11月

Tuning the chiral cavity of macrocyclic receptor for chiral recognition and discrimination

Tadashi Ema, Daisuke Tanida, Kazuki Hamada, Takashi Sakai

Journal of Organic Chemistry 73 ( 22 ) 9129 - 9132 2008年11月

掲載種別：研究論文（学術雑誌）

(Chemical Equation Presented) The size and shape of the chiral cavity of a macrocyclic receptor were tuned by the alteration of the binaphthyl moiety to improve the chiral recognition/discrimination ability. For example, host 3 with the 3,5-bis(trifluoromethyl)phenyl group at the 3,3′-positions showed improved enantioselectivity for small molecules such as 2-chloropropionic acid and methyl lactate as evaluated by the binding constants. This host 3 also had an excellent ability as an NMR chiral solvating agent. © 2008 American Chemical Society.

DOI： 10.1021/jo801584b

Highly efficient chemoenzymatic synthesis of methyl (R)-o-chloromandelate, a key intermediate for clopidogrel, via asymmetric reduction with recombinant Escherichia coli

Tadashi Ema, Sayaka Ide, Nobuyasu Okita, Takashi Sakai

Advanced Synthesis and Catalysis 350 ( 13 ) 2039 - 2044 2008年9月

掲載種別：研究論文（学術雑誌）

Methyl (R)-o-chloromandelate [(R)-1], which is an intermediate for a platelet aggregation inhibitor named clopidogrel, was obtained in >99% ee by the asymmetric reduction of methyl o-chlorobenzoylformate (2) with recombinant Escherichia coli overproducing a versatile carbonyl reductase. A remarkable temperature effect on productivity was observed in the whole-cell reduction of 2, and the optimum productivity as high as 178 g/L was attained at 20°C on a 2-g scale (1.0 M). The optimized reaction could be scaled up easily to transform 20 g of 2 in 100 mL of buffer. Three synthetic methods for 2 are compared. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/adsc.200800292

Lipase-catalyzed dynamic kinetic resolution giving optically active cyanohydrins: use of silica-supported ammonium hydroxide and porous ceramic-immobilized lipase

Takashi Sakai, Kefei Wang, Tadashi Ema

Tetrahedron 64 ( 9 ) 2178 - 2183 2008年2月

掲載種別：研究論文（学術雑誌）

Synthetically useful cyanohydrin acetates, ArCH(OAc)CN (Ar=C6H5, 3,4-methylenedioxyphenyl, 4-Me-C6H4, 4-Cl-C6H4, 4-F-C6H4, 4-CF3-C6H4), were successfully synthesized in high enantiomeric purities (79-93% ee) via the lipase-catalyzed dynamic kinetic resolution (DKR) of cyanohydrins synthesized in situ from the corresponding aldehydes and acetone cyanohydrin. The combined use of silica-supported BTAH (benzyltrimethylammonium hydroxide) and porous ceramic-immobilized lipase under the optimized reaction conditions enabled the remarkable acceleration of the enantioselective DKR reactions. © 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2007.12.030

Hydrolase-catalyzed kinetic resolution of 5-[4-(1-hydroxyethyl)phenyl]-10, 15,20-tris(pentafluorophenyl)porphyrin in ionic liquids

Tadashi Ema, Tokuhiro Doi, Takashi Sakai

Chemistry Letters 37 ( 1 ) 90 - 91 2008年1月

Chiral selector with multiple hydrogen-bonding sites in a macrocyclic cavity

Tadashi Ema, Daisuke Tanida, Kyoko Sugita, Takashi Sakai, Ken Ichiro Miyazawa, Atsushi Ohnishi

Organic Letters 10 ( 12 ) 2365 - 2368 2008年

掲載種別：研究論文（学術雑誌）

(Chemical Equation Presented) Chiral macrocycles with the hydrogen bond donor/acceptor sites in the cavity were synthesized and covalently bonded to silica gel to give chiral stationary phases (CSPs), which showed excellent abilities to resolve various chiral compounds, such as benzoin and Co(acac) 3, in HPLC. Various organic solvents could be used as the mobile phase to optimize the resolution efficiency of CSPs, and in some cases, even MeCN, MeOH, and CO2 could be used for the complete resolution of enantiomers. © 2008 American Chemical Society.

DOI： 10.1021/ol800940j

Biomimetic trifunctional organocatalyst showing a great acceleration for the transesterification between vinyl ester and alcohol

Tadashi Ema, Daisuke Tanida, Tatsuya Matsukawa, Takashi Sakai

Chemical Communications ( 8 ) 957 - 959 2008年

Highly active and robust organic-inorganic hybrid catalyst for the synthesis of cyclic carbonates from carbon dioxide and epoxides

Takashi Sakai, Yoshihiro Tsutsumi, Tadashi Ema

Green Chemistry 10 ( 3 ) 345 - 349 2008年

掲載種別：研究論文（学術雑誌）

A high-throughput combinatorial strategy enabled us to find a highly active organic-inorganic hybrid catalyst for the production of cyclic carbonates from CO2 and epoxides. The best hybrid catalyst 1a was prepared by the coupling of 3-(triethoxysilyl)propyltriphenylphosphonium bromide and mesoporous silica, and the organic and inorganic moieties had a synergistic effect on catalytic activity. The pore size of silica was found to be important for catalysis; mesoporous silica with the mean pore size of 19 nm exhibited much better performance than silica with that of 6 nm. The solvent-free and metal-free reactions proceeded successfully under very mild conditions (1 MPa, 90 °C, 1 mol% loading of catalyst, 6 h), and the hybrid catalyst could be recycled ten times. © The Royal Society of Chemistry.

DOI： 10.1039/b718321f

Versatile and practical macrocyclic reagent with multiple hydrogen-bonding sites for chiral discrimination in NMR

Tadashi Ema, Daisuke Tanida, Takashi Sakai

Journal of the American Chemical Society 129 ( 34 ) 10591 - 10596 2007年8月

掲載種別：研究論文（学術雑誌）

Bifunctional macrocycles 1-4 and diamide 5 were designed and synthesized. NMR studies demonstrated that, among them, receptor 1 functions as the best chiral solvating agent (shift reagent), which is effective for a wide range of chiral compounds having a carboxylic acid, oxazolidinone, carbonate, lactone, alcohol, sulfoxide, sulfoximine, sulfinamide, isocyanate, or epoxide functionality. The addition of only 5 mol % (69 μg, 0.15 mM) of 1 splits the enantiomeric signals of sulfoxide 13. The excellent performance of 1 as a chiral solvating agent, such as versatility, signal sharpness, high splitting ability, high sensitivity, wide detection window, and synthetic accessibility, is reported. NMR studies revealed that the principal binding site of 1 is the two amide NH groups of the lower segment and that the additional binding site is the pyridyl nitrogen. The V-shaped arrangement of the two 2,6-diacylaminopyridine moieties as constructed in 1 was found to be much more effective for binding a variety of compounds than the parallel alignment of the two binding motifs as constructed in 4. The NO2 group in 1 enhanced not only the binding ability but also the degree of enantioselectivity. Unexpectedly, the comparisons between 1 and 3 enabled us to find the importance of the relative orientation of the binaphthyl moiety; the orthogonal disposition of the binaphthyl moiety in 1 most effectively brings about the differential ring-current effect on the chiral guest molecule bound, which leads to the high degree of chiral discrimination in NMR. © 2007 American Chemical Society.

DOI： 10.1021/ja073476s

Highly enantioselective and efficient synthesis of methyl (R)-o-chloromandelate with recombinant E. coli: Toward practical and green access to clopidogrel

Tadashi Ema, Nobuyasu Okita, Sayaka Ide, Takashi Sakai

Organic and Biomolecular Chemistry 5 ( 8 ) 1175 - 1176 2007年

掲載種別：研究論文（学術雑誌）

Methyl (R)-o-chloromandelate ((R)-1), which is an intermediate for a platelet aggregation inhibitor named clopidogrel, was obtained in >99% ee by the asymmetric reduction of methyl o-chlorobenzoylformate (2) (up to 1.0 M) with recombinant E. coli overproducing a versatile carbonyl reductase. © The Royal Society of Chemistry.

DOI： 10.1039/b703463f

Versatile and practical chiral shift reagent with hydrogen-bond donor/acceptor sites in a macrocyclic cavity

Tadashi Ema, Daisuke Tanida, Takashi Sakai

Organic Letters 8 ( 17 ) 3773 - 3775 2006年8月

掲載種別：研究論文（学術雑誌）

Bifunctional macrocycle 1 with C2 symmetry was newly synthesized. NMR studies demonstrated that receptor 1 functions as a chiral shift reagent (solvating agent) that is highly effective for a wide range of chiral compounds having a carboxylic acid, oxazolidinone, lactone, alcohol, sulfoxide, sulfoximine, isocyanate, or epoxide functionality. Binding constants were determined to investigate the binding behavior of 1. © 2006 American Chemical Society.

DOI： 10.1021/ol0613665

Asymmetric reduction of ketones using recombinant E. coli cells that produce a versatile carbonyl reductase with high enantioselectivity and broad substrate specificity

Tadashi Ema, Hideo Yagasaki, Nobuyasu Okita, Masahiro Takeda, Takashi Sakai

Tetrahedron 62 ( 26 ) 6143 - 6149 2006年6月

掲載種別：研究論文（学術雑誌）

The gene encoding a versatile biocatalyst that shows high enantioselectivity for a variety of ketones, SCR (Saccharomyces cerevisiae carbonyl reductase), has been identified, cloned, and expressed in Escherichia coli. Two types of expression systems with high NADPH-regenerating capacities have been constructed. One is the tandem system, where the genes encoding SCR and GDH (glucose dehydrogenase) are located in the same plasmid, and the other is the two-plasmid system, where each of the SCR and GDH genes is located in separate plasmids that can coexist in one E. coli cell. Asymmetric reduction of ketones with the recombinant E. coli cells gave synthetically useful 20 alcohols, 11 of which were enantiomerically pure. The productivity of one of these products was as high as 41 g/L. © 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2006.04.061

Synthesis of molecular tweezers bearing pentafluorophenyl and several pendant aryl groups. Effective application of the modified Suzuki-Miyaura coupling reaction

Toshinobu Korenaga, Takahiro Kosaki, Yusuke Kawauchi, Tadashi Ema, Takashi Sakai

Journal of Fluorine Chemistry 127 ( 4-5 SPEC. ISS. ) 604 - 609 2006年5月

掲載種別：研究論文（学術雑誌）

A molecular tweezer bearing two pentafluorophenyl groups 2b and its o-methylated aryl homologue 2c were newly synthesized by the slight modification of the known procedure. The low yield in the introduction of pentafluorophenyl group to the precursor dibromide 6 was improved by application of the modified Suzuki-Miyaura coupling reaction using C6F5B(OH)2 with Pd2(dba)3/P(t-Bu)3/CsF/Ag2O catalytic system, which was recently developed by us. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jfluchem.2005.12.007

Suzuki-Miyaura coupling reaction using pentafluorophenylboronic acid

Toshinobu Korenaga, Takahiro Kosaki, Rokki Fukumura, Tadashi Ema, Takashi Sakai

Organic Letters 7 ( 22 ) 4915 - 4917 2005年10月

掲載種別：研究論文（学術雑誌）

(Chemical Equation Presented) We have found new conditions for the Suzuki-Miyaura coupling reaction applicable to pentafluorophenylboronic acid (C6F5B(OH)2) (1), which is an inactive substrate under normal conditions. The reactions of 1 with phenyl iodide or bromide under Pd(PPh3)4/CsF/Ag2O or Pd 2(dba)3/ P(t-Bu)3/CsF/Ag2O catalytic system conditions gave 2,3,4,5,6-pentafluoro-1,1′-biphenyl (3a) in more than 90% yields. Combination of CsF and Ag2O was essential for promoting these reactions. © 2005 American Chemical Society.

DOI： 10.1021/ol051866i

Rational control of enantioselectivity of lipase by site-directed mutagenesis based on the mechanism

Tadashi Ema, Toshiyuki Fujii, Misa Ozaki, Toshinobu Korenaga, Takashi Sakai

Chemical Communications ( 37 ) 4650 - 4651 2005年10月

Highly sensitive chiral shift reagent bearing two zinc porphyrins

Tadashi Ema, Nozomi Ouchi, Tokuhiro Doi, Toshinobu Korenaga, Takashi Sakai

Organic Letters 7 ( 18 ) 3985 - 3988 2005年9月

掲載種別：研究論文（学術雑誌）

(Chemical Equation Presented) A new type of chiral receptor (R,R)- or (S,S)-1b with C2 symmetry was synthesized. An induced-fit type of binding behavior of 1b for diamines was revealed by CD spectroscopy. NMR studies demonstrated that 1b can function as a highly sensitive chiral shift reagent for the determination of the enantiomeric purity of chiral diamines, aziridine, and isoxazoline at the microgram level. © 2005 American Chemical Society.

DOI： 10.1021/ol0514808

Kinetic resolution of 5-(hydroxymethyl)-3-phenyl-2-isoxazoline by using the 'low-temperature method' with porous ceramic-immobilized lipase

Takashi Sakai, Hiroshi Mitsutomi, Toshinobu Korenaga, Tadashi Ema

Tetrahedron Asymmetry 16 ( 8 ) 1535 - 1539 2005年4月

掲載種別：研究論文（学術雑誌）

A significant enhancement of the enantioselectivity (E value = 249) in the lipase-catalyzed resolution of a primary alcohol, racemic 5-(hydroxymethyl)-3- phenyl-2-isoxazoline (±)-1, was obtained by using the 'low-temperature method' (-60°C) with porous ceramic-immobilized lipase (Amano PS-C II) and vinyl acetate in acetone. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetasy.2005.02.025

Asymmetric reduction of a variety of ketones with a recombinant carbonyl reductase: Identification of the gene encoding a versatile biocatalyst

Tadashi Ema, Hideo Yagasaki, Nobuyasu Okita, Kumiko Nishikawa, Toshinobu Korenaga, Takashi Sakai

Tetrahedron Asymmetry 16 ( 6 ) 1075 - 1078 2005年3月

掲載種別：研究論文（学術雑誌）

The gene encoding a versatile biocatalyst that shows high enantioselectivity for a variety of ketones, SCR (Saccharomyces cerevisiae carbonyl reductase), has been identified, cloned, and expressed in E. coli. Recombinant E. coli co-producing SCR and GDH (glucose dehydrogenase) is an easy-to-use, synthetically useful biocatalyst, and 8 out of the 16 alcohols obtained had enantiomeric purities of >98% ee. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetasy.2005.02.004

Lipase-catalyzed resolution of (2R*,3S*)- and (2R*,3R*)-3-methyl-3-phenyl-2-aziridinemethanol at low temperatures and determination of the absolute configurations of the four stereoisomers

Takashi Sakai, Yu Liu, Hiroshi Ohta, Toshinobu Korenaga, Tadashi Ema

Journal of Organic Chemistry 70 ( 4 ) 1369 - 1375 2005年2月

掲載種別：研究論文（学術雑誌）

(Chemical Equation Presented) Lipase-catalyzed resolution of (2R*,3S*)-3-methyl-3-phenyl-2-aziridinemethanol, (±)-2, at low temperatures gave synthetically useful (2R,3S)-2 and its acetate (2S,3R)-2a with (2S)-selectivity (E = 55 at -40 °C), while a similar reaction of (2R*,3R*)-3-methyl-3-phenyl-2-aziridinemethanol, (±)-3, gave (2S,3S)-3 and its acetate (2R,3R)-3a with (2R)-selectivity (E = 73 at -20 °C). Compound (±)-2 was prepared conveniently via diastereoselective addition of MeMgBr to tert-butyl 3-phenyl-2H-azirine-2-carboxylate, (±)-1a, which was successfully prepared by the Neber reaction of oxime tosylate of tert-butyl benzoyl acetate 7a. The tert-butyl ester was requisite to promote this reaction. For determination of the absolute configuration of (2S,3R)-2a, enantiopure (2S,3R)-2 was independently prepared in three steps involving diastereoselective methylation of 3-phenyl-2H-azirine-2-methanol, (S)-10, with MeMgBr. The absolute configuration of (2S,3S)-3 was determined by X-ray analysis of the corresponding N-(S)-2-(6-methoxy-2-naphthyl)propanoyl derivative (S,S,S)-13.

DOI： 10.1021/jo048243n

Synthesis of a molecular tweezer containing pentafluorophenyl groups and investigation of the π-π stacking interaction for a pentafluorophenyl group in a polar organic solvent

Toshinobu Korenaga, Yusuke Kawauchi, Takahiro Kosaki, Tadashi Ema, Takashi Sakai

Bulletin of the Chemical Society of Japan 78 ( 12 ) 2175 - 2179 2005年

掲載種別：研究論文（学術雑誌）

A molecular tweezer having two bidentate pentafluorophenyl (C 6F 5) groups was synthesized, and the π-π stacking ability of the C 6F 5 groups toward benzene derivatives in a polar organic solvent was evaluated. The structure of the molecular tweezer was revealed to be dimeric in the crystalline state by X-ray analysis. Association constants (K a) between the molecular tweezer and aromatic guests in THF were found to be roughly correlated with the quadrupole moment (Q zz) of the guests, suggesting that the quadrupole-quadrupole contribution plays a significant role in the π-π interaction even in a polar organic solvent. © 2005 The Chemical Society of Japan.

DOI： 10.1246/bcsj.78.2175

Reestimation of the Taft's substituent constant of the pentafluorophenyl group

Toshinobu Korenaga, Koichi Kadowaki, Tadashi Ema, Takashi Sakai

Journal of Organic Chemistry 69 ( 21 ) 7340 - 7343 2004年10月

掲載種別：研究論文（学術雑誌）

The Taft's substituent constant of the pentafluorophenyl group (σ*C6F5)) was reestimated to be 1.50 by correlation between IR spectral data (vC=O) and σ* constants for a series of esters (involving the pentafluorobenzyl group) of 3-phenylpropanoic acid and butanoic acid. The possibility of the disturbance of the correlation by the intramolecular π-π interaction between C 6F5 and C6H5 groups in pentafluorobenzyl 3-phenylpropanoate was excluded by ab initio and DFT calculations of the stable conformations and their carbonyl frequencies. The reestimated σ* (C6F5) value was used for calculation of the pKa value of pentafluorobenzyl alcohol [14.5 (or 14.3)].

DOI： 10.1021/jo048939g

Rational strategies for highly enantioselective lipase-catalyzed kinetic resolutions of very bulky chiral compounds: Substrate design and high-temperature biocatalysis

Tadashi Ema

Tetrahedron Asymmetry 15 ( 18 ) 2765 - 2770 2004年9月

Rational approaches to successful lipase-catalyzed kinetic resolutions of very bulky chiral compounds are briefly reviewed: substrate design and high-temperature biocatalysis. The molecular design based on a stereo-sensing mechanism was the key to the success in the kinetic resolution of 5-[4-(1-hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin. The lipase-catalyzed transesterification of 1,1-diphenyl-2-propanol in n-decane proceeded with excellent enantioselectivity at high temperatures up to 120°C in an autoclave. © 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetasy.2004.06.055

Mechanism of enantioselectivity of lipases and other synthetically useful hydrolases

Tadashi Ema

Current Organic Chemistry 8 ( 11 ) 1009 - 1025 2004年7月

Lipases are biocatalysts most widely used in organic synthesis. Unusual but attractive feature of lipases is that, in addition to high catalytic activity and thermostability in organic solvents, lipases show high enantioselectivity and broad substrate specificity simultaneously. They show excellent enantioselectivity especially toward a wide range of secondary alcohols. The mechanistic details or stereoselective organic reactions are relatively well understood, and knowledge has been used to develop new chemical reagents. In contrast, biocatalysts are behind chemical reagents in rational design approaches, which is partly due to the mechanistic ambiguity or enzymatic reactions. The mechanistic aspects of enantioselective biocatalysts are nevertheless becoming clear. This review provides an overview of the studies aimed at understanding the mechanisms of enantioselectivity of synthetically useful hydrolases such as lipases, subtilisins and chymotrypsins toward unnatural chiral substrates. Several methods for addressing the mechanism are introduced: (i) substrate mapping, (ii) X-ray crystallographic analysis, (iii) computational calculations, (iv) kinetic analysis, (v) thermodynamic analysis, (vi) site-directed or random mutagenesis, (vii) spectroscopic methods such as fluorescence, ESR, and mass spectroscopy. Different models and mechanisms proposed so far are selected and explained. The chemical principles revealed by the mechanistic studies will be useful for (i) using the enzymes in organic synthesis efficiently, (ii) altering the features or the enzymes rationally, (iii) utilizing them as a tool for determining the absolute stereochemistry of molecules, and (iv) designing new artificial catalysts mimicking the catalytic machinery of the enzymes. © 2004 Bentham Science Publishers Ltd.

DOI： 10.2174/1385272043370230

The effect of temperature on the lipase-catalyzed asymmetric protonation of 1-acetoxy-2-methylcyclohexene giving (R)-2-methylcyclohexanone

Takashi Sakai, Akiko Matsuda, Yuko Tanaka, Toshinobu Korenaga, Tadashi Ema

Tetrahedron Asymmetry 15 ( 12 ) 1929 - 1932 2004年6月

掲載種別：研究論文（学術雑誌）

Lipase-catalyzed enantioface-selective protonation of the enol acetate of 2-methylcyclohexanone was performed by using Burkholderia cepacia lipase immobilized on porous ceramic particles, 'Lipase PS-C II' (Amano Enzyme Inc.), in i-Pr2O and ethanol, giving (R)-2-methylcyclohexanone with 77% ee at best with 82% conversion at 0°C. The enantioselectivity (E-value) was found to be temperature dependent and significant in controlling the efficiency of the asymmetric protonation. © 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetasy.2004.05.008

Synthesis of enantiomerically pure (R,R)- and (S,S)-1,2-Bis(pentafluorophenyl)ethane-1,2-diamine and evaluation of the pK <inf>a</inf> value by ab initio calculations

Takashi Sakai, Toshinobu Korenaga, Noriyuki Washio, Yuji Nishio, Shinichi Minami, Tadashi Ema

Bulletin of the Chemical Society of Japan 77 ( 5 ) 1001 - 1008 2004年

掲載種別：研究論文（学術雑誌）

1,2-Bis(pentafluorophenyl)ethane-1,2-diamine (1) was synthesized by the imino pinacol coupling of 4-methoxy-N-(pentafluorobenzylidene)benzylamine using a Zn-Cu couple and p-TsOH·H2O. The optical resolution of (±)-1 by means of chiral HPLC gave enantiomerically pure (R,R)- and (S,S)-1. The pKa value of 1 was estimated by a titration experiment and ab initio calculations, showing that 1 has a basicity comparable to aniline derivatives.

DOI： 10.1246/bcsj.77.1001

Highly enantioselective lipase-catalyzed reactions at high temperatures up to 120°C in organic solvent

Tadashi Ema, Masafumi Kageyama, Toshinobu Korenaga, Takashi Sakai

Tetrahedron Asymmetry 14 ( 24 ) 3943 - 3947 2003年12月

掲載種別：研究論文（学術雑誌）

Lipase-catalyzed kinetic resolutions of 1,1-diphenyl-2-propanol were performed at high temperatures up to 120°C. Burkholderia cepacia lipase immobilized on porous ceramic particles, lipase PS-C II (Amano Enzyme Inc.), gave an enantiopure product at 40-120°C, with the highest conversion (39%) at 80-90°C. The mechanism of high enantioselectivity retained even at 120°C is also described briefly. © 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetasy.2003.09.040

Intermolecular oxygen atom⋯π interaction in the crystal packing of chiral amino alcohol bearing a pentafluorophenyl group

Toshinobu Korenaga, Hikaru Tanaka, Tadashi Ema, Takashi Sakai

Journal of Fluorine Chemistry 122 ( 2 ) 201 - 205 2003年8月

掲載種別：研究論文（学術雑誌）

Presence of an unique atom-to-face alcoholic oxygen atom⋯π interaction between a pentafluorophenyl group and alcoholic oxygen (O⋯π) has been demonstrated by X-ray analysis of the novel chiral amino alcohol instead of the well-known interaction between usual aromatic ring and alcoholic hydrogen atom (OH⋯π). © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-1139(03)00089-7

Enhancement of the efficiency of the low temperature method for kinetic resolution of primary alcohols by optimizing the organic bridges in porous ceramic-immobilized lipase

Takashi Sakai, Kyoko Hayashi, Fumika Yano, Mie Takami, Megumi Ino, Toshinobu Korenaga, Tadashi Ema

Bulletin of the Chemical Society of Japan 76 ( 7 ) 1441 - 1446 2003年7月

掲載種別：研究論文（学術雑誌）

For the enhancement of enantioselectivity and acceleration of the reaction rate in the lipase-catalyzed resolution of primary alcohols, the use of a very low reaction temperature (-30 °C) and an immobilized lipase on organic bridges-coated porous ceramic support was found to be highly effective. Furthermore, the structure of the organic bridges greatly influenced the temperature effect between in E and 1/T as well as the reaction rate. Among the organic bridges examined in the resolution of (±)-2-hydroxymethyl-1,4-benzodioxane, the 6-(2-methylpropanoyloxy)hexylsilanetrioxyl bridge was the best choice for both the E value and the reaction rate at -30 °C.

DOI： 10.1246/bcsj.76.1441

Transition-state models are useful for versatile biocatalysts: Kinetics and thermodynamics of enantioselective acylations of secondary alcohols catalyzed by lipase and subtilisin

Tadashi Ema, Kunihiro Yamaguchi, Yuji Wakasa, Akinori Yabe, Ryoichi Okada, Minoru Fukumoto, Fumika Yano, Toshinobu Korenaga, Masanori Utaka, Takashi Sakai

Journal of Molecular Catalysis B: Enzymatic 22 ( 3-4 ) 181 - 192 2003年6月

掲載種別：研究論文（学術雑誌）

Lipases and subtilisins are versatile enzymes capable of showing high enantioselectivity and broad substrate specificity simultaneously. The transition-state models previously proposed to rationalize this important feature were intensively examined from kinetic and thermodynamic viewpoints. Kinetic measurements reaffirmed that chiral discrimination originates from the transition state and that the enantioselectivity results from the reduced activity of the enzymes for the slower-reacting enantiomer, but not from the enhanced activity for the faster-reacting enantiomer relative to a reference alcohol, cyclopentanol. The larger substituent of the slower-reacting enantiomers interacts repulsively with the protein in the transition state, and even the larger substituent of the faster-reacting enantiomers interacts unfavorably to some degree with the protein. A number of thermodynamic parameters, ΔΔH‡ and ΔΔS‡, for the subtilisin-catalyzed acylations of secondary alcohols were determined. A linear compensation effect was found between the ΔΔH‡ and ΔΔS‡ values. As the ΔΔH‡ value becomes negatively large, the ΔΔS‡ value also becomes negatively large. This observation is explained in terms of the transition-state model. Because the widely accepted concepts such as the lock-and-key mechanism and the induced-fit mechanism cannot account for the peculiar behavior of these enzymes toward unnatural substrates, a new category, the non-lock-and-key mechanism, has been proposed. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1381-1177(03)00034-1

Practical resolution of 3-phenyl-2H-azirine-2-methanol at very low temperature by using lipase immobilized on porous ceramic and optimized acylating agent

Takashi Sakai, Akiko Matsuda, Toshinobu Korenaga, Tadashi Ema

Bulletin of the Chemical Society of Japan 76 ( 9 ) 1819 - 1821 2003年

Mechanism-based enzymatic method for reliable determination of absolute configuration of chiral 1-substituted ethanols: Combination with NMR method

Tadashi Ema, Masataka Yoshii, Toshinobu Korenaga, Takashi Sakai

Tetrahedron Asymmetry 13 ( 11 ) 1223 - 1229 2002年6月

掲載種別：研究論文（学術雑誌）

It has been demonstrated that lipase is useful not only for kinetic resolution but also for the rapid determination of absolute configurations. We have previously proposed a mechanism represented by transition-state models to rationalize the enantioselectivity in the lipase- and subtilisin-catalyzed kinetic resolutions of secondary alcohols. The mechanism indicates that the enzyme-catalyzed reactions can be used as a tool for determining the absolute stereochemistry of secondary alcohols. In order to increase reliability, the enzymatic method was combined with Mosher's method using MTPA, to give a protocol which is named the double-confirmation method. The absolute configurations of six 1-substituted ethanols were determined consistently by this new procedure. The enzymatic method is quick, easy, economical, and reliable. An interesting similarity in conformation between the transition-state models and MTPA esters is also described. © 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0957-4166(02)00318-X

5-[4-(1-Hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin as a probe of the transition-state conformation in hydrolase-catalyzed enantioselective transesterifications

Tadashi Ema, Masahito Jittani, Kenji Furuie, Masanori Utaka, Takashi Sakai

Journal of Organic Chemistry 67 ( 7 ) 2144 - 2151 2002年4月

掲載種別：研究論文（学術雑誌）

5-[4-(1-Hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin (1a) and zinc porphyrin 1b were designed and synthesized to experimentally examine the validity of the transition-state model previously proposed for the lipase-catalyzed kinetic resolution of secondary alcohols. The lipases from Pseudomonas cepacia (lipase PS), Candida antarctica (CHIRAZYME L-2), Rhizomucor miehei (CHIRAZYME L-9), and Pseudomonas aeruginosa (lipase LIP) exhibited excellent enantioselectivity (E > 100 at 30 °C). Subtilisin Carlsberg from Bacillus licheniformis (ChiroCLEC-BL) also showed high enantioselectivity for 1a (E = 140 at 30 °C), and the thermodynamic parameters were determined: ΔΔH‡ = -6.8 ± 0.8 kcal mol-1, ΔΔS‡ = -13 ± 3 cal mol-1 K-1. Lipases and subtilisin showed R- and S-preference for 1, respectively. The mechanisms underlying the experimental observations are explained in terms of the transition-state models. The large secondary alcohol 1 is a powerful tool for investigating the conformation of the transition state of the enzyme-catalyzed reactions. The fact that 1 was resolved with high enantioselectivity strongly suggests that the gauche conformation, but not the anti conformation, is taken in the transition state, in agreement with the transition-state models involving the stereoelectronic effect.

DOI： 10.1021/jo0109063

High enantioselectivity and broad substrate specificity of a carbonyl reductase: Toward a versatile biocatalyst

T. Ema, H. Moriya, T. Kofukuda, T. Ishida, K. Maehara, M. Utaka, T. Sakai

Journal of Organic Chemistry 66 ( 25 ) 8682 - 8684 2001年12月

Lipase-catalyzed transesterification of 2-hydroxy-2- (pentafluorophenyl)acetonitrile leading to (1R,2R)-and (1S,2S)-bis (pentafluorophenyl)ethane-1,2-diol

Takashi Sakai, Yasushi Miki, Masashi Tsuboi, Hiroaki Takeuchi, Tadashi Ema, Kenji Uneyama, Masanori Utaka

Journal of Organic Chemistry 65 ( 9 ) 2740 - 2747 2000年5月

掲載種別：研究論文（学術雑誌）

Optically pure (IR,2R)- and (1S,2S)-1,2-bis(pentafluorophenyl)ethane- 1,2-diol (1) were synthesized from key intermediates (R)- and (S)-2-hydroxy- 2-(pentafluorophenyl)acetonitrile (2), both of which were prepared by the lipase LIP-catalyzed transesterification (E - 465). The absolute configuration of (S)-2 was determined by X-ray structural analysis after transformation into (S)-a-cyano-2,3,4,5,6-pentafluorobenzyl (S)-6-methoxy-a- methyl-2-naphthaleneacetate (S,S)-9. In addition, the crystal structure of (S,S)-9 has an interesting well-ordered packing pattern which shows face-to- face stacking interactions and end-to-end parallel contacts between the pentafluorophenyl and 6-methoxynaphthyl groups of the adjacent molecules.

DOI： 10.1021/jo9918551

Compensation effect between differential activation enthalpy and entropy in subtilisin-catalyzed kinetic resolutions of secondary alcohols

Tadashi Ema, Kunihiro Yamaguchi, Yuji Wakasa, Nobuaki Tanaka, Masanori Utaka, Takashi Sakai

Chemistry Letters ( 7 ) 782 - 783 2000年

Transition-state model for subtilisin-catalyzed transesterifications of secondary alcohols

Ema Tadashi, Ryoichi Okada, Minoru Fukumoto, Masahito Jittani, Mikiko Ishida, Kenji Furuie, Kunihiro Yamaguchi, Takashi Sakai, Masanori Utaka

Tetrahedron Letters 40 ( 23 ) 4367 - 4370 1999年6月

掲載種別：研究論文（学術雑誌）

In the subtilisin-catalyzed transesterications of a variety of secondary alcohols, the (S)-enantiomers were acylated faster. Kinetic measurements indicated that the enantioselectivily originates from chiral discrimination in the transition state. A transition-state model capable of explaining the S-preference of subtilisin toward secondary alcohols has been proposed.

DOI： 10.1016/S0040-4039(99)00750-9

Low-temperature method for enhancement of enantioselectivity in the lipase-catalyzed kinetic resolutions of solketal and some chiral alcohols

Takashi Sakai, Tetsuo Kishimoto, Yukie Tanaka, Tadashi Ema, Masanori Utaka

Tetrahedron Letters 39 ( 43 ) 7881 - 7884 1998年10月

Lipase-catalyzed kinetic resolution of large secondary alcohols having tetraphenylporphyrin

Tadashi Ema, Masahito Jittani, Takashi Sakai, Masanori Utaka

Tetrahedron Letters 39 ( 35 ) 6311 - 6314 1998年8月

掲載種別：研究論文（学術雑誌）

Large secondary alcohols, 5-[4-(1-hydroxyethyl)phenyl]-10,15,20- triphenylporphyrin (1a) and the zinc complex 1b, designed on the basis of the transition-state model recently proposed by us, were subjected to the lipase- catalyzed transesterifications. The alcohols were resolved using lipases from Pseudomonas cepacia (lipase PS), Candida antarctica (CHIRAZYME L-2), Rhizomucor miehei (CHIRAZYME L-9), and Pseudomonas aeruginosa (lipase LIP) with high enantioselectivities (E > 100).

DOI： 10.1016/S0040-4039(98)01338-0

Control of enantioselectivity in the baker's yeast asymmetric reduction of γ-chloro β-diketones to γ-chloro (S)-β-hydroxy ketones

Jing Nan Cui, Tadashi Ema, Takashi Sakai, Masanori Utaka

Tetrahedron Asymmetry 9 ( 15 ) 2681 - 2692 1998年8月

掲載種別：研究論文（学術雑誌）

1-Chloro-2,4-alkanediones 1a-f prepared in one step were reduced using baker's yeast to afford 1-chloro-2-hydroxy-4-alkanones 2a-f regioselectively in S 29% to R 58% ee. Use of a small amount of organic solvents to dissolve the substrate enhanced the enantiomeric excess in favor of the S configuration. The function of the organic solvents was studied with reducing enzymes isolated from baker's yeast. Some polar solvents selectively inhibited the enzymes, while nonpolar solvents enhanced the concentration of substrate in water. Application of inhibitors with heat-treatment and organic solvents as additives enhanced the enantiomeric excesses of the products to S 66-96% ee.

DOI： 10.1016/S0957-4166(98)00269-9

Highly Enantioselective Reduction of Carbonyl Compounds Using a Reductase Purified from Bakers' Yeast

Tadashi Ema, Yasushi Sugiyama, Minoru Fukumoto, Hiroyuki Moriya, Jing Nan Cui, Takashi Sakai, Masanori Utaka

Journal of Organic Chemistry 63 ( 15 ) 4996 - 5000 1998年7月

掲載種別：研究論文（学術雑誌）

An NADPH-dependent reductase that shows reducing activity for 1-chloro-2-hexanone has been purified from bakers' yeast. SDS-PAGE and gel filtration suggested that the purified reductase is a monomeric enzyme with a molecular weight of ca. 37 kDa. Asymmetric reduction of several carbonyl compounds using the purified reductase has been carried out. 1-Chloro-2-hexanone, 1-acetoxy-2-heptanone, methyl acetoacetate, ethyl pyruvate, 1-chloro-2,4-pentanedione, and 2,4-hexanedione were reduced to the corresponding alcohols with high enantiomeric purities (>98% ee). The reductase showed high specificity constants (kcat/Km = 103-105 s-1 M-1) and relatively low Michaelis constants (Km = 10-4-10-3 M) for all the substrates examined.

DOI： 10.1021/jo980165e

Lipase-catalyzed kinetic resolution of 2-acyloxy-2- (pentafluorophenyl)acetonitrile

Takashi Sakai, Yasushi Miki, Mayumi Nakatani, Tadashi Ema, Kenji Uneyama, Masanori Utaka

Tetrahedron Letters 39 ( 29 ) 5233 - 5236 1998年7月

掲載種別：研究論文（学術雑誌）

The lipase-catalyzed kinetic resolution of (±)-2-acyloxy-2- (pentafluorophenyl)acetonitrile (±)-1 gave optically active cyanohydrin (S)- 2 and its antipodal ester (R)-1 (E = 211), the former of which was transformed (TBSOTf, DMAP) into its TBS-ether (S)-3, a new fluorinated chiral building block, and into naproxen ester 4 for X-ray analysis to determine the absolute configuration.

DOI： 10.1016/S0040-4039(98)01029-6

Origin of the Enantioselectivity of Lipases Explained by a Stereo-Sensing Mechanism Operative at the Transition State

Tadashi Ema, Juka Kobayashi, Soichi Maeno, Takashi Sakai, Masanori Utaka

Bulletin of the Chemical Society of Japan 71 ( 2 ) 443 - 453 1998年2月

掲載種別：研究論文（学術雑誌）

The stereoelectronic considerations and the molecular modeling using an X-ray structure of Rhizomucor miehei lipase suggested that the lipase-catalyzed reactions proceed under the stereoelectronic control. This suggestion was supported by the semiempirical MO (MNDO-PM3) calculations carried out on the imidazole-catalyzed transesterification as a model reaction. The stereoelectronic effect operates at the transition state (TS) more effectively than at the tetrahedral intermediate (THI). The stabilization energy due to the stereoelectronic effect operating at the TS was estimated to be ca. 5 kcal mol-1. The enantioselectivities for 1-phenylethanol, l-phenyl-2-propanol, and 1-cyclohexylethanol were estimated in terms of the lipase-induced strain caused at the TS. A TS model generally applicable to chiral secondary alcohols is proposed. The kinetic study supported the TS model. The result that the enantioselectivity in the lipase-catalyzed transesterifications arises from the difference in Vmax between the two enantiomers rather than from the difference in Km indicates that the ability of Upases to discriminate between the enantiomers at the TS is high, while the ability to recognize the chirality in the binding step is poor. Furthermore, the difference in Vmax between the enantiomers was found to result not from the enhanced reactivity of the (R)-enantiomers but from the reduced reactivity of the (S)-enantiomers.

DOI： 10.1246/bcsj.71.443

Enhancement of the Enantioselectivity in Lipase-Catalyzed Kinetic Resolutions of 3-Phenyl-2H-azirine-2-methanol by Lowering the Temperature to -40°C

Takashi Sakai, Isamu Kawabata, Tetsuo Kishimoto, Tadashi Ema, Masanori Utaka

Journal of Organic Chemistry 62 ( 15 ) 4906 - 4907 1997年7月

Highly regio- and enantioselective reduction of 1-chloro-2,4-alkanediones using baker's yeast: Effects of organic solvents as additives

Jing Nan Cui, Ryoji Teraoka, Tadashi Ema, Takashi Sakai, Masanori Utaka

Tetrahedron Letters 38 ( 17 ) 3021 - 3024 1997年4月

掲載種別：研究論文（学術雑誌）

Bakers' yeast reduction of 1-chloro-2,4-alkanediones 1a afforded 1-chloro-2-hydroxy-4-alkanones 2a regioselectively with low optical purities. Application of inhibitors and heat-treatment of bakers' yeast enhanced the optical purities toward the S enantiomer (88-91% ee). Organic solvents added in small amounts were also found to enhance the S selectivity significantly. High optical purities 94-96% ee were achieved by the combined action of the inhibitor, heat-treatment, and organic solvent.

DOI： 10.1016/S0040-4039(97)00524-8

Lipase-catalyzed efficient kinetic resolution of 3-Hydroxy-3-(pentafluorophenyl)propionitrile

Takashi Sakal, Tetsuo Takayama, Takafumi Ohkawa, Osamu Yoshio, Tadashi Ema, Masanori Utaka

Tetrahedron Letters 38 ( 11 ) 1987 - 1990 1997年3月

掲載種別：研究論文（学術雑誌）

Efficient kinetic resolution of racemic 3-hydroxy-3-(pentafluorophenyl)- propionitrile (±)-1 by a lipase-catalyzed transesterification gave optically pure (S)-3-hydroxy-3-(pentafluorophenyl-)propionitrile (S)-1 and (R)-(+)-3-acetoxy-3-(penta-fluorophenyl)propionitrile (R)-1 [>99% ee, respectively, E = 1057], the former of which was further transformed into (S)-(-)-3-amino-1-(pentafluorophenyl)-1-propanol (S)-7 in four steps.

DOI： 10.1016/S0040-4039(97)00255-4

New optically active diporphyrin having a chiral cyclophane as a spacer

Tadashi Ema, Shigeharu Misawa, Shuichi Nemugaki, Takashi Sakai, Masanori Utaka

Chemistry Letters ( 6 ) 487 - 488 1997年

Kinetic resolution of racemic 2-substituted 3-cyclopenten-1-ols by lipase-catalyzed transesterifications: A rational strategy to improve enantioselectivity

Tadashi Ema, Soichi Maeno, Yusuke Takaya, Takashi Sakai, Masanori Utaka

Journal of Organic Chemistry 61 ( 24 ) 8610 - 8616 1996年11月

掲載種別：研究論文（学術雑誌）

The effect of the acyl group of acylating agents on the enantioselectivity in the Pseudomonas cepacia lipase-catalyzed acylations of racemic alcohols has been studied. 2-[(N,N-Dimethylcarbamoyl)-methyl]-3-cyclopenten-1-ol (1) and 2-[2-(tert-butyldimethylsilyloxy)ethyl]-3-cyclopenten-1-ol (4) were resolved with a variety of enantioselectivities. In the case of alcohol 1, the enantiomeric ratio (the E value) was increased by changing the acylating agent from vinyl acetate (E = 30) to vinyl butyrate (E = 156) and dropped substantially with longer acyl donors. With vinyl chloroacetate, the reaction rate was fast and the enantioselectivity was high (E = 89), whereas the resolution with vinyl trifluoroacetate resulted in a very poor enantioselectivity (E = 4). The bulky acylating agent, vinyl pivalate, gave a moderate enantioselectivity (E = 15). In the case of alcohol 4, the enantioselectivities were excellent (E > 142) except vinyl pivalate (E = 12). It is indicated that the acyl group transiently attached at the active site of the lipase acts as a stereochemical controller. The solvent effect is also described briefly. A clear correlation was observed between the E values and the log P values of the organic solvents; the smaller the log P value of the solvent, the higher the E value.

DOI： 10.1021/jo961144s

Significant effect of acyl groups on enantioselectivity in lipase-catalyzed transesterifications

Tadashi Ema, Soichi Maeno, Yusuke Takaya, Takashi Sakai, Masanori Utaka

Tetrahedron Asymmetry 7 ( 3 ) 625 - 628 1996年3月

掲載種別：研究論文（学術雑誌）

The effect of the acyl group of acylating agents on the enantioselectivity in the lipase-catalyzed transesterification of racemic 2-[(N,N-dimethylcarbamoyl)methyl]-3-cyclopenten-1-ol in diisopropyl ether was found to be significant. The enantioselectivity was enhanced markedly by changing the acylating agent from vinyl acetate to vinyl butyrate, and dropped substantially with longer acyl donors. Other acyl donors were also examined.

DOI： 10.1016/0957-4166(96)00049-3

Highly efficient and convenient regeneration of NADPH for asymmetric reduction using bakers' yeast cell free extract

Masanori Utaka, Tomoko Yano, Ema Tadashi, Takashi Sakai

Chemistry Letters ( 12 ) 1079 - 1080 1996年

Unusual picosecond ¹(π, π^*) deactivation of ruffled nonplanar porphyrins

Steve Gentemann, Craig J. Medforth, Tadashi Ema, Nora Y. Nelson, Kevin M. Smith, Jack Fajer, Dewey Holten

Chemical Physics Letters 245 ( 4-5 ) 441 - 447 1995年11月

掲載種別：研究論文（学術雑誌）

Time-resolved and steady-state optical data are presented for metal-free meso-tetraalkylporphyrins, H2T(alkyl)P. Introduction of bulky tertiary-butyl or adamantyl substituents at the meso positions induces large ruffling distortions of the macrocycle skeleton that give rise to highly novel photophysical properties of the porphyrins. These include ultrashort 1(π, π*) lifetimes of 10-50 ps at 296 K that, intriguingly, lenghten to 10-15 ns at 78 K, the typical timescale found at both temperatures for planar derivatives such as tetra(n-pentyl) and tetraphenyl porphyrins. The ability of the nonplanar ruffled porphyrins to undergo additional structural deformations in the excited singlet state likely underlies their dramatically enhanced rates of internal conversion. © 1995.

DOI： 10.1016/0009-2614(95)01030-D

Molecular recognition: New chiral metalloporphyrins as receptor models

Hisanobu Ogoshi, Tadashi Ema, Yusuke Kato, Tadashi Mizutani, Yasuhisa Kuroda

Supramolecular Chemistry 6 ( 1-2 ) 115 - 124 1995年10月

掲載種別：研究論文（学術雑誌）

New chiral metalloporphyrins capable of multi-point recognition are prepared and their recognition behavior, especially chiral recognition, is studied. The first part of the paper is concerned with general formalism for multi-point recognition, where uniqueness of multi-point recognition, isolation of interaction in terms of free energy, enthalpy and entropy, and the meaning of these thermodynamic parameters are discussed. Enantioselective binding of amino acid esters to two new chiral porphyrins is investigated by UV-vis, NMR and IR spectroscopic methods. Chiral recognition is achieved by combination of three recognition interactions between host and guest. © 1995, Taylor & Francis Group, LLC. All rights reserved.

DOI： 10.1080/10610279508032527

Synthesis and CD spectrum of chiral porphyrin dimer

Tadashi Ema, Shuichi Nemugaki, Sadao Tsuboi, Masanori Utaka

Tetrahedron Letters 36 ( 33 ) 5905 - 5908 1995年8月

Restricted internal rotation of amino acid esters. Quantitative evaluation of rigidity of a molecule in terms of internal rotation entropy

Tadashi Mizutani, Tadashi Ema, Hisanobu Ogoshi

Tetrahedron 51 ( 2 ) 473 - 484 1995年1月

掲載種別：研究論文（学術雑誌）

As a model of molecular recognition of a flexible guest through multi-point recognition, the two-point fixation of the NH2 group and the C=O group of amino acid esters to porphyrin host was investigated from thermodynamic point of view. The negative entropy change owing to restriction of internal rotation around the Cα-C(carbonyl) bond of guest as driven by the two-point fixation was calculated from the following steps: (1) ab initio molecular orbital calculations at the 3-21G level to generate a potential energy surface for internal rotation along the Cα-C(carbonyl) bond and the Cα-Cβ bond, and (2) a calculation of partition function of the system based on classical statistical mechanics. The entropy loss due to the restriction of a rotation around the Cα-C(carbonyl) bond was 5.0 cal·K-1·mol-1 for alanine methyl ester and 1.9 cal·K-1·mol-1 for valine methyl ester, indicating that valine methyl ester is more rigid with respect to the Cα-C(carbonyl) rotation. This entropy loss was found to originate from the correlated rotation of the Cα-C(carbonyl) bond and the Cα-Cβ bond. © 1994.

DOI： 10.1016/0040-4020(94)00909-E

Crystal structure of a remarkably ruffled nonplanar porphyrin (pyridine)[5,10,15,20-tetra(tert-butyl)porphyrinato]zinc(II)

Mathias O. Senge, Tadashi Ema, Kevin M. Smith

Journal of the Chemical Society, Chemical Communications ( 7 ) 733 - 734 1995年

Ruffling in a Series of Nickel(II) meso-Tetrasubstituted Porphyrins as a Model for the Conserved Ruffling of the Heme of Cytochromes c

W. Jentzen, M. C. Simpson, J. D. Hobbs, X. Song, J. A. Shelnutt, T. Ema, N. Y. Nelson, C. J. Medforth, K. M. Smith, M. Veyrat, M. Mazzanti, R. Ramasseul, J. C. Marchon, T. Takeuchi, W. A. Goddard

Journal of the American Chemical Society 117 ( 45 ) 11085 - 11097 1995年

掲載種別：研究論文（学術雑誌）

Metalloporphyrins undergo remarkable nonplanar distortions of the macrocycle that perturb the chemical and photochemical properties of these important protein cofactors. Further, the tertiary structure of the surrounding protein can manipulate these distortions as a means of regulating biological function. For cytochromes c, for example, an energetically unfavorable, conserved nonplanar distortion of the heme exists and likely plays a role in its electrontransfer function. The heme distortion is primarily of the ruffling (ruf) type (corresponding to the lowest frequency B1u-symmetry normal mode) in which the pyrroles are twisted about the metal–Npyrrole bond. This B1u-symmetry nonplanar distortion is commonly observed in metalloporphyrin crystal structures, as are the saddling (sad) B2u-symmetry distortion, waving (wav) Eg-symmetry distortions, and doming (dom) A2u-symmetry distortion. Each of these nonplanar distortions is expected to result in unique alterations of the chemical and physical properties of the nominally planar porphyrin macrocycle. Symmetrical porphyrin substitution with tetrahedrally bonded atoms at the four meso bridging carbons generally results in the B1u ruffling distortion; therefore, we investigated a series of meso-tetrasubstituted porphyrins for which the substituents vary in size (methyl, ethyl, propyl, pentyl, isopropyl, cyclopropyl derivative 11a, cyclohexyl, apopinenyl (10), tert-butyl, adamantyl), increasing the steric crowding at the periphery. Molecular mechanics calculations show increasing degree of ruffling (CαNNCα angle for opposite pyrroles varies from 0 to 57°) for this series of porphyrins, generally agreeing with the X-ray structures that are available. In addition, the frequencies of the structure-sensitive Raman lines decrease nonlinearly with increasing ruffling angle. The localization of the B1u nonplanar distortion in only the Cα-Cm bond torsion (not the case for the B2u sad distortion) suggests a means by which the B1u distortion might be distinguished from other types of nonplanar distortion by using resonance Raman spectroscopy. Also, the size of the red shifts in the π → π* absorption bands depends on Cα–Cm torsion angle in a nonlinear fashion and the shift is accurately predicted by INDO/s molecular orbital calculations when the nonplanar structures obtained from molecular mechanics are used. © 1995, American Chemical Society. All rights reserved.

DOI： 10.1021/ja00150a008

Complexation-induced Catalysis in Zinc Insertion into Cationic Porphyrin 査読

Mizutani, T, Koyama, H, Ema, T, Nomura, A, Yoshida, T, Ogoshi, H

Chem. Lett. ( 10 ) 941 - 942 1995年

5,10,15,20‐Tetra‐tert‐butylporphyrin and Its Remarkable Reactivity in the 5‐ and 15‐Positions

Tadashi Ema, Mathias O. Senge, Nora Y. Nelson, Hisanobu Ogoshi, Kevin M. Smith

Angewandte Chemie International Edition in English 33 ( 18 ) 1879 - 1881 1994年9月

掲載種別：研究論文（学術雑誌）

Owing to the steric bulk of the tert‐butyl groups, the reactivity of the novel porphyrin 1, which has a nonplanar macrocyclic framework, deviates distinctly from that of any other known porphyrin. For example, prolonged treatment of 1 in HClO4/MeOH leads to formation of 5,15‐dihydroporphyrin (“porphodi‐methene”) 2. (Figure Presented.) Copyright © 1994 by VCH Verlagsgesellschaft mbH, Germany

DOI： 10.1002/anie.199418791

Mechanism of Induced Circular Dichroism of Amino Acid Ester-Porphyrin Supramolecular Systems. Implications to the Origin of the Circular Dichroism of Hemoprotein

Tadashi Mizutani, Tadashi Ema, Takashi Yoshida, Thomas Renné, Hisanobu Ogoshi

Inorganic Chemistry 33 ( 16 ) 3558 - 3566 1994年8月

掲載種別：研究論文（学術雑誌）

Circular dichroism (CD) spectra of the complexes between metalloporphyrins and chiral amino acid derivatives exhibited either split type induced CD or single peak induced CD in the Soret region depending on the host-guest combination. Systematic studies on the complexation of amino acid derivatives by porphyrin hosts indicate that intermolecular hydrogen bonding to the carbonyl group of the guest is necessary for the split type induced CD to occur. Molecular orbital calculations of the rotational strength of a porphyrin-amino acid ester complex by the MNDO method predict that the ICD of porphyrin-amino acid ester complexes is determined by the relative geometry of the carbonyl group and the porphyrin plane. The relative geometry of the chromophores expected from the X-ray crystallographic analysis of a complex between leucine methyl ester and a similar host then gives split type induced CD, in agreement with experiment. These experimental and theoretical results indicate that the coupling between the magnetic transition dipole moment (mj) and the electric transition dipole moment (μj) of a carbonyl group and the electric transition dipole moment (μi) of the porphyrin Soret band makes an important contribution to the observed induced CD. © 1994, American Chemical Society. All rights reserved.

DOI： 10.1021/ic00094a020

Design and Synthesis of a Trifunctional Chiral Porphyrin with C<inf>2</inf> Symmetry as a Chiral Recognition Host for Amino Acid Esters

Tadashi Mizutani, Tadashi Ema, Takashi Tomita, Yasuhisa Kuroda, Hisanobu Ogoshi

Journal of the American Chemical Society 116 ( 10 ) 4240 - 4250 1994年5月

掲載種別：研究論文（学術雑誌）

An intrinsic chiral recognition host, (R,R)- or (S,S)-[trans-5,15-bis(2-hydroxyphenyl)-10-{2,6-bis((methoxycarbonyl)methyl)phenyl}-2,3,17,18-tetraethylporphyrinato]zinc(II) (1), was synthesized by the coupling between (3,3',4,4'-tetraethyl-5,5'-bis(α-hydroxy-2-methoxybenzyl)-2,2'-dipyrryl)methane (8) and dimethyl 2-(bis(2-pyrryl)-methyl)-l,3-benzenediacetate (16). This pyrrylmethanol method made it possible to perform the regiospecific coupling between differently functionalized dipyrromethane units. Host 1 was designed to have three recognition elements: metal coordination, hydrogen bond donor, and hydrogen bond acceptor (and/or steric repulsion) groups. These groups are arranged in a convergent fashion, forming a chiral recognition pocket. Host 1 was resolved into two enantiomers, (+)-1 and (-)-1. The binding constants in CHC13 were determined by UV-vis titration. Host (+)-1 was found to show an enantioselectivity of 2.0-2.8 in respect to l- and d-enantiomers of I1e-OMe, Leu-OMe, Leu-OBzl, Val-OMe, Pro-OMe, and Phe-OMe. Host (+)-1 showed an enantioselectivity of 0.47 in respect to l- and d-enantiomers of serine benzyl ester, indicating that the enantioselectivity was reversed. Reference porphyrins 2-4, which lack some of recognition groups, were also synthesized by the pyrrylmethanol method to clarify the roles of the recognition groups of (+)-1 in thermodynamics of the binding processes. Total free energy change upon binding of l- and d-Ile-OMe to host (+)-l (ΔG°total for L, -5.05, and d, -4.46 kcal/mol) was separated into three terms: metal coordination energy (ΔG°Zn)>-4.15 kcal/mol; hydrogen bond energy (ΔΔG°OH),-1.30 kcal/mol; and steric repulsion energy (ΔΔG°LCOOMe or ΔΔG°DcooMe), +0.40 kcal/mol for l- and +0.99 kcal/mol for d-Ile-OMe. The third recognition group (CH2CO2Me) of (+)-l was found to destabilize the complexes due to steric repulsions. In contrast, the CH2CO2Me group was found to stabilize the complex between d-Ser-OBzl and (+)-l, suggesting that hydrogen bonding between the OH group of serine and the C=O group of (+)-l takes place. On the basis of these thermodynamic studies, chiral recognition was found to be achieved by cooperative functions of these three recognition groups. © 1994, American Chemical Society. All rights reserved.

DOI： 10.1021/ja00089a013

Recognition of α-Amino Acid Esters by Zinc Porphyrin Derivatives via Coordination and Hydrogen Bonding Interactions. Evidence for Two-Point Fixation from Thermodynamic and Induced Circular Dichroism Spectroscopic Studies

Tadashi Mizutani, Tadashi Ema, Takashi Yoshida, Yasuhisa Kuroda, Hisanobu Ogoshi

Inorganic Chemistry 32 ( 10 ) 2072 - 2077 1993年

掲載種別：研究論文（学術雑誌）

Association constants between [trans-5,15-bis(2-hydroxy-1-naphthyl)-2,3,7,8,12,13,17,18-octaethylporphyrinato]-zinc(II) (1) and a series of α-amino acid esters (RCHNH2CO2CH3) were determined in chloroform by use of a UV-vis titration method. Association constants increased in the order Ala-OMe < Gly-OMe < Val-OMe < Leu-OMe, showing a preference for bulky amino acid esters. Contributions from the metal coordination and hydrogen bonding interactions to the total free energy change were estimated by use of reference compounds having no hydrogen bonding site. The free energy change for the binding of Leu-OMe to 1 in chloroform at 15 °C was −5.3 kcal/mol, which was separated into two contributions, (1) the metal coordination interaction ΔGMC = −3.8 kcal/mol and (2) the hydrogen bonding interaction ΔGHB = −1.5 kcal/mol. Circular dichroism (CD) induced in the porphyrin Soret band of 1 by complexation with optically active amino acid esters was of the split type for all the amino acid esters examined, whereas induced CD of a reference host, [trans-5,15-bis(2-methoxy-1-naphthyl)-2,3,7,8,12,13,17,18-octaethylporphyrinato]zinc(II) (2), was reduced in intensity and not of the split type. We found that the fixation of the carbonyl group of the guest by two-point recognition caused marked enhancements in induced CD. We suggest that the induced CD of 1 was caused by the coupling between the magnetic transition dipole moment of the carbonyl group of guest and the electric transition dipole moment of the Soret band of host. © 1993, American Chemical Society. All rights reserved.

DOI： 10.1021/ic00062a032

Recognition of chirality and residual groups of amino acid esters using new trifunctional chiral porphyrins with C<inf>2</inf> symmetry

Tadashi Mizutani, Tadashi Ema, Takashi Tomita, Yasuhisa Kuroda, Hisanobu Ogoshi

Journal of the Chemical Society, Chemical Communications ( 6 ) 520 - 522 1993年

掲載種別：研究論文（学術雑誌）

An intrinsic chiral recognition host, [trans-5,15-bis(2-hydroxyphenyl)-10- {2,6-bis(methoxycarbonylmethyl)phenyl}-2,3,17,18-tetraethylporphyrinato]zinc(II) 1, is synthesized and found to show an enantioselectivity of ca. 2: 1 for L- and D-amino acid esters having non-polar residues, whereas it shows a reversed enantioselectivity of ca. 1: 2 for L- and D-Ser-OBzl.

DOI： 10.1039/C39930000520

Synthesis and Photoreaction of 1,2,3,4-Tetra-t-butylnaphthalene: A Highly Crowded Naphthalene Derivative and Its Valenceisomers

Sadao Miki, Tadashi Ema, Rie Shimizu, Hiroshi Nakatsuji, Zen ichi Yoshida

Tetrahedron Letters 33 ( 12 ) 1619 - 1620 1992年3月

掲載種別：研究論文（学術雑誌）

1,2,3,4-Tetra-t-butylnaphthalene (2), a highly crowded naphthalene derivative, has been synthesized. Upon irradiation, 2 underwent photovalence isomerization to afford 1,2,5,6-tetra-t-butyl-3,4-benzo-3-tricyclo[3.1.0.02,6]-hexene (3). The synthesis of 1,4,5,6-tetra-t-butyl-2,3-benzo-2,5-bicyclo[2.2.0]hexadiene (1), which was used for the synthesis of 2, is also described. © 1992.

DOI： 10.1016/S0040-4039(00)91689-7

Selective syntheses of unsymmetrical meso-arylporphyrins

Tadashi Ema, Yasuhisa Kuroda, Hisanobu Ogoshi

Tetrahedron Letters 32 ( 35 ) 4529 - 4532 1991年

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