研究者詳細 - 依馬　正

論文 - 依馬　正

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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

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