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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

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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

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DOI： 10.1021/acs.orglett.3c01304

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DOI： 10.1002/adsc.202300031

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DOI： 10.1021/acs.orglett.3c00047

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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

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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

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Bifunctional aluminum porphyrins catalyzed the terpolymerization of cyclohexene oxide (CHO), bis(CHO), and CO₂ to give cross-linked polycarbonates.

DOI： 10.1039/D3PY00870C

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DOI： 10.1039/D3OB00938F

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DOI： 10.1021/acs.joc.2c01666

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DOI： 10.1021/acscatal.2c03583

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DOI： 10.1002/chem.202202210

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DOI： 10.1002/anie.202204609

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DOI： 10.1002/chem.202104212

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DOI： 10.1039/D1GC04599G

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Chiral carbazole-based porphyrins were synthesized for the first time via the incorporation of hydrobenzoin units at the thiophene moieties. They showed absorption and circular dichroism in the near-infrared (NIR) region. The NIR absorption was further red-shifted by solvent-induced aggregation.

DOI： 10.1142/S1088424619500937

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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

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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

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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

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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

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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

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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

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Doubly (R)-binaphthyl-strapped porphyrins with methylene chains were synthesized. The CD spectra showed the positive Cotton effect around the Soret bands, and several porphyrins showed CPL. In addition, we found that the chiral porphyrins were applicable to kinetic resolution of epoxide with CO2.

DOI： 10.1039/c8cc09114e

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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

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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

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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

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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

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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

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(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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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The simultaneous addition of 40% tetrabutylammonium hydroxide (TBAH) and crown ether (18-crown-6) promptly produced a clear aqueous solution of cellulose (10 wt%) at room temperature. © 2014 The Royal Society of Chemistry.

DOI： 10.1039/c3ra45888a

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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

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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

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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

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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

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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

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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

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We have developed a very active bifunctional porphyrin catalyst showing a high turnover number (TON = 103 000) for the synthesis of cyclic carbonates from CO2 and epoxides under solvent-free conditions. © 2012 Royal Society of Chemistry.

DOI： 10.1039/c2cc30591g

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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

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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

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Chiral diporphyrin receptor 1, which has a macrocyclic cavity to sandwich aromatic guest molecules via double π–π stacking interactions, enabled the naked-eye detection of an aromatic explosive as well as chiral discrimination in NMR. © 2011 The Royal Society of Chemistry.

DOI： 10.1039/c1cc11572c

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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

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Bifunctional organocatalysts bearing an ammonium betaine framework have been developed as a new catalytic motif for the activation of carbon dioxide and epoxides to produce cyclic carbonates. © 2010 American Chemical Society.

DOI： 10.1021/ol102539x

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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

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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

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(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

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The biogenous iron oxide (BIO) from Leptothrix ochracea was transformed to an organic-inorganic hybrid support to prepare an excellent immobilized enzyme showing high catalytic performance. © 2010 The Royal Society of Chemistry.

DOI： 10.1039/b919497e

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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

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Bicyclic tertiary alcohols 1 bearing quaternary stereocenters at the two adjacent bridgehead positions were synthesized with high stereoselectivity via the intramolecular crossed benzoin reactions catalyzed by NHC organocatalysts. © 2009 American Chemical Society.

DOI： 10.1021/ol9019293

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(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

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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

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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

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Bulky alcohol, 5-[4-(1-hydroxyethyl)phenyl]-10,15,20-tris- (pentafluorophenyl)porphyrin (1b), was synthesized, and enantiomerically pure alcohol 1b and ester 2b were obtained by a single kinetic resolution catalyzed by Candida antarctica lipase in i-Pr2O and in [bdmim] [PF 6]. Copyright © 2008 The Chemical Society of Japan.

DOI： 10.1246/cl.2008.90

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(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

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Trifunctional organocatalysts 1a and 1b mimicking the active site of serine hydrolases showed high catalytic activity with up to a 3 700 000-fold acceleration for the acyl-transfer reactions from vinyl trifluoroacetate to alcohol. © The Royal Society of Chemistry.

DOI： 10.1039/b718763g

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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

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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

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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

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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

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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

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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

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(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

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The enantioselectivity of a Burkholderia cepacia lipase toward secondary alcohols could be both increased and decreased rationally by introducing only a single mutation on the basis of the mechanism proposed previously. © The Royal Society of Chemistry 2005.

DOI： 10.1039/b508244g

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(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

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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

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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

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(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

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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

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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

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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

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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

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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

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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

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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

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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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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

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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

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A synthetically useful primary alcohol, 3-phenyl-2H-azirine-2-methanol, was resolved efficiently by a reaction at -40 °C with a lipase immobilized on the porous ceramic (Toyonite) and vinyl butanoate in ether (E value of 130 and TTN/h value of 7800).

DOI： 10.1246/bcsj.76.1819

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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

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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

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DOI： 10.1021/jo0108257

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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

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Thermodynamic parameters for subtilisin-catalyzed kinetic resolutions of secondary alcohols were determined, and a compensation effect between ΔΔH‡ and ΔΔS‡ was found. These data are explained in terms of the transition-state model.

DOI： 10.1246/cl.2000.782

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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

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Low-temperature method (-40 °C at best) for enhancement of the enantioselectivity in a lipase-catalyzed transesterification was proved to be widely applicable to primary and secondary alcohols and enabled theoretical prediction of the course of enhancement of the enantioselectivity physicochemically.

DOI： 10.1016/S0040-4039(98)01747-X

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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

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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

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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

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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

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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

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DOI： 10.1021/jo970581j

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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

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Publishing type：Research paper (scientific journal)  

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

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Publishing type：Research paper (scientific journal)  

Optically active dimeric porphyrin covalently linked by a chiral cyclophane was synthesized; the two porphyrin chromophores were disposed in a slipped cofacial fashion, which was found to be tunable by cooperative coordination of diamines with various chain lengths.

DOI： 10.1246/cl.1997.487

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Publishing type：Research paper (scientific journal)  

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

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Publishing type：Research paper (scientific journal)  

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

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Publishing type：Research paper (scientific journal)  

An asymmetric reduction of ethyl pyruvate was carried out using bakers' yeast cell free extract with addition of NADPH in catalytic amounts and glucose as a hydride source. The total turnover number of NADPH reached 7680. The efficiency of the cell free extract is discussed.

DOI： 10.1246/cl.1996.1079

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Publishing type：Research paper (scientific journal)  

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

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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

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Publishing type：Research paper (scientific journal)  

Chiral porphyrin dimer 1 was synthesized. The UV-vis spectrum of 1 was almost identical with that of the corresponding monomer 2. The circular dichroism induced in the Soret region of 1 was very strong and of the split type due to the chiral exction coupling. © 1995.

DOI： 10.1016/00404-0399(50)11388-

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Publishing type：Research paper (scientific journal)  

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

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Publishing type：Research paper (scientific journal)  

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

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The title compound presents the first example of a sterically ruffled porphyrin bearing only meso substituents; the degree of ruffling is severe, with Cm-displacements of up to 1 Å.

DOI： 10.1039/C39950000733

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Publishing type：Research paper (scientific journal)  

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

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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

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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

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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

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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

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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

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A selective synthetic route to unsymmetrical meso-arylporphyrins is described. New hybrid type of unsymmetrical porphyrin with C2v symmetry was prepared according to the new method. © 1991.

DOI： 10.1016/0040-4039(91)80031-Z

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Country：Japan

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