研究者詳細 - 依馬　正

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1039/c2ob25614b

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

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

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

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/j.tetlet.2011.11.044

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

Tadashi Ema, Norichika Ura, Katsuya Eguchi, Takashi Sakai

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1246/bcsj.20110230

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

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

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

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1039/c1gc15877e

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

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

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

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

Tadashi Ema, Taro Kadoya, Kumiko Akihara, Takashi Sakai

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/j.molcatb.2010.05.009

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1039/c001561j

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1021/jo1006587

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

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

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

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/j.tet.2009.09.058

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

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

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

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

Tadashi Ema, Daisuke Tanida, Kazuki Hamada, Takashi Sakai

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1021/jo801584b

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

Tadashi Ema, Sayaka Ide, Nobuyasu Okita, Takashi Sakai

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1002/adsc.200800292

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

Takashi Sakai, Kefei Wang, Tadashi Ema

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/j.tet.2007.12.030

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

Tadashi Ema, Tokuhiro Doi, Takashi Sakai

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

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

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

Organic Letters 10 ( 12 ) 2365 - 2368 2008年

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1021/ol800940j