研究者詳細 - 依馬　正

論文 - 依馬　正

分割表示 156 件中 121 - 140 件目／全件表示 >>

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1246/bcsj.76.1441

Scopus

researchmap

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/S1381-1177(03)00034-1

Scopus

researchmap

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

Takashi Sakai, Akiko Matsuda, Toshinobu Korenaga, Tadashi Ema

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

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

Tadashi Ema, Masataka Yoshii, Toshinobu Korenaga, Takashi Sakai

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/S0957-4166(02)00318-X

Scopus

researchmap

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1021/jo0109063

Scopus

PubMed

researchmap

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

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

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

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1021/jo9918551

Scopus

researchmap

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

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

Chemistry Letters ( 7 ) 782 - 783 2000年

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/S0040-4039(99)00750-9

Scopus

researchmap

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

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

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

Lipase-catalyzed kinetic resolution of large secondary alcohols having tetraphenylporphyrin

Tadashi Ema, Masahito Jittani, Takashi Sakai, Masanori Utaka

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/S0040-4039(98)01338-0

Scopus

researchmap

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/S0957-4166(98)00269-9

Scopus

researchmap

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1021/jo980165e

Scopus

researchmap

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/S0040-4039(98)01029-6

Scopus

researchmap

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1246/bcsj.71.443

Scopus

researchmap

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

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

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

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/S0040-4039(97)00524-8

Scopus

researchmap

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1016/S0040-4039(97)00255-4

Scopus

researchmap

New optically active diporphyrin having a chiral cyclophane as a spacer

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

Chemistry Letters ( 6 ) 487 - 488 1997年

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

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

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

掲載種別：研究論文（学術雑誌）

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

DOI： 10.1021/jo961144s

Scopus

researchmap

　前のページ - 次のページ　

<依馬 正>

論文 - 依馬 正

<依馬　正>

論文 - 依馬　正