• Current Applied Physics
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• 제18권12호
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• pp.1480-1485
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• 2018

Mesoporous carbon-silica composites supported Pt nanoparticle catalysts (Pt/MCS) were firstly applied to the heterogeneous asymmetric hydrogenation of ethyl 2-oxo-4-phenylbutyrate (EOPB). A series of different silica contents were investigated in the fabrication of this mesoporous material. When the volume of added tetraethyl orthosilicate (TEOS) during the preparation of composites is 8 mL, Pt/MCS-8 holds carbon and silica as the main components and possesses relatively strong acidity, mesoporous structures with micropores, appropriate Pt nanoparticle size and high dispersibility showing by XRD, XPS, TPD, $N_2$ sorption and TEM. These properties cause its good catalytic performance in the heterogeneous asymmetric hydrogenation of EOPB with the enantiomeric excess value and conversion up to 85.6% and 97.8%, respectively.

• 한국미생물·생명공학회지
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• 제35권4호
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• pp.285-291
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• 2007

대장균 BL21(DE3)에 Caulobacter crescentus epoxide hydrolase (CcEH)를 발현시킨 제조합균주를 이용하여 광학수렴 가수분해(enantioconvergent hydrolysis) 반응을 수행하였으며 라세믹 에폭사이드 기질로부터 광학활성 diol을 생합성하는 조건을 최적화하였다. 반응최적화를 위하여, 계면활성제의 첨가와 반응온도가 생성물인 diol의 광학순도 및 수율에 미치는 영향을 분석하였으며 또한 생성물인 diol에 의한 EH의 가수분해활성 저해효과를 측정하였다. 재조합 CcEH를 생촉매로 사용한 광학수렴 반응에서 Tween 80을 2%(w/v)첨가하여 $10^{\circ}C$로 반응시켰을 때 20 mM 라세믹 styrene oxide로부터 광학순도 92%의 (R)-phenyl-1,2-ethanediot을 수율 56%로 얻을 수 있었다. 기질인 라세믹 styrene oxide를 50 mM 농도로 사용한 경우, 광학순도 87% (R)-phenyl-1,2-ethanediol을 77% 얻을 수 있었다. 생성물인 diol의 저해효과를 실험한 경우, 라세믹 phenyl-1,2-ethanediol, (R)-phenyl-1,2-ethanediol 및 (S)-phenyl-1,2-ethanediol은 10 mM 농도에서부터 재조합 CcEH의 가수분해활성을 현저하게 저해하는 것으로 나타났다. 위의 결과들로 볼 때 CcEH를 사용하여 높은 광학순도의 (R)-phenyl-1,2-ethanediol을 생성하기 위해서는 (R)-styrene oxide의 린치를 선택적으로 공격하는 동시에 생성물에 의해 저해를 받지 않는 partner EH를 개발하는 것이 중요할 것이다.

• 대한화학회지
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• 제39권4호
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• pp.275-280
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• 1995

수소이온 존재하에서 $cis-[Co(en)_2(NO_2)_2]^+$과 라세미-$[Co(Y)]^2-(Y=EDTA,\; PDTA,\; CyDTA)$간에 일어나는 전자전달반응속도를 조사하였다. 속도자료로부터 $cis-[Co(en)_2(NO_2)_2]^+$과 라세미-$[Co(Y)]^2$간에 일어나는 전자전달반응은 수소이온이 촉매로 작용하여 내부권으로 진행되는 것을 알 수 있었다. 한편, 광학활성인 △-cis-$[Co(en)_2(NO_2)_2]^+$과 라세미-$[Co(Y)]^2-(Y=EDTA,\; PDTA,\; CyDTA)$간의 입체선택적 전자전달반응에서는 △-[Co(EDTA)]-, △-[Co(PDTA)]- , △-[Co(CyDTA)]-가 각각 6.0, 2.9, 3.0% e.e.(e.e.=enantiomeric excess) 생성되었다. 이것은 두 착물이 접근하여 먼저 선택적 이온회합을 이루고 전자전달반응이 일어나는 것으로 볼 수 있다. 따라서 △-cis-$[Co(en)_2(NO_2)2_]^+$과 라세미-$[Co(Y)]^{2-}$간의 입체선택적 전자전달반응은 산촉매에 의한 내부적 반응과 입체선택적 이온회합에 따른 외부권 반응으로 진행된다고 추정할 수 있다.

• Journal of Microbiology and Biotechnology
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• 제17권1호
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• pp.74-80
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• 2007

An enantioselective lipase gene (esf) for the kinetic resolution of optically active (S)-flurbiprofen was cloned from the new strain Serratia marcescens ES-2. The esf gene was composed of a 1,845-bp open reading frame encoding 614 amino acid residues with a calculated molecular mass of 64,978 Da. The lipase expressed in E. coli was purified by a three-step procedure, and it showed preferential substrate specificity toward the medium-chain-length fatty acids. The esf gene encoding the enantioselective lipase was reintroduced into the parent strain S. marcescens ES-2 for secretory overexpression. The transformant S. marcescens BESF secreted up to 217kU/ml of the enantioselective lipase, about 54-fold more than the parent strain, after supplementing 3.0% Triton X-207. The kinetic resolution of (S)-flurbiprofen was carried out even at an extremely high (R,S)-flurbiprofen ethyl ester [(R,S)-FEE] concentration of 500 mM, 130 kU of the S. marcescens ES-2 lipase per mmol of (R,S)-FEE, and 1,000 mM of succinyl ${\beta}-cyclodextrin$ as the dispenser at $37^{\circ}C$ for 12h, achieving the high enantiomeric excess and conversion yield of 98% and 48%, respectively.

• Journal of Microbiology and Biotechnology
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• 제23권10호
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• pp.1395-1402
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• 2013

Reductases convert some achiral ketone compounds into chiral alcohols, which are important materials for the synthesis of chiral drugs. The Saccharomyces cerevisiae reductase YOR120W converts ethyl-4-chloro-3-oxobutanoate (ECOB) enantioselectively into (R)-ethyl-4-chloro-3-hydroxybutanoate ((R)-ECHB), an intermediate of a pharmaceutical. As YOR120W requires NADPH as a cofactor for the reduction reaction, a cofactor recycling system using Bacillus subtilis glucose dehydrogenase was employed. Using this coupling reaction system, 100 mM ECOB was converted to (R)-ECHB. A homology modeling and site-directed mutagenesis experiment were performed to determine the NADPH-binding site of YOR120W. Four residues (Q29, K264, N267, and R270) were suggested by homology and docking modeling to interact directly with 2'-phosphate of NADPH. Among them, two positively charged residues (K264 and R270) were experimentally demonstrated to be necessary for NADPH 2'-phosphate binding. A mutant enzyme (Q29E) showed an enhanced enantiomeric excess value compared with that of the wild-type enzyme.

• Journal of Microbiology and Biotechnology
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• 제29권11호
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• pp.1769-1776
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• 2019

Ethyl (S)-3-hydroxy-3-(2-thienyl) propanoate ((S)-HEES) acts as a key chiral intermediate for the blockbuster antidepressant drug duloxetine, which can be achieved via the stereoselective bioreduction of ethyl 3-oxo-3-(2-thienyl) propanoate (KEES) that contains a 3-oxoacyl structure. The sequences of the short-chain dehydrogenase/reductases from Chryseobacterium sp. CA49 were analyzed, and the putative 3-oxoacyl-acyl-carrier-protein reductase, ChKRED12, was able to stereoselectively catalyze the NADPH-dependent reduction to produce (S)-HEES. The reductase activity of ChKRED12 towards other substrates with 3-oxoacyl structure were confirmed with excellent stereoselectivity (>99% enantiomeric excess) in most cases. When coupled with a cofactor recycling system using glucose dehydrogenase, the ChKRED12 was able to catalyze the complete conversion of 100 g/l KEES within 12 h, yielding the enantiopure product with >99% ee, showing a remarkable potential to produce (S)-HEES.

• Biotechnology and Bioprocess Engineering:BBE
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• 제6권3호
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• pp.179-182
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• 2001

Porcine liver esterase was immobilized in polyacrylamide gel for the enantioselective production of levofloxacin from ofloxacin butyl ester. The initial activity of immobilized esterase was found to be significantly affected by the polyacrylamide gel composition. The optimum concentrations of monomer and crosslinker were determined to be 20% and 8.3%, respectively. The activity of immobilized esterase was 55.4% compared to a free enzyme. Enantiomeric excess was maintained at 60%, almost the same level as that of free enzyme. In addition, the immobilized esterase could be used repeatedly up to 10 times without experiencing any severe loss of activity and enantioselectivity.

• Korean Membrane Journal
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• 제5권1호
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• pp.25-30
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• 2003

Chitosan membranes crosslinked with glutaraldehayde that contained chiral environment were prepared. The chitosan membranes were characterized using FTIR and swelling index measurements. Their swelling index in water ranged from 100 to 70%, depending on the crosslinking time. The separation of D- and L-isomers of tryptophan was achieved through a pressure driven membrane separation process, using the self-supporting crosslinked chitosan membranes. The chiral separation performance of the membranes depended strongly on the swelling index of the membranes and the separation conditions such as concentration of feed solutions and different operating pressures. Especially when a chitosan membrane with a swelling index of 70% was used, almost complete optical resolution of D- and L-tryptophan was obtained ; enantiomeric excess (ee %) of 97.92% and flux of 2.26 g/㎡$.$h.

• 한국막학회:학술대회논문집
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• 한국막학회 2003년도 The 4th Korea-Italy Workshop
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• pp.61-64
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• 2003

Optical resolution of a-amino acid (tryptophan and tyrosine) optical isomers was achieved by a pressure driven membrane separation process, using self-supporting crosslinked membranes base on polysaccharide with different swelling indices that ranged from 100 to 70%. The membranes prepared by casting and drying the polymer solution containing 5wt% acetic acid on an acryl plate followed by crosslinking with glutaraldehyde were characterized using such analytical methods as FTIR and swelling index measurements. On the way of separating the optical isomers, several experimental factors such as the concentration of the feed solutions, operating pressure and temperature, and degree of crosslinking of the membranes have been studied. When the chitosan membranes with 70% of swelling index were used , almost complete optical resolution was obtained; 97.92% of enantiomeric excess (ee %) and 2.26 g/$m^2$ㆍh of flux. The operating pressure and the concentration of feed solutions were respectively 1.0 kgf/$\textrm{cm}^2$ and 0.49 mmol/L.

• 공업화학
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• 제18권3호
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• pp.279-283
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• 2007

한 종류의 epoxide hydrolase (EH) 효소 자체가 광학수렴 가수분해(enantioconvergent hydrolysis) 활성을 가지는 Caulobacter crescentus의 epoxide hydrolase (CcEH) 유전자를 PCR로 클로닝하여 재조합시킨 Escherichia coli 생촉매를 개발하였다. 재조합 E. coli 세포 10 mg을 10 mM styrene oxide와 반응시킨 다음 기질과 반응생성물을 chiral GC와 HPLC로 각각 분석 한 결과, (S)-styrene oxide 기질에 대해서는 위치 선택적으로 에폭사이드 링의 ${\alpha}$-탄소를 공격하여 (R)-diol로 전환시켰다. 반면에 (R)-styrene oxide에 대하여는 ${\beta}$-탄소를 공격하여 (R)-diol로 전환시키는 위치선택성을 가지고 있었다. 재조합 CcEH를 단일 생촉매로 사용한 광학수렴 가수분해반응을 통해 20 mM racemic styrene oxide에 대하여 광학순도 85%의 (R)-phenyl-1,2-ethanediol을 수율 69%로 생합성 할 수 있었다