• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.98-102
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• 2014

The organocatalytic enantioselective Michael addition reaction promoted by chiral binaphthyl-modified squaramide catalyst have been developed, allowing facile synthesis of the corresponding chiral 2-amino-4H-chromenes derivatives with excellent enantioselectivity (up to 99% ee). The method reported represents a practical entry for the preparation of chiral 2-amino-4H-chromenes derivatives.

• Journal of the Korean Chemical Society
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• v.52 no.6
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• pp.727-733
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• 2008

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.291-295
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• 2011

The catalytic enantioselective conjugate addition reaction of $\alpha$-nitroacetate to $\alpha,\beta$-unsaturated enones promoted by chiral bifunctional organocatalysts is described. The treatment of $\alpha$-nitroacetate to $\alpha,\beta$-unsaturated enones afforded the corresponding Michael adducts with high enantioselectivity. The conjugate addition adducts are easily converted to chiral $\gamma$-nitro ketones and $\delta$-keto esters.

• Bulletin of the Korean Chemical Society
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• v.30 no.6
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• pp.1317-1324
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• 2009

Asymmetric transfer hydrogenation of α-functionalized arylketones has been studied. The chiral Rh-catalyst effectively performed in transfer hydrogenation of $\alpha$-mesyloxyketones with an azeotropic mixture of formic acid/triethylamine to produce optically active 1-arylethandiols with excellent enantioselectivity.

• Bulletin of the Korean Chemical Society
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• v.24 no.5
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• pp.537-538
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• 2003

• Bulletin of the Korean Chemical Society
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• v.19 no.4
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• pp.475-481
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• 1998

Details of various equilibria involved in the reactions of oxaza- and thiazazincolidine catalysts, generated from either β-amino alcohol or β-amino thiol, with aldehyde were studied by colligative measurements. The results indicated that the coordination of diethylzinc prior to the coordination of aldehyde is essential for high enantioselectivity of the thiol catalyzed reaction. The probable origin of asymmetric nonlinearity is also presented.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.218-226
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• 2007

The stereoselective synthesis of chiral terminal epoxides is of immense academic and industrial interest due to their utility as versatile starting materials as well as chiral intermediates. In this study, new dinuclear chiral Co (salen) complexes bearing gallium-, indium- and tallium-chloride have been synthesized and characterized. The mass and EXAFS spectra provided the direct evidence of formation of dinuclear complex. Their catalytic activity and selectivity have been demonstrated for the asymmetric ring opening of various terminal epoxides having ether or ester groups by hydrolytic kinetic resolution technology. The easily prepared dimeric complexes exhibited very high enantioselectivity for the asymmetric ring opening of epoxides with $H_2O$ nucleophile, providing enantiomerically enriched terminal epoxides (> 99% ee). The dimeric structured chiral salen showed remarkably enhanced reactivity and may be employed substantially lower loadings than its monomeric analogues. The system described in this work is very efficient for the synthesis of chiral epoxide and 1,2-diol intermediates

• KSBB Journal
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• v.14 no.2
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• pp.225-229
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• 1999

Enzymatic resolution reactions were investigated using Candida rugosa lipase for the production of potically pure S-(+)-Ketoprofen. When the enzymatic hydroysis (and esterification) of recemic ketoprofen esters (and recemic ketoprofen with alcohol) was investigated comparatively, aqueous media was more specific for S-enantiomer than organic media. In the enzymatic hydrolysis of racemic ketoprofen ethyl ester in aqueous media, optimal temperature and pH for enantioselectivity were $37^{\circ}C$ and 4, respectively. The stereoselectivity of the enzyme was enhanced by adding dialcohols such as ethylene glycol and propylene glycol. The enantiomeric ratio obtained in the 40 %(v/v) ethylene glycol was 2-fold higher than that without the additive. By adding $CH_2Cl_2$, $CHCl_3$ and $CCl_4$ (5%,v/v), the enantioselectivity was reversed. A dramatic increase in the stereoselectivity was achieved using lipase purified by anion exchange chromatography. The type A lipase(the first eluted lipase fraction) showed an enantiomeric ratio of >100, whereas the type B lipase(the second eluted lipase fraction) exhibited enantimomer ratio of 9.0 in the hydrolysis of racemic ketoprofen ethyl ester.

• Applied Chemistry for Engineering
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• v.26 no.2
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• pp.132-137
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• 2015

BEA-zeolite was modified by alkaline solution to introduce mesoporosity in the crystals and the homogeneous chiral Co(III) salen was immobilized in the mesopores. The dinuclear chiral Co(salen)-$GaCl_3$ catalyst immobilized on mesoporous BEA-zeolite showed high activity for the regioselective ring opening of terminal epoxides by carboxylic acids. Various chiral monoester derivatives could be synthesized with moderate enantioselectivity (47~69 ee%) from racemic epoxides through above reaction. When the chiral (S)-ECH was used as a reactant, it was efficiently resolved by carboxylic acid with a high enantioselectivity in the presence of heterogenized chiral salen catalyst, and the ring opened product afforded optically pure monoester epoxide (R)-GB (up to 98 ee%) through the ring closing in the basic solution by elimination of HCl. The heterogeneous catalyst could be fabricated easily, and the catalytic activity was retained for several times reuse without any further regeneration step.

• KSBB Journal
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• v.16 no.6
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• pp.562-567
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• 2001

Aspergillus niger LK harboring the enantioselective epoxide hydrolase (EHase) activity was isolated, and enantioselectivity of EHase was tested for various racemic aromatic epoxides. The gene encoding epoxide hydrolase was cloned from cDNA library generated by reverse transcriptase-polymerase chain reaction of the isolated total mRNA. Sequence analysis showed that the cloned gene encodes 398 amino acids with a deduced molecular mass of 44.5 kDa. Database comparison of the amino acid sequence reveals that it is similar to fungal EHase, whereas the sequence identity with bacterial EHase is very low. Recombinant expression of the cloned EHase in Escherichia coli BL21 yielded an active EHases, which can offer a potential biocatalyst for the production of chiral epoxides.