• Applied Chemistry for Engineering
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• v.18 no.6
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• pp.630-635
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• 2007

New chiral Co-salen complexes with one $C_3-^tBu$ group in the structure have been synthesized and applied as a chiral catalyst. A dimeric chiral salen having aluminum group metal salts such as $AlCl_3$ displayed very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of epoxides to synthesize optically pure ${\alpha}$-aryloxy alcohols via phenolic kinetic resolution. The salen complexes immobilized on the inorganic support were also used as effective catalysts in that reaction. The identity of metal salts in the new chiral salen complex has proved to be important in the enantioselective reactions.

• KSBB Journal
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• v.17 no.4
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• pp.321-325
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• 2002

Chiral epoxides are valuable intermediates for the asymmetric synthesis of enantiopure bioactive compounds. Microbial epoxide hydrolases (EHs) are newly discovered enzymes and versatile biocatalysts for the preparation of chiral epoxides by enantioselective hydrolysis of cheap and easily available racemic epoxide substrates. EHs are commercially potential biocatalysts due to their characteristics such as high enantioselectivity, cofactor-independent catalysis, and easy-to-Prepare catalysts. In this Paper, recent progresses in biochemistry and molecular biology of EH and developments of novel reaction systems are reviewed to evaluate the commercial feasibility of EH-catalyzed hydrolytic kinetic resolution for the production of chiral epoxides.

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.2978-2982
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• 2013

A doubly tethered $N-CH_3$ amide chiral stationary phase (CSP 4) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of an antiarrythmic agent, tocainide, and its analogues and the chromatographic resolution results were compared with those on a singly tethered N-H amide CSP (CSP 1), a singly tethered $N-CH_3$ amide CSP (CSP 2) and a doubly tethered N-H amide CSP (CSP 3) under an identical aqueous mobile phase condition. CSP 4 was found to be generally better than other CSPs in terms of the separation factors (${\alpha}$) and resolutions (RS). The retention times of analytes denoted by the retention factors ($k_1$) on CSP 4 were quite long compared to those on other CSPs because of the improved lipophilicity of CSP 4. The long retention times of analytes on CSP 4 were successfully controlled by the addition of a small amount of ammonium acetate to aqueous mobile phase without hurting the chiral recognition efficiency. The variation of the content and type of organic and acidic modifier in aqueous mobile phase was found not to change the chiral recognition efficiency significantly.

• Bulletin of the Korean Chemical Society
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• v.26 no.10
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• pp.1549-1554
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• 2005

Chiral separation of arylalcohols such as 1-phenyl-1-propanol, 1-phenyl-2-propanol, and 2-phenyl-1-propanol by capillary electrophoresis was studied using sulfonated $\beta$-cyclodextrin (CD) as a chiral selector and Ag colloids as an additive. The optimum separation condition of arylalcohols was found to be the chiral selector concentration of 6.5 mM, applied voltage of 15 kV, and pH of 7.0. In order to improve chiral separation, an Ag colloid was mixed with a running buffer. The resolution in the Ag colloid-mixed running buffer was considerably superior to that obtained with the sulfonated $\beta$-CD alone. The molar ratio of sulfonated $\beta$-CD to Ag colloid, which is one of critical parameters affecting resolution, was found to be optimum at 65 : 1. In order to elucidate the resolution mechanism, an inclusion-complex of the arylalcohols with sulfonated $\beta$-CD was prepared by mixing and shaking in solution, and then characterized by cyclic voltammetry (CV). The inclusion mechanism was also discussed using experimental results.

• Bulletin of the Korean Chemical Society
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• v.31 no.3
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• pp.678-682
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• 2010

A doubly tethered chiral stationary phase (CSP) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid were applied to the liquid chromatographic resolution of racemic tocainide, an antiarrhythmic agent, and its analogues. The chiral recognition efficiency of the doubly tethered CSP for tocainide and its analogues was generally greater than that of the corresponding singly tethered CSP especially in terms of the resolution ($R_S$). The resolution of tocainide and its analogues on the doubly tethered CSP were dependent on the content and the type of the organic and acidic modifiers in aqueous mobile phase and the column temperature. Especially, the retention behaviors of analytes on the doubly tethered CSP with the variation of the content of organic modifier in aqueous mobile phase were opposite to those on the corresponding singly tethered CSP and these opposite retention behaviors were rationalized by the lipophilicity differences of the two CSPs.

• Proceedings of the PSK Conference
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• 2002.10a
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• pp.399.1-399.1
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• 2002

The chiral stationary phase derived from (＋) (18-crown-6)-2.3, 11.12-tetracarboxylic acid (18-C-6- TA) as a chiral selector has been employed for resolution of several $\alpha$-amino acids in HPLC. In a quest for the origin of chiral recognition of $\alpha$-amino acids in the presence of 18-C-6- T, A, as a chiral selector, these interactions responsible for the differential affinities shown toward enantioners were investigated by NNR spectroscopy. (omitted)

• KSBB Journal
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• v.28 no.6
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• pp.423-427
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• 2013

A new convenient derivatization method of ${\alpha}$-amino acid esters as nitrobenzoxadiazole (NBD) derivatives for chiral resolution was introduced and the enantiomer separation of ${\alpha}$-amino acid esters as NBD derivatives was performed by normal HPLC using chiral columns based on polysaccharide derivatives. The NBD derivatives were readily prepared by stirring NBD-Cl and ${\alpha}$-amino acid methyl ester HCl with $NaHCO_3$ in ethanol. The performance of Chiralpak IA was superior to the other chiral stationary phases for enantiomer resolution of NBD derivatives of several ${\alpha}$-amino acid methyl esters. Owing to fluorescence detection as well as strong UV absorption, it is expected that the convenient analytical method developed in this study will be very useful for enantiomer separation of ${\alpha}$-amino acid esters as NBD derivatives on polysaccharide-derived chiral columns.

• KSBB Journal
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• v.14 no.3
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• pp.291-296
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• 1999

Chiral epoxides are key intermediates for the production of chiral pharmaceuticals, agrochemicals, and functional food additives. Chiral epoxides can be produced by either chemical or biological method. In biocatalytic production routes, chiral epoxides can be produced via epoxidations of prochiral alkenes by monooxygenase or peroxidase. Kinetic resolution of racemic epoxides using whole cells of bacteria or fungi might be commercially useful, since it is possible to obtain chiral epoxides with high optical purities from relatively cheap and readily avaiable racemic epoxides. Some bioprocesses already are commercially developed: the biocatalytic production of chiral epichlorohydrin via microbial stereospecific dehalogenation, and lipase-catalyzed enantioselective hydrolysis in a hollow fiber membrane bioreactor for the production of chiral methyl trans-3-(4-methoxyphenyl)glycidate. the intermediate for calcium antagonist diltiazem. The importance of biocatalytic production of chiral epoxides with several examples from literature are presented.

• Bulletin of the Korean Chemical Society
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• v.26 no.6
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• pp.989-992
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• 2005

Dynamic kinetic resolution of $\alpha$-bromo carboxylic acid derivatives in nucleophilic substitution with chiral $\alpha$-amino ester nucleophiles in the presence of TBAI and DIEA has been investigated for stereoselective syntheses of 1,1'-iminodicarboxylic acid derivatives. Nucleophilic substitutions with various chiral $\alpha$-amino esters gave iminodiacetates 2-8 with stereoselectivities up to 87 : 13 dr. Also, the reactions of N-($\alpha$-bromo-$\alpha$-phenylacetyl)-L-alanine methyl ester with L-alanine, D-alanine and glycine methyl ester nucleophiles afforded N-carboxyalkyl dipeptide analogues 10-12 up to 90 : 10 dr.

• Bulletin of the Korean Chemical Society
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• v.10 no.6
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• pp.491-495
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• 1989

Resolution of enantiomers of DNS-amino acids has been achieved by a reversed phase liquid chromatography with an addition of a copper(Ⅱ) complex of N-benzyl-L-hydroxyproline to the mobile phase. N-Benzyl-L-hydroxyproline was prepared and used as a chiral ligand of copper(Ⅱ) chelate for the optical resolution. The pH and the concentration of copper(Ⅱ) chelate, organic solvent, and buffer agent in the mobile phase all affect the optical resolutions of dansyl amino acids. The elution orders between D and L-DNS-amino acids were different depending on the structure of the side chain of the amino acids. The retention mechanism for the chiral separation of the dansyl amino acids can be illustrated by the equilibrium of ligand exchange and by hydrophobic interaction with $C_{18}$ stationary phase. The chiral separation can be illustrated with cis and trans effect of the ligand exchange reaction.