[CH3:1][O:2][C:3](=[O:14])[C@@H:4]1[CH2:8][C:7](=[O:9])[CH2:6][N:5]1[C:10]([O:12][CH3:13])=[O:11].CCCCCCCCCCCCCCCC>C([O-])(=O)C.[Na+].ClCCl>[CH3:1][O:2][C:3](=[O:14])[C@H:4]1[CH2:8][C:7](=[O:9])[CH2:6][N:5]1[C:10]([O:12][CH3:13])=[O:11]An aqueous solution (5.0 mL) containing 25 mM N-(methoxycarbonyl)-4-keto-Dproline methyl ester and 25 mM N-(methoxycarbonyl)-4-keto-L-proline methyl ester in 0.200M sodium acetate (pH 5.0) was mixed with 2.5 g of immobilized Candida antartica lipase fraction B (Boehringer Mannheim, CHIRAZYME® L-2, c.-f., C2, lyo.) at 25° C. The reaction mixture was analyzed after 31 h by mixing the entire reaction mixture with 5.0 mL of 20 mM hexadecane in dichloromethane for 10 minutes, which resulted in the complete extraction of the unreacted D- and L-isomers. The dichloromethane extract was then analyzed by chiral gas chromatography on a Chiraldex G-TA column (Advanced Separation Technologies, Inc., 50 m×0.32 mm ID) to determine the amounts of the unreacted D- and L-isomers. After 31 h, an 85% enantiomeric excess of N-(methoxycarbonyl)-4-keto-D-proline methyl ester was obtained at 41% conversion of the racemic mixture.
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