Kinetic resolution of alpha-lipoic acid via enzymatic differentiation of a remote stereocenter.

Kinetic resolution of alpha-lipoic acid, a case of remote stereocenter discrimination, was accomplished using lipase from Aspergillus oryzae WZ007. Performance of this lipase was investigated for enantioselective esterification of (S)-alpha-lipoic acid, leaving the target product (R)-alpha-lipoic acid in unreacted form. The effects of chain length of alcohol, type of solvent, molar ratio of alcohol:acid, and reaction temperature were studied. The optimum reaction conditions were found to be esterification with n-octanol at 50 degrees C in heptane with an alcohol:acid molar ratio of 5:1. The conversion rate of alpha-lipoic acid was 75.2%, with an enantiomeric excess of 92.5% towards unreacted substrate in a reaction time of 48 h.