Studies on the enhancement of enantioselectivity in the microbial protease-catalyzed hydrolysis of N-free non-protein amino acid esters

We have recently reported a marked enhancement of enantioselectivity by switching the conventional methyl ester to esters with a longer alkyl chain such as the isobutyl ester in the Aspergillus oryzae protease-catalyzed enantioselective hydrolysis of N-unprotected amino acid esters. The present study reveals that the enantioselectivity enhancement is also attained by changing the pH of the reaction mixture, the optimal pH in terms of enantioselectivity being around 6.2. Kinetic measurements indicate that the most significant factor responsible for the observed enantioselectivity enhancement is the change of the Km value for the l-series.