Enhancement of Enantioselectivity in the Bacillus subtilis Protease-catalyzed Hydrolysis of N-free Amino Acid Esters using the Ester Grouping-modification Approach

The generality of enantioselectivity enhancement through the modification of the alcohol moiety of a substrate ester was ascertained, for in the Bacillus subtilis protease-catalyzed hydrolysis of N-unprotected amino acid esters the enantioselectivity was enhanced largely by switching the conventional methyl ester to esters with a longer alkyl chain such as the isobutyl ester (from E = 3 to E = 130–170 in the case of 4-fluorophenylalanine esters) as in the enzymatic hydrolysis mediated by Aspergillus oryzae protease. There was indeed a profound dependence of E on the nature of the ester grouping.