Enzyme-mediated enantioselective protonation to enolates in an aqueous medium

An enzyme sometimes provides a entirely hydrophobic chiral reaction field to a synthetic substrate. This is one of the most characteristic features of an enzyme compared to ordinary chemical catalyst. Taking advantage of being able to carry out a reaction of a prochiral compound in this special pocket, it is possible to prepare an optically active product via asymmetric protonation in an aqueous medium. Two such examples are demonstrated in this article, i.e., asymmetric hydrolysis of enol esters, and asymmetric decarboxylation of alpha-aryl-alpha-methylmalonic acid to give optically active ketones and alpha-arylpropionic acids, respectively. Some related reactions are described as well.