Biocatalytic Asymmetric Decarboxylation

Abstract

Biocatalytic decarboxylation is a unique reaction, in the sense that it can be considered to be a protonation reaction to a “carbanion equivalent” intermediate in aqueous medium. Thus, if optically active compounds can be prepared via this type of reaction, it would be a very characteristic biotransformation, as compared to ordinary organic reactions. An enzyme isolated from a specific strain of Alcaligenes bronchisepticus catalyzes the asymmetric decarboxylation of α-aryl-α-methylmalonic acid to give optically active α-arylpropionic acids. The effect of additives revealed that this enzyme requires no biotin, no co-enzyme A, and no ATP, as ordinary decarboxylases and transcarboxylases do. Studies on inhibitors of this enzyme and spectroscopic analysis made it clear that the Cys residue plays an essential role in the present reaction. The unique reaction mechanism based on these results and kinetic data in its support are presented.