A new type of carboxypeptidase A inhibitor: Design, synthesis, and mechanistic implication

2-Benzyl-3,4-epoxybutanoic acid (BEBA) which was designed rationally as an irreversible inhibitor of carboxypeptidase A on the basis of the known topology of the active site and catalytic mechanism of the enzyme indeed inactivated the enzyme very efficiently with a covalent modification at the carboxylate of Glu-270. The partition ratio of BEBA was determined to be 20.3. Of four stereoisomers of BEBA, (2S, 3R)-and (2R, 3S)-BEBA show the inhibitory activity, and the other two isomers are essentially inactive. This stereospecificity of BEBA in the inhibition was explained with a proposition of a three-dimensional representation of the active site of the enzyme. All four stereoisomers were synthesized effectively and conveniently starting with optically active 2-benzyl-2-vinylacetic acid which was obtained by a kinetic resolution of racemic methyl ester of the acid using a-chymotrypsin.