Relaxing Substrate Specificity in Antibody-Catalyzed Reactions: Enantioselective Hydrolysis of <i>N</i>-Cbz-Amino Acid Esters

For a catalytic antibody to be generally useful for organic synthetic chemistry, it must be able to accept a broad range of substrates, yet retain high selectivity. In this work, we propose a hapten design to endow antibody catalysts with two opposing qualities, such as high enantioselectivity and broad substrate specificity. Racemic hapten 2 induced two separate classes of catalytic antibodies to hydrolyze either the l- or d-isomers of N-Cbz-amino acid esters 1. In the kinetic resolution of racemic ester 9, antibodies 7G12 and 3G2 gave 96% ee of l-10 and 94% ee of d-10, respectively. In addition, antibody 7G12 displayed broad substrate specificity, hydrolyzing the l-esters of Ala (1a), Leu (1b), Norleu (1c), Met (1d), Phe (1e), Val (1f), and phenylglycine (1g) with high enantioselectivity. Antibody 3G2 also hydrolyzed the d-isomers of these esters without sacrificing the enantioselectivity. This observation suggests that the use of haptens that fit snugly into the antigen-combining site, and leave the linker moiety outside, is an effective approach for the generation of catalytic antibodies with high selectivity and broad substrate applicability.