Antibody-Catalyzed Decarboxylative Oxidation of Vanillylmandelic Acid

Abstract

The most important industrial process for the synthesis of vanillin is performed in two steps involving an electrophilic aromatic substitution of glyoxylic acid on guaiacol followed by an oxidative decarboxylation of the intermediary α-hydroxy acids formed, thereby producing not only vanillin, but also byproducts which have to be eliminated. In the present study, we took advantage of the high specificity of catalytic antibodies to improve the synthesis of vanillin. Among 11 monoclonal antibodies elicited against the quaternary ammonium hapten H3, antibody H3-12 was found to catalyze the oxidative decarboxylation of vanillylmandelic acid (VMA), the precursor of vanillin, in the presence of sodium metaperiodate. The kinetic data of the antibody-catalyzed reaction are consistent with an ordered binding mechanism. At pH 9.0, H3-12 catalyzed the transformation of VMA into vanillin with a kcat of 2.70 min-1, a Michaelis−Menten constant Ka for the binary complex of 260 μM, and a Kb for the ternary complex of 2100 μM. The catalyzed reaction was fully inhibited by a hapten analogue with a Ki of 10 μM. The fine specificity of anti-H3 monoclonal antibodies was determined using H3-related compounds with a competitive enzyme immunoassay. Controls demonstrating that catalytic activity is actually related to antibody binding, and mechanistic studies, are also presented.