ANALYSIS OF SOLVENT EFFECTS ON THE DECARBOXYLATION OF BENZISOXAZOLE-3-CARBOXYLATE IONS USING LINEAR SOLVATION ENERGY RELATIONSHIPS - RELEVANCE TO CATALYSIS IN AN ANTIBODY-BINDING SITE

The mechanisms by which specific solvent properties influence the title reaction, which is extremely medium-sensitive, have been investigated using multiparametric methods. The results of this analysis have been compared with previous experimental studies of the reaction mechanism. Hydrogen-bond donation by solvent and hydrogen-bond donation by tetramethylguanidinium ion in tight ion pairs with the carboxylate greatly retard the reaction. Solvent dipolarity and basicity accelerate the reaction, most likely by helping to break up hydrogen-bonded ion pairs. The rate of decarboxylation in the binding pocket of a catalytic antibody developed for this reaction is slower than that expected of a free carboxylate in an aprotic environment. Therefore, the binding site may contain a hydrogen-bond-donating species. A better catalyst might be developed by approaches that reduce hydrogen bonding in the active site without reducing substrate binding.