Catalysis by aromatic aldehydes and carbon dioxide of the hydrolysis of the p-nitrophenyl esters of L-leucine, glycine, and L-β-phenylalanine

Abstract

The aromatic aldehyde and bicarbonate catalysed hydrolyses of the p-nitro-phenyl esters of L-leucine, glycine, and L-β-phenylalanine have been studied over a range of pH. The pH-rate profile for bicarbonate catalysis indicates that carbon dioxide is the active carbonate species, which presumably reacts with the substrates to give the carbamic acid, which hydrolyses by intramolecular nucleophilic participation by the carboxylate group. In the case of the aldehyde catalysis, aldehydes containing electron withdrawing groups in the aromatic ring are more effective than those with electron donating groups. The pH-rate profile for the catalysed reactions indicates attack by the free amino group of the ester on the aldehyde. The active species in the reaction is probably a carbinolamine, with the ester group undergoing hydrolysis with intramolecular nucleophilic participation by the hydroxyl group. The kinetics are consistent with the view that decomposition of the carbinolamine intermediate is rate-determining.