The acid hydrolysis of glycosides : V. Effect of the nature of the aglycon on the hydrolysis of glycosiduronic acids (glycuronides)

Abstract

Rate coefficients and kinetic parameters have been determined for the acid-catalyzed hydrolysis of fourteen β- D-glucopyranosiduronic acids containing aglycons of different electron-affinity. Energies and entropies of activation of all of these compounds were lower than those of the corresponding β- D-glucopyranosides. The glucopyranosiduronic acids were hydrolyzed at rates that were inversely proportional to the electron affinity of the aglycon, whereas the rates of hydrolysis of the glucopyranosides were independent of the polarity of the aglycon. (Carboxymethyl) β- D-glucopyranosiduronic acid was hydrolyzed at one hundredth of the rate expected. The phenomena are discussed, assuming a catalytic interaction between the carboxyl groups and the glycosidic oxygen atom. Substitution, in the aglycon, of alkyl groups for hydrogen atoms at the carbon atom adjacent to the glycosidic oxygen atom increased the rate of hydrolysis both of the glucopyranosiduronic acids and of the glucopyranosides.