Hydrolysis and Isomerization of Sugar Phosphates and Carbohydrate Phosphodiesters

Phosphoesters are abundant in carbohydrate structures, yet their chemical reactivity is less well known than that of nucleoside phosphoesters. Both classes of compounds contain sugar bound phosphoesters, but structural versatility of carbohydrates means that the reactivity range is wider, and reaction mechanisms not feasible in nucleic acid chemistry, are possible. Sugar phosphates, as well as their phosphodiester and phosphoanhydride derivatives with a phosphate group in glycosylic position, react like acetals under acidic conditions. Substrates with a phosphate group attached to an alcoholic OH react by intramolecular transesterification similar to that of RNA provided that there is a suitably positioned HO-group and a suitable leaving group. If there is a free carbonyl group allowing anomeric equilibria, base-catalyzed phosphate elimination through enediolate intermediates may compete with the cleavage, particularly under alkaline conditions. The few reports on phosphate migration show that the reaction is conceivable, but the competition between cleavage and phosphate migration possibly is different from reactions of nucleic acids and nucleotides.