Change of the hydrolytic mechanism of 2-hydroxy H-phosphonodiesters in aprotic organic media. cis-1,2-diol monoanions as leaving groups

The hydrolysis of H-phosphonodiesters bearing a vicinal hydroxyl group is f ound to be subject to two competing reaction pathways in aprotic organic me dia. An observation of the increased proportion of cis-1,2-diol leaving wit h decrease of the water content is interpreted in terms of a change of the hydrolytic mechanism on changing the reaction medium from aqueous to nonaqu eous. The hydroxyl group in cis-1,2-diol monoanions hydrogen bonds strongly to the adjacent oxyanion, implying a low-energy route closely related to r eactions, catalyzed by large ribozymes.