Studies on Hydrogen Exchange. XII. Reaction Mechanism for Hydrogen Exchange of C-8 Hydrogen of Purine Ribosides

Abstract

The reaction mechanism for the hydrogen exchange of C-8 hydrogens of purine ribosides was discussed on the basis of the pD-rate profiles and the effect of 6-substituents on the rate. It was shown that the rate depended on concentrations of the purine and D₂O and that the observed second-order rate constant was expressed as k_OD-K_D2O/Ka (N₇) where k_OD-was the rate constant for hydrogen exchange of N₇-protonated purines by attack with the OD^-, K_D2O was the dissociation constant of D₂O, and Ka (N₇) was the dissociation constant of N₇-protonated purines.