Proton transfer from heterocyclic compounds. Part IV. Guanine, guanosine, hypoxanthines, and inosine

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Abstract
Rates of detritiation from C-8 of guanine, guanosine, hypoxanthine, 9-methylhypoxanthine, and inosine have been measured over a pH range at 85°. Two parallel rate-determining reactions are involved: one involves attack by hydroxide ion on the N-7 protonated substrates to form an ylide that is then reprotonated in a fast step; the other involves attack by hydroxide ion on the netural substrates. This second mechanism becomes increasingly important at high pH (>9). The kinetic data provide no evidence for the involvement of a guanosine zwitterion.