Tautomerism and ionisation of purin-8-one and its N-methyl derivatives

Abstract

U.v. and n.m.r. spectra show that in aqueous solutions purin-8-one is present predominantly as the 7H,9H-tautomer. Anion formation takes place preferentially at N-9. Protonation of purin-8-one and its 7- and 9-methyl derivatives occurs at N-1 and causes splitting of the 6-H and 2-H n.m.r. signals. In purin-8-one and its N-methyl derivatives, the 2-H is more deshielded than the 6-H; the reverse is the case for purine itself.