The tautomeric state of N(4)-hydroxy- and of N(4)-amino-cytosine derivatives

Abstract

The tautomeric equilibria of N(4)-hydroxy- and N(4)-amino-1-methylcytosine have been studied by comparing their i.r., u.v., and n.m.r. spectra and their dissociation constants with those of methylated derivatives. In water, N(4)-hydroxy-1-methylcytosine is predominantly in the oximino-form, with K_Tca. 10, whereas the N(4)-amino-compound has K_Tca. 30 in favour of the hydrazino-form. The possible significance of these results to hydroxylamine and hydrazine mutagenesis is discussed.