PHOTOCHEMICAL REACTIONS OF CYTOSINE AND 5‐METHYLCYTOSINE WITH METHYLAMINE ANDn‐BUTYLAMINE

Abstract
The photoinduced exchange reactions of cytosine (la) and 5‐methylcytosine (IIa) with two primary amines have been studied. The reactions ofIaandIIawith methylamine lead, respectively, to 1‐methylcytosine (Ib) and 1,5‐dimethylcytosine (IIb) as final products; the reactions of the same two starting materials withn‐butylamine gives the correspondingn‐butyl compounds. The reactions ofIIawith the two amines also gave small amounts of 1‐methylthymine and 1‐n‐butylthymine. An opened ring intermediate, N‐(N'‐methylcarbamoyl)‐3‐arnino‐2‐methylacrylamidine (IVa), was isolated from theIIa‐methylamine system irradiated at pH 7 and shown to be a precursor of bothIIband 1‐methylthymine. The pH profiles for rate of production ofIIb, 1‐methylthymine andIVain the reaction ofIIawith methylamine were determined and found to be similar in shape. All three profiles show a maximum in reactivity at about pH 8.7 with some reactivity being detectable at pH values as low as 5.