Synthesis, Tautomerism and Calculations of Mesomeric Betaines of Guanine

Abstract

Reaction of purine-N-oxide (4) with 4-(dimethylamino)pyridine and acetyl chloride, followed by the treatment with hydrochloric acid gave the purine-pyridinium salt (6) which was deprotonated to the mesomeric betaine (7). Depending on the reaction conditions, 4-methylpyridine and pyridine, respectively, converted the nucleoside (8) into the pyridinium salts (9) and (10), or into the mesomeric betaines (11) and (12). According to calculations, the conjugated tautomers (A-D) of betaine (7) are more stable than the cross-conjugated tautomer (7E).