v-Triazolo[5,4-d]pyrimidines (8-azapurines). Part 20. 1-Alkyl derivatives

Abstract

9-Benzyl-1-methyl-8-azapurin-6-one (2b) was made (a) by heating 4-amino-3-benzyl-1,2,3-triazole-5-(N-methylcarboxamide)(7a) with formamide, and (b), quantitatively, by methylating 9-benzyl-8-azapurin-6-one. It was debenzylated to 1-methyl-8-azapurin-6-one (2a), which was also prepared by condensing 4-amino-1,2,3-triazole-5-(N-methylcarboxamide)(7c) with formamide. The i.r. spectrum of compound (2a) indicates an unusually dipolar nature. 1-Butyl-8-azapurin-6-one and its 9-benzyl derivative were synthesized analogously. 1-Methyl-8-azapurine-6-thione (10), prepared from the 6-oxo-analogue (2a), resisted further changes. Attempted chlorination of the oxo-compound (2a), with thionyl chloride and dimethylformamide, produced what appears to be the pyrimidine (12).

4-Amino-5-aminomethyl-3-benzyl-1,2,3-triazole was mono- and bis-trifluoroacetylated, and the former product (13c) was N-methylated then deacylated to 4-amino-3-benzyl-5-methylaminomethyl-1,2,3-triazole (13f). The latter was condensed with formamidine to 9-benzyl-1,6-dihydro-1-methyl-8-azapurine (11b). 1-Methyl-8-azapurine (3) was made by nitrosating 5-amino-1,4-dihydro-4-imino-1-methylpyrimidine hydrochloride (16). Compound (3) was found to be about 15% covalently hydrated at equilibrium in D₂O whereas the cation was completely hydrated (n.m.r. and u.v. evidence). The physical properties in which the neutral species differs most from its known isomers are m.p., volatility, and extractability from water, in all of which it behaves as a much more polarized substance.