Reaction of 1-methyl-5-(methylamino) imidazole-4-carboxamide (6a) with a boiling mixture of ethyl orthoformate and acetic anhydride produced 3, 9-dimethylhypoxanthine (7a) in 60% yield and 1-methyl-5-(N-methylformamido) imidazole-4-carboxamide (5a) in 39% yield. Compound 5a was transformed into 7a by treatment with NaH in 78% yield. Compound 7a was alternatively prepared by cyclocondensation of 6a with diethoxymethane followed by oxidation with I2. The pyrimidine moiety of 7a has been shown to be reactive : 7a affords the 1, 2-dihydro derivative 9 under reductive conditions and undergoes ring opening to 5a in aqueous NaOH. 3-Ethyl-9-methyl-(7b), 3-benzyl-9-methyl-(7c), 9-ethyl-3-methyl-(7d), and 3, 9-dibenzylhypoxanthine (7e) were also prepared from the corresponding carboxamides 6b-e.
