3-Methylisoguanosine : Synthesis and Acidic Hydrolysis of the Glycosyl Bond

Abstract

Dehydration of 5-(cyanomethylamino)-1-methyl-1H-imidazole-4-carboxamide (14a) with a combination of phosphorus oxychloride and triethylamine afforded the nitrile 17a. This compound underwent selective hydration at the cyanamide moiety to furnish the urea 18a followed by cyclization to 3, 9-dimethylisaguaninae (19a) under alkaline conditions. Similar dehydration of the nucleoside analog 14b followed by treatment with 0.1 N aqueous sodium hydroxide led to the first access to 3-methylisoguanosine (19c). Although 3-methylisoguanosine (19c) proved to undergo hydrolysis at the N-glycosidic bond most slowly among the known 3-methyl-9-β-D-ribofuranosylpurines in 0.1 N hydrochloric acid at 25°C, the rate was 650 times faster than that for the unmethylated isoguanosine (3).