Treatment of dimethyl alpha-ethoxymethylidineacetonedicarboxylate with hydrazine gave methyl 3-(methoxy-carbonylmethyl)pyrazole-4-carboxylate which, upon ammonolysis and dehydration, afforded methyl 3-(cyanomethyl)pyrazole-4-carboxylate. This compound, when heated with liquid ammonia, gave 6-aminopyrazolo[4,3-c]pyridin-4(5H)-one, a new guanine analogue, which did not possess any of the potent antiviral activity shown by 6-aminoimidazo[4,5-c]pyridin-4(5H)-one (3-deazaguanine).