To a solution of 5-ethyl-6-mercapto-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one potassium (2.0 g) in DMF (25 ml) was added 28% sodium methoxide (1.75 ml). Then, 3-dimethylaminopropyl chloride hydrochloride (1.62 g) was added and the mixture was stirred at 60° C. for 1 day. To this reaction mixture was added 60% sodium hydride (232 mg) and the mixture was stirred at room temperature for 10 minutes. Thereafter, 4-(4-chlorobenzoyl)benzyl bromide (1.778 g) was added and the reaction mixture was stirred at room temperature for 30 minutes. This reaction mixture was concentrated and the residue was dissolved in ethyl acetate, washed with water, dried, and concentrated. The residue was purified by silica gel column chromatography (chloroform: methanol: concentrated aqueous ammonia=50:1:0.1) and treated with hydrogen chloride/ethyl acetate to provide the title compound (A) (518 mg) and (B) (262 mg) both as colorless solid.
