To a stirring mixture of (R)-7,8-dihydro-1-methyl-3-(5-tert-butyldimethylsilyloxyhexyl)-1H-imidazo[2,1-f]-purine-2,4(3H,6H)-dione (280 mg, 0.65 mmol) and p-dimethylaminopyridine (160 mg, 1.30 mmol) in dichloromethane (10 ml) was added acetic anhydride (100 mg, 0.98 mmol). After stirring at room temperature for 2 hours, the reaction mixture was treated with methanol. After concentration under reduced pressure, the residue was purified by column chromatography on silica gel eluting with ethyl acetate to provide (R)-8-acetyl-7,8-dihydro-1-methyl-3-(5-tert-butyldimethylsilyloxyhexyl)-1H-imidazo[2,1-f]-purine-2,4(3H,6H)-dione (200 mg, 67% yield) as a white powder.
