(R)-1-(5-acetoxyhexyl)-8-bromo-7-(2-(N-tert-butoxycarbonylamino)ethyl)-3-methylxanthine (6.10 g, 11.2 mmol) was added to a solution of trifluoroacetic acid (50 ml) and dichloromethane (50 ml) and stirred at room temperature for 3 hours. Concentration under reduced pressure provided an oil to which was added acetonitrile (30 ml) followed by potassium carbonate (13.8 g, 100 mmol). The mixture was stirred at 650° C. for 3 hours and filtered to remove solids. The filtrate was concentrated under reduced pressure and the residue was purified by column chromatography on silica gel eluting with ethyl acetate-methanol (4:1) to provide (R)-3-(5-acetoxyhexyl)-1-methyl-6,7,8,9-tetrahydro-pyrimido[2,1-f]purine-2,4(1H,3H)-dione (3.58 g, 88% yield) as a white powder.
