4-[1-(2,2-Dimethylpropionyloxymethyl)-3-ethoxycarbonylmethyl-2,6-dioxo-7-(2-vinylphenyl)-2,3,6,7-tetrahydro-1H-purin-8-yl]piperazine-1-carboxylic acid tert-butyl ester (89 mg) was dissolved in tetrahydrofuran (1 ml) and methanol (2 ml), sodium hydride (7 mg) was added to the solution, and the mixture was stirred at room temperature for 3.5 hours. The reaction mixture was diluted with ethyl acetate and washed with water. The organic layer was dried over anhydrous magnesium sulfate and filtered, followed by concentration of the filtrate under reduced pressure. The residue was purified by silica gel column chromatography to give 60 mg of the title compound from the elution fraction of hexane-ethyl acetate (1:2).
