4-[3-Ethoxycarbonylmethyl-2,6-dioxo-7-(2-vinylphenyl)-2,3,6,7-tetrahydro-1H-purin-8-yl]piperazine-1-carboxylic acid tert-butyl ester (60 mg) was dissolved in N,N-dimethylformamide (2 ml), methyl iodide (17 μl) and potassium carbonate (17 mg) were added to the solution, and the mixture was stirred at room temperature for 13 hours. The reaction mixture was diluted with ethyl acetate and washed with water. The organic layer was dried over anhydrous magnesium sulfate and filtered. The filtrate was concentrated under reduced pressure to give 48 mg of the title compound.
