[OH-].[Na+].[CH3:3][N:4]1[C:12]2[N:11]=[CH:10][NH:9][C:8]=2[C:7](=[O:13])[NH:6][C:5]1=[O:14].[CH2:15](Br)[C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1>O.CO>[CH2:15]([N:9]1[C:8]2[C:7](=[O:13])[NH:6][C:5](=[O:14])[N:4]([CH3:3])[C:12]=2[N:11]=[CH:10]1)[C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=120 g (0.5 mol) of sodium hydroxide dissolved in 200 ml of water were added to a suspension of 83 g (0.5 mol) of 3-methylxanthine in 500 ml of methanol and the reaction mixture was stirred at 70° C. for one hour, then treated dropwise at the same temperature with 85.5 g (0.5 mol) of benzyl bromide and kept between 700 and 800 for 5 hours. The mixture was then cooled and filtered cold on a suction filter, the product was washed with water on the suction filter and dissolved hot in 1000 ml of 1N sodium hydroxide solution, filtered and slowly brought to pH 9.5 using 4N hydrochloric acid with stirring. The crystallizate was filtered off from the still warm solution, washed with water until chloride-free and dried in a vacuum drying oven overnight. Yield: 81.7 g (63.8% of theory); melting point: 263° C. C13H12N4O2 (MW=256.2 g/mol)
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