A mixture of 8-(1-benzyl-1H-pyrazol-4-yl)-2-chloro-1-propyl-1,7-dihydro-purin-6-one (prepared as given in Example 1) (1.2 g, 3.2 mmol), pyrrolidine (0.34 g, 4.8 mmol), Diisopropyl ethyl amine (0.826 g, 6.4 mmol) and N-methylpyrrolidone (12 ml) were heated at 80-90° C. for 20 hours. Reaction mixture was cooled to 20-25° C. and water (20 ml) was added, solid separated out. The solid material was filtered off and purified by column chromatography to get pure 8-(1-Benzyl-1H-pyrazol-4-yl)-1-propyl-2-pyrrolidin-1-yl-1,7-dihydro-purin-6-one as off white solid (0.83 g, 64%).
