To a mixture of 1-cyclopentyl-3-ethyl-4-cyano-5-(4-quinolinecarboxamido)-1H-pyrazole (4.6 g, 12.7 mmol), potassium hydroxide (1.7 g, 25.4 mmol) and water (250 ml) at room temperature was added 30% hydrogen peroxide (7.8 ml, 76.0 mmol). The reaction mixture was heated to reflux and stirred for 24 hours. One equivalent of potassium hydroxide and 2 equivalents of 30% hydrogen peroxide were added and the mixture was refluxed for another 24 hours. One equivalent of potassium hydroxide and 2 equivalents of 30% hydrogen peroxide were again added and the mixture was heated at reflux for 3 days. The reaction mixture was cooled to room temperature, treated with acetic acid until a pH of 6.5 was obtained and the resulting precipitate was collected by filtration. The product was purified by column chromatography on silica eluting with ethyl acetate to afford 1.3 g (35%) of 1-cyclopentyl-3-ethyl-6-(4-quinolinyl)-pyrazolo[3,4-d]pyrimidin-4-one as a white solid, m.p. 205°-206° C., when recrystallized from ethyl acetate and dried at 110° C. for 16 hours in high vacuum.
