7-Methoxy-2-(propylsulfanyl)-3-[4-(2,2,2-trifluoroethoxy)phenyl]pyrido[2,3-d]pyrimidin-4(3H)-one (200 mg) was dissolved in ethanol (15 ml), sodium ethoxide (20% ethanol solution, 850 mg) was added thereto, and the mixture was stirred at 60° C. for 1 hr. The reaction mixture was poured into 0.2M hydrochloric acid (15 ml), and the precipitated precipitate was collected by filtration, and dissolved in tetrahydrofuran (15 ml). The solution was diluted with ethyl acetate (30 ml), and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure, and the obtained residue was purified by silica gel column chromatography (ethyl acetate/hexane) to give the title compound (95 mg).
