To a mixture of 3-t-butyl-5-[4-(3-ethoxycarbonyl-5-isoxazolyl)phenyl]-4-(2-methoxyphenyl)-4,5-dihydro-1H-pyrrolo[3,4-c]pyrazol-6-one (1.26 g, 2.5 mmol), methanol (4 mL), THF (4 mL) and water (3 mL), 2N aqueous sodium hydroxide (1.5 mL, 3 mmol) was added and the mixture was stirred at 50° C. for 1 hr. Water (40 mL) and 1N hydrochloric acid (2 mL) were added to the mixture, which was then extracted with ethyl acetate. The organic layer was washed with brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The crude product was suspended in ether, and the precipitate was collected to give 3-t-butyl-5-[4-(3-carboxy-5-isoxazolyl)phenyl]-4-(2-methoxyphenyl)-4,5-dihydro-1H-pyrrolo[3,4-c]pyrazol-6-one (0.84 g, 71%) as pale yellow crystals.
