To a mixture of 3-t-butyl-5-[4-(3-carboxy-5-isoxazolyl)phenyl]-4-(2-methoxyphenyl)-4,5-dihydro-1H-pyrrolo[3,4-c]pyrazol-6-one (0.080 g, 0.17 mmol), triethylamine (0.031 mL, 0.22 mmol) and THF (2 mL), ethyl chlorocarbonate (0.019 mL, 0.20 mmol) was added under ice-cooling conditions and the mixture stirred at r.t. for 2 hr. Sodium borohydride (0.026 g, 0.68 mmol), water (0.3 mL) and methanol (1 mL) were added to the mixture and the mixture was stirred at r.t. for 10 min. Water was added to the mixture, the mixture was extracted with ethyl acetate. The organic layer was washed with 1N hydrochloric acid, saturated sodium bicarbonate and brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The residue was crystallized from dichloromethane, diethyl ether and ethyl acetate, and the precipitate was collected by filtration to give 3-t-butyl-5-[4-(3-hydroxymethyl-5-isoxazolyl)-phenyl]-4-(2-methoxyphenyl)-4,5-dihydro-1H-pyrrolo[3,4-c]pyrazol-6-one (0.068 g, 88%) as colorless crystals.
