In a dried reaction flask, the crude 2-(3-chloro-4-cyanophenyl)-3-cyclopentyl-3,3a,4,5-tetrahydro-2H-pyrazolo[3,4-f]quinoline-7-carboxylic acid (Compound 1) (0.4 g, about 0.9 mmol), DIEA (0.5 mL, 2.89 mmol) and HATU (1.047 g, 2.754 mmol) were added to DMF (4.5 mL). To the mixture was added dropwise a solution of dichloromethane (9 mL) dissolved in 4-hydroxylpiperidine (0.446 g, 4.409 mmol) under an ice-salt bath. After the completion of the dropwise addition, the mixture was stirred at room temperature for 4 days. Water and ethyl acetate were added. The mixture was extracted with ethyl acetate. The combined organic phase was washed with water and saturated salt water, dried over anhydrous sodium sulfate, and concentrated at reduced pressure to produce a crude yellow solid, which were washed with ethyl ether and ethyl acetate respectively to produce a purified product (0.217 g) in 47.8% yield.
