In a similar manner to Step 2 of Example 147, 4-[3-(tert-butoxycarbonylamino)propoxy]-7-[1-(tert-butoxycarbonyl)-5-formylindol-2-yl]isoindolinone (104 mg, 0.188 mmol) was dissolved in acetonitrile (5.2 mL), and the solution was treated with 3-hydroxypiperidine (76.0 mg, 0.752 mmol), acetic acid (0.215 mL, 3.76 mmol) and sodium triacetoxyborohydride (160 mg, 0.752 mmol). The reaction mixture was added with 1 mol/L hydrochloric acid and extracted with ethyl acetate. The organic layer was washed with saturated aqueous sodium carbonate solution and saturated brine, and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure to obtain 4-[3-(tert-butoxycarbonylamino)propoxy]-7-[1-(tert-butoxycarbonyl)-5-(3-hydroxypiperidinomethyl)indol-2-yl]isoindolinone (40.9 mg, yield 34%).
