3-Amino-6-[1-(tert-butoxycarbonyl)-5-formylindol-2-yl]phthalimide (45.0 mg, 0.111 mmol) was dissolved in acetonitrile (2 mL), and the solution was added with 1-(2-hydroxyethyl)piperazine (57 mg, 0.440 mmol), acetic acid (0.508 mL, 8.87 mmol) and sodium triacetoxyborohydride (118 mg, 0.557 mmol), followed by stirring at room temperature for 2.5 hours. The reaction mixture was added with water and sodium carbonate, extracted with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure and the residue was purified by flash column chromatography (hexane/ethyl acetate=4/1, 1/1) to obtain 3-amino-6-{1-(tert-butoxycarbonyl)-5-[4-(2-hydroxyethyl)piperazin-1-ylmethyl]indol-2-yl}phthalimide (22.2 mg, yield 38%).
