In a similar manner to Step 2 of Example 6, 4-chloro-7-[1-(tert-butoxycarbonyl)-5-formylindol-2-yl]isoindolinone (37.6 mg, 0.0922 mmol) was dissolved in acetonitrile (2 mL), and the solution was treated with diethanolamine (0.035 mL, 0.37 mmol), acetic acid (0.106 mL, 1.85 mmol) and sodium triacetoxyborohydride (98 mg, 0.46 mmol), followed by purification by preparative thin-layer chromatography (hexane/ethyl acetate=1/2) to obtain 4-chloro-7-(1-(tert-butoxycarbonyl)-5-[di(2-hydroxyethyl)aminomethyl]indol-2-yl)isoindolinone (29.2 mg, yield 64%).
