4-Hydroxy-7-[1-(tert-butoxycarbonyl)-5-(piperidinomethyl)indol-2-yl]isoindolinone (0.230 g, 0.498 mmol) was dissolved in dichloromethane (4.6 mL), and the solution was added with triethylamine (0.139 mL, 0.997 mmol) and methanesulfonyl chloride (0.0460 mL, 0.598 mmol), followed by stirring under ice-cooling for 1.5 hours. The reaction mixture was added with water and extracted with chloroform. 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 (chloroform/methanol=85/15) to obtain 4-methanesulfonyloxy-7-[1-(tert-butoxycarbonyl)-5-(piperidinomethyl)indol-2-yl]isoindolinone (0.104 g, yield 61%).
