To a solution of 2,3-bis(1H-indol-3-yl)maleic anhydride (100 mg, 0.3 mmol) synthesized according to a known method (Tetrahedron, Vol. 44, p. 2887, 1988) and dissolved in DMF (10 mL) and water (10 mL) was added benzylamine (0.13 mL, 1.2 mmol), and the whole was stirred at 100 ° C. for 2 hours. The reaction mixture was concentrated under reduced pressure to remove DMF, and the concentrate was extracted with ethyl acetate. The extract was washed with water, dried over sodium sulfate, and then concentrated under reduced pressure. The residue was purified by column chromatography over silica gel (ethyl acetate:n-hexane=2:1) to obtain 2,3-bis(1H-indol-3-yl)-N-benzylmaleimide (110 mg, 86.6%) as red solids.
