A mixture (645 mg) of (1R*,2S*,4R*,5S*)-4,5-dimethoxy-1,2-cyclohexanediamine hydrochloride and (1R*,2S*,4S*,5R*)-4,5-dimethoxy-1,2-cyclohexane-diamine hydrochloride was suspended in N,N-dimethylformamide (50 ml), and triethylamine (1.10 ml) and p-nitrophenyl 5-chloroindole-2-carboxylate (920 mg) were added to stir the mixture overnight at room temperature. The reaction mixture was concentrated under reduced pressure, and a saturated aqueous solution of sodium hydrogencarbonate was added to the residue to conduct extraction with dichloromethane. The resultant organic layer was dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure, and the residue was purified by column chromatography on silica gel (methanol:dichloromethane=1:9) to obtain a mixture (330 mg) of (1R*,2S*,4R*,5S*)-N1-[(5-chloroindol-2-yl)carbonyl]-4,5-dimethoxy-1,2-cyclohexanediamine and (1R*,2S*,4S*,5R*)-N1-[(5-chloroindol-2-yl)carbonyl]-4,5-dimethoxy-1,2-cyclohexanediamine as pale yellow powder.
