N-Boc-6-aminocaproic acid (7.58 g) prepared by the method described in a Journal of Medicinal Chemistry (J. Med. Chem., 35, p.272 (1993)) and 7.58 g of 3-amino-9-ethylcarbazole were dissolved in 75 mL of dimethylformamide, and the solution was added with 10.4 g WSC hydrochloride and stirred at room temperature for 3.5 hours. The reaction mixture was added with water and extracted with ethyl acetate. The organic layer was washed with 1 N aqueous sodium hydroxide, 10% aqueous citric acid and saturated brine, then dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by silica gel chromatography (eluent: hexane/ethyl acetate=1/1) to obtain 10.3 g of 3-(N-Boc-6-aminocaproyl)amino-9-ethylcarbazole.
