Indole-5-carboxylic acid (1.00 g, 6.21 mmol) was dissolved in DMF (10 mL) and the solution was added with EDCI (2.38 g, 12.4 mmol), HOBT monohydrate (839 mg, 6.21 mmol) and 1-(tert-butoxycarbonyl)piperazine (1.73 g, 9.29 mmol), followed by stirring 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 saturated aqueous sodium hydrogencarbonate solution, 1 mol/L hydrochloric acid, and saturated brine, and was dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure to obtain 5-[4-(tert-butoxycarbonyl)piperazin-1-ylcarbonyl]indole (2.26 g).
