Triethylamine (0.75 mL, 5.4 mmol), 2-amino-5-chlorobenzoic acid (840 mg, 4.9 mmol), EDCI (940 mg, 4.9 mmol) and HOBt (660 mg, 4.9 mmol) were added to a chloroform (25 mL) solution of 4-[(glycylamino)methyl]-1-(tert-butoxycarbonyl)piperidine (1.33 g, 4.90 mmol). The resulting mixture was stirred at room temperature for 3 hours, and a 2 M aqueous solution of NaOH (20 mL) was then added to the mixture. The organic layer was separated, and the aqueous layer was extracted with dichloromethane (20 mL×3). The organic layers were combined, dried over anhydrous sodium sulfate, filtered and concentrated. The obtained crude product was purified by column chromatography (SiO2, ethyl acetate) to thereby provide 4-[[(N-(2-amino-5-chlorobenzoyl) glycyl)amino]methyl]-1-(tert-butoxycarbonyl)piperidine as a solid (1.63 g, 78%).
