Triethylamine (1.1 mL, 8 mmol), 2-(tert-butoxycarbonylamino)-4,5-difluorobenzoic acid (607 mg, 2.2 mmol), EDCI (422 mg, 2.2 mmol) and HOBt (337 mg, 2.2 mmol) were added to a dichloromethane (20 mL) solution of 1-(4-chlorobenzyl)-4-[(glycylamino)methyl]piperidine dihydrochloride (738 mg, 2 mmol), and the resulting mixture was stirred at room temperature for 14 hours. A 0.6 M aqueous solution of NaOH (50 mL) was then added to the mixture, and the obtained mixture was extracted with dichloromethane (3 times). The organic layers were combined, dried over anhydrous sodium sulfate, filtered and concentrated to thereby provide 4-[[(N-(2-(tert-butoxycarbonylamino)-4,5-difluorobenzoyl) glycyl)amino]methyl]-1-(4-chlorobenzyl)piperidine (1.01 g, 92%). ESI/MS m/e 551.3 (M++H, C27H33ClF2N4O4).
