Acetic acid (10 mL) was added to a mixture of 4-[[N-(2-(tert-butoxycarbonylamino)-5-(trifluoromethoxy)benzoyl)glycyl]aminomethyl]piperidine (0.050 mmol) with 4-isopropylbenzaldehyde (0.060 mmol), NaH3CN (0.15 mmol) and methanol (1.3 mL), and the resulting mixture was stirred at 60° C. for 8 hours, cooled to room temperature, then loaded onto a Varian™ SCX column and washed with methanol (10 mL). The obtained crude product was eluted with a 2 M methanol solution of NH3 (5 mL) and concentrated. A 4 M dioxane solution of HCl (2 mL) was then added to the resulting residue, and the obtained solution was stirred at room temperature overnight, concentrated and then purified by preparative TLC to provide 4-[[N-(2-amino-5-trifluoromethoxybenzoyl)glycyl]aminomethyl]-1-(4-isopropylbenzyl)piperidine (Compd. No. 1903) (6.6 mg, 26%). The purity was determined by RPLC/MS (93%). ESI/MS m/e 507 (M++H, C26H33F3N4O3).
