A 25-mL RB-flask was charged with 6-oxo-6-phenylhexanoic acid (51.0 mg, 0.250 mmol), tert-butyl-4-(3-amino-4-fluorophenyl)-1-piperidinecarboxylate (59.0 mg, 0.200 mmol), 1-[3-(Dimethylamino)propyl]-3-ethylcarbodimide hydrochloride (0.400 mmol, 62.0 mg), 4-dimethylaminopyridine (10 mg) in DMF:DCM (0.2:2.0 mL) at room temperature. The reaction mixture was stirred for 12 h and water (10.0 mL) was added to the reaction mixture. The organic layer was separated and the aqueous layer was extracted with CHCl3 (3×10 mL). The combined organic extracts were washed with brine, dried over MgSO4, filtered and concentrated in vacuo. The crude residue was purified by chromatography (silica gel, hexanes:EtOAc 6:1) to afford tert-butyl 4-{4-fluoro-3-[(6-oxo-6-phenylhexanoyl)amino]phenyl}-1-piperidinecarboxylate (49.0 mg, 51.0%): 1H NMR (400 MHz, CDCl3) δ 8.30-8.14 (m, 1H), 8.04-7.89 (m, 2H), 7.62-7.50 (m, 1H), 7.50-7.37 (m, 3H), 7.09-6.93 (m, 1H), 6.93-6.76 (m, 1H), 4.38-4.01 (br, 2H), 3.13-2.95 (m, 2H), 2.89-2.69 (m, 2H), 2.65-2.54 (m, 1H), 2.54-2.35 (m, 2H), 1.95-1.74 (m, 6H), 1.69-1.48 (m, 2H), 1.47 (s, 9H).
