Reaction Steps
To a solution of DIEA (0.019 mL, 0.11 mmol) in 0.5 mL of 1,2-dichloroethane was added 4-(N-(N-(3,4-difluorobenzyl)carbamoyl)-N-ethylamino)piperidine trifluoroacetate (41 mg, 0.1 mmol, from Step B). To this solution, a solution of 2-(R)-(3-(R)-formyl-4-(S)-phenyl-pyrrolidin-1-yl)-2-(cyclohexyl)acetic acid, (4-methoxy)benzyl ester (26 mg, 0.05 mmol, Aldehyde 5) was added. After mixing well, a slurry of sodium triacetoxyborohydride (35 mg, 0.17 mmol) in 0.5 mL of 1,2-dichloroethane was added. The reaction mixture was stirred well and allowed to stand at rt for 16 h. The solvent was removed and the product was purified by preparative HPLC (column: YMC Combiprep ODS-A 20×50 mm, gradient: 10% acetonitrile/water w/0.1% TFA for 1.5 min then ramp to 90% acetonitrile/water w/0.1% TFA over 7.5 min, flow: 20 mL/min). The isolated material was stirred in 3 mL formic acid for 16 h. After removal of solvent, the residue was purified by ion exchange chromatography (0.5 grams Varian SCX resin, eluting with 100% MeOH, then with 2.0 M NH3/MeOH) to give 16 mg (53%) of the title compound. 1H-NMR (400 MHz, CD3OD) δ1.06-1.14 (m, 6H), 1.33 (m, 2H), 1.54 (m, 1H), 1.67-2.05 (m, 10H), 2.57 (m, 1H), 2.87 (br d, J=13, 1H), 2.98 (br t, J=12, 1H), 3.11 (m, 1H), 3.18 (m, 2H), 3.25 (m, 1H), 3.48 (br t, J=11, 2H), 3.65 (m, 2H), 3.71 (d, J=3.1, 1H), 3.79 (dd, J=6.8, 11, 1H), 3.87 (m, 1H), 4.16 (brt, J=12, 1H), 4.29 (s, 2H), 7.04 (m, 1H), 7.10-7.19 (m, 2H), 7.35-7.46 (m, 5H); ESI-MS: 597.4 (M+H); HPLC A: 2.27 min.
