To a solution of benzyl 2-(1-aminocyclopentyl)acetate hydrochloride (66 mg, 0.245 mmol), 4-(benzyloxy)-3-(biphenyl-4-ylmethyl)-4-oxobutanoic acid (78 mg, 0.209 mmol), WSC.HCl (60.1 mg, 0.314 mmol) and 1-hydroxy-7-azabenzotriazole (42.7 mg, 0.314 mmol) in DMF (2 ml) was added DIPEA (0.055 ml, 0.314 mmol) at room temperature. After stirred for 4 hours, the reaction was quenched with H2O. The product was extracted with EtOAc, and the organic layer was washed with brine, dried over MgSO4, filtered, and concentrated under reduced pressure. The obtained residue was purified by flash column chromatography on silica gel (eluent: heptane/EtOAc=100:0 to 0:100) to give benzyl 4-(1-(2-(benzyloxy)-2-oxoethyl)cyclopentylamino)-2-(biphenyl-4-ylmethyl)-4-oxobutanoate (93 mg); Retention time=1.85 minutes (condition B); MS (m+1)=590.3; 1H NMR (400 MHz, CDCl3, mixture of rotamers) δ ppm 1.61-1.72 (m, 6H) 1.96-2.06 (m, 2H) 2.17-2.46 (m, 2H) 2.81-3.00 (m, 4H) 3.22-3.29 (m, 1H) 5.02-5.12 (m, 4H) 5.62 (br s, 1H) 7.15-7.57 (m, 19H).
