To a solution of (S)-2-amino-5-(3-carbomethoxyphenyl)-pentanamide HCl (0.30 g, 0.80 mmol), of 3-methyl-N-(2,2-diphenylacetyl)-L-phenylalanine (0.23 g, 0.80 mmol), 1-hydroxybenzotriazole hydrate (0.135 g, 0.89 mmol) and N-methylmorpholine (0.35 ml, 3.2 mmol) in CH2Cl2 (25 mL) is added 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.HCl (0.23 g, 1.2 mmol) in one portion, and the mixture is stirred at room temperature for 16 hours. The solution is then washed with 1 N HCl (100 mL), saturated aqueous NaHCO3 (1×50 mL), water (1×50 mL) and brine (1×50 mL), dried over MgSO4, and evaporated. The residual solid is triturated with ether to yield N-[4-(3-methoxycarbonyl-phenyl)-1(S)-(aminocarbonyl)-butyl]-3-methyl-Nα-(2,2-diphenylacetyl)-L-phenylalaninamide as a light yellow solid.
