Oxalyl chloride (0.12 mL, 1.39 mmol) is added dropwise to DMF (10 mL), and the resulting solution is cooled to 0° C. After the solution is clear, pyridine (0.22 mL, 2.78 mmol) is added, followed by N-[4-(3-methoxycarbonylphenyl)-1(S)-(aminocarbonyl)butyl]-3-methyl-Nα-(2,2-diphenylacetyl)-L-phenylalaninamide (0.42 g, 0.70 mmol), in one portion. The yellow reaction solution is stirred at 0° C. for 1.5 hours, after which time it is diluted with EtOAc (50 mL), and washed with saturated aqueous NaHCO3 solution (1×50 mL), saturated aqueous LiCl solution (1×50 mL), dried over MgSO4, and evaporated. The residue is chromatographed to yield N-[4-(3-methoxycarbonyl-phenyl)-1(S)-cyanobutyl]-3-methyl-Nα-(2,2-diphenylacetyl)-L-phenylalaninamide, as a yellow solid.
