To a solution of 2-amino-4-[3-(methoxycarbonyl)-phenoxy]-butyronitrile (0.5 g, 2.13 mmol), 3-methyl-N-(2,2-diphenylacetyl)-L-phenylalanine (see example 1, 0.80 g, 2.13 mmol) and diisopropylethylamine (1.1 mL, 6.39 mmol) in CH2Cl2 (15 mL) is added benzotriazol-1-yloxy-tris-(pyrrolidino)-phosphonium hexafluorophosphate (PyBop, 1.22 g, 2.34 mmol) in one portion. After stirring 1.5 hour, an additional portion of PyBop (0.61 g, 1.2 mmol) is added, and the solution is stirred overnight. The reaction mixture is washed with 1 N HCl (50 mL), saturated aqueous NaHCO3 (1×50 mL), water (1×50 mL) and brine (1×50 mL), dried over MgSO4, and evaporated. The residue is chromatographed (silica, 50% EtOAc/hexane) to yield N-[3-(3-(methoxycarbonyl)-phenoxy)-1-cyanopropyl]-3-methyl-Nα-(2,2-diphenylacetyl)-L-phenylalaninamide as a white solid, m.p. 152-153° C.
