1-Hydroxybenztriazole (207 mg, 1.53 mmole) and N-methylmorpholine (235 mg, 2.36 mmole) were added to a stirred solution of N2 -acetyl-N6 -benzyloxycarbonyl-L-lysine (456 mg, 1.41 mmole) in dry dichloromethane at 0° C., followed by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (361 mg). The solution was stirred at 0° C. for 20 minutes and 3-{1-[(cis-4-ethoxycarbonylcyclohexyl)-carbamoyl]cyclopentyl}-2-(aminomethyl)propanoic acid t-butyl ester (500 mg, 1.18 mmole) in dichloromethane (10 ml) was added in one portion and the reaction mixture allowed to warm to room temperature and stirred for 16 hours. The solution was concentrated under vacuum to a volume of 10 ml and partitioned between ethyl acetate and water. The organic phase was washed with water (2×50 ml), 2M hydrochloric acid (50 ml, 2×25 ml), sodium bicarbonate solution (2×25 ml) and brine and then dried (MgSO4) and the solvent evaporated. The residue was chromatographed on silica eluting with ethyl acetate to give the title compound (610 g, 71%). Found: C,63.34; H,8.61; N,7.45. C39H60N4O9 (0.25H2O) requires C,63.48; H,8.33; N,7.59%.
