To a mixture of D-Lac(OAc)-L-Ala-D-GluOBzl (2) (1.20 g) and N-methylmorpholine (0.28 ml) in methylene chloride (17 ml) was added isobutyl chlorocarbonate (0.33 ml). The resulting mixture was stirred at -15° C. to -10° C. for 30 minutes and then cooled to -40° C. To the resulting mixture was added a mixture of Z-D-LysOH (1) (725 ml) and bis(trimethylsilyl)acetamide (3 ml) in dimethylformamide (3 ml) and methylene chloride (8 ml) at -40° C. The resulting mixture was stirred at -15° C. to -10° C. for an hour and gradually allowed to warm to ambient temperature. The resulting mixture was concentrated, taken up into ethyl acetate (80 ml) and washed with dil hydrochloric acid, water and brine, in turn. The concentrate was dried over magnesium sulfate and the solvent was distilled off to give an oil which was crystallized from a mixture of chloroform and isopropyl ether to give D-Lac(OAc)-L-Ala-γ-D-Glu(α-OBzl)-ε-Z-D-LysOH (3)(1.60 g).
