Boc-Ile-OH (12.01 @, 0.05 mole) in DMF (50 ml) was cooled to 0° C. and NMM (5.49 ml) was added. After cooling the solution to -15° C. isobutylchloroformate (6.48 ml) was added slowly while maintaining the temperature at -15° C. and st1rred for 10 minutes at which time HOBt (7.65 g) was added and stirring was continued for additional 10 minutes. A pre-cooled solution of HCL-H-Pro-OBzl (12.09 g. 0.05 mole) in DMF (50 ml) and NMM (5.49 ml) was added to the above solution and the completeness of the reaction was followed by TLC. The reaction mixture was poured into a cold saturated NaHCO3 solution and stirred for one hour. The peptide was extracted into CHCl3 and washed with acid and base (0.5 N NaOH to remove HOBt), and on evaporating the solvent the product was obtained as an oil in 92% yield. Rf1, 0.65. Anal. Calcd. for C23H34N2O5 : C 66.00, H 9.19, N 6.69%. Found: C 65.58, H 8.28, N 7.13%.
