A solution of carbobenzoxy-(S)-valine (1.26 g, 5 mmol) in anhydrous THF (20 ml) was vigorously stirred and thereto were added triethylamine (0.70 ml, 5 mmol) and isobutyl chloroformate (0.66 ml, 5 mmol) at 0° C. To this mixture was added cyclohexylamine (0.57 ml, 5 mmol) and this mixture was stirred for 2 hours at 0° C. and further for 24 hours at room temperature. The solvent was removed to obtain white crystals. These crystals were dissolved in a mixture of CH2Cl2 (80 ml) and water (30 ml). The organic layer was washed with 0.5M boric acid, a saturated aqueous sodium chloride solution, a saturated aqueous sodium hydrogencarbonate solution, a saturated aqueous sodium chloride solution and water (50 ml each) in succession, dried over Na2SO4 and concentrated under reduced pressure to obtain crude carbobenzoxy-(S)-valine cyclohexylamide (1.45 g, 87%), which was used as it was for the following reaction.
