To (2-propylmercapto)acetic acid (44.3 mg, 0.33 mmol) in the THF (3 mL) at 0°(b) was added N-methylmorpholine (37 microliters, 0.34 mmol) followed by isobutylchloroformate (43 microliters, 0.33 mmol). The mixture was stirred at 0° C. for 15 minutes and (3S,4S)-1-amino-3-hydroxy-4-t-butyloxycarbonylamino-5-cyclohexylpentane (51.0 mg, 0.17 mmol) was added followed by stirring at 0° C. for 15 minutes and at 25° C. for 2 hours. The mixture was poured into ethyl acetate, washed with 0.5 M H3PO4, 2 M Na2SO4 and evaporated to afford 36 mg (50%) of the desired compound. Mass spectrum: (M+1)+ =417.
