To a solution of Boc-L-alanyl-L-alanyl-L-proline (1.0 g, 2.80 mmol) in dry acetonitrile (25 ml) was added N-methylmorpholine (0.34 ml, 3.06 mmol). The solution was cooled to -20° C. and isobutylchloroformate (0.37 ml, 2.88 mmol) was added dropwise. To this solution, a pre-cooled (-20° C.) mixture of 3-amino-1,1,1-trifluoro-4-methyl-2-pentanol hydrochloride (0.61 g, 2.91 mmol), N,N-dimethylformamide (4 ml) and N-methylmorpholine (0.34, 3.06 mmol) was added. The reaction mixture was stirred at -20° C. for 4 hr, allowed to warm to room temperature and stirred overnight. Removal of the solvents in vacuo produced a pale yellow residue, which was purified by flash chromatography using ethyl acetate as an eluent to give 1,1,1-Trifluoro-3-[(N-tert-butyloxycarbonylalanyl)alanylprolylamino]-4-methylpentane-2-ol (1.09 g, 2.1 mmol) in 76% yield.
