A solution of (2S,3S)-[2-(tert-butoxycarbonylamino)-3-hydroxy-hex-4-ynyl]-carbamic acid benzyl ester (0.25 g, prepared as in WO PCT 0250019) in methylene chloride (9 mL) was cooled to 0° C. and charged with trifluoroacetic acid (3 mL). The mixture was allowed to warm to RT and stirred for 45 min before being concentrated in vacuo. The residue was dissolved in methylene chloride and the resultant solution concentrated; this was repeated twice more to afford the TFA salt of (2S,3S)-2-amino-3-hydroxy-hex-4-ynyl-carbamic acid benzyl ester, MS found: (M+H)+=263.3. A solution of this amine in CH2Cl2 (12 mL) was charged successively with N,N-diisopropylethylamine (1.2 mL), 2-(2-(3-ethylureido)-5-(trifluoromethyl)benzamido)acetic acid (240 mg, see WO-02/50019), and BOP (382 mg). The reaction was stirred for 14 h at RT before being partitioned between EtOAc and water. The organic phase was washed with sat. NH4Cl, water, and brine before being dried (Na2SO4), filtered, and concentrated in vacuo. The residue was purified by flash chromatography to afford benzyl (2S,3S)-3-hydroxy-2-(2-(2-(3-isopropylureido)-5-(trifluoromethyl)benzamido)acetamido)hex-4-ynylcarbamate (289 mg). MS found: (M+H)+=592.35.
