(1S*,2R*,4R*)-4-azido-2-benzenesulfonylmethyl-cyclohexylamine trifluoroacetate (see 37c) (2.5 g, 6.3 mmol) was dissolved in DMF (15 mL) prior to the addition of BOP reagent (3.4 g) and N-Boc-L-Met-OH (1.9 g). After cooling to 0° C., NMM (2.6 mL) was added. The resulting mixture was warmed to rt and was stirred overnight. The solution was diluted with EtOAc, and was washed successively with brine and sat. NaHCO3. The organic phase was dried (MgSO4), filtered, and concentrated. Flash chromatography of the resulting residue gave tert-butyl (S)-1-((1S*,2R*,4R*)-4-azido-2-(phenylsulfonylmethyl)cyclohexylamino)-4-(methylthio)-1-oxobutan-2-ylcarbamate (2.8 g) as a mixture of diastereomers. MS found: (M+H)+=526.2.
