(S)-3-tert-Butoxycarbonylamino-1-nitro-2-oxo-4-phenylbutane was converted to tert-butyl (2S,3R)-4-amino-3- hydroxy-1-phenylbutane-2-yl carbamate by NaBH4 reduction followed by hydrogenation, which was converted to Carbamic acid[(1S,2R)-2-hydroxy-3-[(2-methylpropyl)[4-nitrophenyl)sulphonyl]amino]-1-(phenylmethyl)propyl]- 1,1 dimethylethyl ester by treatment with nocyl chloride followed by n-butyl bromide in favorable diastereselectivity,a component of the HIV protease inhibitor Amprenavir