(S)-3-(4-phenoxybenzenesulfonamido)-2-(tritylamino)propanol (2.26 g, 4.0 mmol) was dissolved in a mixture of chloroform and methanol (1:1, 8 mL) and cooled to 0° C. in an ice bath. The reaction mixture was stirred at 0° C. for 2.5 h, after dropwise addition of trifluoroacetic acid (5.2 mL, 70 mmol). Solvents were removed and the resulting residue was azeotroped 5 times with diethyl ether (5×2 mL) and partitioned between diethyl ether (50 mL) and water (25 mL). The ether layer was washed with water (10 mL) and the combined aqueous fractions are basified with NaHCO3 (1.34 g, 16 mmol). Aqueous fraction was diluted with EtOAc (100 mL) and the mixture was cooled to 0° C. in an ice bath. Then benzyl chloroformate (0.57 mL, 4.0 mmol) was added to the reaction mixture and stirred vigorously at RT for 1.5 h. The layers were separated and the aqueous layer was washed with EtOAc (2×20 mL). The combined organic fractions were washed with brine (20 mL), dried over anhydrous Na2SO4, concentrated and column purified (silica gel, 5% MeOH in EtOAc) to provide (S)-2-(benzyloxycarbonyla-mino)-3-(4-phenoxybenzenesulfonamido) propanol in 76% (1.38 g, 4.0 mmol) yield as colorless solid.
