3-(4-(3(S)-Aminopyrrolidin-1-yl)-3-fluorophenyl)-5(R)-(N-(2,2,2-trichloroethyl-oxycarbonyl)isoxazol-3-ylaminomethyl)oxazolidin-2-one hydrochloride salt (400 mg, 0.74 mM) was dissolved in water (5 ml) and treated with aqueous sodium bicarbonate solution (5 ml) and dichloromethane (10 ml) in an ice-bath. Acetic anhydride (216 mg, 2 mM) was added, the mixture stirred 18 hours, allowing the temperature to rise to ambient, followed by addition of a further portion of acetic anhydride (216 mg), and a further period of 10 hours stirring. The organic phase was separated, washed with aqueous sodium dihydrogen phosphate (2%, 2×15 ml), brine (10 ml), and dried (magnesium sulfate). Evaporation gave the desired product (338 mg).
