To a cooled solution (−78° C.) of sodium hexamethyldisilazide (0.38 mL, 0.38 mmol) in THF (0.5 mL) was added tert-butyl 3-{(1R)-3-[(4R)-4-benzyl-2-oxo-1,3-oxazolidin-3-yl]-3-oxo-1-pyridin-2-ylpropyl}benzoate from the previous step (0.153 g, 0.314 mmol) in THF (1 mL) dropwise and stirred for 45 min. 2-(Phenysulfonyl)-3-phenyloxaziridine (0.167 g, 0.629 mmol) dissolved in THF (0.5 mL) was added to cold solution and the mixture was stirred for 10 min. Camphorsulfonic acid, dissolved in THF (2 mL), was quickly added and the bath was removed. The reaction was warmed to room temperature, diluted with saturated aqueous NaHCO3, extracted with EtOAc, washed with saturated aqueous NaHCO3 and brine, dried over MgSO4, filtered, and the solvent removed under reduced pressure. The residue was chromatographed on a 35 g ISCO column using 0-50% EtOAc/hexanes over 40 min and the lowest spot fractions were combined and the solvent removed under reduced pressure to give an oil. This oil was purified by preparative HPLC on a Waters PrepPak using 10% to 100% CH3CN/H2O with 0.1% TFA as eluant over 60 min. The product-containing fractions were combined and the acetonitrile was removed under reduced pressure. The remaining aqueous solution was basicified with saturated aqueous NaHCO3, extracted with 4×20 mL CH2Cl2, dried over Na2SO4 and filtered. The filtrate solvent was removed under reduced pressure to give tert-butyl 3-{(1R,2R)-3-[(4R)-4-benzyl-2-oxo-1,3-oxazolidin-3-yl]-2-hydroxy-3-oxo-1-pyridin-2-ylpropyl}benzoate as an oil (0.068 g, 43%). TLC Rf=0.3 (1:1 EtOAc:hexanes, UV visualization); HPLC RT=2.61 min, method B; M+H=503.
