To a solution of methyl 3-hydroxy-2-(4-methoxybenzenesulfonylamino)-propionate (15.0 g 51.85 mmol) in N,N-dimethylformamide (125 ml), cooled in an ice bath, was added, portionwise, NaH (2.29 g 57.03 mmol, 60% in oil). The mixture was stirred at 0° C. for 20 minutes and then a solution of 2-nitrobenzyl bromide (12.32 g 57.03 mmol) in dry N,N-dimethylformamide (25 ml) was added, dropwise. The solution was stirred at room temperature for 48 hours and diluted with ethyl acetate (500 ml) and water. The organic layer was separated and the aqueous layer extracted with additional f ethyl acetate (250 ml). The combined organic layers were washed with water (200 ml), 1N sodium bicarbonate (200 ml), saturated sodium chloride (200 ml) and dried over sodium sulfate The solvent was removed in vacuo and the residual solid was triturated with ethyl acetate, cooled and filtered to give 13.5 g (61%) of white crystals, mp 127-129° C.
