To a suspension of 4-((3,5-dichloro-N-(4-fluorobenzyl)-2-hydroxyphenylsulfonamido)methyl)benzoic acid (0.726 g, 1.5 mmol) in DCM (20 mL) at rt was added oxalyl chloride (0.394 mL, 4.50 mmol) and a few drops of DMF. The mixture was stirred at rt to give a yellow solution. The reaction mixture was concentrated and the residue was dissolved in DCM. At 0° C., a mixture of N,O-dimethylhydroxylamine hydrochloride (0.439 g, 4.50 mmol) and TEA (1.045 mL, 7.50 mmol) were added. The resulting mixture was stirred at rt for 1 h. The mixture was diluted with DCM and washed with water and brine. The organic extract was dried, concentrated and purified by flash column chromatography (ISCO system, eluting with DCM/EtOAc) to give the desired product (0.516 g, 62%) as a light yellow solid. MS (ESI): 527.1 (M+H)+.
