Oxalyl chloride (0.58 g, 0.39 ml, 4.57 mmol) was added drop wise to a solution of 5-(4-chlorophenyl)-4-(dimethylamino)-3-(4-sulfamoylphenyl)thiophene-2-carboxylic acid (compound 34f, 1.00 g, 2.28 mmol) in a mixture of dichloromethane (30 ml) and DMF (0.33 g, 0.35 ml, 4.57 mmol) at 0° C. The reaction mixture was then allowed to warm to room temperature and stirred for 1.5 hr under a nitrogen atmosphere. The progress of the reaction was monitored by TLC. The mixture was then concentrated under reduced pressure. The residue so obtained was dissolved in dry dichloromethane (30 ml) and cooled to 0° C. To the cooled reaction mixture was then added triethylamine (1.38 g, 1.90 ml, 13.68 mmol) followed by the addition of N,O-dimethylhydroxylamine hydrochloride (0.40 g, 4.57 mmol) under stirring. The reaction mixture was then stirred at room temperature for 2 hr. The progress of the reaction was monitored by TLC. The reaction mixture was then diluted with DCM (25 ml) and washed with water (2×25 ml). The combined organic layer was then dried over anhydrous sodium sulphate, and concentrated under reduced pressure to obtain a crude product, which was then purified by column chromatography over silica gel (100-200 mesh) using 1.6% methanol in DCM as an eluent to obtain the title compound (0.8 g, 65.35%).
