6-(3-((5-fluoro-2-oxoindolin-3-ylidene)methyl)benzamido)hexanoic acid (396 mg, 1 mmol), triethylamine (151 mg, 1.5 mmol) and 20 ml of DMF were stirred at 0° C. while ethyl chloroformate (163 mg, 1.5 mmol) was added. The mixture was stirred at 0° C. for 2 hours, and then 50% aqueous solution of hydroxylamine (1.32 g, 20 mmol) was added. The mixture was stirred for 3 hours at room temperature, and then diluted with 1000 mL of brine. The solids were collected by vacuum filtration, washed with water and dried under vacuum to give the title compound (168 mg, 41%) as a brown solid. LC-MS (m/z) 412 (M+1).
