A mixture of [3-[[[1-(6-chlorobenzothiazole-2-yl)pyrrolidine-3-yl]-(2-nitrobenzensulphonyl)amino]methyl]phenyl]acetic acid methyl ester (412 mg), mercaptoacetic acid (95 mL), 1,8-diazabicyclo[5,4,0]-7-undecene (4 mL) and dimethylformamide (4 mL) was stirred at room temperature for 1 hour. To the reaction solution was added water and extracted with ethyl acetate. The organic layer was washed with water and brine, and dried over sodium sulphate. The solvent was evaporated under reduced pressure and the residue was purified by column chromatograph on silica gel to give the title compound (204 mg). Yield: 71%.
