To a stirred solution of 5-chloro-thiophene-2-carboxylic acid {(1S,2S,4R)-4-[2-fluoro-4-(2-oxo-2H-pyridin-1-yl)-phenylcarbamoyl]-2-hydroxy-cyclopentyl}-amide (318 mg; example 1C) in DMSO/CH2Cl2 1:1 (6 ml) were added triethylamine (0.73 ml) and SO3-pyridine complex (638 mg). The mixture was stirred overnight at r.t. The clear brown solution was diluted with dichloromethane, washed with 0.5 N HCl, H2O and brine, dried over MgSO4, filtered and concentrated. The crude product was purified by column chromatography (silica gel; gradient: CH2Cl2→CH2Cl2/MeOH 95:5) to give 5-chloro-thiophene-2-carboxylic acid {(1S,4R)-4-[2-fluoro-4-(2-oxo-2H-pyridin-1-yl)-phenylcarbamoyl]-2-oxo-cyclopentyl}-amide (225 mg) as light yellow amorphous solid. MS 474.1 ([M+H]+).
