Triethylamine (30 g) was added dropwise to a solution of 3-(piperidin-2-yl)propionic acid ethyl ester hydrochloride (30 g) in methylene chloride (210 ml) at 0° C. and the mixture was then stirred at room temperature for 10 minutes. Chloro-2,5-dimethylbenzene-1-sulfonyl chloride (32.3 g) was then added slowly and the mixture was stirred for 2 hours. The reaction was observed by thin layer chromatography. Because of incomplete conversion, the mixture was stirred for a further 17 hours before the reaction was ended by addition of water (200 ml). The phases were separated and the aqueous phase was extracted with MC (150 ml). The combined organic phases were dried with Na2SO4, filtered and concentrated in vacuo. Purification of the crude product was carried out by chromatography on silica gel (5% ethyl acetate in hexane). The yield was 47.23 g (90%).
