To a solution of 0.219 g ethyl 8-amino-4-[3-(3-pyridyl)propyl]-3-thiaoctanoate in 1.5 ml methylene chloride is added a few crystals of 4-dimethylaminopyridine followed by 60 mcl triethylamine and 0.068 g p-chlorophenylsulfonyl chloride. The mixture is stirred at room temperature for 18 h, diluted with ether and washed with saturated aqueous sodium bicarbonate. The ether layer is dried, filtered and evaporated to leave an amber oil which is chromatographed using 3:2 ethyl acetate/hexane to give ethyl 8-(p-chlorophenylsulfonamido)-4-[3-(3-pyridyl)propyl]-3-thia-octanoate as an oil; NMR (CDCl3): delta 8.0 (d,2H), 7.55 (d,2H), 3.15 (s,2H); such being the compound of formula X wherein X represents sulfur, Ar represents p-chlorophenyl, Het represents 3-pyridyl and R1 represents ethoxy.
