Piperazine-2(R)-carboxylic acid dihydrochloride (5.0 g, 24.6 mmol) was suspended in hexamethyldisilazane (50 ml). The reaction mixture was heated at about 120° C. to achieve complete dissolution and then cooled to about 80° C. A solution of dimethylcarbamoyl chloride (3.18 g, 29.5 mmol) in acetonitrile (5 ml) was added and the reaction mixture is stirred overnight at about 80° C. A solution of 4-(4-fluorophenyl)-1,2,3,6-tetrahydropyridine sulfamoyl chloride (5.4 g, 19.58 mmol) in acetonitrile (10 ml) was added and the resulting reaction mixture was stirred at about 80° C. till the completion of the reaction (followed by HPLC). The reaction mixture was cooled and then quenched with methanol. The resulting slurry was concentrated and then replaced into water. The aqueous slurry was made alkaline with ammonium hydroxide and then washed with dichloromethane. The aqueous phase was acidified with dilute HCl and extracted with dichoromethane. The organic extracts were washed with water and then evaporated to dryness to yield 4-(N,N-dimethylaminocarbonyl)-1-[4-(4-fluoropheny)-1,2,3,6-tetrahydropyridinesulfonyl]piperazine-2(R)-carboxylic acid (6.1 g) as a beige colored solid.
