In benzene (10 ml), 5-tert-butoxycarbonyl-4,5,6,7-tetrahydrothieno[3,2-c]pyridine-2-carboxylic acid (WO94/21599)(283 mg) was dissolved. To the resulting solution, triethylamine (0.14 ml) and diphenylphosphoryl azide (0.21 mg) were added, followed by heating under reflux for 2 hours. After the reaction mixture was cooled to room temperature, 1-[(6-chloronaphthalen-2-yl)sulfonyl]piperazine hydrochloride (347 mg) and triethylamine (0.28 ml) were added and the mixture was heated under reflux overnight. After cooling to room temperature, to the reaction mixture was added dichloromethane and a 3N aqueous sodium hydroxide solution. The resulting mixture was separated and aqueous layer was extracted with dichloromethane. The combined organic layer thus extracted was washed with 0.5N hydrochloric acid, a saturated aqueous solution of sodium bicarbonate and saturated aqueous NaCl solution, dried over anhydrous sodium sulfate and distilled under reduced pressure to remove the solvent. The residue was purified by chromatography on a silica gel column (hexane:ethyl acetate=3:1 to 2:1), whereby the title compound (284 mg, 48%) was obtained.
