Acetyl chloride → N,O-diacetyl-2-{2-[2-(4-(3-fluorophenyl)piperazin-1-yl)ethyloxy]phenyl}thiazolidine-3-carboximidic acid

1.08 g of 2-{2-[2-(4-(3-fluorophenyl)piperazin-1-yl)ethyloxy]phenyl}thiazolidine-3-carboxamide are dissolved in 20 ml of tetrahydrofuran, and 0.76 g of triethylamine is added thereto. A solution of 0.59 g of acetyl chloride in one ml of tetrahydrofuran is added to the mixture under ice-cooling, and the mixture is stirred at room temperature for 3 days. 0.59 g of acetyl chloride and 0.76 g of triethylamine are added to the mixture, and the mixture is stirred at room temperature for 24 hours. The mixture is concentrated under reduced pressure to remove solvent. The residue is dissolved in ethyl acetate, and the solution is washed with a saturated sodium chloride solution, an aqueous sodium bicarbonate solution and a sodium chloride solution, successively. The ethyl acetate solution is dried and concentrated under reduced pressure to remove solvent. The residue is purified by silica gel chromatography (solvent, chloroform:ethyl acetate=2:1). The eluate is concentrated under reduced pressure to remove solvent, and the residue is recrystallized from a mixture of chloroform and ether. 0.72 g of N,O-diacetyl-2-{2-[2-(4-(3-fluorophenyl)piperazin-1-yl)ethyloxy]phenyl}thiazolidine-3-carboximidic acid is obtained. Yield: 56%.