Dicyclohexylcarbodiimide (0.82 g) was added to a mixture of 0.84 g of 2-(3-pyridyl)thiazolidine-4-carboxylic acid, 0.79 g of 1-octylpiperazine, 0.54 g of 1-hydroxybenzotriazole and 20 ml of N,N-dimethylformamide with ice cooling, and the resultant mixture was stirred overnight at room temperature. The reaction mixture was diluted with ethyl acetate, and the insoluble matter was filtered off. The filtrate was washed in sequence with saturated aqueous solution of sodium hydrogen carbonate, water and saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate. The solvent was then distilled off under reduced pressure. Ethyl acetate was added to the residue, the insoluble matter was filtered off, and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent 10% methanol-ethyl acetate), the oil obtained was dissolved in 25 ml of ethanol, and 0.32 g of fumaric acid was added. After allowing the mixture to stand for 2 days, the resultant crystals were collected by filtration, washed with cold ethanol and dried. Thus was obtained 0.72 g of 1-octyl-4-[2-(3-pyridyl)thiazolidin-4-ylcarbonyl]piperazine fumarate. Melting point 135° C.
