1.0 Gram of 6-carboxy-3,4-dihydrocarbostyril, 1.3 g of DCC and 1.1 g of benzylpiperazine were suspended in 10 ml of dioxane and the suspension was stirred at 70° C. for 5 hours. After the reaction was completed, the solvent was removed by distillation and ether was added to the residue and crystals formed were removed by filtration. After the mother liquor was concentrated, the residue was dissolved in chloroform and the chloroform solution was washed with water and a saturated sodium chloride aqueous solution then dried with anhydrous sodium sulfate and the solvent was removed by distillation. Recrystallized from ethanol to obtain 330 mg of 6-(4-benzyl-1-piperazinylcarbonyl)-3,4-dihydrocarbostyril. Colorless needle-like crystals. Melting point: 198°-200° C.
