Into 200 ml of methylene chloride was suspended 2.4 g of 6-(3-carboxypropoxy)carbostyril, and 2 ml of pyridine was added to the suspension. Then 1.4 g of thionyl chloride was added dropwise thereinto under stirring condition while the inside of the reaction vessel was kept at a temperature within the range from 0° to 20° C. After the addition operation, the reaction was continued at the same temperature for 1 hour under stirring condition. Then 2 ml of N-(2-hydroxyethyl)cyclohexylamine was added dropwise to the reaction mixture, then the reaction was continued at a room temperature for 4 hours under stirring. The reaction mixture was washed thoroughly with a K2CO3 aqueous solution, then further washed with water and a diluted hydrochloride acid, then dried with anhydrous sodium sulfate. The solvent was removed by distillation and the residue thus obtained was purified and isolated by a silica-gel column chromatography [the silica-gel used was "Wako C-200" and the solvent used was a mixture of chloroform:methanol=20:1 (V/V)] and was recrystallized from chloroform-petroleum ether. 1.2 Grams of 6-{3-[N-(2-hydroxyethyl)-N-cyclohexylaminocarbonyl]propoxy}carbostyril was obtained as in the form of colorless needle-like crystals. Melting point: 165°-166° C.
