Into 300 ml of chloroform were added 9.9 g of 6-(3-carboxypropoxy)carbostyril and 6.5 ml of DBU. The outside of the reaction vessel containing the abovementioned mixture was ice-cooled and 5.7 ml of isobutyl chloroformate was added dropwise under stirring condition. After the addition operation, stirring was continued for 1 hour at a room temperature and 5.4 g of 2-ethylaminopyridine was added dropwise, then the reaction was continued for 5 hours under stirring condition. The reaction mixture was washed with a diluted NaHCO3 aqueous solution and water, and was concentrated. The residue thus obtained was treated by a silica-gel column chromatography (solvent used was a mixture of chloroform:methanol=20:1) and the elute thus obtained was concentrated then was recrystallized from methanol, to obtain 4.5 g of 6-{3-[N-ethyl-N-(2-pyridyl)aminocarbonyl]propoxy}carbostyril in the form of colorless needle-like crystals. Melting point: 148°-149° C.
