Cl.[NH2:2][C:3]1[CH:4]=[CH:5][C:6]([OH:14])=[C:7]2[C:12]=1[NH:11][C:10](=[O:13])[CH2:9][CH2:8]2.[C:15](Cl)(=[O:19])[O:16][CH2:17][CH3:18].Cl>[OH-].[Na+]>[CH2:17]([O:16][C:15]([NH:2][C:3]1[CH:4]=[CH:5][C:6]([OH:14])=[C:7]2[C:12]=1[NH:11][C:10](=[O:13])[CH2:9][CH2:8]2)=[O:19])[CH3:18]10.7 g of 8-amino-5-hydroxy-3,4-dihydrocarbostyril hydrochloride was dissolved in 200 ml of a 10% aqueous sodium hydroxide solution, 5.4 g of ethyl chlorocarbonate was added to the solution while stirring at room temperature followed by stirring for one hour at 30° C. After completion of the reaction, the reaction mixture was rendered acidic with hydrochloric acid under ice-cooling, the precipitated crystals were recovered by filtration, washed with water and dried. Recrystallization of the dried crystals from ethanol yielded 7.95 g of 8-ethoxycarbonylamino-5-hydroxy-3,4-dihydrocarbostyril as colorless needle crystals having a melting point of 283.8°-284.6° C.
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