[NH2:1][C:2]1[CH:3]=[CH:4][C:5]([OH:13])=[C:6]2[C:11]=1[NH:10][C:9](=[O:12])[CH2:8][CH2:7]2.C([O-])(=O)C.[Na+].[CH3:19][S:20](Cl)(=[O:22])=[O:21].O>C(O)(=O)C>[OH:13][C:5]1[CH:4]=[CH:3][C:2]([NH:1][S:20]([CH3:19])(=[O:22])=[O:21])=[C:11]2[C:6]=1[CH2:7][CH2:8][C:9](=[O:12])[NH:10]2
5.0 g of 8-amino-5-hydroxy-3,4-dihydrocarbostyril was suspended in 30 ml of acetic acid, and 4.0 g of sodium acetate was added to the suspension while stirring. 3.5 g of methanesulfonyl chloride was then added to the mixture followed by heating for 7 hours while refluxing. After completion of the reaction, 100 ml of water was added to the reaction mixture which was then concentrated to dryness under reduced pressure. The resulting residue was added to 200 ml of water, and the mixture was stirred. The crystals formed were recovered by filtration, washed with water and recrystallized from methanol to obtain 3.89 g of 5-hydroxy-8-methanesulfonylamino-3,4-dihydrocarbostyril as colorless amorphous crystals having a melting point of 269.4°-269.8° C.
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