[CH3:1][NH:2][N:3]1[C:12]2[C:7](=[CH:8][C:9]([F:15])=[C:10](F)[C:11]=2[F:13])[C:6](=[O:16])[C:5]([C:17]([OH:19])=[O:18])=[CH:4]1.[NH:20]1[CH2:25][CH2:24][NH:23][CH2:22][CH2:21]1.N1C=CC=CC=1.Cl>O>[CH3:1][NH:2][N:3]1[C:12]2[C:7](=[CH:8][C:9]([F:15])=[C:10]([N:20]3[CH2:25][CH2:24][NH:23][CH2:22][CH2:21]3)[C:11]=2[F:13])[C:6](=[O:16])[C:5]([C:17]([OH:19])=[O:18])=[CH:4]1
A mixture of 1.95 g of 1-methylamino-6,7,8-trifluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid, 3.05 g of anhydrous piperazine and 20 ml of dry pyridine is refluxed for 6 hours. The solvent is stripped off in vacuo, the residue is taken up in 20 ml of water, the pH is brought to 7-8 with half-concentrated hydrochloric acid, with cooling, and the precipitate is filtered off with suction, washed with ice-water and dried at 100° C. in vacuo. 1.8 g of 1-methylamino-6,8-difluoro-7-(1-piperazinyl)-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid of decomposition point 276°-278° C. are obtained.
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