Pyridonecarboxylic acids as antibacterial agents. 9. Synthesis and antibacterial activity of 1-substituted 6-fluoro-1,4-dihydro-4-oxo-7-(4-pyridyl)-1,8-naphthyridine-3- carboxylic acids

The title compounds (7a-e) with ethyl, 2-fluoroethyl, 2-hydroxyethyl, vinyl, or cyclopropyl groups, respectively, at C-1 were prepared by the method involving the Balz-Schiemann reaction of 2-(4-pyridyl)pyridine- and 7-(4-pyridyl)-1,8-naphthyridinediazonium tetrafluoroborates (15 and 27). The 1-ethyl, 1-(2-fluoroethyl), and 1-vinyl derivatives showed in vitro activities as potent as the corresponding 7-(1-piperazinyl) analogues against Staphylococcus aureus 209P JC-1 and Escherichia coli NIHJ JC-2 but were less active against Pseudomonas aeruginosa 12. Among the 7-(4-pyridyl) derivatives having the different C-1 substituent, 1-cyclopropyl derivative 7e was found to be the most active. In vivo efficacy of 7e was superior to that of enoxacin against experimental infections due to S. aureus 50774. Some aspects of structure-activity relationships associated with the C-1, C-6, and C-7 substituents were discussed.