The synthesis and biological evaluation of a novel series of C7 non-basic substituted fluoroquinolones as antibacterial agents

A series of non-basic building blocks was synthesized and introduced to the C7 position of a quinolone nucleus 7-chloro-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylic acid to afford the corresponding fluoroquinolones in 46-85% yields. Among them, the sulfur-containing quinolone, 7-(2-thia-5-azabicyclo[2.2.1]heptan-5-yl)-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylic acid exhibited superior antibacterial activity against quinolone-susceptible and multidrug-resistant strains in comparison with clinically used fluoroquinolone ciprofloxacin and vancomycin, especially to the Streptococcus pneumonia and multidrug-resistant S. pneumonia clinical isolates.