Studies on pyridonecarboxylic acids. III. Synthesis and antibacterial activity evaluation of 1,8-disubstituted 6-fluoro-4-oxo-7-piperazinyl-4H-[1,3]thiazeto[3,2- a]quinoline-3-carboxylic acid derivatives.

A series of 1,8-disubstituted 6-fluoro-4-oxo-7-piperazinyl-4H-[1,3]thiazeto[3,2-a]quinoline-3- carboxylic acid derivatives was prepared and evaluated for antibacterial activity. In the 7-piperazinyl series, addition of a fluorine at C-8, which increased the in vitro activity for the 1-hydrogen and 1-methyl analogues and decreased it for the 1-phenyl analogue, improved the in vivo activity of all the analogues. Introduction of a methoxy group at C-8 of the 1-methyl-7-piperazinyl analogue also improved its in vivo antibacterial activity. The effect of 8-substituents on the in vitro and in vivo antibacterial activity of the 1-methyl-7-(4-methyl-1-piperazinyl) series is also discussed.