A series of novel 3-quinolinecarboxylic acid derivatives have been prepared and their antibacterial activity evaluated. These derivatives are characterized by fluorine attached to the 6-position and substituted amino groups appended to the 1- and 7-positions. Structure-activity relationship studies indicate that antibacterial potency is greatest when the 1-substituent is methylamino and the 7-substituent is either 4-methyl-1-piperazinyl, 16, or 1-piperazinyl, 21. Derivatives 16 and 21, the 1-methylamino analogues of pefloxacin and norfloxacin, respectively, show comparable in vitro and in vivo antibacterial potency to these two known agents. The activity (vs. Escherichia coli Vogel) of 16 (amifloxacin) is the following: in vitro MIC (microgram/mL) = 0.25; in vivo (mice) PD50 (mg/kg) = 1.0 (po), 0.6 (sc).
