As part of a search for new synthetic antibacterial agents to combat systemic infection, various analogs of 7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de][1,4]benzoxazine-6-carboxylic acids were synthesized. Among the compounds newly synthesized, 9-fluoro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de][1,4]benzoxazine-65-carboxylic acid (DL-8280) showed potent antibacterial activity against Gram-positive and -negative pathogens, including Pseudomonas aeruginosa and its metabolic disposition was shown in separate experimentals to be favorable.