As part of a search for new synthetic antibacterial agents to combat systemic infection, various analogues 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-6-carboxylic acid (DL-8280) showed potent antibacterial activity against Gram-positive and-negative pathogens, including Psedomonas aeruginosa, and its metabolic disposition was shown in separate experimentals to be favorable.