A series of [1, 3] thiazeto [3, 2-alquinoline-3-carboxylic acids and their esters were prepared and evaluated for antibacterial activity. The derivatives with a hydrogen or methyl group at (2- 1, fluorine at (2-6, and piperazinyl or 4-methyl-1-piperazinyl group at C-7 showed superior in vitro antibacterial activity, and the derivatives with 4-methyl-1-piperazinyl group at C-7 had potent in vivo activity. Compound 29a (NM394) showed excellent in vitro antibacterial ...