Conformationally constrained analogs of N-substituted piperazinylquinolones: synthesis and antibacterial activity of N-(2,3-dihydro-4-hydroxyimino-4H-1-benzopyran-3-yl)-piperazinylquinolones.

A series of novel quinolone agents bearing a particular bulky and conformationally constrained bicyclic substituent (2,3-dihydro-4-hydroxyimino-4H-1-benzopyran-3-yl- moiety) on the piperazine ring of 7-piperazinyl quinolones (norfloxacin, enoxacin, ciprofloxacin, and levofloxacin) were synthesized and evaluated against a panel of Gram-positive and Gram-negative bacteria. Among these derivatives, ciprofloxacin counterpart 9c, highly inhibited the tested Gram-positive bacteria, superior to that of the reference drugs, and displayed antibacterial activity at non-cytotoxic concentrations.