Heterocycles [h]-fused to 4-oxoquinoline-3-carboxylic acid. Part XI: Synthesis and antibacterial activity of 4-fluoro-6-oxoimidazo[4,5-h]quinoline-7-carboxylic acids

A series of 2-hetaryl-4-fluoro-9-cyclopropyl- 6-oxo-1H-imidazo[4,5-h]quinoline-7-carboxylic esters ( 3a–f) and their corresponding acids 4a–f have been prepared via microwave-assisted cyclocondensation reaction with some hetarene carboxaldehydes. The structures for these new esters and acids are based on spectral (IR, MS, and NMR) data. The in vitro antimicrobial assay of 4a–f hetaryl derivatives, their aryl analogues 1d–g, and the imidazo-unsubstituted acid 1a showed that all of these tricyclic heterocycles possess a good level of antibacterial activity. Among them, compound 1a exhibited the highest effect against both, Gram-positive (minimum inhibitory concentrations [MICs] 0.15–3.0 μg mL-1) and Gram-negative bacteria (MICs 0.7–3.0 μg mL-1). An excellent activity was recorded also for the halo-phenyl derivatives 1f,g and for the furan derivatives 4e,f, especially toward Gram-positive strains and Bacillus subtilis and Haemophilus influenzae, respectively.