Antimycobacterial and phototoxic evaluation of novel 6-fluoro/nitro-4-oxo-7-(sub)-4H-[1,3]thiazeto[3,2-a]quinoline-3-carboxylic acid

Several newer 6-fluoro/nitro-4-oxo-7-(sub)-4H-[1,3]thiazeto[3,2-a]quinoline-3-carboxylic acids (10–11a–q) were synthesised from 3,4-difluoro aniline and 3-fluoro-4-nitro aniline by nine-step synthesis. The compounds were evaluated for in vitro and in vivo antimycobacterial activities against Mycobacterium tuberculosis H37Rv (MTB), multidrug-resistant M. tuberculosis (MDR-TB) and Mycobacterium smegmatis (MC2) as well as being tested for their ability to inhibit the supercoiling activity of DNA gyrase from M. smegmatis. Among the synthesised compounds, 7-(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)-6-nitro-4-oxo-4H-[1,3]thiazeto[3,2-a]quinoline-3-carboxylic acid (11l) was found to be the most active compound in vitro, with minimum inhibitory concentrations (MICs) of 0.09 μM and <0.09 μM against MTB and MTR-TB, respectively. Compound 11l was found to be 4 times and >506 times more potent than isoniazid against MTB and MDR-TB, respectively. In the in vivo animal model, 11l decreased the bacterial load in lung and spleen tissues by 30% and 42%, respectively, at a dose of 50 mg/kg body weight.