Synthesis and antimycobacterial evaluation of certain fluoroquinolone derivatives

A number of fluoroquinolone derivatives were synthesized and evaluated for antimycobacterial activity. Preliminary results are (1) for 1-aryl fluoroquinolones, 1-(4-nitrophenyl) derivatives were inactive while their 1-(2-fluoro-4-nitrophenyl) counterparts were active anti-TB agents (3a vs 4a; 3b vs 4b) indicated the fluoro substituent at C-2 position is important. For the 1-(2-fluoro-4-nitrophenyl)quinolones, 7-piperidinyl derivative 4a and 7-(3,5-dimethylpiperazinyl) derivative 4e, which exhibited 97% and 98% inhibition, respectively, were more active than their 7-morpholinyl, 7-(4-methylpiperazinyl) and 7-piperazinyl congeners, 4b,4c and 4d, respectively. In addition, 7-[4-(8-hydroxyquinolin-2-ylmethyl)piperazin-1-yl] derivative 9d exhibited 44% inhibition on the growth of Mycobacterium tuberculosis while its 7-(4-methylpiperazin-1-yl) counterpart 3c was inactive implied the metal-chelating 8-hydroxyquinoline moiety was capable of enhancing the anti-TB activity, (2) for the bifunctional fluoroquinolone-hydroxyquinoline complexes, ciprofloxacin and ofloxacine derivatives, which exhibited the same anti-TB activity (98% inhibition), are more potent than norfloxacin counterpart, which in turn is more potent than 1-aryl congeners (9b, 9c>9a>9d, 9e).