Evaluation of antibacterial activity of new N-piperazinyl Quinolone derivatives with 1,3,4-Thiadiazole group

Quinolones are broad-spectrum antibacterial agents. They have many clinical uses which are increasing. Quinolones exert antibacterial activity primarily by inhibiting bacterial DNA gyrase. The inhibition of DNA gyrase by the quinolones are greatly influenced by the nature of the C-7 substituent on the quinolones molecule. Substitution of bulky functional groups is also possible in C-7 position. Furthermore, benzylthio and benzylsulfonyl-1, 3, 4-thiadiazole derivatives have antibacterial activity. Accordingly, a series of N-piperazinyl at C-7 position of standard quinolones structure were evaluated for their antibacterial activity against gram positive and gram negative bacteria using serial dilution test in solid media. The minimum inhibitory concentration (MIC) for each derivative was recorded as microgram per milliliter and comparied with ciprofloxacin as standard drug. The results showed that antibacterial activity of these compounds were higher than ciprofloxacin against tested gram positive bacteria (S.aureus, S.epidermidis, B.subtillis), though the potency against tested gram-negative bacteria (E.coli, E.aeruginosa, K.pneumoniae) was significantly less than that of quinolones as control drugs. In some cases there are selective activities against gram-positive bacteria. Meanwhile compounds that have benzylthio-1, 3, 4-thiadiazole attached to the piperazine group at C-7 position of the quinolone molecule had a stronger antibacterial activity as compaired with that of benzylsulfonyl 1, 3, 4-thiadiazole. Furthermore, changing the substitution on the phenyl ring had no significant difference in the spectrum of antibacterial activity.