Synthesis of novel nalidixic acid-based 1,3,4-thiadiazole and 1,3,4-oxadiazole derivatives as potent antibacterial agents.

Novel nalidixic acid-based 1,3,4-thia(oxa)diazoles, their thio ethers, sulfones, bis mercapto, and Mannich bases were synthesized and characterized by Infrared spectra, (1) H NMR, (13) C NMR, and elemental analysis. These compounds were evaluated for their antibacterial activity against two Gram-positive and three Gram-negative bacteria. The preliminary bioassay showed that most of the compounds had better antibacterial activity than the parent compounds, 1,3,4-thia(oxa)diazoles, at the dosage 50µg/mL toward five test bacteria. Four Mannich bases of nalidixic acid-based 1,3,4-thiadiazole exhibited maximum antibacterial activity against Bacillus subtilis, Klebsiella pneumoniae, and Pseudomonas aeruginosa with minimum inhibitory concentration in the range of 6.25-125µg/mL.