Synthesis, Antibacterial, Antioxidant Activity and QSAR Studies of Novel 2-Arylidenehydrazinyl-4-arylthiazole Analogues

A novel series of 2-arylidenehydrazinyl-4-arylthiazole analogues (3a-p) was designed and synthesized in excellent yields using a rapid, simple, efficient methodology. Sixteen novel compounds were screened for in vitro antimicrobial activities against eleven bacteria, namely, Staphylococcus aureus, Listeria monocytogenes, Enterococcus faecalis, Bacillus subtilis, Klebsiella pneumonia, Citrobacter freundii, Cronobacter sakazakii, Salmonella enteritidis, Escherichia coli, Yersinia pestis, and Pseudomonas aeruginosa. All 16 compounds showed significant anti-bacterial activities against both Gram-positive and Gram-negative bacteria. In particular, compound 3g showed potent inhibition of E. coli and K. pneumonia, compound 3i inhibited E. faecalis, compound 3n S. tythi and E. faecalis, and compound 3c E. coli and C. sakazakii. In fact, our results indicate that most of the compounds synthesized exhibit strong antibacterial activity. The qualitative structure-antibacterial activity relationships (QSAR) were studied using the physicochemical and quantum-chemical parameters of the ab initio Hartree-Fock model at the RHF/6-31G level of theory. A good qualitative correlation between predicted physicochemical parameters (logP and polar surface area (PSA)) and antibacterial activity has been found. The synthesized compounds were also evaluated for antioxidant activity. Compounds 3j, 3a and 3i exhibited the greatest antioxidant activity, with IC50 values of 0.66, 0.81, and 1.08 mu m, respectively, which were comparable to that of ascorbic acid (IC50 0.87 mu m). The promising antibacterial and antioxidant activities of some of these synthesized 2-arylidenehydrazinyl-4-arylthiazole derivatives, together with the results of quantum-chemical studies, could be helpful for the development of drugs to combat diseases caused by microorganisms and oxidative stress.