Antimicrobial and Anti-pathogenic Activity of New Naphtho [1,2,4] Triazol-Thiadiazin Derivatives

Background: Antimicrobials are one of the extremely important categories of drugs for the treatment, control, and prevention of microbial diseases, but the development of drug resistance against clinically used antibacterial agents has increased the demand for the design and synthesis of new drugs. We have previously synthesized new series of 10-substituted-5H-naphtho[1,2-e][1,2,4]triazolo[3,4-b] [1,3,4]thiadiazin derivatives (4a-4f). In this study, we evaluated the antimicrobial activity of these derivatives against some pathogenic microorganisms. Methods: The reaction of 2-bromo-1,4-naphthoquinone with 4-amino-5-aryl-4H-1,2,4-triazole-3- thiols in ethanol at 50 ̊C gave the corresponding 2-[(4-amino-5-aryl-4H-1,2,4-triazol-3 yl)thio] naphthalene-1,4- diones. Moreover, their treatment with EtOH/HCl under reflux conditions produced 10-substituted-5H-naphtho[1,2-e][1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-5- ones through intramolecular cyclization. The well agar diffusion and agar dilution methods were used during the preliminary evaluation of antimicrobial activity for the determination of inhibition zone (IZ) and minimum inhibitory concentration (MIC). Results: Seven tetracyclic heterocyclic ring systems were produced under reflux conditions. The structures of all the products were identified by their FT-IR, 1H, and 13C NMR spectral data and by elemental analysis. The results revealed that the antibacterial activity of compounds 4a, 4b, 4c, and 4d are higher than that of the others, and compounds 4d, 4a, 4e, and 4f exerted the greatest effect on fungal samples. Conclusion: All synthesized compounds exhibited promising antibacterial and antifungal activity. In this study, compounds 4a-4g exhibited highly potent antimicrobial activity and acceptable selectivity index against Staphylococcal and Candida infections.