Pyridine hybrid 1,2,4-triazole-5-thione–Schiff base derivatives: synthesis, characterization, antimicrobial, and antioxidant activity evaluations

Abstract

Antimicrobials are fundamental agents in the control and treatment of infections; however, increasing antimicrobial resistance severely reduces therapeutic efficacy and exacerbates the global burden of disease and mortality. In this context, a novel series of pyridine-containing 1,2,4-triazole-5-thione Schiff base derivatives (6a–g) were synthesized in good to excellent yields and evaluated for their antimicrobial and antioxidant potential. The structural elucidation of the synthesized compounds was accomplished through FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopy. Antimicrobial activity was assessed using both disc diffusion and minimum inhibitory concentration (MIC) methods against a panel of Gram-positive, Gram-negative bacteria, and the yeast Candida albicans. Compounds 6b, 6d, and 6 g showed potent antibacterial activity against Streptococcus pyogenes ATCC 19615 with low MIC values (19.531 µg/mL), while compound 6 g demonstrated broad-spectrum activity, also inhibiting Staphylococcus aureus and C. albicans. In antioxidant assays, compound 6f exhibited the highest radical scavenging activity in the DPPH assay, whereas compound 6d showed superior reducing power in the FRAP assay (290.16 mg TE/g). The results indicated that electron-donating (e.g. methoxy) and electron-withdrawing (e.g. nitro) groups on the aromatic ring significantly influenced biological activity. These findings highlight compounds 6d and 6 g as promising candidates for further pharmacological development owing to their multifunctional bioactivity profiles.