Synthesis, Characterization, and Antimicrobial Evaluation of Some Novel Hydrazinecarbothioamides.

Objectives: This study focused on synthesizing and characterizing novel thiosemicarbazide derivatives containing a 1,2,4-triazole moiety and evaluating their antimicrobial activity against several bacterial strains. The research aimed to identify key structural features that enhance antimicrobial efficacy through structure-activity relationship analysis and identify the minimum inhibitory concentration (MIC) of the most potent compounds to assess their potential for further development as antimicrobial agents.

Materials and methods: Nine novel thiosemicarbazide derivatives containing a 1,2,4-triazole moiety were synthesized by reacting 1,2,4-triazole derivatives with thiosemicarbazide precursors, and the products were characterized using infrared spectroscopy, proton nuclear magnetic resonance (¹H-NMR), carbon-13 nuclear magnetic resonance (¹³C-NMR) spectroscopy, and elemental analysis. The antimicrobial activity of these compounds (5a-i) was tested against Klebsiella pneumoniae (K. pneumoniae),Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Pseudomonas aeruginosa (P. aeruginosa), using microdilution, disk diffusion, and broth microdilution methods. Dimethyl sulfoxide was used as a negative control, and Vancomycin and Meropenem were used as positive controls, with all results converted to µM for consistent analysis.

Results: The synthesized thiosemicarbazide derivatives (5a-i) were confirmed to be structurally correct through Fourier-transform infrared spectroscopy, ¹H-NMR, and ¹³C-NMR spectroscopy. Among the tested compounds, 5e (4-bromophenyl) and 5g (n-propyl) showed significant antimicrobial activity, with 5g exhibiting the strongest effects against S. aureus and P. aeruginosa. Other derivatives, such as 5b (4-NO₂Ph), 5c (4-FPh), and 5d (4-ClPh), showed moderate activity, while no significant activity was observed against K. pneumoniae or E. faecalis.

Conclusion: The study successfully synthesized a series of novel thiosemicarbazide derivatives with a 1,2,4-triazole moiety and evaluated their antimicrobial potential. Compounds 5e and 5g exhibited significant antibacterial activity, particularly against S. aureus and P. aeruginosa, with MIC values in the low micromolar range. These findings suggest that the compounds hold promise as potential antimicrobial agents, and further studies should focus on optimizing their efficacy and exploring their mechanism of action.