Synthesis, Spectral Characterization, and Antibacterial Evaluation of Novel Isatin-Based 1,2,4-Triazole Derivatives

Antibiotic resistance remains a major global public health challenge, necessitating the development of innovative and improved therapeutic strategies. Molecular hybridization could serve as a strategy to develop multi-target antibacterial agents capable of overcoming existing resistance mechanisms. The objective of this investigation was to design, synthesize, and assess the antibacterial activity of two novel isatin-1,2,4-triazole hybrid substances against clinically significant multidrug-resistant strains of bacteria. Synthesized hybrid compounds (ST1 and ST2) through the condensation of isatin with various amino acid derivatives. The synthesis procedure was conducted within a controlled laboratory environment to ensure reproducibility.  Infrared Fourier transform (FTIR), proton (^1H NMR) spectroscopy using nuclear magnetic resonance and carbon (^13C NMR) nuclear magnetic resonance spectroscopy were employed to verify the chemical structures of the synthesized compounds. We employed the zone of inhibition assay to evaluate the efficacy of ST1 and ST2 in eliminating clinical isolates for Klebsiella pneumoniae and Acinetobacter spp. Furthermore, the MIC (minimum inhibitory concentration) and the MBC (minimum bactericidal concentration) were determined to assess antibacterial efficacy in a more comprehensive manner. We also examined the compounds' capacity to inhibit biofilm formation to assess their antibiofilm activity. The MTT assay was also employed to evaluate the cytotoxicity of the synthesized compounds on HEK-293 cell lines to assess their safety. Antibacterial activities of ST2 were even superior to that of ST1. For ST2, the inhibition zones were 14.2-15.8 mm at 32-64 mg/ml and MIC was as low as 16-32 mg/ml. Antibacterial activity indices were 6.1 for ST1 and 12.2 for ST2, suggesting the more pronounced effect of ST2 on tested bacteria. Both compounds inhibited biofilm formation. Percentage of biofilms inhibition by ST2 58–62% versus ST1: 35–38%. The activity against the studied bacterial isolates was augmented when these synthetic compounds and antibiotics were used in combination. The isatin-1,2,4-triazole hybrids identified in this study are interesting scaffolds for the creation of next-generation antimicrobials targeting a range of molecular pathways. ST2, in particular, has the potential to be developed and optimised as a treatment for drug-resistant diseases.