Novel [1,2,4]triazolo[1,5-a]pyrimidine derivatives as promising antioxidant and antimicrobial agents: Synthesis, antibiofilm, DFT calculations, molecular docking, ADMET analysis, and MD simulations.

The escalating threat of antimicrobial resistance necessitates the discovery of novel therapeutic scaffolds with distinct mechanisms of action. A novel series of [1,2,4]triazolo[1,5-a]pyrimidine derivatives (FNT01-12) featuring various aromatic substitutions at positions 5 and 7 was designed, synthesized, and evaluated as antioxidant and antimicrobial agents. The reaction of 1H-1,2,4-triazol-5-amine with freshly synthesized chalcones (5-16) yielded the targeted [1,2,4]triazolo[1,5-a]pyrimidine derivatives (FNT01-12) in excellent yields. The chemical structures of these compounds were confirmed using spectral data and elemental analyses. The in vitro antimicrobial screening revealed a high degree of structure-dependent selectivity. Compound FNT09 emerged as a potent broad-spectrum agent, exhibiting significant efficacy against both Gram-positive and Gram-negative pathogens, including an MIC of 5.00 μg/mL against P. aeruginosa. Conversely, FNT11 and FNT12 demonstrated exceptional, narrow-spectrum potency exclusively against P. aeruginosa (MIC = 5.00 μg/mL), substantially outperforming Ciprofloxacin. Furthermore, FNT11 and FNT12 exhibited profound antibiofilm capabilities, disrupting established P. aeruginosa biofilms by 40.21 and 44.32%, respectively. DFT optimization showed that FNT11 had the highest stability (lowest energy: -1388.7095 Eh). FNT10 was the strongest electron donor (HOMO = -4.7870 eV), while FNT11 exhibited the narrowest HOMO-LUMO gap (2.338 eV) and highest nucleophilicity (4.677 eV), indicating high reactivity and electron-donating ability. Molecular docking and Dynamics (MD) simulations confirmed that the most active derivatives form highly stable, thermodynamically favorable complexes with critical bacterial targets: dihydropteroate synthase (DHPS), DNA gyrase, LasR, and Penicillin-Binding Protein 4 (PBP4). Trajectory analyses (RMSD, RMSF, PCA) and MM-GBSA binding free energy calculations indicated that robust van der Waals interactions primarily drive stability. Finally, predictive ADMET profiling confirmed that these lead candidates possess favorable pharmacokinetic properties and comply with Lipinski's Rule of Five, establishing FNT09, FNT10, FNT11, and FNT12 as promising scaffolds for the targeted treatment of recalcitrant bacterial infections.