Rational design and synthesis of theophylline-based hybrids as bacterial DHFR inhibitors: integrating molecular...

A novel library of 1,2,3-triazole-based theophylline-isatin hybrids (L-1 to L-16) was designed and evaluated through molecular docking, and the top-ranked compounds were subsequently synthesized using a click chemistry approach. The synthesized compounds were assessed for antibacterial activity against both Gram-positive and Gram-negative bacterial strains, including Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus, and Bacillus subtilis. Among all the synthesized compounds, L-13 exhibited a notable zone of inhibition against E. coli as compared to the other tested bacterial strains. Moreover, L-13 showed moderate activity against E. coli (MIC 62.5 µg/mL, 138 µM) and exhibited dose-dependent biofilm inhibition with visible morphological changes as observed by scanning electron microscopy. Enzymatic assays revealed that L-13 effectively inhibited dihydrofolate reductase enzyme, with an IC₅₀ value of 25.56 ± 1.47 µg/mL, in comparison to the reference drug. Afterwards, the structure-activity relationship revealed that the presence of electron-withdrawing groups on the isatin scaffold (-F, -Cl, -Br), along with an ethyl chain bridge between triazole and theophylline nucleus, improved activity potential, which was consistent with docking results. Additionally, molecular dynamics simulations, MM-GBSA binding energy calculations, and DFT analysis supported the potential of L-13. In vitro toxicity study was performed on HepG2 and HEK293 cell lines, indicating lower toxicity in comparison to the standard drug. Overall, these findings suggest that compound L-13 interacts with the DHFR active site and may serve as a possible lead compound for further optimization as antibacterial agents.

The online version contains supplementary material available at 10.1007/s40203-026-00661-0.