Drug design, green synthesis, in-vitro antibacterial and antifungal activities, computational investigation, and molecular docking studies of novel spiro-indoline-pyrano-pyrimidine and pyrazolo derivatives

This study focuses on the green synthesis of novel Spirooxindole derivatives featuring indoline and pyrano[2,3-c] pyrazole or pyrimidine moieties. These derivatives were synthesized via a one-pot reaction using isatin, active methylene compounds, malononitrile, and MTPPBr as an eco-friendly catalyst. Their structural integrity was confirmed through 1H NMR, 13C NMR, and MS analyses. The in vitro antibacterial and antifungal activities of these compounds were evaluated, revealing that their biological efficacy is strongly influenced by their chemical structures and functional groups. Among the derivatives, compound 7l exhibited the strongest antibacterial activity, particularly against Escherichia coli (MIC = 1.25 mg/ml). Its potent activity was attributed to the synergistic effects of chlorophenyl, thioketone, and dioxo functional groups, which enhance membrane penetration and enzyme binding. Compound 7k showed broad-spectrum antibacterial activity, especially against Klebsiella pneumoniae (MIC = 1.25 mg/ml). In contrast, compounds 7c and 7f displayed weaker activity due to the absence of additional reactive groups necessary for effective bacterial targeting. In antifungal evaluations, spiro[indolinepyrano-pyrazolo] derivatives outperformed spiro[indoline-pyrano-pyrimidine] compounds. Notably, 7l exhibited the highest antifungal activity against Candida albicans (MIC = 10 mg/ml), driven by the combined effects of thioketone, dioxo, and diethyl groups, which enhanced lipophilicity and enzyme interactions. Compounds 7i and 7k also demonstrated moderate antifungal potential due to their hydrophilic and hydrophobic balance. DFT studies supported these findings by analyzing electronic structures, highlighting the role of HOMO-LUMO energies and charge transfer dynamics in determining biological activity. Molecular docking revealed key interactions with bacterial (3UDI) and fungal (1DI8) enzymes, while drug-likeness evaluations and toxicity predictions confirmed their therapeutic potential. This study identifies 7l and 7k as promising agents for combating bacterial and fungal infections.