Ionic liquid-catalyzed, microwave-assisted green synthesis of novel Coumarin-Schiff bases: Characterization, molecular docking, biological and DFT studies

Abstract

A microwave assisted green protocol for the synthesis of coumarin-linked novel Schiff base compounds (CSB-I and CSB-II) were demonstrated by employing [TMG][OAc] ionic liquid (IL) as dual catalyst and solvent. The resulted compounds were characterized by several spectroscopic techniques such as FT-IR, 1H NMR, 13C NMR and GC–MS. The efficiency of the ionic liquid employed is evaluated by recycle and reuse of the same for number of cycles (upto 5). The HOMO and LUMO energy levels for each Schiff base were meticulously calculated using Density Functional Theory (DFT). The electrophilic and nucleophilic sites were identified by Molecular Electrostatic Potential (MESP) 3D plots, based on DFT computational analysis. Further, Global Chemical Reactivity Descriptor (GCRD) parameters including chemical potential (μ), chemical hardness (ղ), softness (S), electrophilicity index (ω) and electronegativity (χ) were also evaluated with precision. The molecular docking studies were also performed to evaluate the behavior of binding interaction of new Schiff bases (CSB-I and CSB-II) with mevalonate-5-diphosphatedecarboxylase (PDB ID: 1FI4) and human lanosterol 14-alpha-demethylase, CYP51 (PDB ID: 3LD6) proteins. The outcome of this study reveals that CSB-I exhibited strong binding to both the proteins as compared to CSB-II. The antibacterial study revealed that CSB-I was highly effective against both Gram-positive and Gram-negative bacteria, while CSB-II showed moderate activity. In antifungal studies, both the compounds showed excellent activity profiles against yeast fungi, while both had only moderate effects on filamentous fungi.