Rhamnopyranoside-Based Fatty Acid Esters as Antimicrobials: Synthesis, Spectral Characterization, PASS, Antimicrobial, and Molecular Docking Studies

Abstract

The most widely used and accessible monosaccharides have a number of stereogenic centers that have been hydroxylated and are challenging to chemically separate. As a result, the task of regioselective derivatization of such structures is particularly difficult. Considering this fact and to get novel rhamnopyranoside-based esters, DMAP-catalyzed di-O-stearoylation of methyl α-l-rhamnopyranoside (3) produced a mixture of 2,3-di-O- (4) and 3,4-di-O-stearates (5) (ratio 2:3) indicating the reactivity of the hydroxylated stereogenic centers of rhamnopyranoside as 3-OH > 4-OH > 2-OH. To get novel biologically active rhamnose esters, di-O-stearates 4 and 5 were converted into six 4-O- and 2-O-esters 6–11, which were fully characterized by FT-IR, 1H, and 13C NMR spectral techniques. In vitro antimicrobial assays revealed that fully esterified rhamnopyranosides 6–11 with maximum lipophilic character showed better antifungal susceptibility than antibacterial activity. These experimental findings are similar to the results found from PASS analysis data. Furthermore, the pentanoyl derivative of 2,3-di-O-stearate (compound 6) showed better antifungal functionality against F. equiseti and A. flavus, which were found to be better than standard antibiotics. To validate the better antifungal results, molecular docking of the rhamnose esters 4–11 was performed with lanosterol 14α-demethylase (PDB ID: 3LD6), including the standard antifungal antibiotics ketoconazole and fluconazole. In this instance, the binding affinities of 10 (−7.6 kcal/mol), 9 (−7.5 kcal/mol), and 7 (−6.9 kcal/mol) were better and comparable to fluconazole (−7.3 kcal/mol), indicating the likelihood of their use as non-azole type antifungal drugs in the future.

Synthesis of a novel hydrazone-based compound applied as a fluorescence turn-on chemosensor for iron(iii) and a colorimetric sensor for copper(ii) with antimicrobial, DFT and molecular docking studies

“…Molecular docking, a subfield of computational chemistry and bioscience, is a powerful tool to investigate and provide several quick insights into ligand–receptor interactions in order to facilitate the design of potential drugs. 36,37…”

“…Molecular docking, a subeld of computational chemistry and bioscience, is a powerful tool to investigate and provide several quick insights into ligand-receptor interactions in order to facilitate the design of potential drugs. 36,37 To investigate and compare the antimicrobial activity of the synthesized compound with experimental data, a docking analysis of L against E. coli was performed. Thus, to get the binding conformations of these compounds, L was docked in the active site of E. coli DNA Gyrase (PDB ID: 1KZN) using the PyRx 0.8.…”