In Silico Testing of Some Protected Galactopyranose as SARS-CoV-2 Main Protease Inhibitors

An outbreak of novel Coronavirus disease (COVID-19 or 2019-nCoV) due to the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has already demonstrated a fatal death toll all over the world. To cure this viral infection, a number of compounds of different categories have been investigated in silico. Some of the compounds showed better binding energy with COVID-19-related proteins. However, until now there is no appropriate drug except a vaccine. It was found that many antifungal drugs are used for COVID-19 patients in hospitals. Many monosaccharide esters have been reported to have antifungal potential. Thus, in the present study, some protected galactopyranose esters are chosen for molecular docking with SARS-CoV-2 main proteases (PDB id: 7BQY and 6LU7). A docking study revealed that galactopyranose esters 5-8 have very good docking scores (-8.4 to -6.5 kcal/mol) compared to the standard drugs azithromycin, remdesivir, and hydroxychloroquine. To explain such good scores interaction between amino acid residues of proteins and compounds in their docked complexes are calculated and duly discussed in this study.

Novel Galactopyranoside Esters: Synthesis, Mechanism, In Vitro Antimicrobial Evaluation and Molecular Docking Studies

One-step direct unimolar valeroylation of methyl α-D-galactopyranoside (MDG) mainly furnished the corresponding 6-O-valeroate. However, DMAP catalyzed a similar reaction that produced 2,6-di-O-valeroate and 6-O-valeroate, with the reactivity sequence as 6-OH > 2-OH > 3-OH,4-OH. To obtain novel antimicrobial agents, 6-O- and 2,6-di-O-valeroate were converted into several 2,3,4-tri-O- and 3,4-di-O-acyl esters, respectively, with other acylating agents in good yields. The PASS activity spectra along with in vitro antimicrobial evaluation clearly indicated that these MDG esters had better antifungal activities than antibacterial agents. To rationalize higher antifungal potentiality, molecular docking was conducted with sterol 14α-demethylase (PDB ID: 4UYL, Aspergillus fumigatus), which clearly supported the in vitro antifungal results. In particular, MDG ester 7−12 showed higher binding energy than the antifungal drug, fluconazole. Additionally, these compounds were found to have more promising binding energy with the SARS-CoV-2 main protease (6LU7) than tetracycline, fluconazole, and native inhibitor N3. Detailed investigation of Ki values, absorption, distribution, metabolism, excretion, and toxicity (ADMET), and the drug-likeness profile indicated that most of these compounds satisfy the drug-likeness evaluation, bioavailability, and safety tests, and hence, these synthetic novel MDG esters could be new antifungal and antiviral drugs.

DFT Based Comparative Studies of Some Glucofuranose and Glucopyranoside Esters and Ethers

Carbohydrate-based molecular scaffolding received significant interest due to its impact on the drug discovery and development in synthetic carbohydrate chemistry during the last couple of decades. In this respect, four glucose compounds in the furanose and pyranose forms with ester and ether functionality were selected for their structural, thermodynamic and chemical reactivity studies. PASS predication indicated that the glucose in the six-membered pyranose form was more prone to biological properties compared to their five-membered furanose form. Also, in the pyranose form acetate ester (3) had more potentiality than the ethyl ether (4). The HOMO-LUMO energy gaps were almost similar for both monosubstituted furanose and pyranose glucose indicating their almost similar reactivities. It was also inferred that these 6-O-substituted compounds followed Lipinski’s rule with the acceptable range of ADMET levels, and hence, safe from lethal proarrhythmic risks. Hopefully, these results can be used in the near future for their probable pharmaceutical use without any remarkable toxicity.

Chemical Reactivity Descriptors and Molecular Docking Studies of Octyl 6-O-hexanoyl-β-D-glucopyranosides

The present study describes different chemical reactivity predictions of 6-O-hexanoylation of octyl β-D-glucopyranosides prepared from octyl β-D-glucopyranoside (OBG). Also, molecular docking of the OBGs was conducted against SARS-CoV-2 main protease (6LU7), urate oxidase (Aspergillus flavus; 1R51) and glucoamylase (Aspergillus niger; 1KUL). DFT optimization indicated that glucoside 1 and its ester derivatives 2-7 exist in 4C1 conformation with C1 symmetry. Interestingly, the addition of ester group(s) decreased the HOMO-LUMO gap (Δԑ) of glucosides indicating their good chemical reactivities, whereas the other chemical reactivity descriptors indicated their moderate reactive nature. This fact of moderate reactivity was confirmed by their molecular docking with 6LU7, 1R51 and 1KUL. All the esters showed a moderate binding affinity with these three proteins. More importantly, incorporation of the ester group(s) increased binding affinity with 6LU7 and 1R51, whereas decreased with 1KUL as compared to non-ester OBG 1.

Efficient Synthetic Technique, PASS Predication, and ADMET Studies of Acylated n-Octyl Glucopyranosides

Direct dimolar pentanoylation of octyl β-D-glucopyranoside (OBG) in pyridine-chloroform solvent system furnished the corresponding 3,6-di-O-pentanoate in improved yield. The pentanoate was further converted into three 2,4-di-O-acyl esters to get novel octyl glucopyranosides. To explore medicinal probability of OBG-based esters all the synthesized compounds were subjected for in silico PASS (prediction of activity spectra for substances) predication and ADMET (absorption, distribution, metabolism, excretion, and toxicity) studies. Both the studies indicated that OBG derived carbohydrate fatty acid (CFA) esters are potential alternative for multidrug resistant (MDR) pathogens, especially for fungal infections.