A novel five‐step synthetic route to 1,3,4‐oxadiazole derivatives with potent α‐glucosidase inhibitory potential and their in silico studies

Synthetic α-glucosidase inhibitors as promising anti-diabetic agents: Recent developments and future challenges

Diabetes mellitus is one of the biggest challenges for the scientific community in the 21st century. It is a well-recognized multifactorial health problem contributes significantly to high mortality rates by causing serious health complications mainly related to cardiovascular diseases, kidney damage and neuropathy. The inhibition of α-glucosidase (enzyme that catalyses starch hydrolysis in the intestine) is an effective therapeutic approach for controlling hyperglycemia associated with type-2 diabetes. However, the presently approved drugs/inhibitors such as acarbose, miglitol and voglibose have several undesirable gastrointestinal side effects impeding their applications. Therefore, search for novel and more effective inhibitors with reduced side effects and less cost remains a fascinating area of research. In this context, a large variety of α-glucosidase inhibitors have been identified in recent years that demands attention from drug development community. This review is therefore an effort to summarize and highlight the promising α-glucosidase inhibitors especially those which are primarily based on aromatic heterocyclic scaffolds such as coumarin, imidazole, isatin, pyrimidine, quinazoline, triazine, thiazole etc, having improved safety and pharmacological profiles.

Design, Synthesis, α-Amylase/α-Glucosidase Inhibition Assay, Induced Fit Docking Study of New Hybrid Compounds Containing 4H-Pyrano[2,3-d]pyrimidine, 1H-1,2,3-Triazole and D-Glucose Components

In this study, the click chemistry between N-propargyl derivatives of substituted 4H-pyrano[2,3-d]pyrimidines and tetra-O-acetyl-α-d-glucopyranosyl azide carried out under catalytic conditions using catalyst CuI@Montmorillonite and additive N,N-diisopropylethylamine (DIPEA). The yields of obtained hybrid compounds having 4H-pyrano[2,3-d]pyrimidine connected to 1H-1,2,3-triazole rings were about 85-94 %. All these synthesized hybrid compounds were examined for in vitro α-amylase (with IC₅₀ values in the range of 103.63±1.13 μM to 295.45±1.11 μM) and α-glucosidase (with IC₅₀ values in the range of 45.63±1.14 μM to 184.52±1.15) inhibitory activity. Amongst this series, ethyl ester 8m showed the best inhibitory activity against α-amylase with IC₅₀ of 103.63±1.13 μM, while ethyl ester 8t exhibited the highest activity against α-glucosidase with IC₅₀ of 45.63±1.14 μM. The kinetics of the inhibition of compound 8t showed the competitive α-glucosidase inhibitor property of this compound. Furthermore, the most potent compounds had any cytotoxicity against human normal cells. Induced fit docking and molecular dynamics simulation calculations indicated that the inhibition potential compounds 8m and 8t had the active interactions with the residues in receptors of corresponding tested enzymes. The calculated binding free energy from MM-GBSA approach showed that the major energy components contributed to the active binding of these studied inhibitors, including Coulomb, lipophilic and van der Waals energy. Further, 300 ns MD simulation showed that studied ligand-protein complexes were stable and indicated the structural observations into mode of binding in these complexes.

Computational Investigation of 1, 3, 4 Oxadiazole Derivatives as Lead Inhibitors of VEGFR 2 in Comparison with EGFR: Density Functional Theory, Molecular Docking and Molecular Dynamics Simulation Studies

Vascular endothelial growth factor (VEGF) is an angiogenic factor involved in tumor growth and metastasis. Gremlin has been proposed as a novel therapeutic pathway for the treatment of renal inflammatory diseases, acting via VEGFR 2 receptor. To date, most FDA-approved tyrosine kinase (TK) inhibitors have been reported as dual inhibitors of EGFR and VEGFR 2. The aim of the present study was to find the potent and selective inhibitor of VEGFR 2 specifically for the treatment of renal cancer. Fourteen previously identified anti-inflammatory compounds i.e., 1, 3, 4 oxadiazoles derivatives by our own group were selected for their anti-cancer potential, targeting the tyrosine kinase (TK) domain of VEGFR2 and EGFR. A detailed virtual screening-based study was designed viz density functional theory (DFT) study to find the compounds' stability and reactivity, molecular docking for estimating binding affinity, SeeSAR analysis and molecular dynamic simulations to confirm protein ligand complex stability and ADMET properties to find the pharmacokinetic profile of all compounds. The DFT results suggested that among all the derivatives, the 7g, 7j, and 7l were chemically reactive and stable derivatives. The optimized structures obtained from the DFTs were further selected for molecular docking, and the results suggested that 7g, 7j and 7l derivatives as the best inhibitors of VEGFR 2 with binding energy values -46.32, -48.89 and -45.01 kJ/mol. The Estimated inhibition constant (IC50) of hit compound 7j (0.009 µM) and simulation studies of its complexes confirms its high potency and best inhibitor of VEGFR2. All the derivatives were also docked with EGFR, where they showed weak binding energies and poor interactions, important compound 7g, 7j and 7i exhibited binding energy of -31.01, -33.23 and -34.19 kJ/mol respectively. Furthermore, the anticancer potential of the derivatives was confirmed by cell viability (MTT) assay using breast cancer and cervical cancer cell lines. At the end, the results of ADMET studies confirmed these derivatives as drug like candidates. Conclusively, the current study suggested substituted oxadiazoles as the potential anticancer compounds which exhibited more selectivity towards VEGFR2 in comparison to EGFR. Therefore, the identified lead molecules can be used for the synthesis of more potent derivatives of VEGFR2, along with extensive in vitro and in vivo experiments, that can be used to treat various cancers, especially renal cancers, and to prevent angiogenesis due to aberrant expression of VEGFR2.

Heterocyclic Compounds as Dipeptidyl Peptidase-IV Inhibitors with Special Emphasis on Oxadiazoles as Potent Anti-Diabetic Agents

Dipeptidyl peptidase-IV (DPP-IV) inhibitors, often known as gliptins, have been used to treat type 2 diabetes mellitus (T2DM). They may be combined with other medications as an additional treatment or used alone as a monotherapy. In addition to insulin, sulfonylureas, thiazolidinediones, and metformin, these molecules appear as possible therapeutic options. Oxadiazole rings have been employed in numerous different ways during drug development efforts. It has been shown that including them in the pharmacophore increases the amount of ligand that may be bound. The exceptional hydrogen bond acceptor properties of oxadiazoles and the distinct hydrocarbon bonding potential of their regioisomers have been established. Beside their anti-diabetic effects, oxadiazoles display a wide range of pharmacological properties. In this study, we made the assumption that molecules containing oxadiazole rings may afford a different approach to the treatment of diabetes, not only for controlling glycemic levels but also for preventing atherosclerosis progression and other complications associated with diabetes. It was observed that oxadiazole fusion with benzothiazole, 5-(2,5,2-trifluoroethoxy) phenyl, β-homophenylalanine, 2-methyl-2-{5-(4-chlorophenyl), diamine-bridged bis-coumarinyl, 5-aryl-2-(6′-nitrobenzofuran-2′-yl), nitrobenzofuran, and/or oxindole leads to potential anti-diabetic activity.

Synthesis, in vitro cholinesterase inhibition, molecular docking, DFT and ADME studies of novel 1,3,4-oxadiazole 2-thiol derivatives

A sequence of 1,3,4-oxadiazole 2-thiol derivatives bearing various alkyl or aryl moieties was designed, synthesized, and characterized by modern spectroscopic methods to yield 17 compounds ( 6a - 6q ) which were screened for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes in search of 'lead' compounds for the treatment of Alzheimer disease (AD). The compounds 6q, 6p, 6k, 6o, and 6l showed inhibitory capability against AChE and BChE, with IC 50 values ranging from 11.730.49 to 27.360.29 µM for AChE and 21.830.39 to 39.430.44 µM for BChE, inhibiting both enzymes within a limited range. The SAR ascertained that the substitution of the aromatic moiety had a profound effect on the AChE and BChE inhibitory potential as compared to the aliphatic substitutions which were supported by the molecular docking studies. In silico ADME studies reinforced the drug-likeness of most of the synthesized molecules. These results were additionally supplemented by the molecular orbital analysis (HOMO-LUMO) and electrostatic potential maps got from DFT calculations. ESP maps expose that on all structures, there are two potential binding sites conquered by the most positive and most negative districts.

Design and synthesis of phenoxymethybenzoimidazole incorporating different aryl thiazole-triazole acetamide derivatives as α-glycosidase inhibitors

A novel series of phenoxymethybenzoimidazole derivatives (9a-n) were rationally designed, synthesized, and evaluated for their α-glycosidase inhibitory activity. All tested compounds displayed promising α-glycosidase inhibitory potential with IC₅₀ values in the range of 6.31 to 49.89 μM compared to standard drug acarbose (IC₅₀ = 750.0 ± 10.0 μM). Enzyme kinetic studies on 9c, 9g, and 9m as the most potent compounds revealed that these compounds were uncompetitive inhibitors into α-glycosidase. Docking studies confirmed the important role of benzoimidazole and triazole rings of the synthesized compounds to fit properly into the α-glycosidase active site. This study showed that this scaffold can be considered as a highly potent α-glycosidase inhibitor.

Identification of phenylcarbamoylazinane-1,3,4-oxadiazole amides as lipoxygenase inhibitors with expression analysis and in silico studies

In search for new anti-inflammatory agents that inhibit the enzymes of arachidonic acid pathway as the drug targets, the present article describes the screening of 1,3,4-oxadiazole analogues against lipoxygenase (LOX) enzyme. The work is based on the synthesis of new N-alkyl/aralky/aryl derivatives (6a-o) of 2-(4-phenyl-5-(1-phenylcarbamoylpiperidine)-4H-1,3,4-oxadiazol-3-ylthio)acetamide which were obtained by the reaction of 1,3,4-oxadiazole (3) with various electrophiles (5a-o), in KOH. The synthesized analogues showed potent to moderate inhibitory activity against the soybean 15-LOX enzyme; especially 6g, 6b, 6a and 6l displayed the potent inhibitory potential with IC₅₀ values 7.15 ± 0.26, 9.32 ± 0.42, 15.83 ± 0.45 & 18.37 ± 0.53 µM, respectively, while excellent to moderate inhibitory profiles with IC₅₀ values in the range of 26.13-98.21 µM were observed from the compounds 6k, 6m, 6j, 6o, 6h, 6f, 6n and 6c. Most of the active compounds exhibited considerable cell viability against blood mononuclear cells (MNCs) at 0.25 mM by MTT assay except 6f, 6h, 6k and 6m which showed around 50% cell viability. Flow cytometry studies of the selected compounds 6a, 6j and 6n revealed that these caused 79.5-88.51% early apoptotic changes in MNCs compared with 4.26% for control quercetin at their respective IC₅₀ values. The relative expression of 5-LOX gene was monitored in MNCs after treatment with these three molecules and all down-regulated the enzyme activity. In silico ADME and molecular docking studies further supported these studies of oxadiazole derivatives and considered it as potential 'lead' compounds in drug discovery and development.

Synthesis of novel 5-(2,5-bis(2,2,2-trifluoroethoxy)phenyl)-1,3,4-oxadiazole-2-thiol derivatives as potential glucosidase inhibitors

BACKGROUND

A hybrid molecule of different biologically active substances can improve affinity and efficiency compared to a standard drug. Hence based on this fact, we predict that a combination of fluorine, oxadiazole, sulfur, etc., may enhance α-glucosidase inhibition activity compared to a standard drug.

METHODS

A series of novel 5-(2,5-bis(2,2,2-trifluoroethoxy)phenyl)-1,3,4-oxadiazole-2-thiol derivatives (2a-2i) were synthesized and characterized using spectroscopic techniques such as ¹HNMR and LC-MS. In order to evaluate its bioactivity, in vitro α-amylase and α-glycosidase inhibitory activity were performed. In vivo study was carried using a genetic model, Drosophila melanogaster, for assessing the antihyperglycemic effects.

RESULTS

The compounds 2a-2i demonstrated α-amylase inhibitory activity in the range of IC₅₀ = 40.00-80.00 μg/ml as compare to standard acarbose (IC₅₀ = 34.71 μg/ml). Compounds 2a-2i demonstrated α-glucosidase inhibitory activity in the range of IC₅₀ = 46.01-81.65 μg/ml as compared to standard acarbose (IC₅₀ = 34.72 μg/ml). Docking studies on a target protein, N-terminal subunit of human Maltase-glucoamylase (PDB:2QMJ) was carried and the compounds were found to dock into the active site of the enzyme (Fig. 1). The predicted binding energies of the compounds were calculated. The in vitro studies indicate that compounds 2b and 2g had better activity among the synthesized compounds. Whereas in vivo study indicates that 2b, 2g, and 2i could lower glucose levels in the Drosophila, but then 17-30% reduced capacity than acarbose and may be overcome by adjusting their dosage.

CONCLUSIONS

The in vitro and in vivo studies indicate that compounds 2b and 2g had better activity among the synthesized compounds. This study has recognized that compounds like 2b, 2g, and 2i may be considered potential candidates for further developing a novel class of antidiabetic agents.

Novel inhibitors with sulfamethazine backbone: synthesis and biological study of multi-target cholinesterases and α-glucosidase inhibitors

The underlying cause of many metabolic diseases is abnormal changes in enzyme activity in metabolism. Inhibition of metabolic enzymes such as cholinesterases (ChEs; acetylcholinesterase, AChE and butyrylcholinesterase, BChE) and α-glucosidase (α-GLY) is one of the accepted approaches in the treatment of Alzheimer's disease (AD) and diabetes mellitus (DM). Here we reported an investigation of a new series of novel ureido-substituted derivatives with sulfamethazine backbone (2a-f) for the inhibition of AChE, BChE, and α-GLY. All the derivatives demonstrated activity in nanomolar levels as AChE, BChE, and α-GLY inhibitors with K_I values in the range of 56.07-204.95 nM, 38.05-147.04 nM, and 12.80-79.22 nM, respectively. Among the many strong N-(4,6-dimethylpyrimidin-2-yl)-4-(3-substitutedphenylureido) benzenesulfonamide derivatives (2a-f) detected against ChEs, compound 2c, the 4-fluorophenylureido derivative, demonstrated the most potent inhibition profile towards AChE and BChE. A comprehensive ligand/receptor interaction prediction was performed in silico for the three metabolic enzymes providing molecular docking investigation using Glide XP, MM-GBSA, and ADME-Tox modules. The present research reinforces the rationale behind utilizing inhibitors with sulfamethazine backbone as innovative anticholinergic and antidiabetic agents with a new mechanism of action, submitting propositions for the rational design and synthesis of novel strong inhibitors targeting ChEs and α-GLY.Communicated by Ramaswamy H. Sarma.

Synthesis of 5-[(1H-indol-3-yl)methyl]-1,3,4-oxadiazole-2(3H)-thiones and their protective activity against oxidative stress

A small library of 2-[(1H-indol-3-yl)methyl]-5-(alkylthio)-1,3,4-oxadiazoles was prepared, starting from indole-3-acetic acid methyl ester and its 5-methyl-substituted derivative. The synthetic route involved the formation of intermediate hydrazides, their condensation with carbon disulfide, and intramolecular cyclization to corresponding 5-[(1H-indol-3-yl)methyl]-1,3,4-oxadiazole-2(3H)-thiones. The latter were then S-alkylated, and in case of ester derivatives, they were further hydrolyzed into corresponding carboxylic acids. All 5-[(1H-indol-3-yl)methyl]-1,3,4-oxadiazole-2(3H)-thiones and their S-alkylated derivatives were then screened for their protective effects in vitro and in vivo. Methyl substitution on the indole ring and propyl, butyl, or benzyl substitution on sulfhydryl group-possessing compounds were revealed to protect Friedreich's ataxia fibroblasts against the effects of glutathione depletion induced by the γ-glutamylcysteine synthetase inhibitor, buthionine sulfoximine. Two of the active compounds also reproducibly increased the survival of Caenorhabditis elegans exposed to juglone-induced oxidative stress.