Syntheses and anti-allergic activity of 2-((bis(trimethylsilyl)methylthio/methylsulfonyl)methyl)-5-aryl-1,3,4-oxadiazoles

The role of silicon in drug discovery: a review

This review aims to highlight the role of silicon in drug discovery. Silicon and carbon are often regarded as being similar with silicon located directly beneath carbon in the same group in the periodic table. That being noted, in many instances a clear dichotomy also exists between silicon and carbon, and these differences often lead to vastly different physiochemical and biological properties. As a result, the utility of silicon in drug discovery has attracted significant attention and has grown rapidly over the past decade. This review showcases some recent advances in synthetic organosilicon chemistry and examples of the ways in which silicon has been employed in the drug-discovery field.

Benzimidazole-Oxadiazole Hybrids-Development in Medicinal Chemistry: An Overview

To increase the success rate of drug discovery, one practical strategy is to begin molecular hybridisation. The presence of two or more pharmacophores in a single unit leads to a pharmacological potency greater than the sum of each individual moiety's potency. Heterocyclic compounds are very widely distributed in nature and are essential for life activities. Benzimidazole and oxadiazole are privileged structures in medicinal chemistry and are widely used in drug discovery and development due to their vast biological properties. The drug-like properties (like pharmacokinetics and pharmacodynamics) of the individual scaffolds can be improved by benzimidazole-oxadiazole chimeric molecules via a molecular hybridisation approach. Benzimidazole and oxadiazole cores can either be fused or incorporated using either functional groups/bonds. Over the last few decades, drug discovery scientists have predicted that these moieties could be interconnected to yield a novel or modified hybrid compound. Benzimidazole and oxadiazole hybrids were identified as the most potent anticancer, antimicrobial, anti-inflammatory, antioxidant, anticonvulsant, antidepressant, antihypertensive and antitubercular agents. In this context, the present review describes the biological properties of benzimidazole-oxadiazole (1,3,4 and 1,2,4) hybrids, their possible structure-activity relationship and the mechanism of action studies presented. This review article is intended to stimulate fresh ideas in the search for rational designs of more active and less toxic benzimidazole-oxadiazole hybrid prospective therapeutic candidates, as well as more effective diagnostic agents and pathologic probes.

Visible-Light-Driven Coupling of 1,3,4-Oxadiazoles and Hydroxamic Acid Derivatives

A visible-light-induced radical-radical cross-coupling reaction between 1,3,4-oxadiazoles and hydroxamic acid derivatives has been realized under base- and metal-free conditions. The protocol was characterized by broad substrate scope, excellent functional group tolerance, and simple operation procedures. By using this protocol, a variety of biologically important 5-aryl-1,3,4-oxadiazole-2-methylamines were obtained in good yields with excellent chemoselectivity.

Design, synthesis, computational molecular docking studies of novel heterocyclics bearing 1,2,4-triazole, 1,3,4-oxadiazole conjugates as potent antibacterial and antitubercular agents

Herein, we report the synthesis, and characterization of a new series of 1,3,4-oxadiazole and 1,2,4-triazole derivatives based on azaindole acetamides and assigned as potential antibacterial and antitubercular substances. The structures of these compounds were established by 1H NMR, 13C NMR, and HRMS spectral analysis. In preliminary antibacterial studies, analogues 6b, 6d, and 6e were found to be most effective against S. aureus with MIC of 12.5, 6.25, and 12.5 μg/mL, whereas 8d displayed excellent activity against S. aureus, B. subtilis, E. coli bacterial strains with zones of inhibition 12.5, 25, and 12.5 μg/mL respectively. Particularly, the prepared scaffolds 8c, 8d, and 8e showed remarkable antifungal activity with MIC value 12.5, 12.5, and 6.25 μg/mL against A. flavus and 6d, 6c producing an increase in the activity against C. Albicans with zones of inhibition 12.5 and 12.5 μg/mL respectively. Also, through the antitubercular studies, we found that compounds 6e and 8b have a strong activity with M. tuberculosis H37Rv with MICs 3.26, and 6.48 μg/mL, respectively. The protein stability, fluctuations of APO-Protein, and protein-ligand complexes were investigated through Molecular Dynamics (MD) simulations studies using Desmond Maestro 11.3, and potential lead molecules were identified. Our findings were further confirmed using molecular docking, revealing that azaindole based ligand 6e, 6f, and 8a has strong hydrophobic Tyr179, Trp183, Ile177, Ile445, and H-bondings interactions Arg151 and Arg454 through molecular dynamics simulation studies, making it potential biological compound. These compounds were further evaluated for their ADMET and physicochemical properties by using SwissADME.Communicated by Ramaswamy H. Sarma.

Design, Synthesis and Bioassay of 2-Phenylglycine Derivatives as Potential Pesticide Candidates

Plant diseases can seriously affect the growth of food crops and economic crops. To date, pesticides are still among the most effective methods to prevent and control plant diseases worldwide. Consequently, to develop potential pesticide molecules, a series of novel 2-phenylglycine derivatives containing 1,3,4-oxadiazole-2-thioethers were designed and synthesized. The bioassay results revealed that G₁₉ exhibited great in vitro antifungal activity against Thanatephorus cucumeris with an EC₅₀ value of 32.4 μg/mL, and in vivo antifungal activity against T. cucumeris on rice leaves at a concentration of 200.0 μg/mL (66.9 %) which was close that of azoxystrobin (73.2 %). Compounds G₂₄ (80.2 %), G₂₅ (89.4 %), and G₂₇ (83.3 %) exhibited impressive in vivo inactivation activity against tobacco mosaic virus (TMV) at a concentration of 500.0 μg/mL, which was comparable to that of ningnanmycin (96.3 %) and markedly higher than that of ribavirin (55.6 %). The antibacterial activity of G₁₆ (63.1 %), G₂₆ (89.9 %), G₂₇ (78.0 %), and G₂₈ (68.0 %) against Xoo at a concentration of 50.0 μg/mL was higher than that of thiadiazole copper (18.0 %) and bismerthiazol (38.9 %). Preliminary mechanism studies on the antifungal activity against T. cucumeris demonstrated that G₁₉ can affect the growth of mycelia by disrupting the integrity of the cell membrane and altering the permeability of the cell. These studies revealed that the amino acid derivatives containing a 1,3,4-oxadiazole moiety exhibited certain antifungal, antibacterial, and anti-TMV activities, and these derivatives can be further modified and developed as potential pesticide molecules.

In vitro anti-TB properties, in silico target validation, molecular docking and dynamics studies of substituted 1,2,4-oxadiazole analogues against Mycobacterium tuberculosis

The alarming increase in multi- and extensively drug-resistant (MDR and XDR) strains of Mycobacterium tuberculosis (MTB) has triggered the scientific community to search for novel, effective, and safer therapeutics. To this end, a series of 3,5-disubstituted-1,2,4-oxadiazole derivatives (3a-3i) were tested against H37Rv, MDR and XDR strains of MTB. Of which, compound 3a with para-trifluorophenyl substituted oxadiazole showed excellent activity against the susceptible H37Rv and MDR-MTB strain with a MIC values of 8 and 16 µg/ml, respectively.To understand the mechanism of action of these compounds (3a-3i) and identify their putative drug target, molecular docking and dynamics studies were employed against a panel of 20 mycobacterial enzymes reported to be essential for mycobacterial growth and survival. These computational studies revealed polyketide synthase (Pks13) enzyme as the putative target. Moreover, in silico ADMET predictions showed satisfactory properties for these compounds, collectively, making them, particularly compound 3a, promising leads worthy of further optimisation.

Synergism of a Novel 1,2,4-oxadiazole-containing Derivative with Oxacillin against Methicillin-Resistant Staphylococcus aureus

Staphylococcusaureus is an important opportunistic pathogen that causes many infections in humans and animals. The inappropriate use of antibiotics has favored the diffusion of methicillin-resistant S. aureus (MRSA), nullifying the efforts undertaken in the discovery of antimicrobial agents. Oxadiazole heterocycles represent privileged scaffolds for the development of new drugs because of their unique bioisosteric properties, easy synthesis, and therapeutic potential. A vast number of oxadiazole-containing derivatives have been discovered as potent antibacterial agents against multidrug-resistant MRSA strains. Here, we investigate the ability of a new library of oxadiazoles to contrast the growth of Gram-positive and Gram-negative strains. The strongest antimicrobial activity was obtained with compounds 3 (4 µM) and 12 (2 µM). Compound 12, selected for further evaluation, was found to be noncytotoxic on the HaCaT cell line up to 25 µM, bactericidal, and was able to improve the activity of oxacillin against the MRSA. The highest synergistic interaction was obtained with the combination values of 0.78 μM for compound 12, and 0.06 μg/mL for oxacillin. The FIC index value of 0.396 confirms the synergistic effect of compound 12 and oxacillin. MRSA treatment with compound 12 reduced the expression of genes included in the mec operon. In conclusion, 12 inhibited the growth of the MRSA and restored the activity of oxacillin, thus resulting in a promising compound in the treatment of MRSA infection.

A novel dipeptide coupled with pyrazine-oxadiazole derivative as a potential antitubercular agent: Synthesis, radioiodination and bioevaluation

Tuberculosis (TB) is a disease caused by Mycobacterium and usually attack the lung. Synthesis of new dipeptide derivatives attached to antitubercular active heterocyclic rings like pyrazine and 1,3,4-oxadiazole called ethyl 2-(2-(5-((pyrazin-2-ylamino) methyl)-1,3,4-oxadiazol-2-ylthio) acetamido) acetamido)-3-(4-hydroxyphenyl) propanoate (EPOGTP) and iodinated EPOGTP are reported. The compounds have been characterized by mass, FT-IR and ¹H NMR spectroscopy. Their in vitro investigation against Mycobacterium tuberculosis cell line indicated good IC₅₀value of 210 μg/ml for EPOGTP and 86 μg/ml for iodo-EPOGTP. For study the biodisriution, the direct radioiodination of EPOGTP with iodine-131 using mild oxidizing agent, N-Bromosuccinimide (NBS), was performed and optimized for obtaining the maximum radiochemical purity (97.3 ± 0.47%). Then, the in vivo biodistribution in healthy mice showed good accumulation of radioiodinated EPOGTP in lung of about 41.83 ± 0.23% (the percentage of injected dose per gram of organ) at 15 min post-injection. As a conclusion, the synthetized dipeptide and its iodinated derivative could be further evaluated as a potential antitubercular agents.

A key review on oxadiazole analogs as potential methicillin-resistant Staphylococcus aureus (MRSA) activity: Structure-activity relationship studies

Methicillin-resistant Staphylococcus aureus (MRSA) is becoming dangerous to human beings due to easy transmission mode and leading to the difficult-to-treat situation. The rapid resistance development of MRSA to many approved antibiotics is of major concern. There is a lot of scope to develop novel, efficient, specific, and nontoxic drug candidates to fight against MRSA isolates. The interesting molecular structure and adaptable feature of oxadiazole moiety which are bioisosteres of esters and amides, and these functional groups show improved resistance to esterases mediated hydrolytic cleavage, attracting researchers to develop required novel antibiotics based on oxadiazole core. This review summarizes the developments of oxadiazole-containing derivatives as potent antibacterial agents against multidrug-resistant MRSA strains and discussing the structure-activity relationship (SAR) in various directions. The current survey is the highlight of the present scenario of oxadiazole hybrids on MRSA studies, covering articles published from 2011 to 2020. This collective information may become a good platform to plan and develop new oxadiazole-based small molecule growth inhibitors of MRSA with minimal side effects.

Contribution of N-heterocycles towards anti-tubercular drug discovery (2014-2019); predicted and reengineered molecular frameworks

Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis, responsible for high death frequency every year all over the world. In this regard, efficient drug-design and discovery towards the prevention of M.tb H₃₇ R_v is of prime concern. Prevention of the infection may include vaccination, and the treatment comprises anti-TB drug regimen. However, the vaccine decreases the risk of tuberculosis infection only to some extent, while drug-resistance limits the efficacy of the existing anti-TB agents. Much improvement has to be achieved to overcome pitfalls such as side effects, high-toxicity, low bioavailability, pharmacokinetics and pharmacodynamics, and hence forth in clinical therapeutics. Amongst heterocyclic compounds, N-heterocycles played a pivotal role in drug-design and discovery. A wide range of microbial diseases are being treated by the N-heterocyclic drugs. The present review comprises description of anti-TB effects of the N-heterocycles such as indoles, triazoles, thiazoles, and pyrazoles. The potent anti-TB activity exerted by the derivatives of these heterocycles is evaluated critically alongside emphasizing structure-activity relationship. Besides, docking studies supporting anti-TB activity is supplemented. Alongside this, based on the potent heterocyclic molecules, the molecular frameworks are designed that would bring about enhanced M. tb H₃₇ R_v inhibitory potencies.

Anti-tuberculosis activity and its structure-activity relationship (SAR) studies of oxadiazole derivatives: A key review

With the increasing number of cases of inactive and drug-resistance tuberculosis, there is an urgent need to develop new potent molecules set for fighting this brutal disease. Medicinal chemistry concerns the discovery, the development, the identification, and the interpretation of the mode of action of biologically active compounds at the molecular level. Molecules bearing oxadiazoles are one such class that could be considered to satisfy this need. Oxadiazole regioisomers have been investigated in drug discovery programs for their capacity to go about as powerful linkers and as pharmacophoric highlights. Oxadiazoles can go about as bioisosteric substitutions for the hydrazide moiety which can be found in first-line anti-TB drugs, and some have been likewise answered to cooperate with more current anti-TB targets. This present review summarizes the current innovations of oxadiazole-based derivatives with potential antituberculosis activity and bacteria discussing various aspects of structure-activity relationship (SAR).

Synthesis of anti-allergic drugs

Histamine is formed by the decarboxylation of histidine catalyzed by enzymes. It is an endogenous biologically active substance involved in multiple complex physiological processes as an important chemical transmitter. Histamine receptors have four subtypes, H₁, H₂, H₃ and H₄, all of which are G protein coupling receptors (GPCRs) with different physiological functions. Histamine plays an important role in the pathophysiological mechanism of allergic diseases, and the antagonistic effect of histamine has become an important way to study anti-allergic drugs, wherein the anti-allergic drugs used in clinical practice are mainly H₁ receptor antagonists. Currently, there are many varieties of H₁ receptor antagonists in clinical applications, which can be divided into ethylenediamine antagonists, amino ether antagonists, propylamine antagonists, tricyclic antagonists, piperazine antagonists and piperidine antagonists depending on their chemical structures. This article mainly reviews the research progress of allergic reactions with histamine H₁ receptor antagonists and expounds the important aspects of the design and synthesis of various new compounds.

Histamine is formed by the decarboxylation of histidine catalyzed by enzymes. It is an endogenous biologically active substance involved in multiple complex physiological processes as an important chemical transmitter.

Design, synthesis and biological activity of a novel ethylenediamine derivatives as H1 receptor antagonists

In this study, a series of novel ethylenediamine compounds were obtained by structural modification of the lead compounds with thonzylamine, and using the principle of modifying by bioisostere formation and modification with alkyl groups. In vitro assay, the biological activities showed that the target compounds have good properties in inhibiting mast cell degranulation and releasing histamine and β-aminohexidase, such as the compounds 5c, 5g, 5k, 5l and 5o, especially of compound 5k to mast cell degranulation is IC₅₀ = 0.0106 ± 0.001 μmol⋅L^-1, histamine release was IC₅₀ = 0.0192 ± 0.005 μmol⋅L^-1 and β-hexosaminidase release was IC₅₀ = 0.0455 ± 0.002 μmol⋅L^-1in vitro. At the same time, in vivo biological activities assay results showed that have a good Histamie induce bronchospasm effect with relatively long duration and good protective effect in vivo, among which the protective effect of compound 5k was 79.74 ± 0.30%, compounds 5c, 5g, 5k, 5l and 5o could inhibit the capillary permeability of increasing which were caused by histamine.

A Review Exploring Therapeutic Worth of 1,3,4-Oxadiazole Tailored Compounds

1,3,4-Oxadiazole, a five-membered aromatic ring can be seen in a number of synthetic molecules. The peculiar structural feature of 1,3,4-oxadiazole ring with pyridine type of nitrogen atom is beneficial for 1,3,4-oxadiazole derivatives to have effective binding with different enzymes and receptors in biological systems through numerous weak interactions, thereby eliciting an array of bioactivities. Research in the area of development of 1,3,4-oxadiazole-based derivatives has become an interesting topic for the scientists. A number of 1,3,4-oxadiazole based compounds with high therapeutic potency are being extensively used for the treatment of different ailments, contributing to enormous development value. This work provides a systematic and comprehensive review highlighting current developments of 1,3,4-oxadiazole based compounds in the entire range of medicinal chemistry such as anticancer, antifungal, antibacterial, antitubercular, anti-inflammatory, antineuropathic, antihypertensive, antihistaminic, antiparasitic, antiobesity, antiviral, and other medicinal agents. It is believed that this review will be of great help for new thoughts in the pursuit for rational designs for the development of more active and less toxic 1,3,4-oxadiazole based medicinal agents.

Synthesis, Molecular Docking and β-Glucuronidase Inhibitory Potential of Indole Base Oxadiazole Derivatives

β-glucuronidase is a lysosomal glycosidase enzyme which catalyzes the extracellular matrix of cancer and normal cells and the glycosaminoglycans of the cell membrane, which is important for cancer cell proliferation, invasion, and metastasis. Liver cancer, colon carcinoma, and neoplasm bladder are triggered by the increase of the level of β-glucuronidase activity. The most valuable structures are indole and oxadiazole which has gain immense attention because of its pharmacological behavior and display many biological properties. Twenty-two (1⁻22) analogs of indole based oxadiazole were synthesized and screened for their inhibitory potential against β-glucuronidase. Majority of the compounds showed potent inhibitory potential with IC₅₀ values ranging between 0.9 ± 0.01 to 46.4 ± 0.9 µM, under positive control of standard drug d-saccharic acid 1,4 lactone (IC₅₀ = 48.1 ± 1.2 µM). Structural activity relationship (SAR) has been established for all synthesized compounds. To shed light on molecular interactions between the synthesized compounds and β-glucuronidase, 1, 4, and 6 compounds were docked into the active binding site of β-glucuronidase. The obtained results showed that this binding is thermodynamically favorable and β-glucuronidase inhibition of the selected compounds increases with the number of hydrogen bonding established in selected compound-β-glucuronidase complexes.

Synthesis of 5-(5-methyl-benzofuran-3-ylmethyl)-3H- [1, 3, 4] oxadiazole-2-thione and investigation of its spectroscopic, reactivity, optoelectronic and drug likeness properties by combined computational and experimental approach

This paper reports the synthesis of 5-(5-methyl-benzofuran-3-ylmethyl)-3H- [1, 3, 4] oxadiazole-2-thione (5MBOT) and characterization by FT-IR, FT-Raman, ¹H NMR, ¹³C NMR and UV spectral studies. The density functional theory (DFT) calculations have been executed for the 5MBOT using B3LYP/6-31++G (d, p) basis set. The fundamental modes of the vibrations were designated by the potential energy distribution (PED), and the computed and experimental values support each other. The ¹H NMR and ¹³C NMR chemical shifts of 5MBOT were estimated by gauge-including atomic orbitals (GIAO) method and compared with the experimental chemical shifts. The UV-Vis method used to study the visible absorption maxima (λ_max) by using Time-Dependent DFT. Further, the Mulliken population analysis (MPA), natural population analysis (NPA) charges, thermodynamic properties at different temperatures were presented. The calculated HOMO and LUMO energies show that charge transfer within the molecule. The natural bonds orbital (NBO) also computed. Optoelectronic properties have been carried out by combination of DFT calculations and molecular dynamics (MD) simulations, in order to assess the potential of this structure for applications in organic electronics. Further, the study encompassed calculations of reorganization energies for holes and electrons and charge transfer rates. DFT calculations have been also used in order to identify locations possibly sensitive towards the autoxidation mechanism, which correlates between bond dissociation energy for hydrogen abstraction and the mechanism. The MD simulations have been used to understand interaction of 5MBOT with water molecules. Molecular docking studies reveals the antifungal activity of 5MBOT may be due to hydrogen bonding and hydrophobic interactions with different antifungal proteins.

Synthesis, biological evaluation and molecular docking study of some novel indole and pyridine based 1,3,4-oxadiazole derivatives as potential antitubercular agents

A series of indole and pyridine based 1,3,4-oxadiazole derivatives 5a-t were synthesized and evaluated for their in vitro antitubercular activity against Mycobacterium tuberculosis H37Ra (MTB) and Mycobacterium bovis BCG both in active and dormant state. Compounds 5b, 5e, 5g and 5q exhibited very good antitubercular activity. All the newly synthesized compounds 5a-t were further evaluated for anti-proliferative activity against HeLa, A549 and PANC-1 cell lines using modified MTT assay and found to be noncytotoxic. On the basis of cytotoxicity and MIC values against Mycobacterium bovis BCG, selectivity index (SI) of most active compounds 5b, 5e, 5g and 5q was calculated (SI=GI50/MIC) in active and dormant state. Compounds 5b, 5e and 5g demonstrated SI values ⩾10 against all three cell lines and were found to safe for advance screening. Compounds 5a-t were further screened for their antibacterial activity against four bacteria strains to assess their selectivity towards MTB. In addition, the molecular docking studies revealed the binding modes of these compounds in active site of enoyl reductase (InhA), which in turn helped to establish a structural basis of inhibition of mycobacteria. The potency, low cytotoxicity and selectivity of these compounds make them valid lead compounds for further optimization.

Synthesis, pharmacological screening and in silico studies of new class of Diclofenac analogues as a promising anti-inflammatory agents

A novel series of 5-[2-(2,6-dichlorophenylamino)benzyl]-3-(substituted)-1,3,4-oxadiazol-2(3H)-thione (4a-k) derivatives have been synthesized by the Mannich reaction of 5-[2-(2,6-dichlorophenylamino)benzyl]-1,3,4-oxadiazol-2(3H)-thione (3) with an appropriately substituted primary/secondary amines, in the presence of formaldehyde and absolute ethanol. Structures of these novel compounds were characterized on the basis of physicochemical, spectral and elemental analysis. The title compounds (4a-k) were screened for in vivo acute anti-inflammatory and analgesic activities at a dose of 10mg/kg b.w. Compound 4k exhibited the most promising and significant anti-inflammatory profile while compounds 4a, 4d, 4e, 4i, and 4j showed moderate to good inhibitory activity at 2nd and 4thh, respectively. These compounds were also found to have considerable analgesic activity (acetic acid induced writhing model) and antipyretic activity (yeast induced pyrexia model). In addition, the tested compounds were also found to possess less degree of ulcerogenic potential as compared to the standard NSAIDs. Compounds that displayed promising anti-inflammatory profile were further evaluated for their inhibitory activity against cyclooxygenase enzyme (COX-1/COX-2), by colorimetric COX (ovine) inhibitor screening assay method. The results revealed that the compounds 4a, 4e, 4g and 4k exhibited effective inhibition against COX-2. In an attempt to understand the ligand-protein interactions in terms of the binding affinity, docking studies were performed using Molegro Virtual Docker (MVD-2013, 6.0) for those compounds, which showed good anti-inflammatory activity. It was observed that the binding affinities calculated were in agreement with the IC50 values.

10-Camphorsulfonic acid ((±)-CSA) catalyzed facile one-pot synthesis of a new class of 2,5-disubstituted 1,3,4-oxadiazoles

A convenient, and efficient one-pot synthesis of 2,5-disubstituted-1,3,4-oxadizoles is described.