Synthesis of novel of 2, 5-disubstituted 1, 3, 4- oxadiazole derivatives and their in vitro anti-inflammatory, anti-oxidant evaluation, and molecular docking study

Eco-friendly approaches to 1,3,4-oxadiazole derivatives: A comprehensive review of green synthetic strategies

This review article offers an environmentally benign synthesis of 1,3,4-oxadiazole derivatives, with a focus on sustainable methodologies that have minimal impact on the environment. These derivatives, known for their diverse applications, have conventionally been associated with synthesis methods that utilize hazardous reagents and produce significant waste, thereby raising environmental concerns. The green synthesis of 1,3,4-oxadiazole derivatives employs renewable substrates, nontoxic catalysts, and mild reaction conditions, aiming to minimize the environmental impact. Innovative techniques such as catalyst-based, catalyst-free, electrochemical synthesis, green-solvent-mediated synthesis, grinding, microwave-mediated synthesis, and photosynthesis are implemented, providing benefits in terms of scalability, cost-effectiveness, and ease of purification. This review emphasizes the significance of sustainable methodologies in the synthesis of 1,3,4-oxadiazole and boots for continued exploration in this research domain.

Novel quinolone substituted 1,3,4-oxadiazole derivatives: design, synthesis, antimicrobial and anti-inflammatory potential

A novel series of quinolone-substituted 1,3,4-oxadiazole derivatives 4(a-l) have been designed and synthesized. The target compounds were investigated for their antibacterial activity against gram positive (Staphylococcus aureus, ATCC 25923, Enterococcus faecalis, ATCC 29212) and gram negative bacterium (Escherichia coli, ATCC 25922, Pseudomonas aeruginosa, ATCC 27853) for antifungal activity using (Candida albicans, ATCC 10231) and anti-inflammatory activity as COX-II inhibitors, respectively. The 1,3,4-oxadiazole functionality was introduced at C-6 position of pipemidic acid derivatives. IR, 1H NMR and Mass spectrometry techniques confirmed the structure of synthesized derivatives. The quinolone (pipemidic acid)-oxadiazole hybrid derivatives were effective against bacterial strains. When compared to ciprofloxacin (MIC 16 µg/mL), the compounds under consideration (4f, 4h, and 4k) showed significant antibacterial activity against all bacterial strains except Enterococcus faecalis, with MICs of 8 µg/mL. On the other hand, synthesized target compounds 4(a-l) did not respond well against Candida albicans fungal strain. The compound (4k) represents high % inhibition against COX-II. The compounds (4f, 4h and 4k) exhibited highest hydrogen bonding interaction with ARG57, ARG72, ARG78, LEU54 and MET16 target residues with a binding energy of - 8.4, - 8.6 and - 8.5 kcal/mol into the active pocket of DNA gyrase enzyme respectively even better in comparison to reference ligands. Based on the docking study, quinolone (pipemidic acid) oxadiazole hybrid structural ligands exhibited strong interaction at binding pockets of DNA gyrase enzyme.

Novel 1,3,4-oxadiazole derivatives of naproxen targeting EGFR: Synthesis, molecular docking studies, and cytotoxic evaluation

The close association between inflammation and cancer inspired the synthesis of a series of 1,3,4-oxadiazole derivatives (compounds H4-A-F) of 6-methoxynaphtalene. The chemical structures of the new compounds were validated utilizing Fourier-transform infrared, proton nuclear magnetic resonance, and carbon-13 nuclear magnetic resonance spectroscopic techniques and CHN analysis. Computer-aided drug design methods were used to predict the compounds biological target, ADMET properties, toxicity, and to evaluate the molecular similarities between the design compounds and erlotinib, a standard epidermal growth factor receptor (EGFR) inhibitor. The antiproliferative effects of the new compounds were evaluated by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay, cell cycle analysis, apoptosis detection by microscopy, quantitative reverse transcription-polymerase chain reaction, and immunoblotting, and EGFR enzyme inhibition assay. In silico analysis of the new oxadiazole derivatives indicated that these compounds target EGFR, and that compounds H4-A, H4-B, H4-C, and H4-E show similar molecular properties to erlotinib. Additionally, the results indicated that none of the synthesized compounds are carcinogenic, and that compounds H4-A, H4-C, and H4-F are nontoxic. Compound H4-A showed the best-fit score against EGFR pharmacophore model, however, the in vitro studies indicated that compound H4-C was the most cytotoxic. Compound H4-C caused cytotoxicity in HCT-116 colorectal cancer cells by inducing both apoptosis and necrosis. Furthermore, compounds H4-D, H4-C, and H4-B had potent inhibitory effect on EGFR tyrosine kinase that was comparable to erlotinib. The findings of this inquiry offer a basis for further investigation into the differences between the synthesized compounds and erlotinib. However, additional testing will be needed to assess all of these differences and to identify the most promising compound for further research.

Substrate-based synthetic strategies and biological activities of 1,3,4-oxadiazole: A review

The five-membered 1,3,4-oxadiazole heterocyclic ring has received considerable attention because of its unique bio-isosteric properties and an unusually wide spectrum of biological activities. After a century since 1,3,4-oxadiazole was discovered, its uncommon potential attracted medicinal chemist's attention, leading to the discovery of a few presently accessible drugs containing 1,3,4-oxadiazole units, and a large number of patents have been granted on research related to 1,3,4-oxadiazole. It is worth noting that interest in 1,3,4-oxadiazoles' biological applications has doubled in the last few years. Herein, this review presents a comprehensive overview of the recent achievements in the synthesis of 1,3,4-oxadiazole-based compounds and highlights the major advances in their biological applications in the last 10 years, as well as brief remarks on prospects for further development. We hope that researchers across the scientific streams will benefit from the presented review articles for designing their work related to 1,3,4-oxadiazoles.

Recent advances in developing modified C14 side chain pleuromutilins as novel antibacterial agents

Owing to the increasing resistance to most existing antimicrobial drugs, research has shifted towards developing novel antimicrobial agents with mechanisms of action distinct from those of current clinical options. Pleuromutilins are antibiotics known for their distinct mechanism of action, inhibiting bacterial protein synthesis by binding to the peptidyl transferase center of the ribosome. Recent studies have revealed that pleuromutilin derivatives can disrupt bacterial cell membranes, thereby enhancing antibacterial efficacy. Both marketed pleuromutilin derivatives and those in clinical trials have been developed by structurally modifying the pleuromutilin C14 side chain to improve their antimicrobial activity. Therefore, this review aims to review advancement in the chemical structural characteristics, antibacterial activities, and structure-activity relationship studies of pleuromutilins, specifically focusing on modifications made to the C14 side chain in recent years. These findings provide a valuable reference for future research and development of pleuromutilins.

1,3,4-Oxadiazole Scaffold in Antidiabetic Drug Discovery: An Overview

Diabetes mellitus is one of the biggest challenges for the scientific community in the 21st century. With the increasing number of cases of diabetes and drug-resistant diabetes, there is an urgent need to develop new potent molecules capable of combating this cruel disease. Medicinal chemistry concerns the discovery, development, identification, and interpretation of the mode of action of biologically active compounds at the molecular level. Oxadiazole-based derivatives have come up as a potential option for antidiabetic drug research. Oxadiazole is a five-membered heterocyclic organic compound containing two nitrogen atoms and one oxygen atom in its ring. Oxadiazole hybrids have shown the ability to improve glucose tolerance, enhance insulin sensitivity, and reduce fasting blood glucose levels. The mechanisms underlying the antidiabetic effects of oxadiazole involve the modulation of molecular targets such as peroxisome proliferator-activated receptor gamma (PPARγ), α-glucosidase, α-amylase and GSK-3β which regulate glucose metabolism and insulin secretion. The present review article describes the chemical structure and properties of oxadiazoles and highlights the antidiabetic activity through action on different targets. The SAR for the oxadiazole hybrids has been discussed in this article, which will pave the way for the design and development of new 1,3,4-oxadiazole derivatives as promising antidiabetic agents in the future. We expect that this article will provide comprehensive knowledge and current innovation on oxadiazole derivatives with antidiabetic potential and will fulfil the needs of the scientific community in designing and developing efficacious antidiabetic agents.

A Bird's Eye Review of Recent Reports on 1,3,4-oxadiazoles' Anti-inflammatory Insights Perspectives

Anti-inflammatory agents suppress inflammatory mediators such as prostaglandins, prostacyclins, cytokines, thromboxane, histamine, bradykinins, COX-I and COX-II, 5-LOX, and other substances. These inflammatory chemicals create inflammatory responses when tissue is injured by trauma, bacteria, heat, toxins, or other factors. These inflammatory reactions may result in fluid flow from the blood vessels into the tissues, resulting in swelling. When the therapeutic importance of these clinically beneficial medications in treating inflammation was recognized, it spurred the invention of even more powerful and important molecules. Oxadiazole derivatives are exceptionally potent NSAIDs, and they are widely used. Comprehensive biochemical, structure-activity-relationship and pharmacological investigations have demonstrated that these 1,3,4-oxadiazole compounds exhibit anti-inflammatory properties. This review article outlines the synthesis scheme for 1,3,4-oxadiazole used in treating inflammation.

Fluorinated 2-arylchroman-4-ones and their derivatives: synthesis, structure and antiviral activity

A number of new biologically interesting fluorinated 2-arylchroman-4-ones and their 3-arylidene derivatives were synthesized based on the p-toluenesulfonic acid-catalyzed one-pot reaction of 2-hydroxyacetophenones with benzaldehydes. It was found that obtained (E)-3-arylidene-2-aryl-chroman-4-ones reacted with malononitrile under base conditions to form 4,5-diaryl-4H,5H-pyrano[3,2-c]chromenes. The structures of the synthesized fluorinated compounds were confirmed by 1H, 19F, and 13C NMR spectral data, and for some representatives of heterocycles also using NOESY spectra and X-ray diffraction analysis. A large series of obtained flavanone derivatives as well as products of their modification (35 examples) containing from 1 to 12 fluorine atoms in the structure was tested in vitro for cytotoxicity in MDCK cell line and for antiviral activity against influenza A virus. Among the studied heterocycles 6,8-difluoro-2-(4-(trifluoromethyl)phenyl)chroman-4-one (IC50 = 6 μM, SI = 150) exhibited the greatest activity against influenza A/Puerto Rico/8/34 (H1N1) virus. Moreover, this compound appeared active against phylogenetically distinct influenza viruses, A(H5N2) and influenza B (SI's of 53 and 42, correspondingly). The data obtained suggest that the fluorinated derivatives of 2-arylchroman-4-ones are prospective scaffolds for further development of potent anti-influenza antivirals.

Identification of 1,3,4-oxadiazolyl-containing β-carboline derivatives as novel α-glucosidase inhibitors with antidiabetic activity

In this study, we designed and synthesized a novel class of 1,3,4-oxadiazolyl-containing β-carboline derivatives, i.e., compounds f1∼f35 as potential α-glucosidase inhibitors. All the synthesized compounds possessed outstanding α-glucosidase inhibitory activity with the IC50 values in the range of 3.07-15.49 μM, representing that they are 36∼183-fold more active than a positive control, acarbose (IC50 = 564.28 μM). Among them, compound f26 exhibited the highest α-glucosidase inhibitory activity (IC50 = 3.07 μM) and was demonstrated to function as a reversible and noncompetitive inhibitor. Mechanistic studies by means of 3D fluorescence spectra, CD spectra and molecular docking suggested that complexation of compound f26 with α-glucosidase through hydrogen bonds and hydrophobic interactions, led to changes in the conformation and secondary strictures of α-glucosidase and further the inhibition of the enzymatic activity. In vivo results showed that oral administration of compound f26 (50 mg/kg/day) could obviously reduce the levels of fasting blood glucose and improve glucose tolerance and dyslipidemia in diabetic mice. The present findings suggest that compound f26 is exploitable as a potential lead compound for the development of new α-glucosidase inhibitors with antidiabetic activity.

Novel flurbiprofen clubbed oxadiazole derivatives as potential urease inhibitors and their molecular docking study

In this study, twenty eight novel oxadiazole derivatives (5-32) of the marketed available non-steroidal anti-inflammatory drug (NSAID), (S)-flurbiprofen (1), were synthesized via I2 mediated cyclo-addition reaction in better yields. The synthesized hydrazone-Schiff bases were cyclized with iodine by using potassium hydroxide as a base in DMSO solvent to obtain oxadiazole derivatives (5-32). Structures of the synthesized products were confirmed with HR-ESI-MS, 1H-NMR spectroscopy and CHN analysis. After structure confirmations all analogs were evaluated for urease (in vitro) inhibitory activity. Amongst the series, fourteen compounds 20, 26, 30, 24, 21, 16, 28, 31, 32, 7, 19, 13, 10, and 6 were found to be excellent inhibitors of urease enzyme, having IC50 values of 12 ± 0.9 to 20 ± 0.5 μM, better than the standard thiourea (IC50 = 22 ± 2.2 μM), whereas the remaining fourteen derivatives displayed good to moderate activity. The in silico study was executed to analyse the interaction between the active site of the enzyme (urease) and the produced compounds. The docking study revealed that compounds 20, 26, 30, 24, 21, 16, 28, 31, 32, 7, 19, 13, 10, and 6 had lower docking scores than the standard compound thiourea and revealed better interactions with the urease enzyme.

Design, synthesis, antimicrobial activity, DFT, and molecular docking studies of pyridine-pyrazole-based dihydro-1,3,4-oxadiazoles against various bacterial and fungal targets

Antimicrobial resistance which is increasing at an alarming rate is a severe public health issue worldwide. Hence, the development of novel antibiotics is an urgent need as microbes have developed resistance against available antibiotics. In search of novel antimicrobial agents, a convenient route for the preparation of substituted 3-(1-phenyl-3-(p-tolyl)-1H-pyrazol-4-yl)-1-(2-phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazol-3(2H)-yl)prop-2-en-1-ones (6a-6o) has been adopted by using pyridine-3-carbohydrazide and various aromatic aldehydes. The newly synthesized compounds were characterized by using various spectral techniques, for example, IR, 1 H NMR, 13 C NMR, and mass spectroscopy. Synthesized hybrids were studied for in vitro antimicrobial potency against various bacterial and fungal strains. Antibacterial results revealed that compounds 6e, 6h, 6i, 6l, and 6m were found to be most active against bacterial strains as they showed minimum inhibitory concentration (MIC) value of 62.5 μg/mL while compounds 6d, 6e, and 6h showed MIC value of 200 μg/mL against Candida albicans. The quantum parameters that relate to the bioavailability of the compounds were computed, followed by docking with different bacterial and fungal targets like sortase A, dihydrofolate reductase, thymidylate kinase, gyrase B, sterol 14-alpha demethylase. The experimental and computational results are in good agreement.

Oxadiazole Schiff Base as Fe3+ Ion Chemosensor: "Turn-off" Fluorescent, Biological and Computational Studies

Compound, (E)-5-(4-((thiophen-2-ylmethylene)amino)phenyl)-1,3,4-oxadiazole-2-thiol (3) was synthesized via condensation reaction of 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol with thiophene-2-carbaldehyde in ethanol. For the synthesis and structural confirmation the FT-IR, ¹H, ¹³C-NMR, UV-visible spectroscopy, and mass spectrometry were carried out. The long-term stability of the probe (3) was validated by the experimental as well as theoretical studies. The sensing behaviour of the compound 3 was monitored with various metal ions (Ca²⁺, Cr³⁺, Fe³⁺, Co²⁺, Mg²⁺, Na⁺, Ni²⁺, K⁺) using UV- Vis. and fluorescence spectroscopy techniques by various methods (effect of pH and density functional theory) which showing the most potent sensing behaviour with iron. Job's plot analysis confirmed the binding stoichiometry ratio 1:1 of Fe³⁺ ion and compound 3. The limit of detection (LOD), the limit of quantification (LOQ), and association constant (K_a) were calculated as 0.113 µM, 0.375 µM, and 5.226 × 10⁵ respectively. The sensing behavior was further confirmed through spectroscopic techniques (FT-IR and ¹H-NMR) and DFT calculations. The intercalative mode of binding of oxadiazole derivative 3 with Ct-DNA was supported through UV-Vis spectroscopy, fluorescence spectroscopy, viscosity, cyclic voltammetry, and circular dichroism measurements. The binding constant, Gibb's free energy, and stern-volmer constant were find out as 1.24 × 10⁵, -29.057 kJ/mol, and 1.82 × 10⁵ respectively. The cleavage activity of pBR322 plasmid DNA was also observed at 3 × 10^-5 M concentration of compound 3. The computational binding score through molecular docking study was obtained as -7.4 kcal/mol. Additionally, the antifungal activity for compound 3 was also screened using broth dilution and disc diffusion method against C. albicans strain. The synthesized compound 3 showed good potential scavenging antioxidant activity against DPPH and H₂O₂ free radicals.

An Understanding of Mechanism-Based Approaches for 1,3,4-Oxadiazole Scaffolds as Cytotoxic Agents and Enzyme Inhibitors

The world's health system is plagued by cancer and a worldwide effort is underway to find new drugs to treat cancer. There has been a significant improvement in understanding the pathogenesis of cancer, but it remains one of the leading causes of death. The imperative 1,3,4-oxadiazole scaffold possesses a wide variety of biological activities, particularly for cancer treatment. In the development of novel 1,3,4-oxadiazole-based drugs, structural modifications are important to ensure high cytotoxicity towards malignant cells. These structural modification strategies have shown promising results when combined with outstanding oxadiazole scaffolds, which selectively interact with nucleic acids, enzymes, and globular proteins. A variety of mechanisms, such as the inhibition of growth factors, enzymes, and kinases, contribute to their antiproliferative effects. The activity of different 1,3,4-oxadiazole conjugates were tested on the different cell lines of different types of cancer. It is demonstrated that 1,3,4-oxadiazole hybridization with other anticancer pharmacophores have different mechanisms of action by targeting various enzymes (thymidylate synthase, HDAC, topoisomerase II, telomerase, thymidine phosphorylase) and many of the proteins that contribute to cancer cell proliferation. The focus of this review is to highlight the anticancer potential, molecular docking, and SAR studies of 1,3,4-oxadiazole derivatives by inhibiting specific cancer biological targets, such as inhibiting telomerase activity, HDAC, thymidylate synthase, and the thymidine phosphorylase enzyme. The purpose of this review is to summarize recent developments and discoveries in the field of anticancer drugs using 1,3,4-oxadiazoles.

Research progress on the synthesis and pharmacology of 1,3,4-oxadiazole and 1,2,4-oxadiazole derivatives: a mini review

Oxadiazole is a five-membered heterocyclic compound containing two nitrogen atoms and one oxygen atom. The 1,3,4-oxadiazole and 1,2,4-oxadiazole have favourable physical, chemical, and pharmacokinetic properties, which significantly increase their pharmacological activity via hydrogen bond interactions with biomacromolecules. In recent years, oxadiazole has been demonstrated to be the biologically active unit in a number of compounds. Oxadiazole derivatives exhibit antibacterial, anti-inflammatory, anti-tuberculous, anti-fungal, anti-diabetic and anticancer activities. In this paper, we report a series of compounds containing oxadiazole rings that have been published in the last three years only (2020-2022) as there was no report or their activities described in any article in 2019, which will be useful to scientists in research fields of organic synthesis, medicinal chemistry, and pharmacology.

A minireview of 1,2,3-triazole hybrids with O-heterocycles as leads in medicinal chemistry

Over the past few decades, the dynamic progress in the synthesis and screening of heterocyclic compounds against various targets has made a significant contribution in the field of medicinal chemistry. Among the wide array of heterocyclic compounds, triazole moiety has attracted the attention of researchers owing to its vast therapeutic potential and easy preparation via copper and ruthenium-catalyzed azide-alkyne cycloaddition reactions. Triazole skeletons are found as major structural components in a different class of drugs possessing diverse pharmacological profiles including anti-cancer, anti-bacterial, anti-fungal, anti-viral, anti-oxidant, anti-inflammatory, anti-diabetic, anti-tubercular, and anti-depressant among various others. Furthermore, in the past few years, a significantly large number of triazole hybrids were synthesized with various heterocyclic moieties in order to gain the added advantage of the improved pharmacological profile, overcoming the multiple drug resistance and reduced toxicity from molecular hybridization. Among these synthesized triazole hybrids, many compounds are available commercially and used for treating different infections/disorders like tazobactam and cefatrizine as potent anti-bacterial agents while isavuconazole and ravuconazole as anti-fungal activities to name a few. In this review, we will summarize the biological activities of various 1,2,3-triazole hybrids with copious oxygen-containing heterocycles as lead compounds in medicinal chemistry. This review will be very helpful for researchers working in the field of molecular modeling, drug design and development, and medicinal chemistry.

Structural Variations in the Central Heterocyclic Scaffold of Tripartite 2,6-Difluorobenzamides: Influence on Their Antibacterial Activity against MDR Staphylococcus aureus

Five series of heterocyclic tripartite 2,6-difluorobenzamides, namely 1,2,3-triazoles, 1,2,4- and 1,3,4-oxadiazoles, analogs of reported model anti-staphylococcal compounds, were prepared. The purpose was to investigate the influence of the nature of the heterocyclic central scaffold on the biological activity against three strains of S. aureus, including two drug-resistant ones. Among the 15 compounds of the new collection, a 3-(4-tert-butylphenyl)-1,2,4-oxadiazole linked via a methylene group with a 2,6-difluorobenzamide moiety (II.c) exhibited a minimal inhibitory concentration between 0.5 and 1 µg/mL according to the strain. Subsequent studies on II.c demonstrated no human cytotoxicity, while targeting the bacterial divisome.

Design and Synthesis of Carbothioamide/Carboxamide-Based Pyrazoline Analogs as Potential Anticancer Agents: Apoptosis, Molecular Docking, ADME Assay, and DNA Binding Studies

To discover anticancer drugs with novel structures and expand our research scope, pyrazoline derivatives (3a-3l) were designed and synthesized through cyclization of chalcones with thiosemicarbazide/semicarbazide in CH₃COOH as a solvent. All newly synthesized pyrazoline derivatives were fully characterized using several spectroscopic experiments such as ¹H, ¹³C NMR, FT-IR spectroscopy, and mass analysis. By HPLC, the purity of all analogs was found above 95% and both lead compounds (3a and 3h) were also validated by HRMS. Anticancer activity of synthesized pyrazoline derivatives (3a-3l) was investigated by the MTT assay against the human lung cancer cell (A549), human cervical cancer cell (HeLa), and human primary normal lung cells (HFL-1). Staurosporine (STS) was used as a standard drug. The anticancer results showed that two potent analogs 3a and 3h exhibit excellent activity against A549 (IC₅₀ = 13.49 ± 0.17 and 22.54 ± 0.25 μM) and HeLa cells (IC₅₀ = 17.52 ± 0.09 and 24.14 ± 0.86 μM) and low toxicity against the HFL-1 (IC₅₀ = 114.50 ± 0.01 and 173.20 ± 10 μM). The flow cytometry was further used to confirm the anticancer activity of potent derivatives against the A549 cancer cell line. DNA binding interaction of anticancer agents 3a and 3h with Ct-DNA has been carried out by absorption, fluorescence, EtBr (dye displacement assay), circular dichroism, cyclic voltammetry and time-resolved fluorescence, which showed noncovalent binding mode of interaction. Anticancer activity of both lead compounds (3a and 3h) may be attributed to DNA binding. The evaluation of the antioxidant potential of pyrazoline analogs 3a and 3h by 2,2-diphenyl-1-picrylhydrazyl free radical showed promising antioxidant activity with IC₅₀ values of 0.132 ± 0.012 and 0.215 ± 0.025 μg/mL, respectively. In silico molecular docking of pyrazoline derivatives was also performed using autodock vina software against the DNA hexamer with PDB ID: 1Z3F and ADMET properties to explore their best hits.

Oxadiazole: A highly versatile scaffold in drug discovery

As a pharmacologically important heterocycle, oxadiazole paved the way to combat the problem associated with the confluence of many commercially available drugs with different pharmacological profiles. The present review focuses on the potential applications of five-membered heterocyclic oxadiazole derivatives, especially 1,2,4-oxadiazole, 1,2,5-oxadiazole, and 1,3,4-oxadiazole, as therapeutic agents. Designing new hybrid molecules containing the oxadiazole moiety is a better solution for the development of new drug molecules. The designed molecules may accumulate a biological profile better than those of the drugs currently available on the market. The present review will guide the way for researchers in the field of medicinal chemistry to design new biologically active molecules based on the oxadiazole nucleus. Antitubercular, antimalarial, anti-inflammatory, anti-HIV, antibacterial, and anticancer activities of various oxadiazoles have been reviewed extensively here.

Biological Evaluation and Molecular Docking Studies of Novel 1,3,4-Oxadiazole Derivatives of 4,6-Dimethyl-2-sulfanylpyridine-3-carboxamide

To date, chronic inflammation is involved in most main human pathologies such as cancer, and autoimmune, cardiovascular or neurodegenerative disorders. Studies suggest that different prostanoids, especially prostaglandin E₂, and their own synthase (cyclooxygenase enzyme-COX) can promote tumor growth by activating signaling pathways which control cell proliferation, migration, apoptosis, and angiogenesis. Non-steroidal anti-inflammatory drugs (NSAIDs) are used, alongside corticosteroids, to treat inflammatory symptoms particularly in all chronic diseases. However, their toxicity from COX inhibition and the suppression of physiologically important prostaglandins limits their use. Therefore, in continuation of our efforts in the development of potent, safe, non-toxic chemopreventive compounds, we report herein the design, synthesis, biological evaluation of new series of Schiff base-type hybrid compounds containing differently substituted N-acyl hydrazone moieties, 1,3,4-oxadiazole ring, and 4,6-dimethylpyridine core. The anti-COX-1/COX-2, antioxidant and anticancer activities were studied. Schiff base 13, containing 2-bromobenzylidene residue inhibited the activity of both isoenzymes, COX-1 and COX-2 at a lower concentration than standard drugs, and its COX-2/COX-1 selectivity ratio was similar to meloxicam. Furthermore, the results of cytotoxicity assay indicated that all of the tested compounds exhibited potent anti-cancer activity against A549, MCF-7, LoVo, and LoVo/Dx cell lines, compared with piroxicam and meloxicam. Moreover, our experimental study was supported by density functional theory (DFT) and molecular docking to describe the binding mode of new structures to cyclooxygenase.

Design, synthesis, in vitro and in vivo evaluation against MRSA and molecular docking studies of novel pleuromutilin derivatives bearing 1, 3, 4-oxadiazole linker

A class of pleuromutilin derivatives containing 1, 3, 4-oxadiazole were designed and synthesized as potential antibacterial agents against Methicillin-resistant staphylococcus aureus (MRSA). The ultrasound-assisted reaction was proposed as a green chemistry method to synthesize 1, 3, 4-oxadiazole derivatives (intermediates 85-110). Among these pleuromutilin derivatives, compound 133 was found to be the strongest antibacterial derivative against MRSA (MIC = 0.125 μg/mL). Furthermore, the result of the time-kill curves displayed that compound 133 could inhibit the growth of MRSA in vitro quickly (- 4.36 log10 CFU/mL reduction). Then, compound 133 (- 1.82 log10 CFU/mL) displayed superior in vivo antibacterial efficacy than tiamulin (- 0.82 log10 CFU/mL) in reducing MRSA load in mice thigh model. Besides, compound 133 exhibited low cytotoxicity to RAW 264.7 cells. Molecular docking studies revealed that compound 133 was successfully localized in the binding pocket of 50S ribosomal subunit (ΔGb = -10.50 kcal/mol). The results indicated that these pleuromutilin derivatives containing 1, 3, 4-oxadiazole might be further developed into novel antibiotics against MRSA.