1,3,4-Oxadiazoles as Anticancer Agents: A Review

Among the deadliest diseases, cancer is characterized by tumors or an increased number of a specific type of cell because of uncontrolled divisions during mitosis. Researchers in the current era concentrated on the development of highly selective anticancer medications due to the substantial toxicities of conventional cytotoxic drugs. Several marketed drug molecules have provided resistance against cancer through interaction with certain targets/growth factors/enzymes, such as Telomerase, Histone Deacetylase (HDAC), Methionine Aminopeptidase (MetAP II), Thymidylate Synthase (TS), Glycogen Synthase Kinase-3 (GSK), Epidermal Growth Factor (EGF), Vascular Endothelial Growth Factor (VEGF), Focal Adhesion Kinase (FAK), STAT3, Thymidine phosphorylase, and Alkaline phosphatase. The molecular structure of these drug molecules contains various heterocyclic moieties that act as pharmacophores. Recently, 1,3,4- oxadiazole (five-membered heterocyclic moiety) and its derivatives attracted researchers as these have been reported with a wide range of pharmacological activities, including anti-cancer. 1,3,4- oxadiazoles have exhibited anti-cancer potential via acting on any of the above targets. The presented study highlights the synthesis of anti-cancer 1,3,4-oxadiazoles, their mechanism of interactions with targets, along with structure-activity relationship concerning anti-cancer potential.

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.

Simple and efficient synthesis of diamino derivatives of bis-1,2,4-oxadiazole via tandem Staudinger/aza-Wittig reaction

BACKGROUND

Two convenient and efficient routes for the synthesis of diamino derivatives of bis-1,2,4-oxadiazoles were described.

OBJECTIVE

This study provides a simple protocol for the synthesis of bis-1,2,4-oxadiazoles.

METHOD

The two procedures were based on tandem Staudinger/aza-Wittig reaction from the same starting material diaziglyoxime, isocyanates and triphenylphosphorus.

RESULTS

In synthesis method I, diaziglyoxime 1 was treated with various aromatic or aliphatic isocyanates to give diazioxalimides 2 in high yield. Diazioxalimides 2 reacted with Ph3P to produce the iminophosphoranes 4, the reaction was directly heated from room temperature to 115℃ to get the desired diamino derivatives of bis-1,2,4-oxadiazole 4 in 72-92% yields. In synthesis method II, the same target compounds 4 were synthesized in one-pot reaction by Ph3P and aromatic or aliphatic isocyanates in toluene for 10 h under 115 ℃ in 53-71% yields.

CONCLUSION

The two procedures provide proficient methods of making nitrogen-containing heterocyclic rings. The structures of target compounds 4 were identified by IR, 1HNMR, 13CNMR and HRMS.

Synthesis of 2-aryl-5-(arylsulfonyl)-1,3,4-oxadiazoles as potent antibacterial and antioxidant agents

Ten novel 2-aryl-5-(arylsulfonyl)-1,3,4-oxadiazoles were produced and assessed for their in vitro antibacterial and antioxidant activities. Diverse spectroscopic methods like 1H NMR, 13C NMR, IR, and LCMS were used for the characterization of the prepared samples and all the data was in good agreement with the anticipated structures. The prepared compounds 6a-j were screened for their in vitro antibacterial activity against bacterial strains Pseudomonas aeruginosa, Enterobacter aerogenes, Escherichia coli (gram-positive), and Bacillus cerus, Staphylococcus aureus, Bacillus subtilis (gram-negative). The antimicrobial screening outcome revealed that the prepared 2-(3,4-dimethylphenyl)-5-tosyl-1,3,4-oxadiazole (6j), 2-(3-isopropylphenyl)-5-tosyl-1,3,4-oxadiazole (6c), and 2-(2-ethylphenyl)-5-tosyl-1,3,4-oxadiazole (6i) are most potent among all the examined compounds. Furthermore, the antioxidant activity of the prepared compounds was also investigated by DPPH radical scavenging method and the results showed that some of the compounds were moderately active.

A Review: Discovering 1,3,4-oxadiazole and chalcone nucleus for cytotoxicity/EGFR inhibitory anticancer activity

INTRODUCTION

Cancer is reported to be one of the most life-threatening diseases. Major limitations of currently used anticancer agents are drug resistance, very small therapeutic index, and severe, multiple side effects.

OBJECTIVE

The current scenario necessitates developing new anticancer agents, acting on novel targets for effectively controlling cancer. The epidermal growth factor receptor is one such target, which is being explored for 1,3,4-oxadiazole and chalcone nuclei.

METHOD

Findings of different researchers working on these scaffolds have been reviewed and analyzed, and the outcomes were summarized. This review focuses on Structure-Activity Relationship studies (SARs) and computational studies of various 1,3,4-oxadiazole and chalcone hybrids/derivatives reported as cytotoxic/EGFR-TK inhibitory anticancer activity.

RESULT AND CONCLUSION

1,3,4-oxadiazole and chalcone hybrids/derivatives with varied substitutions are found to be effective pharmacophores in obtaining potent anticancer activity. Having done a thorough literature survey, we conclude that this review will surely provide firm and better insights to the researchers to design and develop potent hybrids/derivatives that inhibit EGFR.

Synthesis of a Series of Novel 2-Amino-5-Substituted 1,3,4-oxadiazole and 1,3,4-thiadiazole Derivatives as Potential Anticancer, Antifungal and Antibacterial Agents

BACKGROUND

Many compounds containing a five-membered heterocyclic ring display exceptional chemical properties and versatile biological activities.

OBJECTIVE

The objective of the present study was the desire to prepare the 5-substituted 2-amino-1,3,4-oxadiazole and 2-amino-1,3,4-thiadiazole derivatives and evaluate their potential anticancer, antibacterial and antifungal activities.

METHODS

Twenty-seven derivatives were synthesized by iodine-mediated cyclization of semicarbazones or thiosemicarbazones obtained from condensation of semicarbazide or thiosemicarbazide and aldehydes. The structures were confirmed by 1H-NMR, 13C-NMR and MS spectra. The antibacterial and antifungal activities were evaluated by diffusion method and the anticancer activities were evaluated by MTT assay.

RESULTS

Twenty-seven derivatives have been synthesized in moderate to good yields. A number of derivatives exhibited potential antibacterial, antifungal and anticancer activities.

CONCLUSION

Compounds (1b, 1e and 1g) showed antibacterial activity against Streptococcus faecalis, MSSA and MRSA with MIC ranging between 4 to 64 µg/mL. Compound (2g) showed antifungal activity against Candida albicans (8 µg/mL) and Aspergillus niger (64 µg/mL). Compound (1o) exhibited high cytotoxic activity against HepG2 cell line (IC50 value 8.6 µM), which is comparable to the activity of paclitaxel, and is non-toxic on LLC-PK1 normal cell line. The structure activity relationship and molecular docking study of the synthesized compounds are also reported.

Design, Synthesis, Anticancer Evaluation, and Molecular Docking Studies of Novel Benzoxazole Linked 1,3,4-Oxadiazoles

BACKGROUND

Cancer disease is making a serious concern globally. Global cancer occurrence is steadily increasing every year. There is always a persistent need to develop new anticancer drugs with reduced side effects or act synergistically with the existing chemotherapeutics.

OBJECTIVE

Benzoxazoles are fused bicyclic nitrogen and oxygen-containing heterocyclic compounds and are considered biologically privileged scaffolds. We designed a synthetic route to link the benzoxazoles with oxadiazoles resulting in a better pharmacophore for anticancer activity.

METHODS

A series of novel amide derivatives of benzoxazole linked 1,3,4-oxadiazoles (10a-j) were synthesized and characterized by ¹H NMR, ¹³C NMR, and mass spectroscopic techniques. The biological properties of the compounds were screened in vitro against four different tumor cell lines.

RESULTS

The results suggest that the compound 10b having 3,4,5-trimethoxy substitution on the phenyl ring exhibited potent anticancer activity in three cell lines (A549 = 0.13 ± 0.014 µM, MCF-7 = 0.10 ± 0.013 µM and HT-29 = 0.22 ± 0.017 µM). Notably, among the synthesized derivatives, compounds 10b, 10c, 10f, 10g, and 10i exhibited potent anticancer activity than the control IC₅₀ in the range of 0.11 ± 0.02 to 0.93 ± 0.034 µM. Molecular docking simulation results showed compounds were stabilized by hydrogen bond and π-π interactions with the protein.

CONCLUSION

The molecules showed comparable binding affinities with standard Combretastatin-A4. The present research work is preliminary and needs further studies to take the synthesized compounds to the next level in the cancer research field.

Rational design-aided discovery of novel 1,2,4-oxadiazole derivatives as potential EGFR inhibitors

A molecular dynamics-based sampling of epidermal growth factor receptor tyrosine kinase (EGFR-TK) was carried out to search for energetically more stable protein, which was then used for molecular docking of a series of 1,2,4-oxadiazole derivatives previously reported from our laboratory. A total of 14 compounds were docked, where compounds 6a and 6b showed better binding to EGFR in silico. Further, physicochemical properties of all the compounds were calculated, which suggested that all the molecules obeyed Lipinski's rule of 5 and had favorable polar surface area and CaCO2 permeability along with the low potential for HERG inhibition. All the compounds were then screened for their ability to produce cytotoxicity in four different cell lines overexpressing EGFR (A549, HCT-116, HEPG2, MCF-7) and one EGFR negative cancer cell line (SW620); at three concentrations: 10, 1, and 0.1 µM. None of the compounds showed activity against SW620, which suggested that the compounds show cytotoxicity through inhibition of EGFR. Compounds that showed promise in this 3-concentration screen were further subjected to multiple dose-response curves to identify the IC₅₀ values for the shortlisted eight compounds. It was encouraging to see 6a and 6b showing the best IC₅₀ values against almost all the cell-lines which further suggests that our design protocol can be applied to optimize this lead (which are currently in the low micromolar range) to design the homologous compounds to achieve the desired potency in the nanomolar range and also to achieve selectivity across a range of kinases.

Synthesis, In vitro α-Glucosidase Inhibitory Potential and Molecular Docking Studies of 2-Amino-1,3,4-Oxadiazole Derivatives

BACKGROUND

In the recent past, we have synthesized and reported different derivatives of oxadiazoles as potential α-glucosidase inhibitors, keeping in mind, the pharmacological aspects of oxadiazole moiety and in continuation of our ongoing research on the chemistry and bioactivity of new heterocyclic compounds.

METHODS

1,3,4-Oxadiazole derivatives (1-14) have been synthesized and characterized by different spectroscopic techniques such as 1H-, 13C-NMR and HREI-MS.

RESULTS

The synthetic derivatives were screened for α-glucosidase inhibitory potential. All compounds exhibited good inhibitory activity with IC50 values ranging between 0.80 ± 0.1 to 45.1 ± 1.7 μM in comparison with the standard acarbose having IC50 value 38.45 ± 0.80 μM.

CONCLUSION

Thirteen compounds 1-6 and 8-14 showed potential inhibitory activity as compared to the standard acarbose having IC50 value 38.45 ± 0.80 μM, however, only one compound 7 (IC50 = 45.1 ± 1.7 μM) was found to be less active. Compound 14 (IC50 = 0.80 ± 0.1 μM) showed promising inhibitory activity among all synthetic derivatives. Molecular docking studies were also conducted for the active compounds to understand the ligand-enzyme binding interactions.

Synthesis and receptor dependent 4D-QSAR studies of 4,5-dihydro-1,3,4-oxadiazole derivatives targeting cannabinoid receptor

Cannabinoid receptor has been shown to be overexpressed in various types of cancers, especially non-small cell lung cancer. As a result, it could be used as novel target for anticancer treatments. Because receptor-dependent 4D-QSAR generates conformational ensemble profiles of compounds by molecular dynamics simulations at the binding site of the enzyme, this work describes the synthesis, biological activity evaluation and 4D-QSAR studies of 4,5-dihydro-1,3,4-oxadiazole derivatives targeting cannabinoid receptor. Compared with WIN55,212-2, compound 5 f showed the best antiproliferative activity. The receptor-dependent 4D-QSAR model was generated by multiple linear regression method using QSARINS. Leave-n-out cross-validation and chemical applicability domain were performed to analyse the independent test set and to verify the robustness of the model. The best 4D-QSAR model showed the following statistics: r² = 0.8487, Q²_LOO = 0.7667, Q²_LNO = 0.7524, and r²_Pred = 0.8358.

Microwave and Conventional Study of Coumarin-Oxadiazole Adducts and their Anti-Microbial Evaluation

INTRODUCTION

Nowadays, researchers are progressively concentrated to generate economical, affordable and also greener synthesis approach for the synthesis of various heterocycles. On look at the beauty of coumarin molecules and oxazoles, it seems to be lead  molecules in the anti-microbial area.

AIM

With the target to identify efficient molecules, we studied 2-oxo-2H-chromen-4-yl-2-((5-substituted aryl-1,3,4-oxadiazol-2-yl) thio)acetate derivatives using two synthetic protocol/methods, i.e. conventional synthesis and microwave-based synthesis.

MATERIALS AND METHODS

Two simultaneous methods, i.e. conventional and microwave synthesis have been used for the synthe-sis of 2-oxo-2H-chromen-4-yl-2-((5-substituted aryl-1,3,4-oxadiazol-2-yl)thio)acetate (6a-l) derivatives. The desired molecules were synthesized by conventional and microwave synthesis and a comparative study was carried out to identify an easy route for industrial applications. The confirmations of the compounds were carried out by spectroscopic techniques such as IR, 1H NMR, 13C NMR, mass spectra and elemental analysis.

RESULTS

All synthesized compounds were evaluated for their in-vitro antibacterial activity against gram-positive bacteria (Staphylococcus aureus, Staphylococcus pyogenes), gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa), and antifungal activity (Candida albicans, Aspergillus niger).

CONCLUSIONS

All conventional synthesis of final coumarin derivatives were completed within 4-6 h. While that of microwave-based reaction took comparatively more reaction time. Surprisingly, the compounds 6f and 6g could not be synthesized by microwave radiation even after 32 minutes of irradiation. As to the medicinal application part, microbial evaluation of synthesized analogues showed that the compounds 6b, 6e, 6d, and 6j were found more potent in comparison to the reference drug.

Significance of 1,3,4-Oxadiazole Containing Compounds in New Drug Development

BACKGROUND

Oxadiazole core displays various pharmacological properties among five membered nitrogen heterocyclic compounds, specially 1,3,4-oxadiazole containing molecules that have occupied a particular place in the field of synthetic medicinal chemistry as surrogates (bioisosteres) of carboxylic acids, carboxamides and esters. Moreover, they are having widespread kind of applications in numerous zones as polymers, as luminescence producing materials and as electron- transporting materials and corrosion inhibitors.

METHODS

This study contains comprehensive and extensive literature survey on chemical reactivity and biological properties associated with 1,3,4-oxadiazole containing compounds.

RESULTS

This review summarises 1,3,4-oxadiazole moiety in numerous compounds with reported pharmacological activity such as antiviral, analgesic and anti-inflammatory, antitumor, antioxidant, insecticidal and anti-parasitic, etc. Nevertheless, ring opening reactions of the 1,3,4-oxadiazole core have also made great attention, as they produce new analogues containing an aliphatic nitrogen atom and to other ring systems.

CONCLUSION

In relation to the occurrence of oxadiazoles in biologically active molecules, 1,3,4- oxadiazole core emerges as a structural subunit of countless significance and usefulness for the development of new drug aspirants applicable to the treatment of many diseases. It concludes that 1,3,4-oxadiazole core compounds are more efficacious and less toxic medicinal agents with respect to new opinions in the search for rational strategies.

Therapeutic potential of oxadiazole or furadiazole containing compounds

As we know that, Oxadiazole or furadi azole ring containing derivatives are an important class of heterocyclic compounds. A heterocyclic five-membered ring that possesses two carbons, one oxygen atom, two nitrogen atoms, and two double bonds is known as oxadiazole. They are derived from furan by the replacement of two methylene groups (= CH) with two nitrogen (-N =) atoms. The aromaticity was reduced with the replacement of these groups in the furan ring to such an extent that it shows conjugated diene character. Four different known isomers of oxadiazole were existed such as 1,2,4-oxadiazole, 1,2,3-oxadiazole, 1,2,5-oxadiazole & 1,3,4-oxadiazole. Among them, 1,3,4-oxadiazoles & 1,2,4-oxadiazoles are better known and more widely studied by the researchers due to their broad range of chemical and biological properties. 1,3,4-oxadiazoles have become important synthons in the development of new drugs. The derivatives of the oxadiazole nucleus (1,3,4-oxadiazoles) show various biological activities such as antibacterial, anti-mycobacterial, antitumor, anti-viral and antioxidant activity, etc. as reported in the literature. There are different examples of commercially available drugs which consist of 1,3,4-oxadiazole ring such as nitrofuran derivative (Furamizole) which has strong antibacterial activity, Raltegravir as an antiviral drug and Nesapidil drug is used in anti-arrhythmic therapy. This present review summarized some pharmacological activities and various kinds of synthetic routes for 2, 5-disubstituted 1,3,4-oxadiazole, and their derived products.

Evaluation of Biological Activity of Derivatives of 1,3,4-Thiadiazole, 1,3,4-Oxadiazole and 1,2,4-Triazole

OBJECTIVE

1,3,4-thiadiazole (A), 1,3,4-oxadiazole (B) and 1,2,4-triazole (C) derivatives have been known for their immense pharmacotherapeutic potential. The current research article attempts to further explore and understand the probable biochemical mechanism related to antiinflammatory activity of derivatives.

METHODS

The screened A, B and C derivatives were investigated for both in-vitro (Erythrocyte Membrane stabilization activity, Proteinase enzyme inhibitory activities) and in-vivo correlation using acute and chronic anti-inflammatory potential by carrageenan induced rats paw edema and cotton pellet granuloma methods, respectively. The activity was studied after interpreting acute toxicity studies results.

RESULTS

In vitro studies in the case of Erythrocyte Membrane stability and Proteinase enzyme inhibitory activities exhibited by A, B, and C at 100 ppm were found to be 48.89%, 51.08% and 50.08% and 66.78%, 76.91% and 57.41%, respectively. The maximum toxic dose was found to be 2000 mg/kg. The derivatives were studied for two-dose levels viz; Lower (100 mg/kg) and higher dose (200 mg/kg). In rat paw edema, maximum decrease was obtained for A (50.05%), B (50.05%) and C (51.06%) at lower and higher dose at 68.76%, 55.61%, and 65.26%, respectively for effect up to 24 h. In the chronic model of cotton pellet granuloma viz; higher and lower doses of A, B and C exhibited 38.15%, 33.19% and 30.25 % and 19.45%, 18.55% and 17.55 %, respectively.

CONCLUSION

The studied models depicted that derivatives A, B and C have the probable potential as anti-inflammatory agents. Further studies need to be undertaken to explore their potential in the different therapeutic areas.

Evaluation of Anxiolytic, Sedative-hypnotic and Amnesic Effects of Novel 2-phenoxy phenyl-1,3,4-oxadizole Derivatives Using Experimental Models

Benzodiazepines (BZDs) are widely used in clinical practice as anxiolytics, hypnotics, anticonvulsants and muscle relaxants. However, they have some undesired effects including memory problems. In continuing our research on novel benzodiazepine ligands, we are looking for ligands with less adverse effects. Previously, 4 novel derivatives of 2-phenoxy phenyl-1,3,4-oxadiazole were synthesized as agonists of BZD receptors. In this study, the pharmacological effects of novel compounds were evaluated. Pentobarbital induced loss of righting reflex, elevated plus maze, open-field locomotor activity and passive avoidance test were used to evaluate the sedative-hypnotic, anxiolytic and amnesic effects of compounds respectively. The results revealed that the novel compounds with NH2, SH and SCH3 substituents at the 2-position of the oxadiazole ring increase righting reflex time significantly. In the elevated plus maze test none of the derivatives increased open arm duration and open arm entry indicating no anxiolytic properties. Moreover, the novel compounds didn't influence step-down latencies in the mice. The fact that the hypnotic activity of these compounds were significantly reduced by flumazenil, confirmed that this effect is mediated by BZD receptors.