Oxadiazole: Synthesis, characterization and biological activities

A patent review on pharmaceutical and therapeutic applications of oxadiazole derivatives for the treatment of chronic diseases (2013-2021)

INTRODUCTION

Oxadiazole is a unique class of heterocycle, possessing numerous important biomedical and therapeutic applications such as anti-bacterial, anti-cancer, anti-inflammatory, inhibitors for diverse enzymes, receptors modulators, and neuroprotective properties. The rapid development in the field of oxadiazole-containing structures is confirmed by the development of numerous clinical drugs such as doxazosin, nesapidil, pleconaril, fasiplon, ataluren, zibotentan, and prenoxdiazine as selected examples.

AREAS COVERED

This review provides a comprehensive overview of the range of biological applications of oxadiazole-containing drugs in a range of patents from 2013 to 2021. The information was collected from available data sources including SciFinder, Reaxys, MedLine, and Chemical Abstracts.

EXPERT OPINION

Oxadiazole is an established class of compounds with fascinating biological properties. The importance of oxadiazoles can be recognized by their enormous application in a wide spectrum of medicinal chemistry from anticancer, antibiotic, and antidiabetic to the use in agriculture and neuroprotection. For instance, the oxadiazole-based compounds have shown the ability to modulate a variety of receptors including the M4 receptor agonists, S1P1 receptor modulators, SSTR5 antagonists, orexin type-2 receptor agonists, liver X receptor agonists, and many more. This testifies to the special features associated with the oxadiazole scaffold making it a significant pharmacophore.

Synthesis, Characterization, Antimicrobial and Molecular Docking Study of Benzooxadiazole Derivatives

In this study, a series of new1,2,5-oxadiazole compounds derived from 4-chloro-7-nitro-benzo 1,2,5-oxadiazole was synthesized using different organic procedures. The resulting derivatives were chemically characterized and their structures were confirmed by FT-IR and NMR analysis. All the compounds were also evaluated for their antibacterial and antifungal activity against four types of pathogenic bacteria: S.aureus, S.epidermidis (as gram-negative bacteria), E.coli, Klebsiella spp. (as gram-positive bacteria) and the fungus Candida albicans using the agar well diffusion method. The synthesized oxadiazole derivatives exhibited significant antibacterial and moderate antifungal activities. Exploring the binding between the potent synthesized derivative 8 within the active site of glucosamine-6-phosphate synthase, the target enzyme for the antimicrobial agents was achieved using Autodock 4.2 package. The interaction modes of the generated conformers inside the binding pocket were found to enhance the in vitro results, and strongly recommended the new derivatives as promising antimicrobial agents.

Conventional and Microwave-Assisted Synthesis, Antitubercular Activity, and Molecular Docking Studies of Pyrazole and Oxadiazole Hybrids

Microwave-assisted organic reaction enhancement (MORE) has become more important in synthetic organic chemistry for efficient resource utilization. In this study, we synthesized bioactive compounds using both traditional and microwave methods. Microwave-assisted synthesis takes less time and produces higher yields and quality than conventional approaches. We reported the synthesis of N'-(1-(2-(3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)-5-phenyl-1,3,4-oxadiazol-3(2H)-yl)ethylidene) substituted hydrazides (4a-t). We also tested them against two strains: M. tuberculosis H₃₇Ra and M. bovis BCG. Against M. tuberculosis H₃₇Ra, the compounds 4e, 4h, 4k, 4p, and 4s were the most effective. Compounds 4f, 4g, and 4s showed significant activity against M. bovis BCG. The structures of newly synthesized molecules were determined using spectral methods. Furthermore, molecular docking investigations into the active site of mycobacterial InhA yielded well-clustered solutions for these compounds' binding modalities producing a binding affinity in the range of -10.366 to -8.037. Theoretical results were in good accord with the observed experimental values. The docking score of compound 4e was -10.366, and the Glide energy was -66.459 kcal/mol.

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.

Green Synthetic Approach: An Efficient Eco-Friendly Tool for Synthesis of Biologically Active Oxadiazole Derivatives

Green synthetic protocol refers to the development of processes for the sustainable production of chemicals and materials. For the synthesis of various biologically active compounds, energy-efficient and environmentally benign processes are applied, such as microwave irradiation technology, ultrasound-mediated synthesis, photo-catalysis (ultraviolet, visible and infrared irradiation), molecular sieving, grinding and milling techniques, etc. Thesemethods are considered sustainable technology and become valuable green protocol to synthesize new drug molecules as theyprovidenumerous benefits over conventional synthetic methods.Based on this concept, oxadiazole derivatives are synthesized under microwave irradiation technique to reduce the formation of byproduct so that the product yield can be increased quantitatively in less reaction time. Hence, the synthesis of drug molecules under microwave irradiation follows a green chemistry approach that employs a set of principles to minimize or remove the utilization and production of hazardous toxic materials during the design, manufacture and application of chemical substances.This approach plays a major role in controlling environmental pollution by utilizing safer solvents, catalysts, suitable reaction conditions and thereby increases the atom economy and energy efficiency. Oxadiazole is a five-membered heterocyclic compound that possesses one oxygen and two nitrogen atoms in the ring system.Oxadiazole moiety is drawing considerable interest for the development of new drug candidates with potential therapeutic activities including antibacterial, antifungal, antiviral, anticonvulsant, anticancer, antimalarial, antitubercular, anti-asthmatic, antidepressant, antidiabetic, antioxidant, antiparkinsonian, analgesic and antiinflammatory, etc. This review focuses on different synthetic approaches of oxadiazole derivatives under microwave heating method and study of their various biological activities.

Investigation of the antibacterial activity of new quinazoline derivatives against methicillin and quinolone resistant Staphylococcus aureus

A series of 1,3,4-oxadiazole-fused and piperazine-fused quinazoline derivatives is synthesized and evaluated as antibacterial agents. The synthetic protocol involves an efficient Suzuki C–C cross-coupling reaction on the quinazoline ring followed by formation of 1,3,4-oxadiazole intermediates. These are further treated with piperazine bases in the presence of formalin in methanol to furnish the final N-Mannich products. The majority of these compounds show potent antibacterial activities against several different strains of Gram-positive bacteria including multidrug-resistant clinical isolates. The cytotoxic activity assay demonstrates that the synthesized compounds do not affect cell viability on Human cervical (HeLa) cells at their minimum inhibitory concentrations. The newly synthesized compounds are characterized by infrared spectroscopy, 1H NMR, 13C NMR, mass spectrometry, and elemental analysis.