Oxadiazoles in medicinal chemistry

Synthesis, X-ray diffraction analysis, quantum chemical studies and α-amylase inhibition of probenecid derived S-alkylphthalimide-oxadiazole-benzenesulfonamide hybrids

Sulphonamide and 1,3,4-oxadiazole moieties are present as integral structural parts of many drugs and pharmaceuticals. Taking into account the significance of these moieties, we herein present the synthesis, single-crystal X-ray analysis, DFT studies, and α-amylase inhibition of probenecid derived two S-alkylphthalimide-oxadiazole-benzenesulfonamide hybrids. The synthesis has been accomplished in high yields. The final structures of both hybrids have been established completely with the help of different spectro-analytical techniques, including NMR, FTIR, HR-MS, and single-crystal X-ray diffraction analyses. In an effort to confirm the experimental findings, versatile quantum mechanical calculations and Hirshfeld Surface analysis have been performed. α-Amylase inhibition assay has been executed to investigate the enzyme inhibitory potential of both hybrids. The low IC50 value (76.92 ± 0.19 μg/mL) of hybrid 2 shows the good α-amylase inhibition potential of the respective compound. Ultimately, the binding affinities and features of the two hybrids are elucidated utilising a molecular docking technique against the α-amylase enzyme.

Synthesis of 4-Hydroxycoumarin-Based Triazoles/Oxadiazoles as Novel Anticancer Agents

A series of novel 3-substituted-4-hydroxycoumarins 7 and 8 containing (5-aryl-1,3,4-oxadiazol-2-yl)thio or (4-amino-5-aryl-4H-1,2,4-triazol-3-yl)thio moieties have been synthesized and evaluated as anticancer agents. The in vitro MTT assay of compounds against hepatocellular carcinoma (HepG2), breast cancer (MCF7) cells, and a human colorectal adenocarcinoma cell line with epithelial morphology (HT29) indicated that the HepG2 cells had more susceptibility to the tested compounds. Indeed, all compounds (with the exception of 7b, 7c, 7g, and 8g) were more potent than the standard drug doxorubicin against HepG2 cells (IC₅₀ values=1.65-3.83 μM). Although, the better result was obtained with the oxadiazole analog 7h against HepG2 (IC₅₀ =1.65 μM), the N-amino-triazole derivatives 8c, 8e, 8f and, 8h with IC₅₀ values of 1.78-6.34 μM showed potent activity against all tested cell lines. The good drug-like properties and in vitro potency and selectivity of 4-hydroxycoumarins 8 make them as good leads for the development of new anticancer agents.

Recent Advances in [3+2]-Cycloaddition-Enabled Cascade Reactions: Application to Synthesize Complex Organic Frameworks

Many natural products and biologically important complex organic scaffolds have convoluted structures around their core skeleton. Interestingly, with just changing the outskirts, the core reflects new and unique degrees of various physical and chemical properties. A very common but intriguing core is a five-membered ring horning heaps of organic molecules crafts. The power of [3+2] cycloaddition reactions to generate five-membered ring systems allocate chemists to envision synthetic procedures of wonder molecules and if it is facilitating a cascade sequence, then the end product will imbibe significant level of complexity having applications in medicinal and pharmaceutical fields. This Account highlights the broad interest in assembling recent advances in cascade reactions involving [3+2] cycloaddition as the power tool in order to conceive breakthrough organic architectures reported in the last ten years. We foresee that our comprehensive collection of astonishing [3+2] cycloaddition enabled cascades will provide valuable insights to polycyclic molecular construction and perseverant approach towards nonconventional synthetic procedures to the organic community.

1 Introduction

2 Synthesis of Oxindoles Skeleton

3 Synthesis of Oxazoles Skeleton

4 Synthesis of Oxadiazoles Skeleton

5 Synthesis of Nitrogen-Containing Heterocycles

6 Synthesis via Formal [3+2] Cycloaddition

7 Synthesis of Miscellaneous Scaffolds

8 Conclusion

Synthesis, Anticancer Activity and Molecular Docking Studies of Novel N-Mannich Bases of 1,3,4-Oxadiazole Based on 4,6-Dimethylpyridine Scaffold

Cancer is one of the greatest challenges in modern medicine today. Difficult and long-term treatment, the many side effects of the drugs used and the growing resistance to treatment of neoplastic cells necessitate new approaches to therapy. A very promising targeted therapy is based on direct impact only on cancer cells. As a continuation of our research on new biologically active molecules, we report herein the design, synthesis and anticancer evaluation of a new series of N-Mannich-base-type hybrid compounds containing morfoline or different substituted piperazines moieties, a 1,3,4-oxadiazole ring and a 4,6-dimethylpyridine core. All compounds were tested for their potential cytotoxicity against five human cancer cell lines, A375, C32, SNB-19, MCF-7/WT and MCF-7/DX. Two of the active N-Mannich bases (compounds 5 and 6) were further evaluated for growth inhibition effects in melanoma (A375 and C32), and normal (HaCaT) cell lines using clonogenic assay and a population doubling time test. The apoptosis was determined with the neutral version of comet assay. The confocal microscopy method enabled the visualization of F-actin reorganization. The obtained results demonstrated that compounds 5 and 6 have cytotoxic and proapoptotic effects on melanoma cells and are capable of inducing F-actin depolarization in a dose-dependent manner. Moreover, computational chemistry approaches, molecular docking and electrostatic potential were employed to study non-covalent interactions of the investigated compounds with four receptors. It was found that all the examined molecules exhibit a similar binding affinity with respect to the chosen reference drugs.

A One-Pot Synthesis-Functionalization Strategy for Streamlined Access to 2,5-Disubstituted 1,3,4-Oxadiazoles from Carboxylic Acids

A one-pot 1,3,4-oxadiazole synthesis-arylation strategy for accessing 2,5-disubstituted 1,3,4-oxadiazoles, from carboxylic acids, N-isocyaniminotriphenylphosphorane (NIITP), and aryl iodides, is reported. The reaction sequence, featuring a second stage copper-catalyzed 1,3,4-oxadiazole arylation, was found to tolerate (hetero)aryl, alkyl, and alkenyl carboxylic acids, and (hetero)aryl iodide coupling partners. The effectiveness of the two-stage strategy was exemplified by the late-stage functionalization of five carboxylic acid-containing APIs, and an extension to the synthesis of aminated 1,3,4-oxadiazoles using N-benzoyloxy amine coupling partners was also demonstrated.

α-Glucosidase and α-Amylase Inhibitory Potentials of Quinoline-1,3,4-oxadiazole Conjugates Bearing 1,2,3-Triazole with Antioxidant Activity, Kinetic Studies, and Computational Validation

Diabetes mellitus (DM) is a multifaceted metabolic disorder that remains a major threat to global health security. Sadly, the clinical relevance of available drugs is burdened with an upsurge in adverse effects; hence, inhibiting the carbohydrate-hydrolyzing enzymes α-glucosidase and α-amylase while preventing oxidative stress is deemed a practicable strategy for regulating postprandial glucose levels in DM patients. We report herein the α-glucosidase and α-amylase inhibition and antioxidant profile of quinoline hybrids 4a–t and 12a–t bearing 1,3,4-oxadiazole and 1,2,3-triazole cores, respectively. Overall, compound 4i with a bromopentyl sidechain exhibited the strongest α-glucosidase inhibition (IC₅₀ = 15.85 µM) relative to reference drug acarbose (IC₅₀ = 17.85 µM) and the best antioxidant profile in FRAP, DPPH, and NO scavenging assays. Compounds 4a and 12g also emerged as the most potent NO scavengers (IC₅₀ = 2.67 and 3.01 µM, respectively) compared to gallic acid (IC₅₀ = 728.68 µM), while notable α-glucosidase inhibition was observed for p-fluorobenzyl compound 4k (IC₅₀ = 23.69 µM) and phenyl-1,2,3-triazolyl compound 12k (IC₅₀ = 22.47 µM). Moreover, kinetic studies established the mode of α-glucosidase inhibition as non-competitive, thus classifying the quinoline hybrids as allosteric inhibitors. Molecular docking and molecular dynamics simulations then provided insights into the protein–ligand interaction profile and the stable complexation of promising hybrids at the allosteric site of α-glucosidase. These results showcase these compounds as worthy scaffolds for developing more potent α-glucosidase inhibitors with antioxidant activity for effective DM management.

Synthesis of 2-Imino-1,3,4-oxadiazolines from Acylhydrazides and Isothiocyanates via Aerobic Oxidation and a DMAP-Mediated Annulation Sequence

In this work, an efficient synthesis of 2-imino-1,3,4-oxadiazolines from acylhydrazides and isothiocyanates is described. In the presence of 4-dimethylaminopyridine (DMAP) and molecular oxygen, various 2-imino-1,3,4-oxadiazolines were produced in good to high yields. The developed method showed a broad substrate scope and was effective on the gram scale. On the basis of the mechanistic studies and previous literature, it was proposed that the mechanism consists of an aerobic oxidation of acylhydrazides facilitated by DMAP and isothiocyanates, followed by a DMAP-mediated annulation of the in situ generated acyldiazenes with isothiocyanates.

A Graphene Acid - TiO2 Nanohybrid as Multifunctional Heterogeneous Photocatalyst for the Synthesis of 1,3,4-Oxadiazoles

The immobilization of TiO₂ nanoparticles on graphene acid (GA), a conductive graphene derivative densely functionalized with COOH groups, is presented. The interaction between the carboxyl groups of the surface and the titanium precursor leads to a controlled TiO₂ heterogenization on the nanosheet according to microscopic and spectroscopic characterizations. Electronic communication shared among graphene and semiconductor nanoparticles shifts the hybrid material optical features toward less energetic radiation but maintaining the conductivity. Therefore, GA-TiO₂ is employed as heterogeneous photocatalyst for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles using ketoacids and hydrazides as substrates. The material presented enhanced photoactivity compared to bare TiO₂, being able to yield a large structural variety of oxadiazoles in reaction times as fast as 1 h with full recyclability and stability. The carbocatalytic character of GA is the responsible for the substrates condensation and the GA-TiO₂ light interaction ability is able to photocatalyze the cyclization to the final 1,3,4-oxadiazoles, demonstrating the optimal performance of this multifunctional photocatalytic material.

Synthesis and Biological Evaluation of Novel Phthalide Analogs-1,2,4-Oxadiazole Hybrids as Potential Anti-Inflammatory Agents

A series of novel pathalide-1,2,4-oxadiazole analogs were synthesized for discovering novel anti-inflammatory agents. After the assessment of their cytotoxicity in vitro, all compounds had been screened for their anti-inflammatory activity by evaluating their inhibitory effect on LPS-induced NO production in RAW 264.7 macrophages. SARs had been concluded, and finally compound E13 was found to be the most potent compound. This compound could also significantly decrease the production of iNOS and COX-2. Preliminary mechanism studies indicated that compound E13 could inhibit the TLR4/NF-κB and ERK/p38 signaling pathways. These findings indicate that E13 holds great potential to be a lead compound for discovering novel anti-inflammatory drugs.

Topologically Driven Pore/Surface Engineering in a Recyclable Microporous Metal-Organic Vessel Decorated with Hydrogen-Bond Acceptors for Solvent-Free Heterogeneous Catalysis

The use of metal-organic frameworks (MOFs) comprising custom-designed linkers/ligands as efficient and recyclable heterogeneous catalysts is on the rise. However, the topologically driven bifunctional porous MOFs for showcasing a synergistic effect of two distinct activation pathways of substrates (e.g., involving hydrogen bonding and a Lewis acid) in multicomponent organic transformations are very challenging. In particular, the novelty of such studies lies in the proper pore and/or surface engineering in MOFs for bringing the substrates in close proximity to understand the mechanistic aspects at the molecular level. This work represents the topological design, solid-state structural characterization, and catalytic behavior of an oxadiazole tetracarboxylate-based microporous three-dimensional (3D) metal-organic framework (MOF), {[Zn₂(oxdia)(4,4'-bpy)₂]·8.5H₂O}_n (1), where the tetrapodal (4-connected) 5,5'-(1,3,4-oxadiazole-2,5-diyl)diisophthalate (oxdia^4-), the tetrahedral metal vertex (Zn(II)), and a 2-connected pillar linker 4,4'-bipyridine (4,4'-bpy) are unique in their roles for the formation, stability, and function. As a proof of concept, the efficient utilization of both the oxadiazole moiety with an ability to provide H-bond acceptors and the coordinatively unsaturated Zn(II) centers in 1 is demonstrated for the catalytic process of the one-pot multicomponent Biginelli reaction under mild conditions and without a solvent. The key steps of substrate binding with the oxadiazole moiety are ascertained by a fluorescence experiment, demonstrating a decrease or increase in the emission intensity upon interaction with the substrates. Furthermore, the inherent polarizability of the oxadiazole moiety is exploited for CO₂ capture and its size-selective chemical fixation to cyclic carbonates at room temperature and under solvent-free conditions. For both catalytic processes, the chemical stability, structural integrity, heterogeneity, versatility in terms of substrate scope, and mechanistic insights are discussed. Interestingly, the first catalytic process occurs on the surface, while the second reaction occurs inside the pore. This study opens new ways to catalyze different organic transformation reactions by utilizing this docking strategy to bring the multiple components close together by a microporous MOF.

Discovery of BMS-986339, a Pharmacologically Differentiated Farnesoid X Receptor Agonist for the Treatment of Nonalcoholic Steatohepatitis

While several farnesoid X receptor (FXR) agonists under clinical investigation for the treatment of nonalcoholic steatohepatitis (NASH) have shown beneficial effects, adverse effects such as pruritus and elevation of plasma lipids have limited their clinical efficacy and approvability. Herein, we report the discovery and preclinical evaluation of compound 32 (BMS-986339), a nonbile acid FXR agonist with a pharmacologically distinct profile relative to our previously reported agonist BMS-986318. Compound 32 exhibited potent in vitro and in vivo activation of FXR, albeit with a context-dependent profile that resulted in tissue-selective effects in vivo. To our knowledge, this is the first report that demonstrates differential induction of Fgf15 in the liver and ileum by FXR agonists in vivo. Compound 32 demonstrated robust antifibrotic efficacy despite reduced activation of certain genes in the liver, suggesting that the additional pharmacology of BMS-986318 does not further benefit efficacy, possibly presenting an opportunity for reduced adverse effects. Further evaluation in humans is warranted to validate this hypothesis.

Potential Synthetic Routes and Metal-Ion Sensing Applications of 1,3,4-Oxadiazoles: An Integrative Review

Oxadiazoles, especially 1,3,4-oxadiazole scaffolds, stand among the foremost heterocyclic fragments with a broad spectrum of applications in diverse fields, including pharmacology, polymers, material science, and organic electronics, among others. In this comprehensive review, we summarize the pivotal synthetic strategies for 1,3,4-oxadiazole derivatives including dehydrogenative cyclization of 1,2-diacylhydrazines, oxidative cyclization of acylhydrazones, condensation cyclization, C-H activation of oxadiazole ring, decarboxylative cyclization and oxidative annulation along with plausible mechanisms. The set of 1,3,4-oxadiazoles selected from the literature and discussed herein epitomize the ease of synthesis as well as the possibility of linking π-conjugated groups; thereby encouraging the use of these molecules as important starting building blocks for a wide variety of fluorescent frameworks, particularly in the development of potential chemosensors. High photoluminescent quantum yield, excellent thermal and chemical stability, and the presence of potential coordination (N and O donor atoms) sites make these molecules a prominent choice for metal-ions sensors. An overview of selective metal-ion sensing, the detection limit along with the sensing mechanisms (photo-induced electron transfer, excited-state intramolecular proton transfer, and complex formation) is also included.

Synthesis, Molecular Docking and Evaluation of 1,3,4-Oxadiazole-Isobenzofuran Hybrids as Antimicrobial and Anticancer Agents

In drug discovery, the hybridization of bioactive pharmacophores is a powerful tool for targeting enzymes involved in cancer and microbial cell growth. A combination of 1,3,4-oxadiazole and isobenzofuran may improve the antitumor and antimicrobial properties of the hybrid molecules. A series of hybrid molecules having 1,3,4-oxadiazole and isobenzofuran were synthesized and structural characterization was done by FT-IR, ¹ H-NMR, ¹³ C-NMR, and mass spectrometry. Molecular docking studies were performed to investigate binding interactions of compounds with proteins (PDB NO: 2R3J and 1GII), and the results were consistent with in vitro anticancer data. All the synthesized compounds were tested for antimicrobial activity against S. aureus, E. faecalis (Gram-positive) and E. coli and P. aeruginosa (Gram-negative) bacterial strains. Among the synthesized compounds, 7a and 7b displayed good activity against the tested bacterial strains. Also, compounds were tested for their anti-tumor activity against breast cancer (MCF-7) and colon cancer (HCT-116) cell lines via SRB assay. In comparison to doxorubicin (1.14 μM), hybrids 7e (4.32 μM), 7f (4.15 μM), 7g (4.66 μM), and 7h (4.83 μM) demonstrated comparable IC₅₀ value against the HCT 116 cell line.

Comparative Study of the Synthetic Approaches and Biological Activities of the Bioisosteres of 1,3,4-Oxadiazoles and 1,3,4-Thiadiazoles over the Past Decade

The bioisosteres of 1,3,4-oxadiazoles and 1,3,4-thiadiazoles are well-known pharmacophores for many medicinally important drugs. Throughout the past 10 years, 1,3,4-oxa-/thiadiazole nuclei have been very attractive to researchers for drug design, synthesis, and the study of their potential activity towards a variety of diseases, including microbial and viral infections, cancer, diabetes, pain, and inflammation. This work is an up-to-date comparative study that identifies the differences between 1,3,4-thiadiazoles and 1,3,4-oxadiazoles concerning their methods of synthesis from different classes of starting compounds under various reaction conditions, as well as their biological activities and structure–activity relationship.

Subtle Ligand Spacer Change in 2D Metal-Organic Framework Sheets for Dual Turn-On/Turn-Off Sensing of Acetylacetone and Turn-On Sensing of Water in Organic Solvents

Metal-organic framework (MOF)-based sensors for the detection of various analyte molecules has been a subject of absolute importance. However, most of these sensors rely on the turn-off (quenching) transduction response, while those reporting turn-on response are very rare. In this article, we have synthesized two new MOF-based sensors, {[Zn₂(oxdz)₂(tpbn)]·14H₂O}_n (1) and {[Zn₂(oxdz)₂(tpxn)]·10H₂O·2C₂H₅OH}_n (2), via the self-assembly of Zn(II) metal ions, a fluorogenic oxdz^2- linker, and bis(tridentate) ligands (tpbn and tpxn) under ambient conditions. Their formation from such a self-assembly process has been evaluated on the basis of the geometry around the five-coordinated Zn(II), preferential meridional binding of the bis(tridentate) ligands, and diverse binding of the carboxylate groups in oxdz^2-. Although 1 and 2 are isostructural, a difference in the transduction mechanism for the sensing of acetylacetone in organic solvents (turn-on for 1 and turn-off for 2) is observed and can be attributed to the spacer in the bis(tridentate) ligands. We have demonstrated the competing effect of the nonradiative interactions and photoinduced electron transfer toward the sensing mechanism. The results are well-supported by the Fourier transform infrared spectroscopy study, intensity versus concentration plots, spectral overlap measurements, time-resolved fluorescence studies, and MM2 and density functional theory calculations. Furthermore, we have showcased the utilization of 1 for the sensing of trace amounts of water in organic solvents.

Cytotoxic effect, enzyme inhibition, and in silico studies of some novel N-substituted sulfonyl amides incorporating 1,3,4-oxadiazol structural motif

Abstract

The acetylcholinesterase and carbonic anhydrase inhibitors (AChEIs and hCAIs) remain key therapeutic agents for many bioactivities such as anti-Alzheimer and antiobesity antiepileptic, anticancer, antiinfective, antiglaucoma, and diuretic effects. Here, it has been attempted to discover novel multi-target AChEIs and hCAIs that are highly potent, orally bioavailable, may be brain penetrant, and have higher effectiveness at lower doses than tacrine and acetazolamide. After detailed investigations both in vitro and in silico, novel N-substituted sulfonyl amide derivatives (6a–j) were determined to be highly potent inhibitors for AChE and hCAs (K_Is are in the range of 23.11–52.49 nM, 18.66–59.62 nM, and 9.33–120.80 nM for AChE, hCA I, and hCA II, respectively). Moreover, according to the cytotoxic effect studies, such as the ADME-Tox, cortex neuron cells, and neuroblastoma SH-SY5Y cell line, compounds 6a, 6d, and 6h, which are the most potent representative versus the target enzymes, were identified as orally bioavailable, highly selective, and brain preferentially distributed AChEIs and hCAIs. The docking studies revealed precise binding modes between 6a, 6d, and 6h and hCA II, hCA I, and AChE, respectively. The results presented here might provide a solid basis for further investigation into more potent AChEIs and hCAIs.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11030-022-10422-8.

Synthesis of ponatinib analogues as novel inhibitors of leukemia stem cells

Aim: To synthesize new analogues of ponatinib and evaluate anti-leukemia cells and cytotoxicity. Methodology & results: The inhibitory activity of compounds 13a and 13c against K562 and HL60 cells was comparable to that of ponatinib (IC₅₀ = 0.74, 0.88 vs 0.64 nM and 0.59, 0.77 vs 0.39 nM, respectively). Compounds 13a and 40b were 34- and 77-fold more potent than ponatinib against KG1a cells (IC₅₀ = 0.091 and 0040 vs 3.6 μM, respectively). Compounds 13a, 13c and 40b also decreased the Abl protein level in the K562 cells, inhibited colony formation in MCF-7 cells and inhibited cell migration in B16BL6 cells. Compound 13a showed low cytotoxicity in 293 cells. Conclusion: Compound 13a was the best lead compound.

5-Aryl-1,3,4-oxadiazol-2-amines Decorated with Long Alkyl and Their Analogues: Synthesis, Acetyl- and Butyrylcholinesterase Inhibition and Docking Study

2,5-Disubstituted 1,3,4-oxadiazoles are privileged versatile scaffolds in medicinal chemistry that have exhibited diverse biological activities. Acetyl- (AChE) and butyrylcholinesterase (BChE) inhibitors are used, e.g., to treat dementias and myasthenia gravis. 5-Aryl-1,3,4-oxadiazoles decorated with dodecyl linked via nitrogen, sulfur or directly to this heterocycle have been designed as potential inhibitors of AChE and BChE. They were prepared from commercially available or in-house prepared hydrazides by reaction with dodecyl isocyanate to form hydrazine-1-carboxamides 2 (yields 67–98%) followed by cyclization using p-toluenesulfonyl chloride and triethylamine in 41–100% yields. Thiadiazole isostere was also synthesized. The derivatives were screened for inhibition of AChE and BChE using Ellman’s spectrophotometric method. The compounds showed a moderate dual inhibition with IC₅₀ values of 12.8–99.2 for AChE and from 53.1 µM for BChE. All the heterocycles were more efficient inhibitors of AChE. The most potent inhibitor, N-dodecyl-5-(pyridin-4-yl)-1,3,4-thiadiazol-2-amine 3t, was subjected to advanced reversibility and type of inhibition evaluation. Structure–activity relationships were identified. Many oxadiazoles showed lower IC₅₀ values against AChE than established drug rivastigmine. According to molecular docking, the compounds interact non-covalently with AChE and BChE and block entry into enzyme gorge and catalytic site, respectively.

A Water Soluble 2-Phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazole Based Probe: Antimicrobial Activity and Colorimetric/Fluorescence pH Response

The growing demand of responsive tools for biological and biomedical applications pushes towards new low-cost probes easy to synthesize and versatile. Current optical probes are theranostic tools simultaneously responsive to biological parameters/analyte and therapeutically operating. Among the optical methods for pH monitoring, simple small organic molecules including multifunctional probes for simultaneous biological activity being highly desired by scientists and technicians. Here, we present a novel pH-responsive probe with a three-ring heteroaromatic pattern and a flexible cationic chain. The novel molecule shows real-time naked-eye colorimetric and fluorescence response in the slightly acidic pH range besides its excellent solubility both in the organic phase and in water. In addition, the small probe shows significant antibacterial activity, particularly against Escherichia coli. Single-crystal X-ray study and density functional theory (DFT) calculations rationalize the molecule spectroscopic response. Finally, molecular dynamics (MD) elucidate the interactions between the probe and a model cell membrane.

Mechanochemical Synthesis of 2,5-Disubstituted 1,3,4-Oxadiazoles Mediated by PPh3-TCCA

Mechanochemical synthesis of 2,5-disubstituted 1,3,4-oxadiazoles was developed as an environmentally benign alternative to conventional solvent-based methods. In the presence of triphenylphosphine and trichloroisocyanuric acid, N-acylbenzotriazoles condense with acylhydrazides leading to oxadiazoles derivatives in good to excellent yields within minutes. The approach circumvents the need for strictly anhydrous conditions, external heating, long reaction times, as well as tedious multistep procedures. A range of substrates with reactive functionalities was also well tolerated.

Oxadiazol-based mTOR inhibitors with potent antiproliferative activities: synthetic and computational modeling

Series of N-aryl-1,3,4-oxadiazole-2-amines and 3-aryl-1,2,4-oxadiazole-5-carboxamides derivatives were synthesized as novel chemotherapeutic agents. Synthesized compounds were evaluated for their anticancer activities against several cancer cell lines. Many analogues of 1,3,4-oxadiazole scaffold showed potent antiproliferative activities against breast cancer cell lines, with higher activities toward the metastatic breast cancer cell line (MDA-MB-231). Active analogues were profiled using in-house pharmacophore database in search for molecular target. Active analogues (2j and 2k) were found to fit the pharmacophoric map of ATP-competitive inhibitors of mTOR. The mTOR inhibitory activities of the most active compounds were confirmed with IC₅₀ values in nanomolar range. The N-aryl-1,3,4-oxadiazole-2-amines linked to a basic head is a novel ATP-competitive inhibitors of mTOR with potential activities for treatment of different types of cancer.

A review on synthetic account of 1,2,4-oxadiazoles as anti-infective agents

Most of the currently marketed drugs consist of heterocyclic scaffolds containing nitrogen and or oxygen as heteroatoms in their structures. Several research groups have synthesized diversely substituted 1,2,4-oxadiazoles as anti-infective agents having anti-bacterial, anti-viral, anti-leishmanial, etc. activities. For the first time, the present review article will provide the coverage of synthetic account of 1,2,4-oxadiazoles as anti-infective agents along with their potential for SAR, activity potential, promising target for mode of action. The efforts have been made to provide the chemical intuitions to the reader to design new chemical entity with potential of anti-infective activity. This review will mark the impact as the valuable, comprehensive and pioneered work along with the library of synthetic strategies for the organic and medicinal chemists for further refinement of 1,2,4-oxadiazole as anti-infective agents.

Ni (II) detection by 2-amino-5-substituted-1,3,4-oxadiazole as a chemosensor using photo-physical method: Antifungal, antioxidant, DNA binding, and molecular docking studies

An oxadiazole derivative 2 was prepared by condensation reaction through cyclization of semicarbazone in the presence of bromine and the structural confirmation was supported by ¹ H and ¹³ C NMR, FT-IR spectroscopy, and LC-MS spectrometry. Its sensing ability was examined towards Ni²⁺ ion with binding constant 1.04 x 10⁵ over the other suitable metal cations (Ca²⁺ , Co²⁺ , Cr³⁺ , Ag⁺ , Pb²⁺ , Fe³⁺ , Mg²⁺ , and K⁺ ) by UV-visible and fluorescence spectroscopic studies and the minimum concentration of Ni²⁺ ion with LOD was found to be 9.4μM. Job's plot method gives the binding stoichiometry ratio of Ni²⁺ ion vs oxadiazole derivative 2 to be 2:1. Furthermore, the intercalative binding mode of oxadiazole derivative 2 with Calf Thymus DNA was supported by UV-Vis, fluorescence, viscosity, cyclic voltammetry, time-resolved fluorescence, and circular dichroism measurements. The molecular docking result gives the binding score for oxadiazole derivative 2 to be -6.5 kcal/mol, which further confirms the intercalative interaction. In addition, the anti-fungal activity of oxadiazole derivative 2 was also screened against fungal strains (C. albicans, C. glabrata, and C. tropicalis) by broth dilution and disc diffusion method. In the antioxidant studies, the oxadiazole derivative 2 showed potential scavenging activity against DPPH and H₂ O₂ free radicals.

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.

Recent updates on Synthetic Strategies and Biological Potential of 1,3,4-oxadiazole: Review

Abstract:

Among the large variety of nitrogen and oxygen-containing heterocycles, 1,3,4-oxadiazole, the scaffold, has attracted considerable attention owing to its ability to show an extensive range of pharmacological actions. According to literature investigations, prepared 1,3,4-oxadiazole and its derivative are pharmacologically significant and consist of a variety of activities, such as anticonvulsant, anticancer, antioxidant, anti-inflammatory, antibacterial, antidiabetic, etc. These heterocyclics are formed mainly by the cyclization reactions of various reactants under diverse reaction circumstances. Therefore, significant efforts of organic chemists have been directed towards the synthesis of new drug candidates containing 1,3,4-oxadiazole subunits connected to an established potential pharmacophore to improve the efficacy and potency. This article aims to highlight recent publications on the various synthesis techniques of 1,3,4-oxadiazole and related compounds over the previous ten years (2011–2021). The purpose of this review is to help researchers by summarizing several synthetic strategies for synthesizing oxadiazole.

SET activation of nitroarenes by 2-azaallyl anions as a straightforward access to 2,5-dihydro-1,2,4-oxadiazoles

The use of nitroarenes as amino sources in synthesis is challenging. Herein is reported an unusual, straightforward, and transition metal-free method for the net [3 + 2]-cycloaddition reaction of 2-azaallyl anions with nitroarenes. The products of this reaction are diverse 2,5-dihydro-1,2,4-oxadiazoles (>40 examples, up to 95% yield). This method does not require an external reductant to reduce nitroarenes, nor does it employ nitrosoarenes, which are often used in N-O cycloadditions. Instead, it is proposed that the 2-azaallyl anions, which behave as super electron donors (SEDs), deliver an electron to the nitroarene to generate a nitroarene radical anion. A downstream 2-azaallyl radical coupling with a newly formed nitrosoarene is followed by ring closure to afford the observed products. This proposed reaction pathway is supported by computational studies and experimental evidence. Overall, this method uses readily available materials, is green, and exhibits a broad scope.

Visible-Light Photocatalytic Ugi/Aza-Wittig Cascade towards 2-Aminomethyl-1,3,4-oxadiazole Derivatives

A new visible-light photocatalytic multicomponent reaction (MCR) involving N-alkyl-N-methylanilines, N-isocyanoiminotriphenylphosphorane, and carboxylic acids leading to 1,3,4-oxadiazole derivatives is reported. The developed mild reaction conditions enable a broad substrate scope and good functional group tolerance, as further highlighted in the late-stage functionalization of amino acids and drugs. Additionally, a two-step one-pot protocol for the synthesis of non-symmetrical diacylhydrazines is also reported.

Synthesis of 1,3,4-Oxadiazoles by Iodine-Mediated Oxidative Cyclization of Methyl Ketones with 4-Phenylsemicarbazide

An efficient one-pot method has been developed to access 5-amino-2-(het)aroyl-1,3,4-oxadiazoles through I2/DMSO-promoted oxidative cyclization of 4-phenylsemicarbazide with (het)aryl methyl ketones under mild conditions. This reaction proceeds smoothly with a wide range of methyl ketones containing various functional groups to give the corresponding products in moderate yields under mild conditions.

Ammonium Formate-Pd/C as a New Reducing System for 1,2,4-Oxadiazoles. Synthesis of Guanidine Derivatives and Reductive Rearrangement to Quinazolin-4-Ones with Potential Anti-Diabetic Activity

1,2,4-Oxadiazole is a heterocycle with wide reactivity and many useful applications. The reactive O-N bond is usually reduced using molecular hydrogen to obtain amidine derivatives. NH4CO2H-Pd/C is here demonstrated as a new system for the O-N reduction, allowing us to obtain differently substituted acylamidine, acylguanidine and diacylguanidine derivatives. The proposed system is also effective for the achievement of a reductive rearrangement of 5-(2'-aminophenyl)-1,2,4-oxadiazoles into 1-alkylquinazolin-4(1H)-ones. The alkaloid glycosine was also obtained with this method. The obtained compounds were preliminarily tested for their biological activity in terms of their cytotoxicity, induced oxidative stress, α-glucosidase and DPP4 inhibition, showing potential application as anti-diabetics.

Development of Potent 3-Br-isoxazoline-Based Antimalarial and Antileishmanial Compounds

Starting from the structure of previously reported 3-Br-isoxazoline-based covalent inhibitors of P. falciparum glyceraldehyde 3-phosphate dehydrogenase, and with the intent to improve their metabolic stability and antimalarial activity, we designed and synthesized a series of simplified analogues that are characterized by the insertion of the oxadiazole ring as a bioisosteric replacement for the metabolically labile ester/amide function. We then further replaced the oxadiazole ring with a series of five-membered heterocycles and finally combined the most promising structural features. All the new derivatives were tested in vitro for antimalarial as well as antileishmanial activity. We identified two very promising new lead compounds, endowed with submicromolar antileishmanial activity and nanomolar antiplasmodial activity, respectively, and a very high selectivity index with respect to mammalian cells.

A Three-Component Ugi-Type Reaction of N-Carbamoyl Imines Enables a Broad Scope Primary α-Amino 1,3,4-Oxadiazole Synthesis

A general synthesis of N-protected primary α-amino 1,3,4-oxadiazoles, from N-carbamoyl imines, N-isocyaniminotriphenylphosphorane (NIITP), and carboxylic acids, is described. Featuring an isocyanide addition reaction with N-carbamoyl imines, this efficient three-component Ugi-type reaction was found to be broad in scope with respect to imine, and carboxylic acid coupling partners. Furthermore, the versatility of this method was demonstrated by α-amino 1,2,4-triazole synthesis, the late-stage functionalization of seven drug molecules, and five divergent derivatizations of a primary α-amino 1,3,4-oxadiazole.