Design, synthesis, and biological activity of novel 1,2,4-oxadiazole derivatives

1,2,4-Oxadiazole as a potential scaffold in agrochemistry: a review

N,O-containing heterocycles have been incorporated into various approved pesticides and pesticide candidates. The persistent challenge in contemporary crop protection lies in the continuous pursuit of novel N,O-heterocycle-containing compounds with pesticidal properties. Among them, the 1,2,4-oxadiazole scaffold is one of the most extensively explored heterocycles in new pesticide discovery and development. This review focuses on elucidating the molecular design strategy employed along with highlighting the bioactivity of 1,2,4-oxadiazole derivatives since 2012. Throughout this time frame, tioxazafen and flufenoxadiazam have emerged as prominent examples in which 1,2,4-oxadiazole derivatives were utilized as the core active structure within numerous applications. Additionally, the preparation methods for substituted 1,2,4-oxadiazole derivatives are elaborated upon, and their potential value within agrochemistry is discussed.

Heterocyclic Compounds as Dipeptidyl Peptidase-IV Inhibitors with Special Emphasis on Oxadiazoles as Potent Anti-Diabetic Agents

Dipeptidyl peptidase-IV (DPP-IV) inhibitors, often known as gliptins, have been used to treat type 2 diabetes mellitus (T2DM). They may be combined with other medications as an additional treatment or used alone as a monotherapy. In addition to insulin, sulfonylureas, thiazolidinediones, and metformin, these molecules appear as possible therapeutic options. Oxadiazole rings have been employed in numerous different ways during drug development efforts. It has been shown that including them in the pharmacophore increases the amount of ligand that may be bound. The exceptional hydrogen bond acceptor properties of oxadiazoles and the distinct hydrocarbon bonding potential of their regioisomers have been established. Beside their anti-diabetic effects, oxadiazoles display a wide range of pharmacological properties. In this study, we made the assumption that molecules containing oxadiazole rings may afford a different approach to the treatment of diabetes, not only for controlling glycemic levels but also for preventing atherosclerosis progression and other complications associated with diabetes. It was observed that oxadiazole fusion with benzothiazole, 5-(2,5,2-trifluoroethoxy) phenyl, β-homophenylalanine, 2-methyl-2-{5-(4-chlorophenyl), diamine-bridged bis-coumarinyl, 5-aryl-2-(6′-nitrobenzofuran-2′-yl), nitrobenzofuran, and/or oxindole leads to potential anti-diabetic activity.

Design, Synthesis, and Biological Activity of Novel Chalcone Derivatives Containing an 1,2,4-Oxadiazole Moiety

To discover a lead compound for agricultural use, 34 novel chalcone derivatives containing an 1,2,4-oxadiazole moiety were designed and synthesized. Their nematocidal activities against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus dipsaci and their antiviral activities against tobacco mosaic virus (TMV), pepper mild mottle virus (PMMoV), and tomato spotted wilt virus (TSWV) were evaluated. Biological assay results indicate that compounds A13 and A14 showed good nematocidal activities against B. xylophilus, A. besseyi, and D. dipsaci, with LC₅₀ values of 35.5, 44.7, and 30.2 μg/ml and 31.8, 47.4, and 36.5 μg/ml, respectively, which are better than tioxazafen, fosthiazate, and abamectin. Furthermore, compound A16 demonstrated excellent protective activity against TMV, PMMoV, and TSWV, with EC₅₀ values of 210.4, 156.2, and 178.2 μg/ml, respectively, which are superior to ningnanmycin (242.6, 218.4, and 180.5 μg/ml).

Design, synthesis, and bioactivity of ferulic acid derivatives containing an β-amino alcohol

Background

Plant diseases caused by viruses and bacteria cause huge economic losses due to the lack of effective control agents. New potential pesticides can be discovered through biomimetic synthesis and structural modification of natural products. A series of ferulic acid derivatives containing an β-amino alcohol were designed and synthesized, and their biological activities were evaluated.

Result

Bioassays results showed that the EC₅₀ values of compound D24 against Xanthomonas oryzae pv. oryzae (Xoo) was 14.5 μg/mL, which was better than that of bismerthiazol (BT, EC₅₀ = 16.2 μg/mL) and thiodiazole copper (TC, EC₅₀ = 44.5 μg/mL). The in vivo curative and protective activities of compound D24 against Xoo were 50.5% and 50.1%, respectively. The inactivation activities of compounds D2, D3 and D4 against tobacco mosaic virus (TMV) at 500 μg/mL were 89.1, 93.7 and 89.5%, respectively, superior to ningnanmycin (93.2%) and ribavirin (73.5%). In particular, the EC₅₀ value of compound D3 was 38.1 μg/mL, and its molecular docking results showed that compound D3 had a strong affinity for TMV-CP with a binding energy of − 7.54 kcal/mol, which was superior to that of ningnanmycin (− 6.88 kcal /mol).

Conclusions

The preliminary mechanism research results indicated that compound D3 may disrupt the three-dimensional structure of the TMV coat protein, making TMV particles unable to self-assemble, which may provide potential lead compounds for the discovery of novel plant antiviral agents.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13065-022-00828-8.

Design, Synthesis and Antifungal/Nematicidal Activity of Novel 1,2,4-Oxadiazole Derivatives Containing Amide Fragments

Plant diseases that are caused by fungi and nematodes have become increasingly serious in recent years. However, there are few pesticide chemicals that can be used for the joint control of fungi and nematodes on the market. To solve this problem, a series of novel 1,2,4-oxadiazole derivatives containing amide fragments were designed and synthesized. Additionally, the bioassays revealed that the compound F15 demonstrated excellent antifungal activity against Sclerotinia sclerotiorum (S. sclerotiorum) in vitro, and the EC₅₀ value of that was 2.9 μg/mL, which is comparable with commonly used fungicides thifluzamide and fluopyram. Meanwhile, F15 demonstrated excellent curative and protective activity against S. sclerotiorum-infected cole in vivo. The scanning electron microscopy results showed that the hyphae of S. sclerotiorum treated with F15 became abnormally collapsed and shriveled, thereby inhibiting the growth of the hyphae. Furthermore, F15 exhibited favorable inhibition against the succinate dehydrogenase (SDH) of the S. sclerotiorum (IC₅₀ = 12.5 μg/mL), and the combination mode and binding ability between compound F15 and SDH were confirmed by molecular docking. In addition, compound F11 showed excellent nematicidal activity against Meloidogyne incognita at 200 μg/mL, the corrected mortality rate was 93.2%, which is higher than that of tioxazafen.

Fabrication of Host-Guest Complexes between Adamantane-Functionalized 1,3,4-Oxadiazoles and β-Cyclodextrin with Improved Control Efficiency against Intractable Plant Bacterial Diseases

Supramolecular chemistry provides huge potentials and opportunities in agricultural pest management. In an attempt to develop highly bioactive, eco-friendly, and biocompatible supramolecular complexes for managing intractable plant bacterial diseases, herein, a type of interesting adamantane-functionalized 1,3,4-oxadiazole was rationally prepared to facilitate the formation of supramolecular complexes via β-cyclodextrin-adamantane host-guest interactions. Initial antibacterial screening revealed that most of these adamantane-decorated 1,3,4-oxadiazoles were obviously bioactive against three typically destructive phytopathogens. The lowest EC₅₀ values could reach 0.936 (III₁₈), 0.889 (III₁₈), and 2.10 (III₁₉) μg/mL against the corresponding Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and Pseudomonas syringae pv. actinidiae (Psa). Next, the representative supramolecular binary complex III₁₈@β-CD (binding mode 1:1) was successfully fabricated and characterized by ¹H nuclear magnetic resonance (NMR), isothermal titration calorimetry (ITC), high-resolution mass spectrometry (HRMS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Eventually, correlative water solubility and foliar surface wettability were significantly improved after the formation of host-guest assemblies. In vivo antibacterial evaluation found that the achieved supramolecular complex could distinctly alleviate the disease symptoms and promote the control efficiencies against rice bacterial blight (from 34.6-35.7% (III₁₈) to 40.3-43.6% (III₁₈@β-CD)) and kiwi canker diseases (from 41.0-42.3% (III₁₈) to 53.9-68.0% (III₁₈@β-CD)) at 200 μg/mL (active ingredient). The current study can provide a feasible platform and insight for constructing biocompatible supramolecular assemblies for managing destructive bacterial infections in agriculture.

Rational Optimization of 1,2,3-Triazole-Tailored Carbazoles As Prospective Antibacterial Alternatives with Significant In Vivo Control Efficiency and Unique Mode of Action

Plant bacterial diseases can potentially damage agricultural products around the world, and few effective bactericides can manage these infections. Herein, to sequentially explore highly effective antibacterial alternatives, 1,2,3-triazole-tailored carbazoles were rationally fabricated. These compounds could suppress the growth of three main intractable pathogens including Xanthomonas oryzae pv oryzae (Xoo), X. axonopodis pv citri (Xac), and Pseudomonas syringae pv actinidiae (Psa) with lower EC₅₀ values of 3.36 (3p), 2.87 (3p), and 4.57 μg/mL (3r), respectively. Pot experiments revealed that compound 3p could control the rice bacterial blight with protective and curative efficiencies of 53.23% and 50.78% at 200 μg/mL, respectively. Interestingly, the addition of 0.1% auxiliaries such as organic silicon and orange oil could significantly enhance the surface wettability of compound 3p toward rice leaves, resulting in improved control effectiveness of 65.50% and 61.38%, respectively. Meanwhile, compound 3r could clearly reduce the white pyogenic exudates triggered by Psa infection and afforded excellent control efficiencies of 79.42% (protective activity) and 78.74% (curative activity) at 200 μg/mL, which were quite better than those of commercial pesticide thiodiazole copper. Additionally, a plausible apoptosis mechanism for the antibacterial behavior of target compounds was proposed by flow cytometry, reactive oxygen species detection, and defensive enzyme (e.g., catalase and superoxide dismutase) activity assays. The current work can promote the development of 1,2,3-triazole-tailored carbazoles as prospective antibacterial alternatives bearing an intriguing mode of action.