Design, Synthesis, and Antifungal Evaluation of Novel Pyrazole-5-sulfonamide Derivatives for Plant Protection

To develop further novel environmentally friendly antifungal agents with high efficacy, a series of pyrazole-5-sulfonamide derivatives were designed and synthesized by using the active molecules synthesized in previous works as lead compounds. Their antifungal activities were evaluated in vitro against ten highly destructive plant pathogenic fungi. The bioassay results indicated that more than half of the target compounds displayed potent antifungal activities (inhibition rate ≥85%) against Valsa mali and Sclerotinia sclerotiorum at 20 mg/L. Among them, compound C22 exhibited significant broad-spectrum antifungal activities against V. mali, S. sclerotiorum, Rhizoctonia solani, Botrytis cinerea, and Trichoderma viride, with EC50 values of 0.45, 0.49, 3.06, 0.57, and 1.43 mg/L, respectively. Moreover, compounds C21 and C22 exhibited remarkable protective effects on apple Valsa canker similar to tebuconazole (89.5%) at 50 mg/L. Preliminary antifungal mechanism investigations demonstrated that compound C22 may have inhibited V. mali mycelial growth by inducing oxidative damage to the mycelium and compromising the integrity of the cell membrane. Meanwhile, compounds C21 and C22 exhibited no obvious toxicity to worker bees (Apis mellifera ligustica). Taken together, these pyrazole-5-sulfonamide derivatives, particularly compound C22, possess huge potential to be developed as novel environmentally friendly fungicides with high efficacy.

Comprehensive Overview of β-Methoxyacrylate Derivatives as Cytochrome bc1 Inhibitors for Novel Pesticide Discovery

β-Methoxyacrylate derivatives represent a new class of pesticides, which have attracted increasing attention owing to their unique structure, broad biological activity, and unique mechanisms of action. They inhibit mitochondrial respiration via preventing electron transfer at the Qo site of the cytochrome bc₁ complex and thus are identified as cyt bc₁ inhibitors. A variety of β-methoxyacrylate derivatives have been reported by many research groups for discovery of novel pesticides with improved expected activities. This review focuses on development of β-methoxyacrylate derivatives with great significance as pesticides such as fungicides, acaricides, insecticides, herbicides, and antiviral agents. In addition, the structure-activity relationships (SARs) of β-methoxyacrylate derivatives are summarized. Moreover, the cause of resistance to β-methoxyacrylate fungicides and some solutions are also introduced. Finally, the development trend of β-methoxyacrylate derivatives as pesticides is explored. We hope the review will give a guide to develop novel β-methoxyacrylate pesticides in the future.

Discovery of Novel Cytochrome bc1 Complex Inhibitor Based on Natural Product Neopeltolide

Background:

Natural products (NPs) are important sources for the design of new drugs and agrochemicals. Neopeltolide, a marine NP, has been identified as a potent Qo-site inhibitor of cytochrome bc1 complex.

Methods:

In this study, a series of neopeltolide derivatives was designed and synthesized by the simplification of its 14-membered macrolactone ring with a diphenyl ether fragment. The enzymatic inhibition bioassays and mycelium growth inhibition experiments against a range of fungi were performed to determine their fungicidal activities.

Results:

The derivatives have potent activity against the porcine bc1 complex. Compound 8q showed the best activity with an IC50 value of 24.41 nM, which was 8-fold more effective than that of positive control azoxystrobin. Compound 8a exhibited a 100% inhibitory rate against Zymoseptoria tritici and Alternaria solani at a 20 mg/L dose.

Conclusion:

Computational results indicated that compounds with suitable physicochemical properties, as well as those forming a hydrogen bond with His161, would have good fungicidal activity. These data could be useful for the design of bc1 complex inhibitors in the future.

Comprehensive Overview of Carboxamide Derivatives as Succinate Dehydrogenase Inhibitors

Up to now, a total of 24 succinate dehydrogenase inhibitors (SDHIs) fungicides have been commercialized, and SDHIs fungicides were also one of the most active fungicides developed in recent years. Carboxamide derivatives represented an important class of SDHIs with broad spectrum of antifungal activities. In this review, the development of carboxamide derivatives as SDHIs with great significances were summarized. In addition, the structure-activity relationships (SARs) of antifungal activities of carboxamide derivatives as SDHIs was also summarized based on the analysis of the structures of the commercial SDHIs and lead compounds. Moreover, the cause of resistance of SDHIs and some solutions were also introduced. Finally, the development trend of SDHIs fungicides was prospected. We hope this review will give a guide for the development of novel SDHIs fungicides in the future.

3,5-Diaryl substituted sclerotiorin: a novel scaffold of succinate-ubiquinone oxidoreductase inhibitors

Novel and potent inhibitors targeting succinate-ubiquinone oxidoreductase were discovered from the natural product sclerotiorin for the first time.

Discovery of a Fungicide Candidate Targeting Succinate Dehydrogenase via Computational Substitution Optimization

Succinate dehydrogenase (SDH, EC 1.3.5.1) has proven to be an important fungicidal target, and the inhibition of SDH is useful in the treatment of plant pathogens. The discovery of a novel active SDH inhibitor is of high value. Herein, we disclose the discovery of a potent, highly active inhibitor as a fungicide candidate by using a computational substitution optimization method, a fast drug design method developed in our laboratory. The greenhouse experiments showed that compound 17c exhibited high protective activity against south corn rust, soybean rust (SBR), and rice sheath blight at a very low dosage of 0.781 mg/L. Moreover, the field trials indicated that compound 17c is comparable to and even better than commercial fungicides against SBR and cucumber powdery mildew at 50 mg/L concentration. Most surprisingly, compound 17c resulted to be strictly better in curative activity than the commercial fungicide benzovindiflupyr. The computation results indicated that 17c could form another hydrogen bond with C_S42 and then lead to strong van der Waals and electronic interactions with SDH. Our results suggested that 17c is a potential fungicide candidate for SDH.

Synthesis of Myrtenal-Based Nanocellulose/Diacylhydrazine Complexes with Antifungal Activity for Plant Protection

In search of novel bioactive compounds with excellent and broad-spectrum antifungal activity and nanopesticides with sustained releasing property, a series of novel myrtenal-based diacylhydrazines were designed, synthesized, and characterized. The preliminary bioassay showed that myrtenal-based 2-picolinyl hydrazide exhibited better or comparable antifungal activity than that of the commercial fungicides boscalid and chlorothalonil against the tested fungi. Furthermore, myrtenal-based nanocellulose was designed as a nanopesticide carrier and prepared from two biomass materials, bleached bagasse pulp and turpentine oil. Drug-loading capacities (LCs) of these carriers and sustained releasing properties of corresponding complexes were also evaluated, and the results indicated that the esterification reaction in the different solvents would affect the micromorphology of carriers, which was the important influential factor for loading or releasing drugs. To our delight, complex VIII-3 (LC = 0.32, total releasing amount/time = 99.8%/168 h) showed a macroporous framework with the drug evenly distributed across the opening network and staged drug-releasing performance that deserved further study as a nanopesticide.

Design, Synthesis, and Antifungal Activity of Novel Longifolene-Derived Diacylhydrazine Compounds

Succinate dehydrogenase (SDH) present in the inner mitochondrial membrane is an important target enzyme for the design of SDH inhibitor-type fungicides. Using SDH as the target enzyme, 22 novel longifolene-derived diacylhydrazine compounds were designed and synthesized using the renewable natural product longifolene as the starting material. Their structures were confirmed by IR, ¹H NMR, ¹³C NMR, electrospray mass spectrometry, and elemental analysis. In vitro antifungal activity of the target compounds was preliminarily evaluated. As a result, some of them showed better or comparable antifungal activity than that of the commercial fungicide chlorothalonil, in which compound 5a had inhibitory rates of 97.5, 80.5, 72.1, and 67.1% against Physalospora piricola, Colletotrichum orbiculare, Alternaria solani, and Gibberella zeae, respectively, presenting excellent and broad-spectrum activity that deserved further study. Besides, a reasonable and effective three-dimensional structure-activity quantitative relationship model has been established. There was a significant positive correlation between the antifungal activity and the docking-based binding energy analyzed using Spearman's rank correlation algorithm. Also, the simulative binding pattern of the target compounds with SDH was investigated by molecular docking study. Furthermore, the diacylhydrazine and phenol groups of the target compounds were proposed to be the potential pharmacophores by frontier molecular orbital analysis.

Discovery of Pyrazine-Carboxamide-Diphenyl-Ethers as Novel Succinate Dehydrogenase Inhibitors via Fragment Recombination

The discovery of novel succinate dehydrogenase inhibitors (SDHIs) has attracted great attention worldwide. Herein, a fragment recombination strategy was proposed to design new SDHIs by understanding the ligand-receptor interaction mechanism of SDHIs. Three fragments, pyrazine from pyraziflumid, diphenyl-ether from flubeneteram, and a prolonged amide linker from pydiflumetofen and fluopyram, were identified and recombined to produce a pyrazine-carboxamide-diphenyl-ether scaffold as a new SDHI. After substituent optimization, compound 6y was successfully identified with good inhibitory activity against porcine SDH, which was about 2-fold more potent than pyraziflumid. Furthermore, compound 6y exhibited 95% and 80% inhibitory rates against soybean gray mold and wheat powdery mildew at a dosage of 100 mg/L in vivo assay, respectively. The results of the present work showed that the pyrazine-carboxamide-diphenyl-ether scaffold could be used as a new starting point for the discovery of new SDHIs.

Diaryl Ether: A Privileged Scaffold for Drug and Agrochemical Discovery

Diaryl ether (DE) is a functional scaffold existing widely both in natural products (NPs) and synthetic organic compounds. Statistically, DE is the second most popular and enduring scaffold within the numerous medicinal chemistry and agrochemical reports. Given its unique physicochemical properties and potential biological activities, DE nucleus is recognized as a fundamental element of medicinal and agrochemical agents aimed at different biological targets. Its drug-like derivatives have been extensively synthesized with interesting biological features including anticancer, anti-inflammatory, antiviral, antibacterial, antimalarial, herbicidal, fungicidal, insecticidal, and so on. In this review, we highlight the medicinal and agrochemical versatility of the DE motif according to the published information in the past decade and comprehensively give a summary of the target recognition, structure-activity relationship (SAR), and mechanism of action of its analogues. It is expected that this profile may provide valuable guidance for the discovery of new active ingredients both in drug and pesticide research.

Design, Synthesis, and Structure-Activity Relationship of Economical Triazole Sulfonamide Aryl Derivatives with High Fungicidal Activity

Plant fungal diseases have caused great decreases in crop quality and yield. As one of the considerable agricultural diseases, cucumber downy mildew (CDM) caused by pseudoperonospora cubensis seriously influences the production of cucumber. Amisulbrom is a commercial agricultural fungicide developed by Nissan Chemical, Ltd., for the control of oomycetes diseases that is highly effective against CDM. However, the synthesis of amisulbrom has a high cost because of the introduction of the bromoindole ring. In addition, the continuous use of amisulbrom might increase the risk of resistance development. Hence, there is an imperative to develop active fungicides with new scaffolds but low cost against CDM. In this study, a series of 1,2,4-triazole-1,3-disulfonamide derivatives were designed, synthesized, and screened. Compound 1j showed a comparable fungicidal activity with amisulbrom, but it was low cost and ecofriendly. It has the potential to be developed as a new fungicide candidate against CDM. Further investigations of structure-activity relationship exhibited the structural requirements of 1,2,4-triazole-1,3-disulfonamide and appropriate modification in N-alkyl benzylamine groups with high fungicidal activity. This research will provide powerful guidance for the design of highly active lead compounds with a novel skeleton and low cost.

Design and synthesis of potent inhibitors of bc1 complex based on natural product neopeltolide

Neopeltolide, a natural product isolated from deep-water sponge specimen of the family neopeltidae, has been proven to be a novel inhibitor of cytochrome bc₁. In this study, a series of neopeltolide derivatives was designed by replacing the 14-membered macrolactone with indole ring and confirmed by ¹H NMR, ¹³C NMR, and HRMS. Based on the binding mode of 12h with bc₁ complex, the IC₅₀ values of compounds 16a-f (ranging from 0.70 to 1.46 μM) were improved significantly than the ester derivatives 12a-u by replacing the ester with amide linker. Subsequently, the molecular docking results indicated that compound 16e could form a π-π interaction with Phe274 and two H-bonds with Glu271 and His161 and the latter H-bond was found to account for its high activity. The present work accelerates the discovery of novel bc₁ complex inhibitors to deal with the resistance that the existing bc₁ complex inhibitors are facing and provides a valuable idea for the design of new fungicides.

Ligand-controlled palladium catalysis enables switch between mono- and di-arylation of primary aromatic amines with 2-halobenzothiazoles

Mono- and di-arylation was switchable simply by varying the applied ligand from Xantphos to a pyridine-functionalized N-heterocyclic carbene (NHC) ligand.

Palladium-Catalyzed Ligand-Free C-N Coupling Reactions: Selective Diheteroarylation of Amines with 2-Halobenzimidazoles

2-Aminobenzimidazoles are widely present in a number of bioactive molecules. Generally, the preparation of these molecules could be realized by the mono-substitution of 2-halobenzimidazoles with amines. However, rare examples were reported for the di-substituted products and the selectivity of mono- vs. di-substitution was relatively low. Considering the potential values of the di-substituted products, we accomplished the first selective diheteroarylation of amines with 2-halobenzimidazoles. Notably, this Pd-catalyzed transformation was realized under ligand-free conditions. Accordingly, numerous target products were efficiently produced from various aromatic or aliphatic amines and 2-halobenzimidazoles. It was worth noting that two representative products were further confirmed by X-ray crystallography. More significantly, this catalytic process could be applied to the synthesis and discovery of new bioactive compounds, which demonstrated the synthetic usefulness of this newly developed approach.

Dual-active antifungal agents containing strobilurin and SDHI-based pharmacophores

Crop disease management often implies repeated application of fungicides. However, the increasing emergence of fungicide-resistant pathogens requires their rotation or combined use. Tank-mix combinations using fungicides with different modes of action are often hard to manage by farmers. An alternative and unexploited strategy are bifunctional fungicides, i.e. compounds resulting from conjugation of the pharmacophores of fungicides with different mechanisms of action. In this paper we describe a new approach to antifungal treatments based on the synthesis of dual agents, obtained by merging the strobilurin and succinate dehydrogenase inhibitor pharmacophores into a new entity. The compounds were tested against important fungal plant pathogens and showed good inhibition of Pyricularia oryzae and Sclerotinia sclerotiorum with activity comparable to commercial fungicides. The inhibition of the cytochrome bc1 and the succinate dehydrogenase enzyme activity confirmed that the new molecules are endowed with a dual mechanism of action. These results were further supported by molecular modelling which showed that selected compounds form stable complexes with both cytochrome b subunit and succinate dehydrogenase enzyme. This work can be considered an important first step towards the development of novel dual-action agents with optimized structure and improved interaction with the targets.

Data for the synthesis of new 4-aryloxy-N-arylanilines as potent succinate-cytochrome c reductase inhibitors

In this data article, we have designed a simple and facile protocol for copper-mediated synthesis of new 4-aryloxy-N-arylanilines under mild reaction conditions. The general information and synthetic procedures of all the target compounds were provided, and they were fully characterized by Nuclear Magnetic Resonance (NMR, including ¹H NMR and ¹³C NMR), melting point measurements, and High-Resolution Mass Spectroscopy (HRMS). Furthermore, the inhibitory activities of these compounds against succinate-cytochrome c reductase (SCR) were evaluated, and the methods and procedures of enzyme inhibition experiments were also recorded in this data article. This article is related to “Synthesis of new 4-aryloxy-N-arylanilines and their inhibitory activities against succinate-cytochrome c reductase” (Cheng et al., 2018) [1].

Use of Phenoxyaniline Analogues To Generate Biochemical Insights into the Interactio n of Polybrominated Diphenyl Ether with CYP2B Enzymes

Human hepatic cytochromes P450 (CYP) are integral to xenobiotic metabolism. CYP2B6 is a major catalyst of biotransformation of environmental toxicants, including polybrominated diphenyl ethers (PBDEs). CYP2B substrates tend to contain halogen atoms, but the biochemical basis for this selectivity and for species specific determinants of metabolism has not been identified. Spectral binding titrations and inhibition studies were performed to investigate interactions of rat CYP2B1, rabbit CYP2B4, and CYP2B6 with a series of phenoxyaniline (POA) congeners that are analogues of PBDEs. For most congeners, there was a <3-fold difference between the spectral binding constants (K_S) and IC₅₀ values. In contrast, large discrepancies between these values were observed for POA and 3-chloro-4-phenoxyaniline. CYP2B1 was the enzyme most sensitive to POA congeners, so the Val-363 residue from that enzyme was introduced into CYP2B4 or CYP2B6. This substitution partially altered the protein-ligand interaction profiles to make them more similar to that of CYP2B1. Addition of cytochrome P450 oxidoreductase (POR) to titrations of CYP2B6 with POA or 2'4'5'TCPOA decreased the affinity of both ligands for the enzyme. Addition of cytochrome b₅ to a recombinant enzyme system containing POR and CYP2B6 increased the POA IC₅₀ value and decreased the 2'4'5'TCPOA IC₅₀ value. Overall, the inconsistency between K_S and IC₅₀ values for POA versus 2'4'5'TCPOA is largely due to the effects of redox partner binding. These results provide insight into the biochemical basis of binding of diphenyl ethers to human CYP2B6 and changes in CYP2B6-mediated metabolism that are dependent on POA congener and redox partner identity.

Identification of a New Isoindole-2-yl Scaffold as a Qo and Qi Dual Inhibitor of Cytochrome bc 1 Complex: Virtual Screening, Synthesis, and Biochemical Assay

Respiratory chain ubiquinol-cytochrome (cyt) c oxidoreductase (cyt bc ₁ or complex III) has been demonstrated as a promising target for numerous antibiotics and fungicide applications. In this study, a virtual screening of NCI diversity database was carried out in order to find novel Qo/Qi cyt bc ₁ complex inhibitors. Structure-based virtual screening and molecular docking methodology were employed to further screen compounds with inhibition activity against cyt bc ₁ complex after extensive reliability validation protocol with cross-docking method and identification of the best score functions. Subsequently, the application of rational filtering procedure over the target database resulted in the elucidation of a novel class of cyt bc ₁ complex potent inhibitors with comparable binding energies and biological activities to those of the standard inhibitor, antimycin.

Discovery of Novel Succinate Dehydrogenase Inhibitors by the Integration of in Silico Library Design and Pharmacophore Mapping

Succinate dehydrogenase (SDH) has been demonstrated as a promising target for fungicide discovery. Crystal structure data have indicated that the carboxyl "core" of current SDH inhibitors contributed largely to their binding affinity. Thus, identifying novel carboxyl "core" SDH inhibitors would remarkably improve the biological potency of current SDHI fungicides. Herein, we report the discovery and optimization of novel carboxyl scaffold SDH inhibitor via the integration of in silico library design and a highly specific amide feature-based pharmacophore model. To our delight, a promising SDH inhibitor, A16c (IC₅₀ = 1.07 μM), with a novel pyrazol-benzoic scaffold was identified, which displayed excellent activity against Rhizoctonia solani (EC₅₀ = 11.0 μM) and improved potency against Sclerotinia sclerotiorum (EC₅₀ = 5.5 μM) and Phyricularia grisea (EC₅₀ = 12.0 μM) in comparison with the positive control thifluzamide, with EC₅₀ values of 0.09, 33.2, and 33.4 μM, respectively. The results showed that our virtual screening strategy could serve as a powerful tool to accelerate the discovery of novel SDH inhibitors.

An ionic liquid promoted approach to bitriazolyl compounds as succinate–ubiquinone oxidoreductase inhibitors

Bitriazolyl compounds, a novel skeleton that is totally different from existing commercialized SQR-inhibiting fungicides, could provide a new lead for further development of SQR inhibitors.

Discovery of cytochrome bc1 complex inhibitors inspired by the natural product karrikinolide

Novel and potent inhibitors targeting the cytochrome bc₁ complex were discovered from the natural product karrikinolide for the first time.