Potential Succinate Dehydrogenase Inhibitors Bearing a Novel Pyrazole-4-sulfonohydrazide Scaffold: Molecular Design, Antifungal Evaluation, and Action Mechanism

Design, synthesis, and antifungal activity of novel pyrazole carboxamide derivatives containing benzimidazole moiety as potential SDH inhibitors

To address the urgent need for new antifungal agents, a collection of novel pyrazole carboxamide derivatives incorporating a benzimidazole group were innovatively designed, synthesized, and evaluated for their efficacy against fungal pathogens. The bioassay results revealed that the EC50 values for the compounds A7 (3-(difluoromethyl)-1-methyl-N-(1-propyl-1H-benzo[d]imidazol-2-yl)-1H-pyrazole-4-carboxamide) and B11 (N-(1-(4-chlorobenzyl)-1H-benzo[d]imidazol-2-yl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide) against B. cinerea were notably low to 0.79 µg/mL and 0.56 µg/mL, respectively, demonstrating the potency comparable to that of the control fungicide boscalid, which has an EC50 value of 0.60 µg/mL. Noteworthy is the fact that in vivo tests demonstrated that A7 and B11 showed superior protective effects on tomatoes and strawberries against B. cinerea infection when juxtaposed with the commercial fungicide carbendazim. The examination through scanning electron microscopy revealed that B11 notably alters the morphology of the fungal mycelium, inducing shrinkage and roughening of the hyphal surfaces. To elucidate the mechanism of action, the study on molecular docking and molecular dynamics simulations was conducted, which suggested that B11 effectively interacts with crucial amino acid residues within the active site of succinate dehydrogenase (SDH). This investigation contributes a novel perspective for the structural design and diversification of potential SDH inhibitors, offering a promising avenue for the development of antifungal therapeutics.

Discovery of a Class of Novel Succinate Dehydrogenase Inhibitors Containing a Coumarin Structure

Succinate dehydrogenase (SDH) has emerged as a highly promising target in modern agricultural research, playing a crucial role in developing environmentally friendly and efficient fungicides for combating agricultural pathogens. This study presents the discovery of a novel class of SDH inhibitors (I-III) incorporating coumarin segments achieved through an active fragment swapping and linking strategy. Fungicidal activity assays revealed that several compounds within this series demonstrate significant inhibitory effects against the tested fungal strains. Through comprehensive structure-activity relationship studies, compound N-(1-((3-butyl-4-methyl-2-oxo-2H-chromen-7-yl)oxy)propan-2-yl)-3-(difluoromethyl)-N-methoxy-1-methyl-1H-pyrazole-4-carboxamide (IIk) exhibited potent inhibitory activity against various fungal species. Notably, it demonstrated superior efficacy against S. sclerotiorum with an EC50 value of 1.14 μg/mL, outperforming the commercial control agent thifluzamide (EC50 = 4.90 μg/mL). Molecular docking simulations indicated that hydrophobic interactions serve as the primary binding mechanism between the ligand and SDH. Intriguingly, compound IIk displayed dual functionality, not only acting as an effective fungicide but also promoting the growth of wheat seedlings and Arabidopsis thaliana, resulting in increased plant biomass. Preliminary investigations into its growth-promoting mechanism suggest that IIk enhances the nitrate reductase activity, thereby facilitating plant growth.

Novel Naphthyl and Phenyl Maleimide Derivatives: Molecular Design, Systematic Optimization, Antifungal Evaluation, and Action Mechanism

A systematic optimization strategy, as an effective screening approach for new antifungal compounds, was implemented to rationally construct novel naphthyl and phenyl maleimide derivatives. The structures of molecules A32 and B6 were further confirmed by single-crystal X-ray diffraction. The in vitro antifungal activity evaluation showed that the target compound A32 obtained by the structure optimization exhibited excellent inhibition (EC50 = 0.59 μg/mL) against Rhizoctonia solani, which was better than the control agent dimethachlone (1.21 μg/mL). Further evaluation by in vivo experiments on rice leaves and potted rice plants against R. solani at 200 μg/mL showed that A32 possessed an outstanding protective efficiency compared to dimethachlone. The mycelium morphology observation by SEM indicated that A32 (25 μg/mL) severely damaged the surface structure of the mycelium, which was in accordance with the increased result of the cell membrane permeability assay. MD simulations and molecular docking analysis revealed that compounds A1 and A32 have a similar binding mode in the active pocket of plasma membrane H+-ATPases (PMA1) as the reference fungicide fluoroimide. In particular, there were more hydrogen bonds in the protein complex of A32 than in the protein complexes of A1 and fluoroimide. This research on constructing novel naphthyl and phenyl maleimide derivatives by a systematic optimization strategy provides a practical way to find new antifungal leads, thereby developing novel fungicides.

Design, Synthesis, Antifungal Evaluation, and Action Mechanism of Novel l-Carvone-Based Derivatives as Potential Succinate Dehydrogenase Inhibitors

Natural products serve as a crucial source of compounds for developing novel agricultural antifungals. In this work, we utilized the natural product l-carvone as a molecular scaffold to design and synthesize three series of novel l-carvone-based derivatives. The in vitro bioassay results indicated that most target compounds exhibited remarkable antifungal activity. Notably, compound C3 demonstrated broad-spectrum antifungal activity against Rhizoctonia solani, Botrytis cinerea, Sclerotinia sclerotiorum, Gibberella zeae, and Valsa mali, with EC50 values of 0.274, 0.985, 4.17, 5.71, and 2.29 μg/mL, respectively. The in vivo preventative efficacies of compounds C3 and C11 against R. solani and of compound C13 against B. cinerea revealed that they had potential as novel agricultural antifungals. In the antifungal mechanism study, the cell membrane permeability experiment showed that compound C3 significantly increased the permeability of the cell membrane, and microscopic observations revealed that compound C3 could significantly destroy the structural integrity of cells and reduce the number of mitochondria, thus affecting the normal growth of mycelia. Furthermore, the mitochondrial membrane potential detection, succinate dehydrogenase (SDH) enzyme assay, molecular dynamics (MD) simulations, and docking experiments further demonstrated that the mechanism of action and binding mode of compound C3 with the SDH may be similar to those of thifluzamide. The abovementioned results provided a valuable reference for the discovery of novel SDH inhibitor fungicides.

Design, synthesis, crystal structure, fungicidal activity, and mechanism of action of novel thiazole-based hydrazide derivatives containing the 4-aminoquinazoline moiety

A family of novel thiazole-based hydrazide derivatives bearing the 4-aminoquinazoline moiety were designed and synthesized by the molecular hybridization strategy, and assessed for their antifungal activities in vitro and in vivo. Among these derivatives, the chemical structure of compound A26 was clearly confirmed via X-ray crystallography. The bioassay results revealed that some of the synthesized compounds exhibited significant inhibition effects against the tested phytopathogenic fungi. For example, in vitro EC50 (half maximal effective concentration) values of compounds A19 and A26 against Rhizoctonia solani, A19 against Verticillium dahliae, A26 against Alternaria solani, and A17 against Colletotrichum gloeosporioides were all less than 3.0 μg/mL. In particular, compound A19 with a 2-fluorophenyl group had an EC50 value as low as 2.87 μg/mL towards R. solani, comparable to that of Chlorothalonil (1.44 μg/mL) and slightly inferior to those of Carbendazim and Boscalid (0.85 and 0.83 μg/mL, respectively). In addition, in vivo assays using this compound displayed the curative and protective efficiencies of 48.4% and 59.6% against R. solani, respectively, at the concentration of 200 μg/mL. Moreover, the mechanistic studies indicated that compound A19 likely exerted its highly antifungal effects by acting as an effective succinate dehydrogenase (SDH) inhibitor with an IC50 value of 29.33 μM, based on SDH enzymatic inhibition assays and molecular docking studies. Meanwhile, the presence of compound A19 adversely impacted the integrity of cell membranes and mycelial morphologies of R. solani.

Design, synthesis, X-ray crystal structure, and antifungal evaluation of new acetohydrazide derivatives containing a 4-thioquinazoline moiety

BACKGROUND

To find efficient agricultural fungicides, 29 new 4-thioquinazoline-containing acetohydrazide derivatives were prepared and tested for their fungicidal properties.

RESULTS

All of the target compounds were characterized by 1H and 13C nuclear magnetic resonance and high-resolution mass spectrometry techniques, and the molecular structure of compound A2 was verified by single-crystal X-ray diffraction measurement. The experimental results revealed that many compounds from this series had impressive inhibition efficacies in vitro against the tested fungi. For example, compound A25 was identified as the best fungicidal agent against Rhizoctonia solani with an EC50 (half-maximal effective concentration) value of 0.66 μg mL-1, superior to those of the commercial fungicides chlorothalonil, carbendazim and boscalid. Additionally, this compound displayed favorable protection and curative activities in vivo against rice sheath blight caused by R. solani. Antifungal mechanistic studies on compound A25 indicated that this compound exerted its strong anti-R. solani effects probably through an effective inhibition of fungal succinate dehydrogenase activity [half-maximal inhibitory concentration (IC50) = 4.88 μm] and the impairment of cell membrane integrity, based on the results from enzymatic bioassays, molecular docking studies, and scanning and transmission electron microscopy observations.

CONCLUSION

Acetohydrazide derivatives containing the 4-thioquinazoline moiety had the potential to be employed as lead compounds for developing more efficient agricultural fungicides in the near future. © 2024 Society of Chemical Industry.

Design, synthesis and antifungal activity of arylhydrazine analogs containing diphenyl ether fragments

BACKGROUND

Succinate dehydrogenase (SDH) represents a critical target in the development of novel fungicides. To address the growing issue of resistance and safeguard the economic viability of agricultural production, the pursuit of new succinate dehydrogenase inhibitors (SDHIs) has emerged as a significant focus of contemporary research.

RESULTS

In this project, 32 arylhydrazine derivatives containing diphenyl ether structural units were synthesized and evaluated for their fungicidal activities against Rhizoctonia solani, Sclerotinia sclerotiorum, Alternaria alternata, Gibberella zeae, Alternaria solani and Colletotrichum gloeosporioides. In an in vitro fungicidal activity assay, compound D6 showed significant inhibitory activity against R. solani with a half-maximum effective concentration (EC50) of 0.09 mg L-1. The in vivo fungicidal activity demonstrated that compound D6 inhibited R. solani by 95.39% in rice leaves, which was significantly better than that of boscalid (85.76%). The results of SDH enzyme assay, molecular docking simulation, mitochondrial membrane potential assay, cytoplasmic release studies and morphological observations demonstrated that the target compound D6 not only had significant SDH inhibitory activity, but also affected the membrane integrity of mycelium.

CONCLUSION

Bioactivity screening and validation of the mechanism of action indicated that compound D6 was a potentially unique SDHI, acting on SDH while also affecting cell membrane permeability, which deserved further study. © 2024 Society of Chemical Industry.

Novel heterocyclic amide derivatives containing a diphenylmethyl moiety: systematic optimizations, synthesis, antifungal activity and action mechanism

BACKGROUND

The development of fungicides with low cross resistance, high efficacy and low resistance plays a central role in protecting crops, reducing yield losses, improving quality and maintaining global food security. Based on this important role, after a systematic optimization strategy, novel heterocyclic amide derivatives bearing diphenylmethyl fragment were screened, synthesized and verified with the spectrographic and x-ray diffraction analysis.

RESULTS

In this study, the aforementioned optimization obtained compound B19 that was measured for antifungal activity against Rhizoctonia solani (median effective concentration, EC50 = 1.11 μg mL-1). Meanwhile, the anti-R. solani protective effect (79.34%) of compound B19 was evaluated in vivo at 100 μg mL-1, which is comparable to that of the control agent fluxapyroxad (80.67%). Thence, morphological observations revealed that compound B19 induced mycelium disruption and shrinking, mitochondrial number reduction and apoptosis acceleration, consistent with the results of the mitochondrial membrane potential and cell membrane permeability. Further investigations found that the potential target enzyme of compound B19 was SDH, which exerted fluorescence quenching dynamic curves similar to that of the commercialized SDHI fluxapyroxad. Additionally, research by molecular docking and MD simulations demonstrated that compound B19 had a similar binding mode acting on the surrounding residues in the SDH active pocket to that offluxapyroxad.

CONCLUSION

The above results demonstrated that heterocyclic amide derivatives containing a diphenylmethyl moiety are promising scaffolds for targeting SDH of fungi and provide valuable antifungal leads with the potential to develop new SDH inhibitors. © 2024 Society of Chemical Industry.

Comprehensive Overview of the Amide Linker Modification in the Succinate Dehydrogenase Inhibitors

Succinate dehydrogenase inhibitors (SDHIs) have become one of the most important classes of agrochemical fungicides. According to the data from FRAC, the resistance risk for SDHIs had reached up to medium and even to high. In general, the chemical structure of SDHIs mainly contained three fragments: an acid core, a hydrophobic tail, and an amide linker, corresponding to three modification directions for each fragment. Among them, amide linker modification (ALM) has become a research hotspot for the design of novel SDHIs fungicides in recent years. We presented here a detailed review on the ALM strategy in the past decade, and some of them had entered the market. According to their chemical structures, ALM strategy were classified into four parts: (1) linked aliphatic chain between amide bond and hydrophobic tail, (2) introducing substituents to replacing hydrogen atom in the amide bond, (3) reverse extending the amide linker, and (4) changed with other bioisosteres. Moreover, the structure-activity relationship and the interaction mechanism of ALM-SDHI with SDH were discussed. This review aims to provide a global perspective on research and development of novel SDHIs, as well as suggestions for food safety management.

Design, Synthesis, Antifungal Activity, and Action Mechanism of Pyrazole-4-carboxamide Derivatives Containing Oxime Ether Active Fragment As Succinate Dehydrogenase Inhibitors

The dearomatization at the hydrophobic tail of the boscalid was carried out to construct a series of novel pyrazole-4-carboxamide derivatives containing an oxime ether fragment. By using fungicide-likeness analyses and virtual screening, 24 target compounds with theoretical strong inhibitory effects against fungal succinate dehydrogenase (SDH) were designed and synthesized. Antifungal bioassays showed that the target compound E1 could selectively inhibit the in vitro growth of R. solani, with the EC50 value of 1.1 μg/mL that was superior to that of the agricultural fungicide boscalid (2.2 μg/mL). The observations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that E1 could reduce mycelial density and significantly increase the mitochondrial number in mycelia cytoplasm, which was similar to the phenomenon treated with boscalid. Enzyme activity assay showed that the E1 had the significant inhibitory effect against the SDH from R. solani, with the IC50 value of 3.3 μM that was superior to that of boscalid (7.9 μM). The mode of action of the target compound E1 with SDH was further analyzed by molecular docking and molecular dynamics simulation studies. Among them, the number of hydrogen bonds was significantly more in the SDH-E1 complex than that in the SDH-boscalid complex. This research on the dearomatization strategy of the benzene ring for constructing pyrazole-4-carboxamides containing an oxime ether fragment provides a unique thought to design new antifungal drugs targeting SDH.

Antifungal Activity and Mechanism of Camphor Derivatives against Rhizoctonia solani: A Promising Alternative Antifungal Agent for Rice Sheath Blight

Rice sheath blight, caused by the fungus Rhizoctonia solani, poses a significant threat to rice cultivation globally. This study aimed to investigate the potential mechanisms of action of camphor derivatives against R. solani. Compound 4o exhibited superior fungicidal activities in vitro (EC50 = 6.16 mg/L), and in vivo curative effects (77.5%) at 500 mg/L were significantly (P < 0.01) higher than the positive control validamycin·bacillus (66.1%). Additionally, compound 4o exhibited low cytotoxicity and acute oral toxicity for adult worker honeybees of Apis mellifera L. Mechanistically, compound 4o disrupted mycelial morphology and microstructure, increased cell membrane permeability, and inhibited both PDH and SDH enzyme activities. Molecular docking and molecular dynamics analyses indicated a tight interaction of compound 4o with PDH and SDH active sites. In summary, compound 4o exhibited substantial antifungal efficacy against R. solani, serving as a promising lead compound for further optimization of antifungal agents.

Design, Synthesis and Antifungal Activity of Nootkatone Derivatives Containing Acylhydrazone and Oxime Ester

In an attempt to search for new natural products-based antifungal agents, fifty-three nootkatone derivatives were designed, synthesized, and evaluated for their antifungal activity against Phytophthora parasitica var nicotianae, Fusarium oxysporum, Fusarium graminearum and Phomopsis sp. by the mycelium growth rate method. Nootkatone derivatives N17 exhibited good inhibitory activity against Phomopsis. sp. with EC50 values of 2.02 μM. The control effect of N17 against Phomopsis. sp. on kiwifruit showed that N17 exhibited a good curative effect in reducing kiwifruit rot at the concentration of 202 μM(100×EC50 ), with the curative effect of 41.11 %, which was better than commercial control of pyrimethanil at the concentration of 13437 μM(100×EC50 ) with the curative effect of 38.65 %. Phomopsis. sp. mycelium treated with N17 showed irregular surface collapse and shrinkage, and the cell membrane crinkled irregularly, vacuoles expanded significantly, mitochondria contracted, and organelles partially swollen by the SEM and TEM detected. Preliminary pharmacological experiments show that N17 exerted antifungal effects by altering release of cellular contents, and altering cell membrane permeability and integrity. The cytotoxicity test demonstrated that N17 showed almost no toxicity to K562 cells. The presented results implied that N17 may be as a potential antifungal agents for developing more efficient fungicides to control Phomopsis sp.

Phenolylazoindole scaffold for facilely synthesized and bis-functional photoswitches combining controllable fluorescence and antifungal properties using theoretical methods

Functionalization is a major challenge for the application of photoswitches. With the aim to develop novel bis-functional azo photoswitches with stationary photophysical properties, a series of phenolylazoindole derivatives were designed, synthesized, and characterized via NMR spectroscopy studies and high-resolution mass spectrometry (HRMS). Herein, UV/Vis and 1H NMR spectra revealed that the photostationary state (PSS) proportions for PSScis and PSStrans were 76-80% and 68-81%, respectively. Furthermore, the thermal half-lives (t1/2) of compounds A2-A4 and B2 ranged from 0.9 to 5.3 h, affected by the diverse substituents at the R1 and R2 positions. The results indicated that azo photoswitches based on the phenolylazoindole scaffold had stationary photophysical properties and wouldn't be excessively affected by modifying the functional groups. Compounds A4 and B2, which were modified with an aryl group, also exhibited fluorescence emission properties (the quantum yields of A4 and B2 were 2.32% and 13.34%) through the modification of the flexible conjugated structure (benzene) at the R2 position. Significantly, compound C1 was obtained via modification with a pharmacophore in order to acquire antifungal activities against three plant fungi, Rhizoctonia solani (R. solani), Botrytis cinerea (B. cinerea), and Fusarium graminearum (F. graminearum). Strikingly, the inhibitory activity of the cis-isomer of compound C1towards R. solani (53.3%) was significantly better than that of the trans-isomer (34.2%) at 50 μg mL-1. In order to further reveal the antifungal mechanism, molecular docking simulations demonstrated that compound C1 effectively integrates into the cavity of succinate dehydrogenase (SDH); the optically controlled cis-isomer showed a lower binding energy with SDH than that of the trans-isomer. This research confirmed that phenolylazoindole photoswitches can be appropriately applied as molecular regulatory devices and functional photoswitch molecules via bis-functionalization.