Design, Synthesis, and Biological Evaluation of Novel Pyrazol-5-yl-benzamide Derivatives Containing Oxazole Group as Potential Succinate Dehydrogenase Inhibitors

Design and development of pyrazol-5-ylbenzamide derivatives containing chiral oxazoline moiety as fungicides based on molecular docking

BACKGROUND

Development of novel chiral antifungal agents for effective control of plant pathogens is urgently needed. In this study, a series of pyrazol-5-yl-benzamide derivatives containing chiral oxazoline moiety were rationally designed and developed based on molecular docking.

RESULTS

The in vitro antifungal assay results indicated that compounds (rac)-4h (R1 = Et), (S)-4 h (R1 = S-Et) and (R)-4 h (R1 = R-Et) exhibited remarkable antifungal activities against Valsa mali with median effective concentration (EC50) values of 0.24, 0.06 and 1.08 mg/L, respectively. Preliminary structure-activity relationships (SARs) revealed that the modification of the chiral substituent group at the oxazoline moiety significantly affected the antifungal activities of the target compounds. Furthermore, compounds (S)-4h (87.5%) and (R)-4h (84.3%) exhibited in vivo protective activities comparable to tebuconazole (87.5%) against V. mali. Subsequent molecular docking analysis, succinate dehydrogenase (SDH) enzyme inhibition assays and molecular dynamic (MD) simulations verified that the potential target enzyme of this class of derivatives could be SDH and helped to explain the large difference in antifungal activities of compounds (S)-4h and (R)-4h. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) observations confirmed that these two compounds severely disrupted the mycelial morphology of V. mali. Theoretical calculation studies provided some insight into the subsequent modification of such pyrazol-5-yl-benzamide derivatives. Resistance frequency studies showed that (S)-4h and (R)-4h treatments were less likely to produce resistant fungal strains than tebuconazole. Meanwhile, compounds (S)-4h and (R)-4h exhibited no apparent toxicity to the Apis mellifera L.

POPULATION

CONCLUSION

Therefore, these derivatives are potential candidates for the development of novel chiral fungicides for crop protection. © 2025 Society of Chemical Industry.

Discovery of Novel Quinazolinone-2-carbohydrazide Derivatives as Effective Succinate Dehydrogenase Inhibitors and Biosafety Assessment on Rice and Zebrafish

To develop potent and safe antifungal agents in agriculture, a total of 48 novel quinazolinone-2-carbohydrazide derivatives were designed and synthesized based on the pharmacophore hybridization method. The bioassay results demonstrated that many compounds exhibited powerful and broad-spectrum inhibition activities in vitro against the tested fungi. For instance, compounds E23 and F23 possessed EC50 (half-maximal effective concentration) values of 0.41 and 0.47 μg/mL against Rhizoctonia solani, comparable to that of the commercial fungicide Boscalid (EC50 = 0.49 μg/mL). Additionally, compound E23 also demonstrated pronounced antifungal effects against Verticillium dahliae, Alternaria solani, and Colletotrichum gloeosporioides with EC50 values of 0.27, 1.15, and 0.27 μg/mL, respectively. In vivo assays on rice plants revealed that this compound at 200 μg/mL exhibited nearly equipotent curative and protective effects against R. solani, as compared with the positive controls Boscalid and Carbendazim. Moreover, compound E23 had an obvious inhibition activity against fungal succinate dehydrogenase (SDH) from R. solani with the half-maximal inhibition concentration (IC50) of 11.76 μM, and the interactions between compound E23 and SDH enzyme were further confirmed by molecular docking studies. Furthermore, the presence of compound E23 also triggered obvious morphological changes of fungal mycelia and increased the conductivity and permeability of fungal cell membranes. Interestingly, the built three-dimensional quantitative structure-activity relationship (3D-QSAR) models showed that the electrostatic effect played a more important role in maintaining anti-R. solani effects of target compounds than other effects. Finally, the biosafety assessment of compound E23 demonstrated its safety toward rice and zebrafish.

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.

Asymmetric Synthesis and Bioactivity Evaluation of Chiral Oxazoline Skeleton Molecules

The utilization of novel organic synthesis methods is increasingly critical in the development of innovative agrochemicals. In this study, we designed and synthesized a series of chiral oxazoline derivatives using a one-pot method. This method involved first catalyzing the asymmetric aldol addition reaction of oxazolinyl esters with paraformaldehyde, followed by esterification with various pharmacophore-containing carboxylic acids. Unexpectedly, many of the target compounds exhibited promising antifungal and antioomycete activities, with their absolute configurations showing pronounced enantioselective activities. Notably, compound (R)-5c demonstrated significant biological activities against Valsa mali and Phytophthora capsica (EC50 = 1.023 mg/L and EC50 = 0.149 mg/L, respectively), which were markedly superior to its enantiomer (S)-5c (EC50 = 9.565 mg/L and EC50 = 0.924 mg/L, respectively). In vivo experiments confirmed that this compound exhibited both curative and protective effects against V. mali and P. capsici. CLSM and SEM analyses further indicated that compounds 5c had distinct physiological effects on P. capsici hyphae. Moreover, acute toxicity tests in zebrafish (Danio rerio) revealed that compound (R)-5c had significantly lower toxicity compared to the control drugs tebuconazole and dimethomorph. Consequently, this study provides valuable insights for the development of novel chiral oxazoline analogues as potential antifungal and antioomycete agrochemicals.

Oxazole and isoxazole-containing pharmaceuticals: targets, pharmacological activities, and their SAR studies

Oxazole, a five-membered aromatic heterocycle featuring a nitrogen and an oxygen atom separated by a carbon atom, and its isomer isoxazole, with directly attached oxygen and nitrogen atoms, have been pivotal in medicinal chemistry. Over the past few decades, the U.S. Food and Drug Administration (FDA) has approved more than 20 drugs containing these nuclei for various clinical conditions, including Tafamidis and Oxaprozin. Due to their unique physicochemical properties, these drugs often exhibit superior pharmacokinetic profiles and pharmacological effects compared to those with similar heterocycles. This review provides a comprehensive overview of all FDA-approved drugs containing oxazole and isoxazole nuclei, focusing on their pharmacological activities and structure-activity relationships.

Evaluation of the antifungal activity of novel bis-pyrazole carboxamide derivatives and preliminary investigation of the mechanism

To facilitate the development of novel agricultural succinate dehydrogenase inhibitor (SDHI) fungicides, we synthesized three series of derivatives by introducing phenyl pyrazole fragments into the structure of pyrazol-4-yl amides. The results of the bioactivity assay showed that most of the target compounds possessed varying degrees of inhibitory activity against the tested fungi. At a concentration of 100 mg/L, the compound B8 exhibited effective protective activity against S. sclerotiorum in vivo. Molecular docking analysis and succinate dehydrogenase (SDH) inhibition assay indicated that B8 was not a potential SDHI. The preliminary antifungal mechanism of studies showed that B8 induced a large amount of reactive oxygen species (ROS) and severe lipid peroxidation damage in S. sclerotiorum mycelium, resulting in mycelial rupture and disruption of the integrity of the cell membrane and leakage of soluble proteins, soluble sugars and nucleic acids. Further transcriptome analysis showed that compound B8 blocked various metabolic pathways by downregulating the differentially expressed genes (DEGs) catalase, disrupting hydrogen peroxide hydrolysis, accelerating membrane oxidative damage, and upregulating neutral ceramidase, accelerating sphingolipid metabolism to disrupt cell membrane structure and cell proliferation and differentiation, potentially accelerating cell death. The above results indicated that the potential target of these dis-pyrazole carboxamide derivatives may be the cell membrane of pathogenic fungi.

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.

Design, Synthesis, Antifungal Activity, and Mechanism of Action of New Piperidine-4-carbohydrazide Derivatives Bearing a Quinazolinyl Moiety

A series of new piperidine-4-carbohydrazide derivatives bearing a quinazolinyl moiety were prepared and evaluated for their fungicidal activities against agriculturally important fungi. Among these derivatives, the chemical structure of compound A45 was clearly verified by X-ray crystallographic analysis. The antifungal bioassays revealed that many compounds in this series possessed good to excellent inhibition effects toward the tested fungi. For example, compounds A13 and A41 had EC50 values of 0.83 and 0.88 μg/mL against Rhizoctonia solani in vitro, respectively, superior to those of positive controls Chlorothalonil and Boscalid (1.64 and 0.96 μg/mL, respectively). Additionally, the above two compounds also exhibited notable inhibitory activities against Verticillium dahliae (with EC50 values of 1.12 and 3.20 μg/mL, respectively), far better than the positive controls Carbendazim and Chlorothalonil (19.3 and 11.0 μg/mL, respectively). More importantly, compound A13 could potently inhibit the proliferation of R. solani in the potted rice plants, showing good in vivo curative and protective efficiencies of 76.9% and 76.6% at 200 μg/mL, respectively. Furthermore, compound A13 demonstrated an effective inhibition of succinate dehydrogenase (SDH) activity in vitro with an IC50 value of 6.07 μM. Finally, the molecular docking study revealed that this compound could be well embedded into the active pocket of SDH via multiple noncovalent interactions, involving residues like SER39, ARG43, and GLY46.

Design, selective synthesis and biological activities evaluation of novel thiazol-2-ylbenzamide and thiazole-2-ylbenzimidoyl chloride derivatives

To promote the development and exploitation of novel antifungal agents, a series of thiazol-2-ylbenzamide derivatives (3A-3V) and thiazole-2-ylbenzimidoyl chloride derivatives (4A-4V) were designed and selective synthesis. The bioassay results showed that most of the target compounds exhibited excellent in vitro antifungal activities against five plant pathogenic fungi (Valsa mali, Sclerotinia scleotiorum, Botrytis cinerea, Rhizoctonia solani and Trichoderma viride). The antifungal effects of compounds 3B (EC50 = 0.72 mg/L) and 4B (EC50 = 0.65 mg/L) against S. scleotiorum were comparable to succinate dehydrogenase inhibitors (SDHIs) thifluzamide (EC50 = 1.08 mg/L) and boscalid (EC50 = 0.78 mg/L). Especially, compounds 3B (EC50 = 0.87 mg/L) and 4B (EC50 = 1.08 mg/L) showed higher activity against R. solani than boscalid (EC50 = 2.25 mg/L). In vivo experiments in rice leaves revealed that compounds 3B (86.8 %) and 4B (85.3 %) exhibited excellent protective activities against R. solani comparable to thifluzamide (88.5 %). Scanning electron microscopy (SEM) results exhibited that compounds 3B and 4B dramatically disrupted the typical structure and morphology of R. solani mycelium. Molecular docking demonstrated that compounds 3B and 4B had significant interactions with succinate dehydrogenase (SDH). Meanwhile, SDH inhibition assay results further proved their potential as SDHIs. In addition, acute oral toxicity tests on A. mellifera L. showed only low toxicity for compounds 3B and 4B to A. mellifera L. populations. These results suggested that these two series of compounds had merit for further investigation as potential low-risk agricultural SDHI fungicides.

Novel Pyrazole-4-Carboxamide Derivatives Containing Oxime Ether Group as Potential SDHIs to Control Rhizoctonia solani

In the search for novel succinate dehydrogenase inhibitor (SDHI) fungicides to control Rhizoctonia solani, thirty-five novel pyrazole-4-carboxamides bearing either an oxime ether or an oxime ester group were designed and prepared based on the strategy of molecular hybridization, and their antifungal activities against five plant pathogenic fungi were also investigated. The results indicated that the majority of the compounds containing oxime ether demonstrated outstanding in vitro antifungal activity against R. solani, and some compounds also displayed pronounced antifungal activities against Sclerotinia sclerotiorum and Botrytis cinerea. Particularly, compound 5e exhibited the most promising antifungal activity against R. solani with an EC50 value of 0.039 μg/mL, which was about 20-fold better than that of boscalid (EC50 = 0.799 μg/mL) and 4-fold more potent than fluxapyroxad (EC50 = 0.131 μg/mL). Moreover, the results of the detached leaf assay showed that compound 5e could suppress the growth of R. solani in rice leaves with significant protective efficacies (86.8%) at 100 μg/mL, superior to boscalid (68.1%) and fluxapyroxad (80.6%), indicating promising application prospects. In addition, the succinate dehydrogenase (SDH) enzymatic inhibition assay revealed that compound 5e generated remarkable SDH inhibition (IC50 = 2.04 μM), which was obviously more potent than those of boscalid (IC50 = 7.92 μM) and fluxapyroxad (IC50 = 6.15 μM). Furthermore, SEM analysis showed that compound 5e caused a remarkable disruption to the characteristic structure and morphology of R. solani hyphae, resulting in significant damage. The molecular docking analysis demonstrated that compound 5e could fit into the identical binding pocket of SDH through hydrogen bond interactions as well as fluxapyroxad, indicating that they had a similar antifungal mechanism. The density functional theory and electrostatic potential calculations provided useful information regarding electron distribution and electron transfer, which contributed to understanding the structural features and antifungal mechanism of the lead compound. These findings suggested that compound 5e could be a promising candidate for SDHI fungicides to control R. solani, warranting further investigation.

Industrial Distillation Fractions of Garlic Essential Oil, Design, Synthesis, and Antifungal Activity Evaluation of Aliphatic Substituted Trisulfide Derivatives

Garlic oil has a wide range of biological activities, and its broad-spectrum activity against phytopathogenic fungi still has the potential to be explored. In this study, enzymatic treatment of garlic resulted in an increase of approximately 50 % in the yield of essential oil, a feasible GC-MS analytical program for garlic oil was provided. Vacuum fractionation of the volatile oil and determination of its inhibitory activity against 10 fungi demonstrated that garlic oil has good antifungal activity. The antifungal activity levels were ranked as diallyl trisulfide (S-3)>diallyl disulfide (S-2)>diallyl monosulfide (S-1), with an EC50 value of S-3 against Botrytis cinerea reached 8.16 mg/L. Following the structural modification of compound S-3, a series of derivatives, including compounds S-4~7, were synthesized and screened for their antifungal activity. The findings unequivocally demonstrated that the compound dimethyl trisulfide (S-4) exhibited exceptional antifungal activity. The EC50 of S-4 against Sclerotinia sclerotiorum reached 6.83 mg/L. SEM, In vivo experiments, and changes in mycelial nucleic acids, soluble proteins and soluble sugar leakage further confirmed its antifungal activity. The study indicated that the trisulfide bond structure was the key to good antifungal activity, which can be developed into a new type of green plant-derived fungicide for plant protection.

Design, synthesis, antifungal activity and molecular docking of novel pyrazole-4-carboxamides containing tertiary alcohol and difluoromethyl moiety as potential succinate dehydrogenase inhibitors

BACKGROUND

Resistance problems with the long-term and frequent use of existing fungicides, and the lack of structure diversity of traditional pyrazole-4-carboxamide succinate dehydrogenase inhibitors, it is highly required to design and develop new fungicides to address the resistance issue.

RESULTS

Different from previous pyrazole-4-carboxamide succinate dehydrogenase inhibitors by breaking the norm of difluoromethyl at the C-3 position of pyrazole and introducing a tertiary alcohol group at the C-3 position, 27 novel pyrazole-4-carboxamide derivatives were designed, synthesized and characterized by proton (1 H) nuclear magnetic resonance (NMR), carbon-13 (13 C) NMR, fluorine-19 (19 F) NMR and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). The crystal structures of compounds A14 and C5 were analyzed by single crystal X-ray diffraction. Their in vitro antifungal activities were evaluated against phytopathogen Fusarium graminearum, Botrytis cinerea, Phytophthora capsica, Sclerotinia sclerotiorum, Thanatephorus cucumeris. The results displayed that most of them exhibited significant antifungal activities against S. sclerotiorum at 50 mg/L, the half maximal effective concentration (EC50 ) data of A8 and A14 were 3.96 and 2.52 mg/L, respectively. Their in vivo antifungal activities were evaluated against Pseudoperonospora cubensis, Puccinia sorghi Schw, Colletotrichum gloeosporioides, F. graminearum, Erysiphe graminis, Thanatephorus cucumeris, the control efficacies of A6, B3, C3, and C6 against E. graminis reached 100% at a concentration of 400 mg/L. The molecular docking results showed that the binding mode of the target compounds containing tertiary alcohols were similar to that of fluxapyroxad in succinate dehydrogenase. In addition, tertiary alcohols were involved in the formation of hydrogen bonds.

CONCLUSION

The excellent in vitro and in vivo inhibitory activities of novel pyrazole-4-carboxamide derivatives against succinate dehydrogenase were reported for the first time, and they could be used as the potential lead compounds. © 2023 Society of Chemical Industry.

Design, Synthesis, and Fungicidal Activities of Novel N-(Pyrazol-5-yl)benzamide Derivatives Containing a Diphenylamine Moiety

To accelerate the development of novel fungicides, a variety of N-(pyrazol-5-yl)benzamide derivatives with a diphenylamine moiety were designed and synthesized using a pharmacophore recombination strategy based on the structure of pyrazol-5-yl-aminophenyl-benzamides. The bioassay results demonstrated that most of the target compounds had excellent in vitro antifungal activities against Sclerotinia sclerotiorum, Valsa mali, and Botrytis cinerea. In particular, compound 5IIIh exhibited remarkable activity against S. sclerotiorum (EC50 = 0.37 mg/L), which was similar to that of fluxapyroxad (EC50 = 0.27 mg/L). In addition, compound 5IIIc (EC50 = 1.32 mg/L) was observed to be more effective against V. mali than fluxapyroxad (EC50 = 12.8 mg/L) and comparable to trifloxystrobin (EC50 = 1.62 mg/L). Furthermore, compound 5IIIh demonstrated remarkable in vivo protective antifungal properties against S. sclerotiorum, with an inhibition rate of 96.8% at 100 mg/L, which was close to that of fluxapyroxad (99.6%). Compounds 5IIIc (66.7%) and 5IIIh (62.9%) exhibited good in vivo antifungal effects against V. mali at 100 mg/L, which were superior to that of fluxapyroxad (11.1%) but lower than that of trifloxystrobin (88.9%). The succinate dehydrogenase (SDH) enzymatic inhibition assay was conducted to confirm the mechanism of action. Molecular docking analysis further revealed that compound 5IIIh has significant hydrogen-bonding, π-π, and p-π conjugation interactions with ARG 43, SER 39, TRP 173, and TYR 58 in the binding site of SDH, and the binding mode was similar to that of the commercial fungicide fluxapyroxad. All of the results suggest that compound 5IIIh could be a potential SDH inhibitor, offering a valuable reference for future studies.

Discovery of Pyrazole-5-yl-amide Derivatives Containing Cinnamamide Structural Fragments as Potential Succinate Dehydrogenase Inhibitors

To promote the development of novel agricultural succinate dehydrogenase inhibitor (SDHI) fungicides, we introduced cinnamamide and nicotinamide structural fragments into the structure of pyrazol-5-yl-amide by carbon chain extension and scaffold hopping, respectively, and synthesized a series of derivatives. The results of the biological activity assays indicated that most of the target compounds exhibited varying degrees of inhibitory activity against the tested fungi. Notably, compounds G22, G28, G34, G38, and G39 exhibited excellent in vitro antifungal activities against Valsa mali with EC50 values of 0.48, 0.86, 0.57, 0.73, and 0.87 mg/L, respectively, and this result was significantly more potent than boscalid (EC50 = 2.80 mg/L) and closer to the specialty control drug tebuconazole (EC50 = 0.30 mg/L). Compounds G22 and G34 also exhibited excellent in vivo protective and curative effects against V. mali at 40 mg/L. The SEM and TEM observations indicated that compounds G22 and G34 may affect normal V. mali mycelial morphology as well as the cellular ultrastructure. Molecular docking analysis results indicated that G22 and boscalid possessed a similar binding mode to that of SDH, and detailed SDH inhibition assays validated the feasibility of the designed compounds as potential SDH inhibitors. Compounds G22 and G3 were selected for theoretical calculations, and the terminal carboxylic acid group of this series of compounds may be a key region influencing the antifungal activity. Furthermore, toxicity tests on Apis mellifera l. revealed that compounds G22 and G34 exhibited low toxicity to A. mellifera l. populations. The above results demonstrated that these series of pyrazole-5-yl-amide derivatives are promising for development as potential low-risk drug-resistance agricultural SDHI fungicides.

Design, Synthesis, and Insecticidal Evaluation of N-Pyridylpyrazole Amide Derivatives Containing 4,5-Dihydroisoxazole Amide as Potential Ryanodine Receptor Activators

Using the 4,5-dihydroisoxazol amide structure to expand the aliphatic amide moiety of chlorantraniliprole, a series of 28 novel N-pyridylpyrazolecarboxamide derivatives containing 4,5-dihydroisoxazol amide fragment were designed and synthesized. All target compounds had been properly characterized and confirmed by 1H NMR, 13C NMR, and HRMS, and the effects were evaluated against Mythimna separata (M. separata) and Plutella xylostella (P. xylostella). The bioassay results indicated that most of the target compounds exhibited good insecticidal activities against M. separata and P. xylostella at 50 mg/L; especially, compound A4 showed an LC50 value of 3.27 mg/L against M. separata. Calcium imaging experiments indicated that the target compound A4 had a similar mechanism of action to chlorantraniliprole, causing an increase in the cytoplasmic Ca2+ concentration. The molecular docking revealed the possible binding mode of compound A4 with a ryanodine receptor.

Design, Synthesis, and Antifungal Activities of Novel Carboxamides Derivatives Bearing a Chalcone Scaffold as Potential SDHIs

In search for SDHIs fungicides, twenty-five novel carboxamides containing a chalcone scaffold were designed, synthesized, and evaluated for antifungal activities against five pathogenic fungi. The results showed that compound 5 k exhibited outstanding antifungal activity against R. solani with an EC50 value of 0.20 μg/mL, which was much better than that of commercial SDHIs Boscalid (EC50 =0.74 μg/mL). Moreover, compound 5 k also displayed promising antifungal activities against S. sclerotiorum, B. cinerea, and A. alternate (IC50 =2.53-4.06 μg/mL), indicating that 5 k had broad-spectrum antifungal activity. Additionally, in vivo antifungal activities results showed that 5 k could significantly inhibit the growth of R. solani in rice leaves with good protective efficacy (57.78 %) and curative efficacy (58.45 %) at 100 μg/mL, both of which were much better than those of Boscalid, indicating a promising application prospect. Moreover, SEM analysis showed that compound 5 k could remarkably disrupt the typical structure and morphology of R. solani hyphae. Further SDH enzyme inhibition assay and molecular docking study revealed that lead compound 5 k had a similar mechanism of action as commercial SDHI Boscalid. These results indicated that compound 5 k showed potential as a SDHIs fungicide and deserved further investigation.