Design, Synthesis, and Antifungal Evaluation of 8-Hydroxyquinoline Metal Complexes against Phytopathogenic Fungi

Quinoline Derivatives in Discovery and Development of Pesticides

Finding highly active molecular scaffold structures is always the key research content of new pesticide discovery. In the research and development of new pesticides, the discovery of new agricultural molecular scaffold structures and new targets still faces great challenges. In recent years, quinoline derivatives have developed rapidly in the discovery of new agriculturally active molecules, especially in the discovery of fungicides. The unique quinoline scaffold has many advantages in the discovery of new pesticides and can provide innovative and feasible solutions for the discovery of new pesticides. Therefore, we reviewed the use of quinoline derivatives and their analogues as molecular scaffolds in the discovery of new pesticides since 2000. We systematically summarized the agricultural biological activity of quinoline compounds and discussed the structure-activity relationship (SAR), physiological and biochemical properties, and mechanism of action of the active compounds, hoping to provide ideas and inspiration for the discovery of new pesticides.

N-succinyl-chitosan as ecofriendly pesticide carriers: Nano encapsulation and synergistic antifungal effect on 4-hydroxyphenyl-2-propenyl-1-one derivatives based on chalcone structure

INTRODUCTION

Traditional pesticides have poor-water solubility, high toxicity and low bioavailability. Therefore, it is of great significance for the sustainable and healthy development of the pesticide industry to develop efficient and ecofriendly new chemical pesticide products and formulations.

OBJECTIVES

This study aims to synthesize a series of derivatives based on chalcone structure (HPPO), and then use the amphiphilic and self-assembly characteristics of N-succinyl-chitosan (NSCS) to prepare HPPO@NSCS nanoparticles (HPPO@NSCS NPs) in order to realize the green application of HPPO, and investigate the antifungal activity and mechanisms of HPPO@NSCS NPs.

METHODS

NSCS was synthesized by structural modification using chitosan as the carrier. Based on its amphiphilic and self-assembly characteristics, HPPO-16@NSCS NPs were reasonably prepared by combining with active small molecule HPPO-16. Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), fluorescence spectroscopy (FS) and high-performance liquid chromatography (HPLC) were used to characterize the physicochemical properties of NSCS and HPPO-16@NSCS NPs. The inhibitory activity of nanopesticides against Rhizoctonia solani (R. solani) was tested in vivo and in vitro. The mechanism of antifungal action was discussed from the observation of pathogen morphology, fluorescence staining and enzyme activity determination.

RESULTS

28 small molecules based on chalcone structure (HPPO-1-28), NSCS and HPPO-16@NSCS were successfully synthesized. The application of HPPO-16@NSCS could impair the development, cell structure, cellular energy utilization, and metabolism pathways of the fungi. The protective effects of HPPO-16@NSCS NPs on rice leaves and leaf sheaths were 80.9 and 76.1 %, respectively, which were better than those of azoxystrobin.

CONCLUSION

This study reveals that these simple chalcone derivatives can be further explored as viable antibacterial alternatives and NSCS as a novel pesticide matrix can be used for the delivery of more insoluble pesticides.

Novel Sulfoximine Derivatives Containing Cyanoguanidine and Nitroguanidine Moieties: Design, Synthesis, and Bioactivities

A total of 32 novel sulfoximines bearing cyanoguanidine and nitroguanidine moieties were designed and synthesized by a rational molecule design strategy. The bioactivities of the title compounds were evaluated and the results revealed that some of the target compounds possessed excellent antifungal activities against six agricultural fungi, including Sclerotinia sclerotiorum, Fusarium graminearum, Phytophthora capsici, Botrytis cinerea, Rhizoctonia solani, and Pyricularia grisea. Among them, compounds 8e1 and 8e4 exhibited significant efficacy against P. grisea with EC50 values of 2.72 and 2.98 μg/mL, respectively, which were much higher than that of commercial fungicides boscalid (47.95 μg/mL). Interestingly, in vivo assays determined compound 8e1 possessed outstanding activity against S. sclerotiorum with protective and curative effectiveness of 98 and 95.6% at 50 μg/mL, which were comparable to those of boscalid (93.2, 91.9%). The further preliminary mechanism investigation disclosed that compound 8e1 could damage the structure of the cell membrane of S. sclerotiorum, increase its permeability, and suppress its growth. Overall, the findings enhanced that these novel sulfoximine derivatives could be potential lead compounds for the development of new fungicides.

Novel Flavonol Derivatives Containing 1,3,4-Thiadiazole as Potential Antifungal Agents: Design, Synthesis, and Biological Evaluation

In order to discover novel compounds with excellent agricultural activities, novel flavonol derivatives containing 1,3,4-thiadiazole were synthesized and evaluated for their antifungal activities. The bioassay results showed that some of the target compounds had good antifungal activities against Botrytis cinerea, Phomopsis sp. and Sclerotinia sclerotiorum in vitro. It is worth noting that the half-effective concentration (EC50) value of Y18 against B. cinerea was 2.4 μg/mL, which was obviously superior to that of azoxystrobin (21.7 μg/mL). The curative activity of Y18 at 200 μg/mL (79.9%) was better than that of azoxystrobin (59.1%), and its protective activity (90.9%) was better than that of azoxystrobin (83.9%). Morphological studies by using scanning electron microscopy and fluorescence microscopy revealed that Y18 could affect the normal growth of B. cinerea mycelium. In addition, the mechanism of action studies indicated that Y18 could affect the integrity of cell membranes by inducing the production of endogenous reactive oxygen species and the release of the malondialdehyde content, leading to membrane lipid peroxidation and the release of cell contents. The inhibitory activity of flavonol derivatives containing 1,3,4-thiadiazole on plant fungi is notable, offering significant potential for the development of new antifungal agents.

Design of a delivery vehicle chitosan-based self-assembling: controlled release, high hydrophobicity, and safe treatment of plant fungal diseases

BACKGROUND

Traditional pesticides are poorly water-soluble and suffer from low bioavailability. N-succinyl chitosan (NSCS) is a water-soluble chitosan derivative, has been recently used to encapsulate hydrophobic drugs to improve their bioavailability. However, it remains challenging to synthesize pesticides of a wide variety of water-soluble drugs and to scale up the production in a continuous manner.

RESULTS

A synthetic method for preparing water-soluble nanopesticides with a polymer carrier was applied. The bioactive molecule BTL-11 was loaded into hollow NSCS to promote drug delivery, improve solubility and anti-fungal activity. The synthesized nanopesticides had well controlled sizes of 606 nm and the encapsulation rate was 80%. The release kinetics, drug toxicity and drug activity were further evaluated. The inhibitory activity of nanopesticides against Rhizoctonia solani (R. solani) was tested in vivo and in vitro. In vivo against R. solani trials revealed that BTL-11 has excellent control efficiency for cultivated rice leaf and sheath was 79.6 and 76.5%, respectively. By contrast, for BTL-11@NSCS NPs, the anti-fungal ability was strongly released and afforded significant control efficiencies of 85.9 and 81.1%. Those effects were significantly better than that of the agricultural fungicide azoxystrobin (51.5 and 66.5%). The proposed mechanism was validated by successfully predicting the synthesis outcomes.

CONCLUSIONS

This study demonstrates that NSCS is a promising biocompatible carrier, which can enhance the efficacy of pesticides, synergistically improve plant disease resistance, protect crop growth, and can be used for the delivery of more insoluble pesticides.

Bioinspired total synthesis and biological activity of Pegaharine A

BACKGROUND

Phytopathogens cause various diseases by parasitizing crops, reducing crop yield and resulting in substantial economic losses in agricultural production. A novel type isolated from the perennial herbaceous Peganum harmala L. seeds, β-carboline alkaloids pegaharine A (PA), has become a hot topic in developing plant-originated green pesticides owing to their significant physiological activities.

RESULTS

A scalable bioinspired total synthesis of PA is accomplished in the present work. The systematical biological assay study showed that PA exhibited moderate inhibitory activity against nine tested plant pathogenic fungi and showed significant inhibitory activity in vitro against the three tested plant pathogenic bacteria. Most noteworthy is the inhibitory rates of PA on Xanthomonas oryzae pv. oryzae (Xoo), X. oryzae pv. oryzicola (Xoc) and X. axonopodis pv. citri (Xac) of 93.6%, 92.1% and 86.1%, respectively, which are better than the control drug, bismerthiazol (63.4%, 61.2% and 53.7% at 100 μg mL-1 concentration). Furthermore, the EC50 value of PA against Xoo, Xoc and Xac was 52.2, 60.0 and 65.1 μg mL-1 , respectively, superior to 72.9, 64.2 and 70.1 μg mL-1 of the control drug. Moreover, the anti-Xoo mechanistic studies revealed that PA exerted its antibacterial effects by increasing the permeability of the bacterial membrane, reducing the extracellular polysaccharide content and inducing morphological changes in bacterial cells.

CONCLUSION

A novel β-carboline alkaloid, PA, was prepared by biomimetic total synthesis. Its significant antibacterial activity was closely related to the permeation of bacterial cell membranes, which was confirmed by anti-Xoo mechanistic studies. More importantly, the structure could be regarded as a model for developing novel bactericides. © 2023 Society of Chemical Industry.

Design, Synthesis, Antibacterial, and Antifungal Evaluation of Phenylthiazole Derivatives Containing a 1,3,4-Thiadiazole Thione Moiety

To effectively control the infection of plant pathogens, we designed and synthesized a series of phenylthiazole derivatives containing a 1,3,4-thiadiazole thione moiety and screened for their antibacterial potencies against Ralstonia solanacearum, Xanthomonas oryzae pv. oryzae, as well as their antifungal potencies against Sclerotinia sclerotiorum, Rhizoctonia solani, Magnaporthe oryzae and Colletotrichum gloeosporioides. The chemical structures of the target compounds were characterized by 1H NMR, 13C NMR and HRMS. The bioassay results revealed that all the tested compounds exhibited moderate-to-excellent antibacterial and antifungal activities against six plant pathogens. Especially, compound 5k possessed the most remarkable antibacterial activity against R. solanacearum (EC50 = 2.23 μg/mL), which was significantly superior to that of compound E1 (EC50 = 69.87 μg/mL) and the commercial agent Thiodiazole copper (EC50 = 52.01 μg/mL). Meanwhile, compound 5b displayed the most excellent antifungal activity against S. sclerotiorum (EC50 = 0.51 μg/mL), which was equivalent to that of the commercial fungicide Carbendazim (EC50 = 0.57 μg/mL). The preliminary structure-activity relationship (SAR) results suggested that introducing an electron-withdrawing group at the meta-position and ortho-position of the benzene ring could endow the final structure with remarkable antibacterial and antifungal activity, respectively. The current results indicated that these compounds were capable of serving as promising lead compounds.

Synthesis and Antifungal Activity of 2-(2-Benzoxazolyl)-1-arylethanone and 2-(2-Benzoxazolyl)-1-alkylethanone Derivatives

To discover more effective antifungal candidates, 33 benzoxazole derivatives, were designed, synthesized, and evaluated for their antifungal activity against seven phytopathogenic fungi by the mycelium growth rate method. Among 33 benzoxazole derivatives had thirteen derivatives no reported, and new derivatives C17 exhibited good inhibitory activity against Phomopsis sp. with EC50 values of 3.26 μM. Structure-activity relationship (SAR) of these derivatives analysis indicated that the substituent played a key role in antifungal activity in ortho-, meta- and para- substituted acetophenones. The preliminary mechanistic exploration demonstrated that C17 might exert its antifungal activity by targeting the mycelia cell membrane, which was verified by the observed changes in mycelial morphology, the formation of extracellular polysaccharides, cellular contents, cell membrane permeability and integrity, among other effects. Furthermore, C17 had potent curative effect against Phomopsis sp. in vivo, which indicated that C17 may be as a novelty potent antifungal agent.

Design, Synthesis, and Biological Evaluation of Novel Camphor-Based Hydrazide and Sulfonamide Derivatives as Laccase Inhibitors against Plant Pathogenic Fungi/Oomycetes

To discover novel natural product-based fungicidal agrochemicals, 41 novel camphanic acid hydrazide and camphor sulfonamide derivatives were designed, synthesized, and tested for their antifungal profile against four plant pathogenic fungi and three oomycetes. As a result, some derivatives presented pronounced inhibitory activities toward Botryosphaeria dothidea, Fusarium graminearum, Phytophthora capsici, and Phytophthora nicotianae. Especially, compound 4b demonstrated the most potent anti-B. dothidea activity (EC50 = 1.28 mg/L), much stronger than positive control chlorthalonil. The in vivo assay showed that 4b displayed significant protective and curative effects on apple fruits infected by B. dothidea. The primary antifungal mechanism study revealed that 4b could obviously enhance the cell membrane permeability, destroy the mycelial surface morphology and the cell ultrastructure, and reduce the ergosterol and exopolysaccharide contents of B. dothidea. Further, 4b showed potent laccase inhibitory activity in vitro with an IC50 value of 11.3 μM, superior to positive control cysteine. The molecular docking study revealed that 4b could dock well into the active site of laccase by forming multiple interactions with the key residues in the pocket. The acute oral toxicity test in rats presented that 4b had slight toxicity with an LD50 value of 849.1 mg/kg bw (95% confidence limit: 403.9-1785.3 mg/kg bw). This research identified that the camphanic acid hydrazide derivatives could be promising leads for the development of novel laccase-targeting fungicides.

Synthesis and Antiphytopathogenic Activity of Novel Oxazolidine-2,4-diones Bearing Phenoxypyridine Moiety

In the present study, we conducted optimization of pyramoxadone and synthesized a series of novel oxazolidinediones. Antifungal assays showed that these compounds exhibited moderate to excellent antifungal activity against various pathogens. Further SAR analysis revealed that the introduction of substituents to the benzene ring of the phenoxy group or the inclusion of bulky groups, such as tert-butyl, on the aniline moiety, had a detrimental effect on the activity. However, the inclusion of fluorine atoms in the aniline moiety significantly enhanced the antifungal efficacy. Notably, compound 2-4 displayed significantly higher activity compared to both pyramoxadone and famoxadone against R. solani, B. cinerea, S. sclerotiorum, and P. oryzae, where it demonstrated EC50 values of 1.78, 2.47, 2.33, and 2.23 μg/mL, respectively. Furthermore, compound 2-4 exhibited potent protective and curative effects against the tomato gray mold in vivo. A mechanistic investigation revealed that compound 2-4 significantly impacted the mycelial morphology, inhibited spore germination, and impeded mycelial respiration, ultimately leading to the inhibition of pathogenic fungus growth. These findings indicate that compound 2-4 has the potential to serve as a cyt bc1 inhibitor and should be further investigated for development.

Design, synthesis and antifungal evaluation of phenylthiazole-1,3,4-oxadiazole thione (ketone) derivatives inspired by natural thiasporine A

BACKGROUND

Plant pathogenic fungal infections have become a severe threat to the yield and quality of agricultural products, and new green antifungal agents with high efficiency and low toxicity are needed. In this study, a series of thiasporine A derivatives containing phenylthiazole-1,3,4-oxadiazole thione (ketone) structures were designed and synthesized, and their antifungal activities against six invasive and highly destructive phytopathogenic fungi were evaluated.

RESULTS

The results found that all compounds showed moderate to potent antifungal activity against six phytopathogenic fungi, and most of the E series compounds showed remarkable antifungal activity against Sclerotinia sclerotiorum and Colletotrichum camelliaet. In particular, compounds E1-E5, E7, E8, E13, E14, E17, and E22 showed more significant antifungal activity against S. sclerotiorum, with half-maximal effective concentration (EC50 ) values of 0.22, 0.48, 0.56, 0.65, 0.51, 0.39, 0.60, 0.56, 0.60, 0.63, and 0.45 μg mL-1 , respectively, which were superior to that of carbendazim (0.70 μg mL-1 ). Further activity studies showed that compound E1 possessed superior curative activities against S. sclerotiorum in vivo and better inhibitory effects on sclerotia germination and the formation of S. sclerotiorum compared with those of carbendazim.

CONCLUSIONS

This study indicates that these thiasporine A derivatives containing phenylthiazole-1,3,4-oxadiazole thione structures might be used as antifungal agents against S. sclerotiorum. © 2023 Society of Chemical Industry.

Venturicidin A Is a Potential Fungicide for Controlling Fusarium Head Blight by Affecting Deoxynivalenol Biosynthesis, Toxisome Formation, and Mitochondrial Structure

Fusarium graminearum, which causes Fusarium head blight (FHB) in cereals, is one of the most devastating fungal diseases by causing great yield losses and mycotoxin contamination. A major bioactive ingredient, venturicidin A (VentA), was isolated from Streptomyces pratensis S10 mycelial extract with an activity-guided approach. No report is available on antifungal activity of VentA against F. graminearum and effects on deoxynivalenol (DON) biosynthesis. Here, VentA showed a high antagonistic activity toward F. graminearum with an EC50 value of 3.69 μg/mL. As observed by scanning electron microscopy, after exposure to VentA, F. graminearum conidia and mycelia appeared abnormal. Different dyes staining revealed that VentA increased cell membrane permeability. In growth chamber and field trials, VentA effectively reduced disease severity of FHB. Moreover, VentA inhibited DON biosynthesis by reducing pyruvic acid, acetyl-CoA production, and accumulation of reactive oxygen species (ROS) and then inhibiting trichothecene (TRI) genes expression and toxisome formation. These results suggest that VentA is a potential fungicide for controlling FHB.

Design, Synthesis, In Vitro Antifungal Activity and Mechanism Study of the Novel 4-Substituted Mandelic Acid Derivatives

Plant diseases caused by phytopathogenic fungi are a serious threat in the process of crop production and cause large economic losses to global agriculture. To obtain high-antifungal-activity compounds with novel action mechanisms, a series of 4-substituted mandelic acid derivatives containing a 1,3,4-oxadiazole moiety were designed and synthesized. In vitro bioassay results revealed that some compounds exhibited excellent activity against the tested fungi. Among them, the EC₅₀ values of E₁₃ against Gibberella saubinetii (G. saubinetii), E₆ against Verticillium dahlia (V. dahlia), and E₁₈ against Sclerotinia sclerotiorum (S. sclerotiorum) were 20.4, 12.7, and 8.0 mg/L, respectively, which were highly superior to that of the commercialized fungicide mandipropamid. The morphological studies of G. saubinetii with a fluorescence microscope (FM) and scanning electron microscope (SEM) indicated that E₁₃ broke the surface of the hyphae and destroyed cell membrane integrity with increased concentration, thereby inhibiting fungal reproduction. Further cytoplasmic content leakage determination results showed a dramatic increase of the nucleic acid and protein concentrations in mycelia with E₁₃ treatment, which also indicated that the title compound E₁₃ could destroy cell membrane integrity and affect the growth of fungi. These results provide important information for further study of the mechanism of action of mandelic acid derivatives and their structural derivatization.

Synthesis, Antifungal Evaluation, 3D-QSAR, and Preliminarily Mechanism Study of Novel Chiral Mandelic Acid Derivatives

To investigate the effect of spatial configuration on the biological activity of the compounds, a series of chiral mandelic acid derivatives with a moiety of 1,3,4-oxadiazole thioether have been designed and synthesized. Bioassay results demonstrated that most title compounds with the S-configuration exhibited better in vitro antifungal activity against three plant fungi, such as H3' (EC₅₀ = 19.3 μg/mL) against Gibberella saubinetii, which was approximately 16 times higher than that of H3 (EC₅₀ = 317.0 μg/mL). CoMFA and CoMSIA models were established for 3D-QSAR analysis and provided an important support for further optimization of this series of compounds. Comparing the preliminary mechanism studies between enantiomers (H3 and H3') found that the S-configuration compound (H3') exhibited a stronger ability to destroy the surface structure of G. saubinetii mycelia, causing the leakage of intracellular substances to accelerate and the growth of the hyphae to be inhibited. The results provided a novel view for the further optimization of this series of active compounds and deep mechanism study of chiral pesticides.

High inhabitation activity of CMCS/Phytic acid/Zn2+ nanoparticles via flash nanoprecipitation (FNP) for bacterial and fungal infections

Plant diseases prompted by fungi and bacteria are one of the most serious threats to global crop production and food security. The destruction of these infections posed a major challenge to plant protection by chemical control. Herein, we develop CMCS/PA/Zn²⁺ nanoparticles (NPs) using carboxymethyl chitosan (CMCS), phytic acid (PA) and metal ions (Zn²⁺) via flash nanoprecipitation (FNP) strategy. Metal complexes of PA with specified antibacterial and antifungal activities are expected to hold the potential and play a significant role in antimicrobial treatment. The size and size distribution of NPs was confirmed through Dynamic and Static Light Scatterer (DSLS). In acidic-infection microenvironment, the CMCS/PA/Zn²⁺ NPs can disintegrate and release Zn²⁺ in situ thus stimulated the corresponding antimicrobial activity. These CMCS/PA/Zn²⁺ NPs showed outstanding antibacterial efficacy (98 %) against S. aureus and E. coli bacteria in vitro, as well as an impressive antifungal efficacy of 98 % and 81 % against R. solani and B. cinerea at 50 μg/mL respectively. This study contributes a prospective idea to the development of organic-inorganic hybrid NPs as environmentally-friendly and safe agricultural antimicrobials.

Design, synthesis, and antifungal activity of novel dithiin tetracarboximide derivatives as potential succinate dehydrogenase inhibitors

BACKGROUND

Succinate dehydrogenase inhibitor (SDHI) fungicides are an important class of agricultural fungicides with the advantages of high efficiency and a broad bactericidal spectrum. To pursue novel SDHIs, a series of N-substituted dithiin tetracarboximide derivatives were designed, synthesized, and characterized by ¹ H NMR, ¹³ C NMR, and high resolution mass spectrum (HRMS).

RESULTS

These engineered compounds displayed potent fungicidal activity against phytopathogens, including Sclerotinia sclerotiorum, Botrytis cinerea, and Rhizoctonia solani, comparable with that of the commercial SDHI fungicide boscalid. In particular, compound 18 stood out with prominent activity against S. sclerotiorum with a half-maximal effective concentration (EC₅₀ ) value of 1.37 μg ml^-1 . Compound 1 exhibited the most potent antifungal activity against B. cinerea with EC₅₀ values of 5.02 μg ml^-1 . As for R. solani, 12 and 13 exhibited remarkably inhibitory activity with EC₅₀ values of 4.26 and 5.76 μg ml^-1 , respectively. In the succinate dehydrogenase (SDH) inhibition assay, 13 presented significant inhibitory activity with a half-maximal inhibitory concentration (IC₅₀ ) value of 15.3 μm, which was approximately equivalent to that of boscalid (14.2 μm). Furthermore, molecular docking studies revealed that 13 could anchor in the binding site of SDH.

CONCLUSION

Taken together, results suggested that the dithiin tetracarboximide scaffold possessed a huge potential to be developed as novel fungicides and SDHIs. © 2023 Society of Chemical Industry.

Synthesis, in vitro α-glucosidase inhibitory activities, and molecular dynamic simulations of novel 4-hydroxyquinolinone-hydrazones as potential antidiabetic agents

In the present study, new structural variants of 4-hydroxyquinolinone-hydrazones were designed and synthesized. The structure elucidation of the synthetic derivatives 6a-o was carried out using different spectroscopic techniques including FTIR, ¹H-NMR, ¹³C-NMR, and elemental analysis, and their α-glucosidase inhibitory activity was also determined. The synthetic molecules 6a-o exhibited good α-glucosidase inhibition with IC₅₀ values ranging between 93.5 ± 0.6 to 575.6 ± 0.4 µM as compared to the standard acarbose (IC₅₀ = 752.0 ± 2.0 µM). Structure-activity relationships of this series were established which is mainly based on the position and nature of the substituent on the benzylidene ring. A kinetic study of the active compounds 6l and 6m as the most potent derivatives were also carried out to confirm the mode of inhibition. The binding interactions of the most active compounds within the active site of the enzyme were determined by molecular docking and molecular dynamic simulations.

Design, synthesis, and antifungal activities of novel sulfoximine derivatives for plant protection

BACKGROUND

Fungicides play a significant role in the integrated management of plant pathogens. However, the irrational application of fungicides with similar structures has led to development of cross-resistance, therefore there is a need to seek novel fungicides with new structures.

RESULTS

Twenty-eight novel sulfoximine derivatives incorporating nitroguanidine moieties were designed, synthesized, and evaluated as antifungal agents. The bioassay results indicated that most of the synthesized compounds displayed excellent fungicidal activities against Sclerotinia sclerotiorum, Rhizoctonia solani, Fusarium graminearum, and Pyricularia grisea. Among these, compounds 6c₄ , 6c₅ , and 6c₆ exhibited remarkable fungicidal activities against P. grisea, with EC₅₀ values of 1.28, 1.17, and 1.68 μg mL^-1 , respectively. In addition, compound 6c₂ displayed the most potent activity against S. sclerotiorum (EC₅₀  = 3.64 μg mL^-1 ). Further in vivo fungicidal activity screening against S. sclerotiorum demonstrated that the protective and curative effects of compound 6c₂ were 98.1% and 91.3% at 25 μg mL^-1 , respectively, comparable to that of boscalid (94.4%, 89.6%). The preliminary mechanism study found that the hyphae of S. sclerotiorum treated with compound 6c₂ was abnormal with mycelial collapse and membrane permeability increase. The present findings can help to develop new fungicides for crop protection.

CONCLUSION

Novel sulfoximine derivatives containing nitroguanidine possess potential antifungal activity, and the unique structure may offer an alternative option for fungicide development in the future. © 2022 Society of Chemical Industry.

Discovery of triphenylphosphonium (TPP)-conjugated N-(1,1'-biphenyl)-2-yl aliphatic amides as excellent fungicidal candidates

BACKGROUND

Succinate dehydrogenase inhibitors (SDHIs) are the fastest growing agricultural fungicides at present, but their rapidly growing resistance is a serious problem for their application. Previously, we screened out a fungicidal lead compound CBUA-TPP (1) through triphenylphosphonium (TPP)-driven mitochondrial-targeting strategy. The targeting led to the rapid accumulation of 1 in mitochondria and the saturation inhibition of complex II in a short time, resulting in electron leakage and the explosion of reactive oxygen species (ROS). However, the contribution of biphenyl-2-amines to the activity of these compounds and their structure-activity relationship are still unknown.

RESULTS

Two series of CBUA-TPP (1) analogues (series 2 and 3) were designed and synthesized. The bioassay results indicated that series 2 compounds generally showed much higher fungicidal activities than series 3, suggesting the crucial contribution of the biarylamine module in these targeted molecules and the pyridinyl substitution of phenyl is unfavorable to their activities. Interestingly, these two series of compounds displayed almost opposite substituent effects. Several compounds showed excellent fungicidal activities in vitro, among which compound 2-1 exhibited excellent field control efficacy on potato late blight.

CONCLUSION

By optimizing the lead compound, the contribution of biarylamine in CBUA-TPP (1) analogs to the fungicidal activity is clarified. Several compounds, represented by 2-1, have great potential as fungicide candidates. They exhibit high and broad-spectrum fungicidal activities and are highly effective against common pathogenic fungi infecting vegetables and fruits both in vitro and field control. It not only provided a new choice for controlling these diseases, but its low resistance tendency also provided a better scheme for resistance management. © 2023 Society of Chemical Industry.

Design, synthesis, crystal structure, and antimicrobial activities of new quinazoline derivatives containing both the sulfonate ester and piperidinylamide moieties

BACKGROUND

To discover more efficient antimicrobial agents in agriculture, a series of new quinazoline derivatives bearing both sulfonate ester and piperidine-4-carboxamide moieties were synthesized and assessed for their antimicrobial effects.

RESULTS

All of the target compounds were fully characterized by proton (¹ H) nuclear magnetic resonance (NMR), carbon-13 (¹³ C) NMR, and high-resolution mass spectroscopy (HRMS), and compound III-6 containing a 3-bromophenyl substituent was clearly confirmed via single-crystal X-ray diffraction analysis. The bioassay results indicated that some compounds displayed noticeable inhibitory effects in vitro against Xanthomonas oryzae pv. oryzicola (Xoc). Further measurements of median effective concentration (EC₅₀ ) values showed that compound III-17 bearing a 4-methoxyphenyl group had the best anti-Xoc efficacy (EC₅₀  = 12.4 μg mL^-1 ), far better than the commercialized bismerthiazol (77.5 μg mL^-1 ). Moreover, this compound also demonstrated good protection and curative activities in vivo against rice bacterial leaf streak caused by Xoc.

CONCLUSION

Compound III-17 had a good potential for further development as a new bactericide for controlling Xoc. © 2023 Society of Chemical Industry.

Discovery of N-Phenylpropiolamide as a Novel Succinate Dehydrogenase Inhibitor Scaffold with Broad-Spectrum Antifungal Activity on Phytopathogenic Fungi

Based on the structural features of both succinate dehydrogenase inhibitors (SDHIs) and targeted covalent inhibitors, a series of N-phenylpropiolamides containing a Michael acceptor moiety were designed to find new antifungal compounds. Nineteen compounds showed potent inhibition activity in vitro on nine species of plant pathogenic fungi. Compounds 9 and 13 showed higher activity on most of the fungi than the standard drug azoxystrobin. Compound 13 could completely inhibit Physalospora piricola infection on apples at 200 μg/mL concentration over 7 days and showed high safety to seed germination and seedling growth of plants at ≤100 μg/mL concentration. The action mechanism showed that 13 is an SDH inhibitor with a median inhibitory concentration, IC₅₀, value of 0.55 μg/mL, comparable with that of the positive drug boscalid. Molecular docking studies revealed that 13 can bind well to the ubiquinone-binding region of SDH by hydrogen bonds and undergoes π-alkyl interaction and π-cation interaction. At the cellular level, 1 as the parent compound could destruct the mycelial structure of P. piricola and partly dissolve the cell wall and/or membrane. Structure-activity relationship analysis showed that the acetenyl group should be a structure determinant for the activity, and the substitution pattern of the phenyl ring can significantly impact the activity. Thus, N-phenylpropiolamide emerged as a novel and promising lead scaffold for the development of new SDHIs for plant protection.

Design, synthesis, cytotoxic activities, and molecular docking of chalcone hybrids bearing 8-hydroxyquinoline moiety with dual tubulin/EGFR kinase inhibition

The present study established thirteen novel 8-hydroxyquinoline/chalcone hybrids3a-mof hopeful anticancer activity. According to NCI screening and MTT assay results, compounds3d-3f, 3i,3k,and3ldisplayed potent growth inhibition on HCT116 and MCF7 cells compared to Staurosporine. Among these compounds,3eand3fshowed outstanding superior activity against HCT116 and MCF7 cells and better safety toward normal WI-38 cells than Staurosporine. The enzymatic assay revealed that3e,3d, and3ihad goodtubulin polymerization inhibition (IC₅₀ = 5.3, 8.6, and 8.05 µM, respectively) compared to the reference Combretastatin A4 (IC₅₀ = 2.15 µM). Moreover,3e,3l, and3fexhibited EGFR inhibition (IC₅₀ = 0.097, 0.154, and 0.334 µM, respectively) compared to Erlotinib (IC₅₀ = 0.056 µM). Compounds3eand3fwere investigated for their effects on the cell cycle, apoptosis induction, andwnt1/β-cateningene suppression. The apoptosis markers Bax, Bcl2, Casp3, Casp9, PARP1, and β-actin were detected by Western blot. In-silico molecular docking, physicochemical, and pharmacokinetic studies were implemented for the validation of dual mechanisms and other bioavailability standards. Hence, Compounds3eand3fare promising antiproliferative leads with tubulin polymerization and EGFR kinase inhibition.

Rhein-Amino Acid Ester Conjugates as Potential Antifungal Agents: Synthesis and Biological Evaluation

In the search for crop protectants, amino acid ester conjugates have been widely investigated as potential antifungal agents. In this study, a series of rhein-amino acid ester conjugates were designed and synthesized in good yields, and their structures were confirmed by ¹H-NMR, ¹³C-NMR and HRMS. The bioassay results revealed that most of the conjugates exhibited potent inhibitory activity against R. solani and S. sclerotiorum. In particular, conjugate 3c had the highest antifungal activity against R. solani with an EC₅₀ value of 0.125 mM. For S. sclerotiorum, conjugate 3m showed the highest antifungal activity with an EC₅₀ value of 0.114 mM. Satisfactorily, conjugate 3c exhibited better protective effects than that of the positive control, physcion, against powdery mildew in wheat. This research supports the role of rhein-amino acid ester conjugates as potential antifungal agents for plant fungal diseases.

Design, synthesis and bioactivity of myricetin derivatives for control of fungal disease and tobacco mosaic virus disease

A series of myricetin derivatives containing isoxazole were designed and synthesized. All the synthesized compounds were characterized by NMR and HRMS. In terms of antifungal activity, Y3 had a good inhibitory effect on Sclerotinia sclerotiorum (Ss), and the median effective concentration (EC₅₀) value was 13.24 μg mL^-1, which was better than azoxystrobin (23.04 μg mL^-1) and kresoxim-methyl (46.35 μg mL^-1). Release of cellular contents and cell membrane permeability experiments further revealed that Y3 causes the destruction of the cell membrane of the hyphae, which in turn plays an inhibitory role. The anti-tobacco mosaic virus (TMV) activity in vivo showed that Y18 had the best curative and protective activities, with EC₅₀ values of 286.6 and 210.1 μg mL^-1 respectively, the effect was better than ningnanmycin. Microscale thermophoresis (MST) data showed that Y18 had a strong binding affinity with tobacco mosaic virus coat protein (TMV-CP), with a dissociation constant (K _d) value of 0.855 μM, which was better than ningnanmycin (2.244 μM). Further molecular docking revealed that Y18 interacts with multiple key amino acid residues of TMV-CP, which may hinder the self-assembly of TMV particles. Overall, after the introduction of isoxazole on the structure of myricetin, its anti-Ss and anti-TMV activities have been significantly improved, which can be further studied.

Triphenylphosphonium-Driven Targeting of Pyrimorph Fragment Derivatives Greatly Improved Its Action on Phytopathogen Mitochondria

Pyrimorph is a carboxylic acid amide (CAA) fungicide, which shows excellent activity against oomycetes such as pepper phytophthora blight, tomato late blight, and downy mildew of cucumber. It works mainly by inhibiting the biosynthesis of cell wall of oomycetes. However, pyrimorph also shows weak activity of inhibiting mitochondrial complex III, which is the first CAA fungicide found to act on mitochondria. To improve this effect on mitochondria and develop fungicides that may have a novel mechanism of action, in this paper, by disassembling pyrimorph and conjugating the fragments with the mitochondrial-targeted delivery system (triphenylphosphonium), three series of mitochondrial-targeting analogues of pyrimorph were designed and synthesized. The results show that the pyridine-containing 1,1-diaryl is the core module of inhibition mitochondrial function of pyrimorph. Among these conjugates, compound 3b with a short linker showed the highest and broad-spectrum fungicidal activity, strong respiratory inhibition activity, and adenosine 5'-triphosphate synthesis inhibition activity, suggesting its potential as a fungicide candidate. 3b exhibited greatly improved action on mitochondria, such as by destroying the mitochondrial function of pathogens, causing mitochondrial swelling, weakening its influence on cell wall morphology, and so on. More importantly, this study provides a method to strengthen the drugs or pesticides with weak mitochondrial action, which is of special significance for developing mitochondrial bioactive molecules with the novel action mechanism.

Novel Design of Citral-Thiourea Derivatives for Enhancing Antifungal Potential against Colletotrichum gloeosporioides

Although much progress has been made in developing botanical fungicides to combat fungal diseases in crops, there remains a great need to improve the efficiency and long-term safety of these fungicides. This study proposes a novel strategy for designing citral-thiourea derivatives that feature such desirable properties. The motivation of the work herein was to enhance the antifungal activity of citral against C. gloeosprioides by exploiting the synergistic effect that arises from combining citral and thiourea compounds, thereby producing citral-thiourea derivatives that exhibit good long-term safety. The results revealed that the generated compounds e1, e3, e6, e18, and g showed remarkable antifungal activities against C. gloeosprioides, with corresponding EC50 values reaching 0.16, 1.66, 1.37, 4.76, and 4.60 mg/L, respectively, showing that the compounds significantly outperformed both the positive control kresoxim-methyl and the commercially available fungicide carbendazim. Furthermore, compound g showed stronger protective efficacy against C. gloeosprioides than carbendazim on mango fruit at 25 mg/L. Investigating the preliminary structure-activity relationship (SAR) of the compounds also revealed that the citral-thiourea derivatives exhibited higher antifungal activities against C. gloeosprioides compared to citral and thiourea compounds. This reinforcement of antifungal activity observed in the derivatives was found to be attributable to the two characteristics of low molecular size and the presence of a fluorine atom in the meta-position of the benzene ring. Beyond this, it was determined from QSAR that two molecular descriptors (the Kier-Hall index (order 3) and Tot dipole of the molecules) were negatively related to the antifungal activity of the citral-thiourea derivatives, while one other (the maximum resonance energy of a C-H bond) was positively related to their antifungal activity. More importantly, the citral-thiourea derivatives with high antifungal activities (i.e., compounds e1, e3, e6, e14, e15, e18, and g) exhibited negligible cytotoxicity to LO2 and HEK293T cell lines. The antifungal mechanism of the generated citral-thiourea derivatives was investigated by scanning electron microscopy (SEM) and relative conductivity. The derivatives were found to affect mycelial morphology and increase fungal cell membrane permeability, thereby resulting in the destruction of fungal cell membranes. These promising results provide novel insights into the study and potential application value of citral-thiourea derivatives as high-efficiency antifungal agents against C. gloeosprioides.

Design, Synthesis and Antifungal Activity of Novel 1,4-Pentadiene-3-one Containing Quinazolinone

Twenty 1,4-pentadiene-3-one derivatives containing quinazolinone (W1-W20) were designed and synthesized. The bioactivity test results showed that some compounds had antifungal activities in vitro. W12 showed excellent bioactivity against Sclerotinia sclerotiorum (S. sclerotiorum) and Phomopsis sp., with EC₅₀ values of 0.70 and 3.84 μg/mL, which are higher than those of the control drug azoxystrobin at 8.15 and 17.25 μg/mL. In vivo activity tests were carried out on oilseed rape and kiwifruit. The protective effect of W12 on oilseed rape infected with S. sclerotiorum (91.7 and 87.3%) was better than that of azoxystrobin (90.2 and 79.8%) at 100 and 50 μg/mL, respectively, and the protective effect on kiwifruit infected with Phomopsis sp. (96.2%) was better than that of azoxystrobin (94.6%) at 200 μg/mL. Scanning electron microscopy results showed the hyphae of S. sclerotiorum treated with compound W12 abnormally collapsed and shriveled, inhibiting the growth of mycelium and, thus, laying the inhibiting effect on S. sclerotiorum. The results of the mechanism research showed that the action of W12 changed the mycelial morphology of S. sclerotiorum, affected the permeability of cells, increased the leakage of cytoplasm and allowed the cell membrane to break down. This study shows that 1,4-pentadiene-3-one derivatives containing quinazolinone have good effects on plant fungi and the potential for becoming new fungicides.

Design, Synthesis and Bioassay of 2-Phenylglycine Derivatives as Potential Pesticide Candidates

Plant diseases can seriously affect the growth of food crops and economic crops. To date, pesticides are still among the most effective methods to prevent and control plant diseases worldwide. Consequently, to develop potential pesticide molecules, a series of novel 2-phenylglycine derivatives containing 1,3,4-oxadiazole-2-thioethers were designed and synthesized. The bioassay results revealed that G₁₉ exhibited great in vitro antifungal activity against Thanatephorus cucumeris with an EC₅₀ value of 32.4 μg/mL, and in vivo antifungal activity against T. cucumeris on rice leaves at a concentration of 200.0 μg/mL (66.9 %) which was close that of azoxystrobin (73.2 %). Compounds G₂₄ (80.2 %), G₂₅ (89.4 %), and G₂₇ (83.3 %) exhibited impressive in vivo inactivation activity against tobacco mosaic virus (TMV) at a concentration of 500.0 μg/mL, which was comparable to that of ningnanmycin (96.3 %) and markedly higher than that of ribavirin (55.6 %). The antibacterial activity of G₁₆ (63.1 %), G₂₆ (89.9 %), G₂₇ (78.0 %), and G₂₈ (68.0 %) against Xoo at a concentration of 50.0 μg/mL was higher than that of thiadiazole copper (18.0 %) and bismerthiazol (38.9 %). Preliminary mechanism studies on the antifungal activity against T. cucumeris demonstrated that G₁₉ can affect the growth of mycelia by disrupting the integrity of the cell membrane and altering the permeability of the cell. These studies revealed that the amino acid derivatives containing a 1,3,4-oxadiazole moiety exhibited certain antifungal, antibacterial, and anti-TMV activities, and these derivatives can be further modified and developed as potential pesticide molecules.

Conversion of fungicide cyprodinil to salts with organic acids: preparation, characterization, advantages

BACKGROUND

As an effective strategy to improve the basic properties of drugs, salt formation was less used in the field of pesticides than the medicine field. It is worth trying to improve the inherent shortcomings of cyprodinil (high K_ow values; polymorphism) in this way to enhance its practicality.

RESULTS

Eight cyprodinil salts (CYP-Salts) were prepared. The properties of CYP-Salts, including solubility in various solvents, polymorphic behavior, soil absorption, photolysis in aquatic water, in vitro fungicidal activity and curative activity, were assessed. It was observed that compared with those of cyprodinil, CYP-Salts had lower soil adsorption, while also having lower log K_ow values and could be more easily photodegraded in water. That is, CYP-Salts have lower impacts on water bodies and aquatic organisms than cyprodinil. Three CYP-Salts showed higher in vitro antifungal activities and curative activity. CYP-Salts have enhanced practicality, as they could avoid possible agglomeration caused by recrystallization.

CONCLUSION

Salt forming enhanced the properties of Cyprodinil in many aspects. CYP-Salts may potentially become a better substitute for cyprodinil. This study offers a more economical and effective strategy to prepare better alternatives to existing fungicides. © 2022 Society of Chemical Industry.

Inhibitory Mechanism of Pinosylvin Monomethyl Ether against Aspergillus flavus

Control of Aspergillus flavus is beneficial for the agricultural economy and food safety. Stilbenes exhibit antifungal properties through an unknown mechanism. Here, six stilbenes isolated from Cajanus cajan were screened for anti-A. flavus activity. Among them, pinosylvin monomethyl ether (PME) showed the strongest anti-A. flavus activity and has a broad antifungal spectrum with negligible hemolysis within the concentration range measured. PME inhibited the spore germination of A. flavus and the accumulation of aflatoxin B1. Mechanistic studies showed that PME could bind the cell membrane phospholipids, resulting in increased permeability and decreased fluidity. Further metabolic analysis showed that PME caused the lysis of cell membranes and subsequent collapse of spores, which resulted in a cell wall autolysis-like phenotype. Structure-activity relationship analysis revealed the importance of maintaining amphiphilicity harmony by substituent groups for the antifungal activity of stilbenes. Together, natural stilbenes are promising antifungal lead compounds worthy of further exploration and research for potential application in the food, pharmaceutical, and agricultural industries.

Biological and chemical control of Ectophoma multirostrata causing root-rot and seedling death of Celosia argentea in Karbala/Iraq

This study was conducted in the College of the Agriculture/University of Karbala to control the fungus Ectophoma multirostrata that causes root rot of Celosia argentea by using Azotobacter chrocooccum, Salicylic acid and the chemical pesticide Beltanol. The pathogenic E. multirostrata was isolated for the first time in Iraq and showed a reduction in seed germination by 16.66% and 16.00%. The results showed that the bio-control bacteria A. chrocooccum, Salicylic acid and Beltanol effectively reduced the infection rate and severity of Celosia argentea root rot disease and increased the growth parameters. Among the treatments, Beltanol was the highest in reducing the infection rate and severity down to 0.00%, followed by the treatment of integration between A. chrocooccum and Salicylic acid to minimize infection and severity to 16.33% and 8.00%, compared to the infected untreated that showed 80%, 62.00% respectively. In addition, the A. chrocooccum and Salicylic acid integration improved plant growth, including shoot length, shoot and root dry weight to be 22.50 cm, 0.423 g and 0.133 g, compared to the untreated infected treatment that resulted in 5.00 cm, 0.090 g, and 0.003g, respectively. Keywords: Celosia argentea, Ectophoma multirostrata, Azotobacter chrocooccum, Root rot

Allicin-Inspired Heterocyclic Disulfides as Novel Antimicrobial Agents

In this work, a series of derivatives with disulfide bonds containing pyridine, pyrimidine, thiophene, thiazole, benzothiazole, and quinoline were designed and synthesized based on the various biological activities of allicin disulfide bond functional groups. The antimicrobial activities of the target compounds were determined, and the structure-activity relationships were discussed. Among them, compound S8 demonstrated the most potent antifungal activity in vitro against Monilinia fructicola (M. fructicola), with an EC₅₀ value of 5.92 μg/mL. Furthermore, an in vivo bioassay revealed that compound S8 exhibited equivalent curative and higher protective effects as the positive drug thiophanate methyl at a concentration of 200 μg/mL. The preliminary mechanism experiments showed that compound S8 could inhibit the growth of M. fructicola' s hyphae in a time- and concentration-dependent manner, and compound S8 could induce the shrinkage of hyphae, disrupt the integrity of the plasma membrane, and cause the damage and leakage of cell contents. More than that, compound S5 also demonstrated an excellent antibacterial effect on Xanthomonas oryzae (X. oryzae), with a MIC₉₀ value of 1.56 μg/mL, which was superior to the positive control, thiodiazole copper.

Discovery of Novel Quinazoline-2-Aminothiazole Hybrids Containing a 4-Piperidinylamide Linker as Potential Fungicides against the Phytopathogenic Fungus Rhizoctonia solani

A total of 29 novel quinazoline-2-aminothiazole hybrids containing a 4-piperidinylamide linker were designed, synthesized, and evaluated for their anti-microbial properties against phytopathogenic fungi and bacteria of agricultural importance. The anti-fungal assays indicated that some of the target compounds exhibited excellent inhibitory effects in vitro against Rhizoctonia solani. For example, 11 compounds within this series (including 4a, 4g, 4h, 4j, 4o, 4s, 4t, 4u, 4v, 4y, and 4b') were found to possess EC₅₀ values (effective concentration for 50% activity) ranging from 0.42 to 2.05 μg/mL against this pathogen. In particular, compound 4y with a 2-chloro-6-fluorophenyl substituent displayed a potent anti-R. solani efficacy with EC₅₀ = 0.42 μg/mL, nearly threefold more effective than the commercialized fungicide Chlorothalonil (EC₅₀ = 1.20 μg/mL) and also slightly superior to the other fungicide Carbendazim (EC₅₀ = 0.53 μg/mL). Moreover, compound 4y could efficiently inhibit the growth of R. solani in vivo on the potted rice plants, displaying an impressive protection efficacy of 82.3% at 200 μg/mL, better than those of the fungicides Carbendazim (69.8%) and Chlorothalonil (48.9%). Finally, the mechanistic studies showed that compound 4y exerted its anti-fungal effects by altering the mycelial morphology, increasing the cell membrane permeability, and destroying the cell membrane integrity. On the other hand, some compounds demonstrated good anti-bacterial effects in vitro against Xanthomonas oryzae pv. oryzae (Xoo). Overall, the presented results implied that 4-piperidinylamide-bridged quinazoline-2-aminothiazole hybrids held the promise of acting as lead compounds for developing more efficient fungicides to control R. solani.

Synthesis, Antifungal Activity, and 3D-QASR of Novel 1,2,3,4-Tetrahydroquinoline Derivatives Containing a Pyrimidine Ether Scaffold as Chitin Synthase Inhibitors

The introduction of active groups of natural products into the framework of pesticide molecules is an effective approach for discovering active lead compounds, and thus has been widely used in the development of new agrochemicals. In this work, a novel series of 1,2,3,4-tetrahydroquinoline derivatives containing a pyrimidine ether scaffold were designed and synthesized by the active substructure splicing method. The new compounds showed good antifungal activities against several fungi. Especially, compound 4fh displayed excellent in vitro activity against Valsa mali and Sclerotinia sclerotiorum with EC₅₀ values of 0.71 and 2.47 μg/mL, respectively. 4fh had slightly stronger inhibitory activity (68.08% at 50 μM) against chitin synthase (CHS) than that of polyoxin D (63.84% at 50 μM) and exhibited obvious curative and protective effects on S. sclerotiorum in vivo. Thus, 4fh can be considered as a new candidate fungicide as a chitin synthase inhibitor. An accurate and reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) model presented a useful direction for the further excogitation of more highly active fungicides. Molecular docking revealed that the conventional hydrogen bond mainly affected the binding affinity of 4fh with chitin synthase. The present results will provide a guidance to discover potential CHS-based fungicides for plant disease control in agriculture.

Novel Antimycin Analogues with Agricultural Antifungal Activities from the Sponge-Associated Actinomycete Streptomyces sp. NBU3104

Phytopathogenic fungi could affect the growth of agricultural products and result in serious economic losses. To develop novel and potent fungicides, secondary metabolites of an oceanic mesophotic zone Streptomyces sp. NBU3104 was isolated by metabolomics and genomics, which led to the discovery of eight novel antimycins I-P (1-8), including antimycin I (1), six rare acetylated actimycins J-N (2-6), P (8), and an unusual deformylated antimycin O (7). The chemical structures of these metabolites were identified using nuclear magnetic resonance (NMR) spectroscopic analysis, high-resolution electrospray ionization mass spectrometry (HRESIMS) data, and the known reported metabolites in the literature. Their absolute configurations were elucidated by comparison of coupling constant and experimental electronic circular dichroism (ECD) spectra. Among them, compound 1 exhibited excellent inhibitory activities against phytopathogenic fungi, such as Candida albicans, Penicillium expansum, Penicillium citrinum, and Botrytis cinerea. Furthermore, compound 1 could effectively control gray mold of apple in vivo (minimum inhibitory concentration (MIC) = 8 μg/mL). The structure-activity relations of antimycins I-P (1-8) suggested that the aldehyde group in 3-formamidosalicylate unit moiety should be the key factor in their antifungal activities.

Eco-Friendly Hybrid PLLA/Chitosan/Trichoderma asperellum Nanomaterials as Biocontrol Dressings against Esca Disease in Grapevines

Fungi constitute the largest number of plant pathogens and are responsible for a range of serious plant diseases. Phaeomoniella chlamydospora (P. chlamydospora) and Phaeoacremonium aleophilum (P. aleophilum) are the main fungal pathogens causing esca disease in grapevines. On the other hand, there are beneficial microorganisms such as Trichoderma spp., which are able to control the growth of many phytopathogens. In the present study, innovative, eco-friendly hybrid nanomaterials were created by electrospinning PLLA, followed by the formation of a film of chitosan/Trichoderma asperellum (T. asperellum) spores on the fibers. The polymer carrier used in this study plays an active role in ensuring the viability of the biological agent during storage and, when placed in contact with moisture, ensures the agent’s normal development. Oligochitosan, as well as low molecular weight and high molecular weight chitosan, were used. The effects of chitosan molecular weight on the dynamic viscosity of chitosan solutions, film formation, mechanical properties, spore incorporation and growth were studied. The morphology of the prepared nanomaterials, and the presence of a film based on the formation of chitosan/T. asperellum spores on the PLLA fibers, were examined using scanning electron microscopy (SEM). The surface chemical compositions of the fibrous materials were studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The mechanical properties of the obtained materials were also tested. The microbiological screening that was performed revealed that the eco-friendly hybrid nanomaterials incorporated with the beneficial microorganism, T. asperellum, to hamper the growth of the pathogenic P. chlamydospora and P. aleophilum fungi. The suppression rate depended on the viscosity of the chitosan solution used for the film formation. The use of oligochitosan resulted in the most effective infection of the material with T. asperellum spores. The environmentally friendly hybrid nanomaterials obtained in this study—in which the bioagent was embedded—are promising bioactive dressings for protecting grapevines against esca disease.

Design, synthesis and fungicidal evaluation of novel psoralen derivatives containing sulfonohydrazide or acylthiourea moiety

To search a novel lead structure for antiphytopathogenic fungus agent, a series of novel psoralen derivatives possessing sulfonohydrazide or acylthiourea structure were designed and synthesized, and their fungicidal activity against seven phytopathogens was evaluated. Their structures were confirmed by melting points, ¹H NMR, ¹³C NMR and HRMS, and the typical crystal structure was determined by X-ray diffraction for validation. Preliminary fungicidal activity showed that some of the title compounds exhibited certain-to-high fungicidal activity. Compound I-13 exhibited good fungicidal activity against Botrytis cinerea, Cercospora arachidicola and Physalospora piricola with EC₅₀ values of 12.49, 13.22 and 12.12 μg/mL, respectively. Compounds II-9 and II-15 showed over 90% inhibition against B. cinerea at 50 μg/mL in vitro. In particular, II-9 exhibited significant higher fungicidal activity with a lower EC₅₀ value of 9.09 μg/mL than the positive control YZK-C22 (13.41 μg/mL). Our studies found that sulfonohydrazide or acylthiourea-containing psoralen derivatives were promising fungicide leads deserve for further study.

Design, synthesis and mechanism study of novel natural-derived isoquinoline derivatives as antifungal agents

In screening for natural fungicidal leads, two series of novel 3-aryl-isoquinoline derivatives 8 and 9 were designed and synthesized based on sanguinarine, chelerythrine and berberine. Their structures were confirmed by 1D, 2D NMR and HRMS. Most of the title compounds showed medium to excellent antifungal activity in vitro at 50 mg/L, which were much more active than the lead of sanguinarine. Especially, 9f possessed the best effective against Alternaria solani (80.4%), Alternaria alternata (88.2%) and Physalospora piricola (93.8%). Furthermore, the EC₅₀ of 9f (3.651 mg/L) against P. piricola was marginally better than chlorothalonil (3.869 mg/L). In vivo antifungal activity of 9f against P. piricola was studied on apples. The curative and protection results at the dosage of 50 and 100 mg/L showed as 70.45 ~ 81.67% and 64.96 ~ 80.34%, respectively, which were equal to that of chlorothalonil (80.30 ~ 86.67%, 73.08 ~ 76.92%). Molecular electrostatic potential and molecular docking analysis revealed that 9f was fully covered by positive potential contour, which was easier to interact with the negative amino acid resides of succinate dehydrogenase than 8f. 9f could be used as a novel antifungal lead compound for further study. Two series of novel isoquinoline derivatives 8, 9 containing 3-aryl were rational designed and synthesized based on quaternary isoquinoline alkaloids. The bioassay and interaction mechanism studies indicated that 9f should be considered as potential antifungal lead.

Design, Synthesis, and Biological Evaluation of Novel Psoralen-Based 1,3,4-Oxadiazoles as Potent Fungicide Candidates Targeting Pyruvate Kinase

Pyruvate kinase (PK) has been considered as a promising fungicide target discovered in our previous studies. Natural compounds are important sources for discovery and development of new pesticides. To continue our ongoing studies on the discovery of novel PK-targeted fungicides, a series of novel psoralen derivatives including a 1,3,4-oxadiazole moiety were designed by a computer-aided pesticide molecular design method, synthesized, and evaluated for their fungicidal activity. The bioassay results indicated that compounds 11d, 11e, 11g, 11i, and 12a showed excellent in vitro fungicidal activity against Botrytis cinerea with EC₅₀ values of 4.8, 3.3, 6.3, 5.4, and 3.9 μg/mL, respectively. They were more active than the corresponding positive control YZK-C22 [3-(4-methyl-1,2,3-thiadiazol-5-yl)-6-(trichloromethyl)-[1,2,4]-triazolo-[3,4-b][1,3,4]-thiadiazole] (with an EC₅₀ value of 13.4 μg/mL). Compounds 11g and 11i displayed promising in vivo fungicidal activity against B. cinerea with 80 and 70% inhibition at a concentration of 200 μg/mL, respectively. They possessed much higher fungicidal activity than the positive control psoralen and comparable activity with the positive control pyrisoxazole. Enzymatic assays indicated that 11i showed good BcPK inhibition with an IC₅₀ value of 39.6 μmol/L, comparable to the positive control YZK-C22 (32.4 μmol/L). Molecular docking provided a possible binding mode of 11i in the BcPK active site. Our studies suggested that the psoralen-based 1,3,4-oxadiazole 11i could be used as a new fungicidal lead targeting PK for further structural optimization.

Design, Synthesis, and Antimicrobial Activity of Quindoline Derivatives Inspired by the Cryptolepine Alkaloid

Based on the structural characteristics of the cryptolepine alkaloid, a series of new quindoline derivatives bearing various substituents were prepared and evaluated for their fungicidal and antibacterial activities. Bioassay results showed that compound D7 displayed superior in vitro fungicidal activities against Sclerotinia sclerotiorum, Botrytis cinerea, Fusarium graminearum, and Rhizoctonia solani with EC₅₀ values of 0.780, 3.62, 1.59, and 2.85 μg/mL, respectively. Compound A7 showed apparent antibacterial activities toward Xanthomonas oryzae pv. oryzae with a minimum inhibitory concentration (MIC) value of 3.12 μg/mL. Significantly, in vivo antifungal activity suggested that the curative effect (98.3%) of compound D7 was comparable to that of the positive control azoxystrobin (96.7%) at 100 μg/mL. Preliminary mechanistic studies showed that compound D7 might cause mycelial abnormality of S. sclerotiorum, cell membrane breakage, accumulation of reactive oxygen species (ROS), and inhibition of sclerotia formation. Therefore, compound D7 could be a novel broad-spectrum fungicidal candidate against plant fungal diseases.

Design, Synthesis, and Biological Activity of Novel Fungicides Containing a 1,2,3,4-Tetrahydroquinoline Scaffold and Acting as Laccase Inhibitors

Laccase is a novel target for fungicides. We previously developed a new fungicide, 4-chlorocinnamaldehyde thiosemicarbazide (PMDD-5Y), as a laccase inhibitor. The introduction of active groups of natural products into the framework of a pesticide molecular structure is an effective method for discovering active lead compounds, and it has applications in the discovery of new pesticides. In this work, PMDD-5Y was selected as a lead compound, and we designed and synthesized a series of novel sulfonyl hydrazide derivatives containing the natural product scaffold 1,2,3,4-tetrahydroquinoline. The new compounds had antifungal activities against several fungi, especially Valsa mali and Sclerotinia sclerotiorum. One compound (4bl) displayed very good in vitro activity against S. sclerotiorum and V. mali, with EC₅₀ values of 3.32 and 2.78 μg/mL, respectively. The results of an enzyme activity assay showed that 4bh had the best inhibitory activity against laccase, with an EC₅₀ value of 14.85 μg/mL. This was more active than the lead compound PMDD-5Y and the positive control cysteine. Using a molecular docking method, we studied the binding mode of the title compounds with laccase. The structural features of these new laccase inhibitors as fungicides will advance research and impact the field of discovering more potent fungicides to control diseases in agriculture.

Design, synthesis and antifungal mechanism of novel acetophenone derivatives containing 1, 3, 4-thiadiazole-2-thioethers

Plant pathogenic fungi could cause significant losses to agricultural productions. To discover new pesticides with novel structures and unique mechanisms of action, a series of novel acetophenone derivatives containing 1,3,4-thiadiazole-2-thioethers...

Synthesis, Structural Characterization, and Antibacterial and Antifungal Activities of Novel 1,2,4-Triazole Thioether and Thiazolo[3,2-b]-1,2,4-triazole Derivatives Bearing the 6-Fluoroquinazolinyl Moiety

A total of 52 novel 1,2,4-triazole thioether and thiazolo[3,2-b]-1,2,4-triazole derivatives bearing the 6-fluoroquinazolinyl moiety were designed, synthesized, and evaluated as antimicrobial agents in agriculture based on the molecular hybridization strategy. Among them, molecular structures of compounds 5g and 6m were further confirmed via the single-crystal X-ray diffraction method. The bioassay results indicated that some of the target compounds possessed excellent antibacterial activities in vitro against the pathogen Xanthomonas oryzae pv. oryzae (Xoo). For example, compound 6u demonstrated a strong anti-Xoo efficacy with an EC₅₀ value of 18.8 μg/mL, nearly 5-fold more active than that of the commercialized bismerthiazol (EC₅₀ = 93.6 μg/mL). Moreover, the anti-Xoo mechanistic studies revealed that compound 6u exerted its antibacterial effects by increasing the permeability of bacterial membrane, reducing the content of extracellular polysaccharide, and inducing morphological changes of bacterial cells. Importantly, in vivo assays revealed its pronounced protection and curative effects against rice bacterial blight, proving its potential as a promising bactericide candidate for controlling Xoo. Moreover, compound 6u had a good pesticide-likeness based on Tice's criteria. More interestingly, compound 6u with high anti-Xoo activity also demonstrated a potent inhibitory effect of 80.8% against the fungus Rhizoctonia solani at 50 μg/mL, comparable to that of the commercialized chlorothalonil (85.9%). Overall, the current study will provide useful guidance for the rational design of more efficient agricultural antimicrobial agents using the thiazolo[3,2-b]-1,2,4-triazole derivatives bearing the 6-fluoroquinazolinyl moiety as lead compounds.

Novel Citral-thiazolyl Hydrazine Derivatives as Promising Antifungal Agents against Phytopathogenic Fungi

To develop new antifungal agents against phytopathogenic fungi, a series of citral-thiazolyl hydrazine derivatives were designed, synthesized, and characterized by FT-IR, ¹H NMR, ¹³C NMR, and HRMS. Antifungal activity results showed that most synthetic compounds exhibited broad-spectrum antifungal activities against six phytopathogenic fungi in vitro. Notably, compounds b and c15 exhibited remarkable antifungal activity against Colletotrichum gloeosprioides, Rhizoctonia solani, Phytophthora nicotianae var. nicotianae, Diplodia pinea, Colletotrichum acutatum, and Fusarium oxysporum f. sp. niveum, which were all superior to the positive control tricyclazole. Structure-activity relationship (SAR) studies demonstrated that introducing electron-withdrawing groups such as F on the benzene ring exhibited outstanding antifungal activities against all the tested fungi. Furthermore, compound b could effectively control rice sheath blight and showed higher curative activities against R. solani than validamycin·bacillus in vivo. In addition, the in vitro cytotoxicity results indicated that compound b possessed moderate cytotoxicity activity, and all citral-thiazolyl hydrazine derivatives exhibited lower or no cytotoxicity to the LO2 and HEK293 cell lines. In addition, the acute oral toxicity test showed that compound b had moderate toxicity (level II) with an LD₅₀ value of 310 mg/kg bw (95% confidence limit: 175-550 mg/kg bw). Finally, a preliminary action mechanism study showed that causing obvious malformation of mycelium and increasing cell membrane permeability are two of the potential mechanisms by which compound b exerts antifungal activity. The present work indicates that some of these derivatives may serve as novel potential fungicides, and compound b is expected to be the leading structure for the development of new antifungal agents.

Design, Synthesis, and Antifungal Evaluation of Luotonin A Derivatives against Phytopathogenic Fungi

Crop diseases caused by fungi threaten food security and exacerbate the food crisis. Inspired by the application of fungicide candidates from natural products in agrochemical discovery, a series of luotonin A derivatives were designed, synthesized, and evaluated for their antifungal activities against five plant fungi. Most of these compounds exhibited significant fungicidal activity against Botrytis cinerea in vitro with EC₅₀ values less than 1 μg/mL. Among them, compounds w7, w8, w12, and w15 showed superior antifungal activity against B. cinerea with EC₅₀ values of 0.036, 0.050, 0.042, and 0.048 μg/mL, respectively, which were more potent than boscalid (EC₅₀ = 1.790 μg/mL). Preliminary mechanism studies revealed that compound w7 might pursue its antifungal activity by disrupting the fungal cell membrane and cell wall. Moreover, in vivo bioassay also indicated that compound w7 could be effective for the control of B. cinerea. The above results evidenced the potential of luotonin A derivatives as novel and promising candidate fungicides.

Design, Synthesis, Antibacterial, Antifungal and Anticancer Evaluations of Novel β-Pinene Quaternary Ammonium Salts

β-pinene is a monoterpene isolated from turpentine oil and numerous other plants' essential oils, which has a broad spectrum of biological activities. In the current work, six novel β-pinene quaternary ammonium (β-PQA) salts were synthesized and evaluated in vitro for their antifungal, antibacterial and anticancer activities. The in vitro assay results revealed that compounds 4a and 4b presented remarkable antimicrobial activity against the tested fungi and bacteria. In particular, compound 4a showed excellent activities against F. oxysporum f.sp. niveum, P. nicotianae var.nicotianae, R. solani, D. pinea and Fusicoccumaesculi, with EC50 values of 4.50, 10.92, 9.45, 10.82 and 6.34 μg/mL, respectively. Moreover, compound 4a showed the best antibacterial action against E. coli, P. aeruginosa, S. aureus and B. subtilis, with MIC at 2.5, 0.625, 1.25 and 1.25 μg/mL, respectively. The anticancer activity results demonstrated that compounds 4a, 4b, 4c and 4f exhibited remarkable activity against HCT-116 and MCF-7 cell lines, with IC50 values ranged from 1.10 to 25.54 μM. Notably, the compound 4c displayed the strongest cytotoxicity against HCT-116 and MCF-7 cell lines, with the IC50 values of 1.10 and 2.46 μM, respectively. Furthermore, preliminary antimicrobial mechanistic studies revealed that compound 4a might cause mycelium abnormalities of microbial, cell membrane permeability changes and inhibition of the activity of ATP. Altogether, these findings open interesting perspectives to the application of β-PQA salts as a novel leading structure for the development of effective antimicrobial and anticancer agents.