Rational modification of melatonin for broad-spectrum antifungal agents discovery.

Natural products, known for their environmental safety, are regarded as a significant basis for the modification and advancement of fungicides. Melatonin, as a low-cost natural indole, exhibits diverse biological functions, including antifungal activity. However, its potential as an antifungal agent has not been fully explored. In this study, a series of melatonin derivatives targeting the mitogen-activated protein kinase (Mps1) protein of fungal pathogens were synthesized based on properties of melatonin, among which the trifluoromethyl-substituted derivative Mt-23 exhibited antifungal activity against seven plant pathogenic fungi, and effectively reduced the severity of crop diseases, including rice blast, Fusarium head blight of wheat and gray mold of tomato. In particular, its EC50 (5.4 µM) against the rice blast fungus Magnaporthe oryzae is only one-fourth that of isoprothiolane (22 µM), a commercial fungicide. Comparative analyzes revealed that Mt-23 simultaneously targets the conserved protein kinase Mps1 and lipid protein Cap20. Surface plasmon resonance assays showed that Mt-23 directly binds to Mps1 and Cap20. In this study, we provide a strategy for developing antifungal agents by modifying melatonin, and the resultant melatonin derivative Mt-23 is a commercially valuable, eco-friendly and broad-spectrum antifungal agent to combat crop disease.

Novel Alkaloids from Aspergillus fumigatus VDL36, an Endophytic Fungus Associated with Vaccinium dunalianum.

Eleven alkaloids (1-11) including seven new ones, 1-7, were isolated from the solid fermentation of Aspergillus fumigatus VDL36, an endophytic fungus isolated from the leaves of Vaccinium dunalianum Wight (Ericaceae), a perennial evergreen shrub distributed across the Southwest regions of China, Myanmar, and Vietnam. Their structures were elucidated on the basis of extensive spectroscopic methods. The isolates were evaluated for in vitro antifungal activities against five phytopathogenic fungi (Fusarium oxysporum, Coriolus versicolor, Fusarium solani, Botrytis cinerea, Fusarium graminearum). As a result, the new compounds fumigaclavine I (1), 13-ethoxycyclotryprostatin A (5), 13-dehydroxycyclotryprostatin A (6), and 12ß-hydroxy-13-oxofumitremorgin C (7) exhibited antifungal activities with MIC values of 7.8-62.5 µg/mL which were comparable to the two positive controls ketoconazole (MIC = 7.8-31.25 µg/mL) and carbendazim (MIC = 1.95-7.8 µg/mL). Furthermore, compounds 1 and 5 demonstrated potent protective and curative effects against the tomato gray mold in vivo. Preliminary structure-activity relationships of the tested indole diketopiperazine alkaloids indicate that the introduction of a substituent group at position C-13 enhances their biological activities.

Enhanced white rot control in garlic bulbil using organic-inorganic hybrid materials as coating membranes.

Organic-inorganic hybrid materials have a range of applications due to their unique properties. Their application in agriculture brings alternatives for the controlled release of nutrients in the soil, the seed coating, the transport of herbicides, and the treatment of plant diseases. The present study aimed to investigate the use of fungicides incorporated into hybrid membranes formed by synthetic hectorite (LAPONITE®) and polymers in the pre-treatment of garlic bulbils exposed to the pathogen Stromatinia cepivora, which causes white rot. The coatings were selected by a germination test, based on the bulbil sprouting index, and by a mycelial growth inhibition test, based on the percentage of mycelial growth inhibition. The chosen membranes were used to coat the bulbils for bioassays conducted in a biochemical oxygen demand incubator at 17 °C. The coated bulbils were planted in soil samples containing three different densities of Stromatinia cepivora: 0.1 g, 1.0 g, and 10 g of sclerotium per L of soil. Membranes containing 2% carboxymethyl cellulose and 2% LAPONITE® incorporated with (i) the fungicide tebuconazole (36 mg L-1) and (ii) the combination of the actives tebuconazole (36 mg L-1) and triadimenol (62 mg L-1) showed the total rate of sprouting and null indices of incidence of symptoms and mortality in its repetitions. The hybrid membranes were characterized employing several techniques, including X-ray diffraction, infrared and Raman spectroscopy, thermogravimetric analysis and differential scanning calorimetry coupled to mass spectrometry, and optical microscopy. Characterization data confirmed the presence of fungicides incorporated into the membranes. Some concentrations of fungicides were low enough not to be detected in all analyses performed, although they guaranteed a protective character to the bulbils about the fungus S. cepivora present in the soil, with a possibility of antifungal pre-treatment with a potential reduction in the concentration used.

Synthesis, Characterization, and Antifungal Activity of Benzimidazole-Grafted Chitosan against Aspergillus flavus.

Aspergillus flavus contamination in agriculture and food industries poses threats to human health, leading to a requirement of a safe and effective method to control fungal contamination. Chitosan-based nitrogen-containing derivatives have attracted much attention due to their safety and enhanced antimicrobial applications. Herein, a new benzimidazole-grafted chitosan (BAC) was synthesized by linking the chitosan (CS) with a simple benzimidazole compound, 2-benzimidazolepropionic acid (BA). The characterization of BAC was confirmed by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance spectroscopy (1H and 13C NMR). Then, the efficiency of BAC against A. flavus ACCC 32656 was investigated in terms of spore germination, mycelial growth, and aflatoxin production. BAC showed a much better antifungal effect than CS and BA. The minimum inhibitory concentration (MIC) value was 1.25 mg/mL for BAC, while the highest solubility of CS (16.0 mg/mL) or BA (4.0 mg/mL) could not completely inhibit the growth of A. flavus. Furthermore, results showed that BAC inhibited spore germination and elongation by affecting ergosterol biosynthesis and the cell membrane integrity, leading to the permeabilization of the plasma membrane and leakage of intracellular content. The production of aflatoxin was also inhibited when treated with BAC. These findings indicate that benzimidazole-derived natural CS has the potential to be used as an ideal antifungal agent for food preservation.

Study on the Design, Synthesis, Bioactivity and Translocation of the Conjugates of Phenazine-1-carboxylic Acid and N-Phenyl Alanine Ester.

The natural pesticide phenazine-1-carboxylic acid (PCA) is known to lack phloem mobility, whereas Metalaxyl is a representative phloem systemic fungicide. In order to endow PCA with phloem mobility and also enhance its antifungal activity, thirty-two phenazine-1-carboxylic acid-N-phenylalanine esters conjugates were designed and synthesized by conjugating PCA with the active structure N-acylalanine methyl ester of Metalaxyl. All target compounds were characterized by 1H NMR, 13C NMR and HRMS. The antifungal evaluation results revealed that several target compounds exhibited moderate to potent antifungal activities against Sclerotinia sclerotiorum, Bipolaris sorokiniana, Phytophthora parasitica, Phytophthora citrophthora. In particular, compound F7 displayed excellent antifungal activity against S. sclerotiorum with an EC50 value of 6.57 µg/mL, which was superior to that of Metalaxyl. Phloem mobility study in castor bean system indicated good phloem mobility for the target compounds F1-F16. Particularly, compound F2 exhibited excellent phloem mobility; the content of compound F2 in the phloem sap of castor bean was 19.12 µmol/L, which was six times higher than Metalaxyl (3.56 µmol/L). The phloem mobility tests under different pH culture solutions verified the phloem translocation of compounds related to the "ion trap" effect. The distribution of the compound F2 in tobacco plants further suggested its ambimobility in the phloem, exhibiting directional accumulation towards the apical growth point and the root. These results provide valuable insights for developing phloem mobility fungicides mediated by exogenous compounds.

Diallyl Trisulfide Acts as a Soil Disinfestation Against the Ilyonectria destructans through Inducing the Burst of Reactive Oxygen Species.

Soil-borne diseases represent an impediment to the sustainable development of agriculture. A soil-borne disease caused by Ilyonectria destructans severely impacts Panax species, and soil disinfestation has proven to be an effective management approach. Here, diallyl trisulfide (DATS), derived from garlic, exhibited pronounced inhibitory effects on the growth of I. destructans in vitro tests and contributed to the alleviation of soil-borne diseases in the field. A comprehensive analysis demonstrated that DATS inhibits the growth of I. destructans by activating detoxifying enzymes, such as GSTs, disrupting the equilibrium of redox reactions. A series of antioxidant amino acids were suppressed by DATS. Particularly noteworthy is the substantial depletion of glutathione by DATS, resulting in the accumulation of ROS, ultimately culminating in the inhibition of I. destructans growth. Briefly, DATS could effectively suppress soil-borne diseases by inhibiting pathogen growth through the activation of ROS, and it holds promise as a potential environmentally friendly soil disinfestation.

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.

Targeting of Antifungal Metabolites from Grapevine Byproducts by UPLC-HRMS/MS Approaches Using Bioactivity-Based Molecular Networking.

This study focuses on countering Fusarium graminearum, a harmful fungal pathogen impacting cereal crops and human health through mycotoxin production. These mycotoxins, categorized as type B trichothecenes, pose significant health risks. Research explores natural alternatives to synthetic fungicides, particularly investigating phenolics in grapevine byproducts. Thirteen eco-extracts from five French grape varieties (Merlot, Cabernet Sauvignon, Sauvignon blanc, Tannat, and Artaban) exhibited substantial antifungal properties, with ten extracts displaying remarkable effects. Extracts from grapevine stems and roots notably reduced fungal growth by over 91% after five days. Through UHPLC-HRMS/MS analysis and metabolomics, the study identified potent antifungal compounds such as ampelopsin A and cyphostemmin B, among other oligomeric stilbenes. Interestingly, this approach showed that flavan-3-ols have been identified as markers for extracts that induce fungal growth. Root extracts from rootstocks, rich in oligostilbenes, demonstrated the highest antifungal activity. This research underscores grapevine byproducts' potential both as a sustainable approach to control F. graminearum and mycotoxin contamination in cereal crops and the presence of different metabolites from the cultivars of grapevine, suggesting different activities.

Antipathogenic Activities of Volatile Organic Compounds Produced by Bacillus velezensis LT1 against Sclerotium rolfsii LC1, the Pathogen of Southern Blight in Coptis chinensis.

This study explores the antipathogenic properties of volatile organic compounds (VOCs) produced by Bacillus velezensis LT1, isolated from the rhizosphere soil of Coptis chinensis. The impact of these VOCs on the mycelial growth of Sclerotium rolfsii LC1, the causative agent of southern blight in C. chinensis, was evaluated using a double Petri-dish assay. The biocontrol efficacy of these VOCs was further assessed through leaf inoculation and pot experiments. Antifungal VOCs were collected using headspace solid-phase microextraction (SPME), and their components were identified via gas chromatography-mass spectrometry (GC-MS). The results revealed that the VOCs significantly inhibited the mycelial growth and sclerotia germination of S. rolfsii LC1 and disrupted the morphological integrity of fungal mycelia. Under the influence of these VOCs, genes associated with chitin synthesis were upregulated, while those related to cell wall degrading enzymes were downregulated. Notably, 2-dodecanone and 2-undecanone exhibited inhibition rates of 81.67% and 80.08%, respectively. This research provides a novel approach for the prevention and management of southern blight in C. chinensis, highlighting the potential of microbial VOCs in biocontrol strategies.

Chemoenzymatic Asymmetric Synthesis of Chiral Triazole Fungicide (R)-Tebuconazole in High Optical Purity Mediated by an Epoxide Hydrolase from Rhodotorula paludigensis.

Tebuconazole is a chiral triazole fungicide used globally in agriculture as a racemic mixture, but its enantiomers exhibit significant enantioselective dissimilarities in bioactivity and environmental behaviors. The steric hindrance caused by the tert-butyl group makes it a great challenge to synthesize tebuconazole enantiomers. Here, we designed a simple chemoenzymatic approach for the asymmetric synthesis of (R)-tebuconazole, which includes the biocatalytic resolution of racemic epoxy-precursor (2-tert-butyl-2-[2-(4-chlorophenyl)ethyl] oxirane, rac-1a) by Escherichia coli/Rpeh whole cells expressed epoxide hydrolase from Rhodotorula paludigensis (RpEH), followed by a one-step chemocatalytic synthesis of (R)-tebuconazole. It was observed that (S)-1a was preferentially hydrolyzed by E. coli/Rpeh, whereas (R)-1a was retained with a specific activity of 103.8 U/g wet cells and a moderate enantiomeric ratio (E value) of 13.4, which was remarkably improved to 43.8 after optimizing the reaction conditions. Additionally, a gram-scale resolution of 200 mM rac-1a was performed using 150 mg/mL E. coli/Rpeh wet cells, resulting in the retention of (R)-1a in a 97.0% ees, a 42.5% yields, and a 40.5 g/L/d space-time yield. Subsequently, the synthesis of highly optical purity (R)-tebuconazole (>99% ee) was easily achieved through the chemocatalytic ring-opening of the epoxy-precursor (R)-1a with 1,2,4-triazole. To elucidate insight into the enantioselectivity, molecular docking simulations revealed that the unique L-shaped substrate-binding pocket of RpEH plays a crucial role in the enantioselective recognition of bulky 2,2-disubstituted oxirane 1a.

Antifungal Activity of Novel Indole Derivatives Containing 1,3,4-Thiadiazole.

In this study, 24 indole derivatives containing 1,3,4-thiadiazole were discovered and synthesized. The target compounds' antifungal efficacy against 14 plant pathogenic fungal pathogens was then determined in vitro. With an EC50 value of 2.7 µg/mL, Z2 demonstrated the highest level of bioactivity among them against Botrytis cinerea (B.c.), exceeding the concentrations of the control prescription drugs azoxystrobin (Az) (EC50 = 14.5 µg/mL) and fluopyram (Fl) (EC50 = 10.1 µg/mL). Z2 underwent in vivo testing on blueberry leaves in order to evaluate its usefulness in real-world settings. A reasonable protective effect was obtained with a control effectiveness of 93.0% at 200 µg/mL, which was superior to those of Az (83.0%) and Fl (52.0%). At 200 µg/mL, this chemical had an efficacy of 84.0% in terms of curative efficacy. These figures outperformed those of Az (69.0%) and Fl (48.0%). Scanning electron microscopy (SEM) experiments and light microscopy experiments showed that Z2 altered the integrity of the cell wall and cell membrane of the pathogenic fungus B.c., which led to an increase in the content of malondialdehyde (MDA), cellular leakage, and cellular permeability. Enzyme activity assays and molecular docking studies indicated that Z2 could act as a potential succinate dehydrogenase inhibitor (SDHI). It was hypothesized that Z2 could cause disruption of mycelial cell membranes, which in turn leads to mycelial death. According to the research, indole derivatives containing 1,3,4-thiadiazole were expected to evolve into new fungicides due to their significant antifungal effects on plant fungi.

Novel Aminocoumarin Derivatives against Phytopathogenic Fungi: Design, Synthesis and Structure-Activity Relationships.

Phytopathogenic fungi is the most devastating reason for the decrease of the agricultural production and food safety. To develop new fungicidal agents for resistance concerning, a novel series of aminocoumarin derivatives were synthesized and their fungicidal activity were investigated both in vitro and in vivo. Transmission electron microscope (TEM), scanning electron microscope (SEM), RNA-Seq, 3D-QSAR and molecular docking were applied to reveal the underlying anti-fungal mechanisms. Most of the compounds exhibited significant fungicidal activity. Notably, compound 10c had a more extensive fungicidal effect than positive control. TEM indicated that compound 10c could cause abnormal morphology of cell walls, vacuoles and release of cellular contents. Transcriptional analysis data indicated that 895 and 653 out of 1548 differential expressed genes (DEGs) were up-regulated and down-regulated respectively. The Go and KEGG enrichment indicated that the coumarin derivatives could induce significant changes of succinate dehydrogenase (SDH), Acetyl-coenzyme A synthetase (ACCA) and pyruvate dehydrogenase (PDH) genes, which contributed to the disorders of glucolipid metabolism and the dysfunction of mitochondrial. The results demonstrated that aminocoumarins with schiff-base as core moieties could be the promising lead compounds for the discovery of novel fungicides.

Novel 5-Sulfonyl-1,3,4-thiadiazole-Substituted Flavonoids as Potential Bactericides and Fungicides: Design, Synthesis, Three-Dimensional Quantitative Structure-Activity Relationship Studies.

Flavonoids, ubiquitous natural products, provide sources for drug discovery owing to their structural diversity, broad-spectrum pharmacological activity, and excellent environmental compatibility. To develop antibacterial and antifungal agents with novel mechanisms of action and innovative structures, a series of novel 5-sulfonyl-1,3,4-thiadiazole-substituted flavonoids were designed and synthesized, and their biological activities against seven agriculturally common phytopathogenic microorganisms were evaluated. The results of the antimicrobial bioassay showed that most of the target compounds displayed excellent inhibitory effects against Xanthomonas oryzae, Rhizoctonia solani, and Colletotrichum orbiculare. Compounds 1, 3, 7, 9, 13, and 14 exhibited remarkable antibacterial activity against X. oryzae pv. oryzae with EC50 values below 10 µg/mL, which were superior to bismerthiazol (70.89 µg/mL). Compound 2 (EC50 = 0.41 µg/mL) displayed the most effective inhibitory potency against R. solani in vivo, comparable protective effects with the positive control carbendizam. Preliminary mechanistic studies indicated that compound 2 induced disordered entanglement of hyphae, shrinkage of hyphal surfaces, extravasation of cellular contents, and vacuole swelling and rupture, which disrupted normal hyphal growth. Subsequently, compounds 35-53 with good antifungal activity were designed and synthesized based on reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) models. Compound 49 showed high efficacy and superior antifungal activity against R. solani, with an EC50 value of 0.28 µg/mL and a half-maximal effective concentration of 0.46 µg/mL.

Design and Discovery of α-Oximido-arylacetamides as Novel Antifungal Leads.

The discovery of novel and easily accessible antifungal compounds is an imperative issue in agrochemical innovation. Our continuing research with the o-aminophenyloxazoline (NHPhOx) scaffold demonstrated the viability of introducing phenylacetamides for identifying novel antifungal leads. An antifungal function-oriented molecular evaluation was conducted for the previously identified lead R-LE008. Fine-tuning of the α-position and scaffold hopping of acid segment and NHPhOx enables α-oximido-arylacetamide as a novel antifungal model. The concomitant function-oriented diversification produces a panel of antifungal leads CN19, CN21b, CN28, and CN31 against Sclerotinia sclerotiorum and Botrytis cinerea. The crucial and multidimensional effect of the configuration of the acquired amides on the antifungal performance is demonstrated specifically by the separable CN21 isomers. The Z-isomer (CN21b), with an EC50 value of 0.97 µM against B. cinerea, is significantly more potent than its E-isomer (CN21a) and the positive control boscalid. More importantly, compound CN21b can efficiently inhibit resistant B. cinerea strains. CN21b demonstrates a better in vivo preventative effect (82.1%) than those of CN21a (48.1%) and boscalid (55.1%) at 100 µM. CN21b showed a distinct binding model from those of the boscalid and CN21a in the molecular docking simulation. A further morphological investigation by scanning electron microscopy revealed the different mycelia shrinkage of B. cinerea treated by CN21 isomers. The easy accessibility and cost-effectiveness demonstrated the practical potential of α-oximido-phenylacetamide containing NHPhOx as a new model for agrochemical innovation.

Isolating Antipathogenic Fungal Coumarins from Coriaria nepalensis and Determining Their Primary Mechanism In Vitro.

Through bioassay-guided isolation, eight undescribed coumarins (1-8), along with six reported coumarins (9-14), were obtained from Coriaria nepalensis. The new structures were determined by using IR, UV, NMR, HRESIMS, and ECD calculations. The results of the biological activity assays showed that compound 9 exhibited broad spectrum antifungal activities against all tested fungi in vitro and a significant inhibitory effect on Phytophthora nicotianae with an EC50 value of 3.00 µg/mL. Notably, compound 9 demonstrated greater curative and protective effects against tobacco balack shank than those of osthol in vivo. Thus, 9 was structurally modified to obtain new promising antifungal agents, and the novel derivatives (17b, 17j, and 17k) exhibited better effects on Sclerotinia sclerotiorum than did lead compound 9. Preliminary mechanistic exploration illustrated that 9 could enhance cell membrane permeability, destroy the morphology and ultrastructure of cells, and reduce the exopolysaccharide content of P. nicotianae mycelia. Furthermore, the cytotoxicity results revealed that compound 9 exhibited relatively low cytotoxicity against HEK293 cell lines with an inhibition rate of 33.54% at 30 µg/mL. This research is promising for the discovery of new fungicides from natural coumarins with satisfactory ecological compatibility.

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.

Design, Synthesis, Antifungal Activity, and 3D-QASR of Novel Oxime Ether-Containing Coumarin Derivatives as Potential Fungicides.

Structural modification of natural products is an effective approach for improving antifungal activity and has, therefore, been used extensively in the development of new agrochemical products. In this work, a series of novel coumarin derivatives containing oxime ether structures were designed, synthesized, and evaluated for antifungal activity. Some of the designed compounds exhibited promising antifungal activities against tested fungi, and compounds 4a, 4c, 5a, and 6b had EC50 values equivalent to those of commercial fungicides. Compound 6b was the most promising candidate fungicide against Rhizoctonia solani (EC50 = 0.46 µg/mL). In vivo antifungal bioassays suggested that compounds 5a and 6b could serve as novel agricultural antifungals. Furthermore, microscopy demonstrated that compound 6b induced the sprawling growth of hyphae, distorted the outline of cell walls, and reduced mitochondrial numbers. Additionally, the effects of the substituent steric, electrostatic, hydrophobic, and hydrogen-bond fields were elucidated using an accurate and reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) model. The results presented here will guide the discovery of potential novel fungicides for plant disease control in agriculture.

Antifungal Activity and Putative Mechanism of HWY-289, a Semisynthetic Protoberberine Derivative, against Botrytis cinerea.

The emergence of resistant pathogens has increased the demand for alternative fungicides. The use of natural products as chemical scaffolds is a potential method for developing fungicides. HWY-289, a semisynthetic protoberberine derivative, demonstrated broad-spectrum and potent activities against phytopathogenic fungi, particularly Botrytis cinerea (with EC50 values of 1.34 µg/mL). SEM and TEM imaging indicated that HWY-289 altered the morphology of the mycelium and the internal structure of cells. Transcriptomics revealed that it could break down cellular walls through amino acid sugar and nucleotide sugar metabolism. In addition, it substantially decreased chitinase activity and chitin synthase gene (BcCHSV) expression by 53.03 and 82.18% at 1.5 µg/mL, respectively. Moreover, this impacted the permeability and integrity of cell membranes. Finally, HWY-289 also hindered energy metabolism, resulting in a significant reduction of ATP content, ATPase activities, and key enzyme activities in the TCA cycle. Therefore, HWY-289 may be a potential candidate for the development of plant fungicides.

Design and Synthesis of Novel Diphenyl Ether Carboxamide Derivatives To Control the Phytopathogenic Fungus Sclerotinia sclerotiorum.

Sclerotinia stem rot (SSR) caused by the phytopathogenic fungus Sclerotinia sclerotiorum has led to serious losses in the yields of oilseed rape and other crops every year. Here, we designed and synthesized a series of carboxamide derivatives containing a diphenyl ether skeleton by adopting the scaffold splicing strategy. From the results of the mycelium growth inhibition experiment, inhibition rates of compounds 4j and 4i showed more than 80% to control S. sclerotiorum at a dose of 50 µg/mL, which is close to that of the positive control (flubeneteram, 95%). Then, the results of a structure-activity relationship study showed that the benzyl scaffold was very important for antifungal activity and that introducing a halogen atom on the benzyl ring would improve antifungal activity. Furthermore, the results of an in vitro activity test suggested that these novel compounds can inhibit the activity of succinate dehydrogenase (SDH), and the binding mode of 4j with SDH was basically similar to that of the flutolanil derivative. Morphological observation of mycelium revealed that compound 4j could cause a damage on the mycelial morphology and cell structure of S. sclerotiorum, resulting in inhibition of the growth of mycelia. Furthermore, in vivo antifungal activity assessment of 4j displayed a good control of S. sclerotiorum (>97%) with a result similar to that of the positive control at a concentration of 200 mg/L. Thus, the diphenyl ether carboxamide skeleton is a new starting point for the discovery of new SDH inhibitors and is worthy of further development.

Design, Synthesis, and Biological Activities of Novel Coumarin Derivatives as Pesticide Candidates.

Food security is an important issue in the 21st century; preventing and controlling crop diseases and pests are the key to solve this problem. The creation of new pesticides based on natural products is an important and effective method. Herein, coumarins were selected as parent structures, and a series of their derivatives were designed, synthesized, and evaluated for their antiviral activities, fungicidal activities, and insecticidal activities. We found that coumarin derivatives exhibited good to excellent antiviral activities against tobacco mosaic virus (TMV). The antiviral activities of I-1, I-2a, I-4b, II-2c, II-2g, II-3, and II-3b are better than that of ribavirin at 500 µg/mL. Molecular docking research showed that these compounds had a strong interaction with TMV CP. These compounds also showed broad-spectrum fungicidal activities against 14 plant pathogenic fungi. The EC50 values of I-1, I-2a, I-3c, and II-2d are in the range of 1.56-8.65 µg/mL against Rhizoctonia cerealis, Physalospora piricola, Sclerotinia sclerotiorum, and Pyricularia grisea. Most of the compounds also displayed good insecticidal activities against Mythimna separata. Pesticide-likeness analysis showed that these compounds are following pesticide-likeness and have the potential to be developed as pesticide candidates. The present work lays a foundation for the discovery of novel pesticide lead compounds based on coumarin derivatives.