Synthesis and antifungal activities of novel thiophene-based stilbene derivatives bearing an 1,3,4-oxadiazole unit

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Design, synthesis, antifungal evaluation and mechanism study of novel norbornene derivatives as potential laccase inhibitors

BACKGROUND

To discover novel fungicide candidates, five series of novel norbornene hydrazide, bishydrazide, oxadiazole, carboxamide and acylthiourea derivatives (2a-2t, 3a-3f, 4a-4f, 5a-5f and 7a-7f) were designed, synthesized and assayed for their antifungal activity toward seven representative plant fungal pathogens.

RESULTS

In the in vitro antifungal assay, some title norbornene derivatives presented good antifungal activity against Botryosphaeria dothidea, Sclerotinia sclerotiorum and Fusarium graminearum. Especially, compound 2b exhibited the best inhibitory activity toward B. dothidea with the median effective concentration (EC50) of 0.17 mg L-1, substantially stronger than those of the reference fungicides boscalid and carbendazim. The in vivo antifungal assay on apples revealed that 2b had significant curative and protective effects, both of which were superior to boscalid. In the preliminary antifungal mechanism study, 2b was able to injure the surface morphology of hyphae, destroy the cell membrane integrity and increase the intracellular reactive oxygen species (ROS) level of B. dothidea. In addition, 2b could considerably inhibit the laccase activity with the median inhibitory concentration (IC50) of 1.02 μM, much stronger than that of positive control cysteine (IC50 = 35.50 μM). The binding affinity and interaction mode of 2b with laccase were also confirmed by molecular docking.

CONCLUSION

This study presented a promising lead compound for the study of novel laccase inhibitors as fungicidal agrochemicals, which demonstrate significant anti-B. dothidea activity and laccase inhibitory activity. © 2024 Society of Chemical Industry.

Medicinal chemistry perspective on the structure-activity relationship of stilbene derivatives

Stilbenes are a small family of polyphenolic secondary metabolites produced in a variety of closely related plant species. These compounds function as phytoalexins, aiding plant defense against phytopathogens and plants' adaptation to abiotic environmental factors. Structurally, some important phenolic compounds have a 14-carbon skeleton and usually have two isomeric forms, Z and E. Stilbenes contain two benzene rings linked by a molecule of ethanol or ethylene. Some derivatives of natural (poly)phenolic stilbenes such as resveratrol, pterostilbene, and combretastatin A-4 have shown various biological activities, such as anti-microbial, anti-cancer, and anti-inflammatory properties as well as protection against heart disease, Alzheimer's disease, and diabetes. Among stilbenes, resveratrol is certainly the most popular and extensively studied for its health properties. In recent years, an increasing number of stilbene compounds have been investigated for their bioactivity. This review focuses on the assessment of synthetic stilbene derivatives in terms of their biological activities and structure-activity relationship. The goal of this study is to consider the structural changes and different substitutions on phenyl rings that can improve the desired medicinal effects of stilbene-based compounds beyond the usual standards and subsequently discover biological activities by identifying effective alternatives of the evaluated compounds.

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

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

Design, Synthesis, and Antifungal/Anti-Oomycete Activities of Novel 1,2,4-Triazole Derivatives Containing Carboxamide Fragments

Plant diseases caused by pathogenic fungi or oomycetes seriously affect crop growth and the quality and yield of products. A series of novel 1,2,4-triazole derivatives containing carboxamide fragments based on amide fragments widely used in fungicides and the commercialized mefentrifluconazole were designed and synthesized. Their antifungal activities were evaluated against seven kinds of phytopathogenic fungi/oomycete. Results showed that most compounds had similar or better antifungal activities compared to mefentrifluconazole's inhibitory activity against Physalospora piricola, especially compound 6h (92%), which possessed outstanding activity. Compound 6h (EC50 = 13.095 μg/mL) showed a better effect than that of mefentrifluconazole (EC50 = 39.516 μg/mL). Compound 5j (90%) displayed outstanding anti-oomycete activity against Phytophthora capsici, with an EC50 value of 17.362 μg/mL, far superior to that of mefentrifluconazole (EC50 = 75.433 μg/mL). The result of molecular docking showed that compounds 5j and 6h possessed a stronger affinity for 14α-demethylase (CYP51). This study provides a new approach to expanding the fungicidal spectrum of 1,2,4-triazole derivatives.

A Review on the Mechanism and Structure-activity Relationship of Resveratrol Heteroaryl Analogues

Resveratrol is one of the most interesting naturally-occurring nonflavonoid phenolic compounds with various biological activities, such as anticancer, neuroprotection, antibacterial, and anti-inflammatory. However, there is no clinical usage of resveratrol due to either its poor activity or poor pharmacokinetic properties. Heteroarenes-modified resveratrol is one pathway to improve its biological activities and bioavailability, and form more modification sites. In this review, we present the progress of heteroaryl analogues of resveratrol with promising biological activities in the latest five years, ranging from the synthesis to the structure-activity relationship and mechanism of actions. Finally, introducing heteroarenes into resveratrol is an effective strategy, which focuses on the selectivity of structure-activity relationship in vivo.

Discovery of Novel Pyrazol-5-yl-benzamide Derivatives Containing a Thiocyanato Group as Broad-Spectrum Fungicidal Candidates

In an effort to promote the development of new fungicides, a series of 48 novel N-(1-methyl-4-thiocyanato-1H-pyrazol-5-yl)-benzamide derivatives A1-A36 and B1-B12 were designed and synthesized by incorporating a thiocyanato group into the pyrazole ring, and their fungicidal activities were evaluated against Sclerotinia sclerotiorum, Valsa mali, Botrytis cinerea, Rhizoctonia solani, and Phytophthora capsici. In the in vitro antifungal/antioomycete assay, many of the target compounds exhibited good broad-spectrum fungicidal activities. Among them, compound A36 displayed the best antifungal activity against V. mali with an EC50 value of 0.37 mg/L, which was significantly higher than that of the positive controls fluxapyroxad (13.3 mg/L) and dimethomorph (10.3 mg/L). Meanwhile, compound B6 exhibited the best antioomycete activity against P. capsici with an EC50 value of 0.41 mg/L, which was higher than that of azoxystrobin (29.2 mg/L) but lower than that of dimethomorph (0.13 mg/L). Notably, compound A27 displayed broad-spectrum inhibitory activities against V. mali, B. cinerea, R. solani, S. sclerotiorum, and P. capsici with respective EC50 values of 0.71, 1.44, 1.78, 0.87, and 1.61 mg/L. The in vivo experiments revealed that compounds A27 and B6 presented excellent protective and curative efficacies against P. capsici, similar to that of the positive control dimethomorph. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses showed that compound B6 could change the mycelial morphology and severely damage the ultrastructure of P. capsici. The results of the in vitro SDH enzymatic inhibition experiments indicated that compounds A27 and B6 could effectively inhibit the activity of P. capsici SDH (PcSDH). Furthermore, molecular docking analysis demonstrated significant hydrogen bonds and Pi-S bonding between the target compounds and the key amino acid residues of PcSDH, which could explain the probable mechanism of action. Collectively, these studies provide a valuable approach to expanding the fungicidal spectrum of pyrazol-5-yl-benzamide derivatives.

Natural product osthole can significantly disrupt cell wall integrity and dynamic balance of Fusarium oxysporum

Dendrobium officinale Kimura et Migo is a traditional Chinese herbal medicinal plant. However, the frequent occurrence of soft rot disease (SRD) is one of the most harmful diseases in D. officinale production in recent years, which can seriously affect its yield and quality. In this study, the major pathogenic fungus (SR-1) was isolated from D. officinale with typical symptoms of SRD, and was identified as Fusarium oxysporum through morphological and molecular identification. The biological activities of five natural products were determined against F. oxysporum using a mycelial growth inhibition assay. The results showed that osthole had the highest antifungal activity against F. oxysporum, with an EC50 value of 6.40 mg/L. Scanning electron microscopy (SEM) showed that osthole caused F. oxysporum mycelia to shrink and deform. Transmission electron microscopy (TEM) showed that the organelles were blurred and the cell wall was thickened in the presence of osthole. The sensitivity of F. oxysporum to calcofluor white (CFW) staining was significantly enhanced by osthole. Relative conductivity measurements and propidium iodide (PI) observation revealed that osthole had no significant effect on the cell membrane. Further experiments showed that the activity of chitinase and β-1,3-glucanase were decreased, and expression levels of chitinase and β-1,3-glucanase related genes were significantly down-regulated after treatment with osthole. In conclusion, osthole disrupted the cell wall integrity and dynamic balance of F. oxysporum, thereby inhibiting normal mycelial growth.

Bioactivity-Guided Subtraction of MIQOX for Easily Available Isoquinoline Hydrazides as Novel Antifungal Candidates

The discovery of novel and easily available leads provides a convincing solution to agrochemical innovation. A bioassay-guided scaffold subtraction of the previous "Chem-Bio Model" isoquinoline-3-oxazoline MIQOX was conducted for identifying the easily available isoquinoline-3-hydrazide as a novel antifungal scaffold. The special and practical potential of this model was demonstrated by a phenotypic antifungal bioassay, molecular docking, and cross-resistance evaluation. A panel of antifungal leads (LW2, LW3, and LW11) was acquired, showing much better antifungal performance than the positive controls. Specifically, compound LW3 exhibited a broad antifungal spectrum holding EC₅₀ values as low as 0.54, 0.09, 1.52, and 2.65 mg/L against B. cinerea, R. solani, S. sclerotiorum , and F. graminearum, respectively. It demonstrated a curative efficacy better than that of boscalid in controlling the plant disease caused by B. cinerea. The candidate LW3 did not show cross-resistance to the extensively used succinate dehydrogenase inhibitor (SDHI) fungicides and can efficiently inhibit resistant B. cinerea strains. The molecular docking of compound LW3 is quite different from that of the positive controls boscalid and fluopyram. This progress highlights the practicality of isoquinoline hydrazide as a novel model in fungicide innovation.

Investigation of the antibacterial mechanism of the novel bactericide dioctyldiethylenetriamine (Xinjunan)

BACKGROUND

Chemical control is an important method for tackling crop diseases. Clarifying the antibacterial mechanisms of bactericides is useful for developing new bactericides and for continuous plant disease control. In this study, the antibacterial mechanism of a novel bactericide, dioctyldiethylenetriamine (Xinjunan), which affects adenosine triphosphate (ATP) synthesis, was investigated.

RESULTS

The results of an in vitro inhibition activity assay showed that dioctyldiethylenetriamine inhibited the growth of a variety of plant pathogenic bacteria, especially that of Xanthomonas spp. Scanning electron microscopy demonstrated that dioctyldiethylenetriamine caused cell distortion and rupture. To investigate the molecular mechanism underlying the antibacterial effect of dioctyldiethylenetriamine, transcriptome sequencing (RNA-seq) was performed for Xanthomonas oryzae pv. oryzae (Xoo, PXO99A) treated with dioctyldiethylenetriamine, which has strong antibacterial effects against xanthomonads. The results showed that differentially expressed genes were enriched mainly in the oxidative phosphorylation and tricarboxylic acid (TCA) cycle pathways after treatment. Moreover, the dioctyldiethylenetriamine treatment exhibited reduction in enzyme activities in the TCA cycle, decreased intracellular nicotinamide adenine dinucleotide and ATP contents, and increased accumulation of reactive oxygen species. In addition, dioctyldiethylenetriamine exhibited an inhibitory effect on the growth of other bacterial pathogens by reducing ATP synthesis.

CONCLUSION

This is the first report of the mechanism by which dioctyldiethylenetriamine inhibits ATP synthesis by affecting oxidative phosphorylation and TCA cycle pathways in bacteria. © 2023 Society of Chemical Industry.

Carboxymethyl cellulose/sulfur-functionalized Ti-based MOF composite: synthesis, characterization, antimicrobial, antiviral and anticancer potentiality

Microbial resistance is the first morbidity and mortality cause for patients as usually a secondary infection. Additionally, the MOF is a promising material that shows a nice activity in this field. However, these materials need a good formulation to enhance biocompatibility and sustainability. Cellulose and its derivatives are well as filers for this gap. In this presented work, a novel green active system based on carboxymethyl cellulose and Ti-MOF (MIL-125-NH₂@CMC) modified with thiophene (Thio@MIL-125-NH₂@CMC) was prepared by a post-synthetic modification (PSM) route based. FTIR, SEM and PXRD were utilized to characterize nanocomposites. In addition, transmission electron microscopy (TEM) was used to corroborate the nanocomposites' particle size and diffraction pattern as well as the DLS affirmed the size as 50 and 35 nm for MIL-125-NH₂@CMC and Thio@MIL-125-NH₂@CMC, respectively. The formulation of the nanocomposites was validated by physicochemical characterization techniques, while morphological analysis confirmed the nanoform of the prepared composites. The antimicrobial, antiviral and antitumor properties of MIL-125-NH₂@CMC and Thio@MIL-125-NH₂@CMC were assessed. Antimicrobial testing revealed that Thio@MIL-125-NH₂@CMC possesses greater antimicrobial activity than MIL-125-NH₂@CMC. Additionally, Thio@MIL-125-NH₂@CMC demonstrated promising antifungal activity against C. albicans and A. niger where MICs were 31.25 and 0.97 µg/mL, respectively. Also, Thio@MIL-125-NH₂@CMC exhibited antibacterial activity against E. coli and S. aureus where MICs were 1000 and 250 µg/mL, respectively. In addition, the results demonstrated that Thio@MIL-125-NH₂@CMC displayed promising antiviral activity against both HSV1 and COX B4, with antiviral activities of 68.89% and 39.60%, respectively. Furthermore, Thio@MIL-125-NH₂@CMC exhibited potential anticancer activity against MCF7 and PC3 cancerous cell lines, where IC₅₀ was 93.16 and 88.45%, respectively. In conclusion, carboxymethyl cellulose/sulfur-functionalized Ti-based MOF composite was successfully synthesized which had antimicrobial, antiviral and anticancer activities.

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.

Natural products in crop protection: thiosemicarbazone derivatives of 3-acetyl-N-benzylindoles as antifungal agents and their mechanism of action

BACKGROUND

Phytopathogenic fungi can cause a direct loss in economic value of agriculture. Especially Valsa mali Miyabe et Yamada, a devastating phytopathogenic disease especially threatening global apple production, is very difficult to control and manage. To discover new potential antifungal agents, a series of thiosemicarbazone derivatives of 3-acetyl-N-benzylindoles were prepared. Their antifungal activities were first tested against six typically phytopathogenic fungi including Curvularia lunata, Valsa mali, Alternaria alternate, Fusarium graminearum, Botrytis cinerea and Fusarium solani. Then their mechanism of action against V. mali was investigated.

RESULTS

Derivatives displayed potent antifungal activity against V. mali. Notably, 3-acetyl-N-benzylindole thiosemicarbazone (IV-1: EC₅₀ : 0.59 μg mL^-1 ), whose activity was comparable to that of a commercial fungicide carbendazim (EC₅₀ : 0.33 μg mL^-1 ), showed greater than 98-fold antifungal activity of the precursor indole. Moreover, compound IV-1 displayed good protective and therapeutic effects on apple Valsa canker disease. By scanning electron microscope (SEM) and RNA-Seq analysis, it was demonstrated that compound IV-1 can destroy the hyphal structure and regulate the homeostasis of metabolism of V. mali via the ergosterol biosynthesis and autophagy pathways.

CONCLUSION

3-Acetyl-N-(un)substituted benzylindoles thiosemicarbazones (IV-1-IV-5) can be studied as leads for further structural modification as antifungal agents against V. mali. Particularly, these ergosterol biosynthesis and autophagy pathways can be used as target receptors for design of novel green pesticides for management of congeneric phytopathogenic fungi. © 2023 Society of Chemical Industry.

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.

Synthesis and Biological Evaluation of Dipeptide-Based Stilbene Derivatives Bearing a Biheterocyclic Moiety as Potential Fungicides

The escalating demand for crop production, environmental protection, and food safety warrants the development of new fungicides with greater efficiency, environmental friendliness, and innocuous metabolites to fight against destructive phytopathogens. Herein, we report on the synthesis and antifungal activity of dipeptide-based stilbene derivatives bearing a thiophene-substituted 1,3,4-oxadiazole fragment for the first time. In vitro bioassay indicated that the target compounds had remarkable antifungal potency superior to previously reported counterparts without a dipeptidyl group, of which compound 3c exhibited the highest activity against Botrytis cinerea with EC₅₀ values of 106.1 μg/mL. Moreover, the in vivo protective effect of compound 3c (59.1%) against tomato gray mold was more potent than that of carboxin (42.0%). Preliminary investigations on the mode of action showed that compound 3c induced marked hyphal malformations and increased the membrane permeability of B. cinerea as well as inhibiting mycelial respiration. These promising results suggest that this novel type of molecular framework has great potential to be further developed as alternative fungicides.

Design, synthesis, and biological evaluation of novel berberine derivatives against phytopathogenic fungi

BACKGROUND

The abuse of chemical fungicides not only leads to toxic residues and resistance in plant pathogenic fungi, but also causes environmental pollution and side effects on in humans and animals. Based on the antifungal activities of berberine, seven different types of berberine derivatives (A1-G1) were synthesized, and their antifungal activities against six plant pathogenic fungi were evaluated (Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, Phytophthora capsici, Sclerotinia sclerotiorum, and Magnaporthe oryzae).

RESULTS

The results for antifungal activities in vitro showed that berberine derivative E1 displayed good antifungal activity against R. solani with a median effective concentration (EC₅₀ ) of 1.77 μg ml^-1 , and berberine derivatives F1 and G1 demonstrated broad-spectrum antifungal activities with EC₅₀ values ranging from 4.43 to 42.23 μg ml^-1 against six plant pathogenic fungi. Berberine derivatives (E2-E29, F2-F18, and G2-G9) were further synthesized to investigate the structure-activity relationship (SAR), and compound E20 displayed significant antifungal activity against R. solani with an EC₅₀ value of 0.065 μg ml^-1 . Preliminary mechanism studies showed that E20 could cause mycelial shrinkage, cell membrane damage, mitochondrial abnormalities and the accumulation of harmful reactive oxygen species, resulting in cell death in R. solani. Moreover, in vivo experimental results showed that the protective effect of E20 was 97.31% at 5 μg ml^-1 , which was better than that of the positive control thifluzamide (50.13% at 5 μg ml^-1 ).

CONCLUSION

Berberine derivative E20 merits further development as a new drug candidate with selective and excellent antifungal activity against R. solani. © 2022 Society of Chemical Industry.

Identification and structural elucidation of bioactive compounds from Scirpoides holoschoenus

Phytochemical investigations of dichloromethane and methanol extracts of roots and rhizomes of Scirpoides holoschoenus afforded 21 stilbenes, six flavonoids, six ferulic acid derivatives and four diterpenes. Among these constituents, six stilbenes, one flavonoid, one diterpene and two ferulic acid derivatives, represent previously unreported natural products. Structure elucidation was performed by HRESI-MS, NMR, GC-MS, and ECD data evaluation. The monoprenylated flavonoid (sophoraflavanone B) and all isolated stilbene oligomers (trans-scirpusin B, scirpusin A, cassigarol E, cyperusphenol B, cyperusphenol D, passiflorinol A, cyperusphenol A and mesocyperusphenol A) showed strong inhibitory activities on spore germination of two Botrytis cinerea strains isolated from field-infected grape berries and apple fruits compared to the reference controls resveratrol, piceid, and fenhexamid at a test concentration of 2.0 mM. For sophoraflavanone B and cyperusphenol A, the EC₅₀ values were determined by concentration response curves and resulted in values of 0.35 mM and 0.53 mM, respectively. The data suggest that stilbene oligomers but also prenylated flavonoids should be examined further to gain more information on their antimicrobial activity and might be a suitable addition to chemical fungicides on the market to combat gray mold.

1,3,4-Oxadiazole Derivatives as Plant Activators for Controlling Plant Viral Diseases: Preparation and Assessment of the Effect of Auxiliaries

Plant viral diseases cause the loss of millions of dollars to agriculture around the world annually. Therefore, the development of highly efficient, ultra-low-dosage agrochemicals is desirable for protecting the health of crops and ensuring food security. Herein, a series of 1,3,4-oxadiazole derivatives bearing an isopropanol amine moiety was prepared, and the inhibitory activity against tobacco mosaic virus (TMV) was assessed. Notably, compound A₁₄ exhibited excellent anti-TMV protective activity with an EC₅₀ value of 137.7 mg L^-1, which was superior to that of ribavirin (590.0 mg L^-1) and ningnanmycin (248.2 mg L^-1). Moreover, the anti-TMV activity of some compounds could be further enhanced (by up to 5-30%) through supplementation with 0.1% auxiliaries. Biochemical assays suggested that compound A₁₄ could suppress the biosynthesis of TMV and induce the plant's defense response. Given these merits, designed compounds had outstanding bioactivities and unusual action mechanisms and were promising candidates for controlling plant viral diseases.

Design, Synthesis and in Vitro Antifungal Mechanism of Novel Phenylalanine Derivatives

To explore novel molecules with unique mechanisms against plant pathogenic fungi, a series of phenylalanine derivatives containing a 1,3,4-oxadiazothioether moiety were designed and synthesized. Bioassays revealed that some target compounds at 100 μg/mL exhibited excellent antifungal activities against Thanatephorus cucumeris, such as G₆ (92.1 %), G₁₀ (94.3 %), G₁₈ (99.1 %), and G₁₉ (98.7 %), better than that of the commercial fungicide azoxystrobin (90.6 %), and the EC₅₀ value of G₁₀ against T. cucumeris was 31.9 μg/mL. Further mechanism studies of T. cucumeris treated with G₁₀ demonstrated that this compound can affect the growth of mycelia by disrupting the integrity of the membrane, and the higher the concentration of the compound is, the greater the degree of membrane integrity damage, similar to the commercial fungicide azoxystrobin. These conclusions provide important information for further mechanism studies of this series of phenylalanine derivatives.

Design, Synthesis, and Biological Profiles of Novel 1,3,4-Oxadiazole-2-carbohydrazides with Molecular Diversity

To unceasingly expand the molecular diversity of 1,3,4-oxadiazole-2-carbohydrazides, herein, small fragments (including -CH₂-, -OCH₂-, and -SCH₂-) were incorporated into the target compounds to screen out the potential succinate dehydrogenase inhibitors (SDHIs). The bioassay results showed that the antifungal effects (expressed by EC₅₀) against Sclerotinia sclerotiorum, Botryosphaeria dothidea, Fusarium oxysporum, and Colletotrichun higginsianum could reach 1.29 (10a), 0.63 (8h), 1.50 (10i), and 2.09 (10i) μg/mL, respectively, which were slightly lower than those of carbendazim (EC₅₀ were 0.69, 0.13, 0.55, and 0.80 μg/mL, respectively). Especially, compound 10h was extremely bioactive against Gibberella zeae (G. z.) with an EC₅₀ value of 0.45 μg/mL. This outcome was better than that of fluopyram (3.76 μg/mL) and was similar to prochloraz (0.47 μg/mL). In vivo trials against the corn scab (infected by G. z.) showed that compound 10h had control activity of 86.8% at 200 μg/mL, which was better than that of boscalid (79.6%). Further investigations found that compound 10h could inhibit the enzymatic activity of SDH in the G. z. strain with an IC₅₀ value of 3.67 μM, indicating that potential SDHIs might be developed. Additionally, the other biological activities of these molecules were screened simultaneously. The anti-oomycete activity toward Phytophthora infestans afforded a minimal EC₅₀ value of 3.22 μg/mL (10h); compound 4d could strongly suppress the growth of bacterial strains Xanthomonas axonopodis pv. citri and Xanthomonas oryzae pv. oryzae with EC₅₀ values of 3.79 and 11.4 μg/mL, respectively; and compound 10a displayed some insecticidal activity toward Plutella xylostella. Given their multipurpose features, these frameworks could be actively studied as potential pesticide leads.

Design, Synthesis, Herbicidal Activity, and Molecular Docking Study of 2-Thioether-5-(Thienyl/Pyridyl)-1,3,4-Oxadiazoles as Potent Transketolase Inhibitors

Transketolase (TK) has been regarded as a new target for the development of novel herbicides. In this study, a series of 2-thioether-5-(thienyl/pyridyl)-1,3,4-oxadiazoles were designed and synthesized based on TK as the new target. The preliminary bioassay results indicated that compounds 4l and 4m displayed the best herbicidal activities against Amaranthus retroflexus (AR) and Digitaria sanguinalis (DS), with the inhibition exceeding 90% at 100-200 mg/L in vitro. Moreover, they also displayed higher postemergence herbicidal activities (90% control) against AR and DS than all of the positive controls at 45-90 g [active ingredient (ai)]/ha in a greenhouse. Notably, compounds 4l and 4m showed a broad spectrum of weed control at 90 g ai/ha. More significantly, compound 4l exhibited good crop selectivity against maize at 90 g ai/ha. Both fluorescent binding experiments and molecular docking analyses indicated that compounds 4l and 4m exhibited strong TK inhibitory activities with superior binding affinities than the others. Preliminary mechanism studies suggested that they might exert their TK inhibitory effects by occupying the active cavity of At TK and forming more strong interactions with amino acids in the active site. Taken together, these results suggested that compound 4l was a potential herbicide candidate for weed control in maize fields targeting TK.

1,3,4-Oxadiazole Contained Sesquiterpene Derivatives: Synthesis and Microbiocidal Activity for Plant Disease

A series of 1,3,4-oxadiazole contained sesquiterpene derivatives were synthesized, and the activity of the target compounds against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and tobacco mosaic virus (TMV) were evaluated. The biological activity results showed that the EC₅₀ values of compounds H4, H8, H11, H12, H14, H16, and H19 for Xac inhibitory activity were 33.3, 42.7, 56.1, 74.5, 37.8, 43.8, and 38.4 μg/ml, respectively. Compounds H4, H8, H15, H19, H22, and H23 had inhibitory effects on Xoo, with EC₅₀ values of 51.0, 43.3, 43.4, 50.5, 74.6, and 51.4 μg/ml, respectively. In particular, the curative and protective activities of compound H8 against Xoo in vivo were 51.9 and 49.3%, respectively. In addition, the EC₅₀ values of the inactivation activity of compounds H4, H5, H9, H10, and H16 against TMV were 69.6, 58.9, 69.4, 43.9, and 60.5 μg/ml, respectively. The results of molecular docking indicated that compound H10 exhibited a strong affinity for TMV-coat protein, with a binding energy of −8.88 kcal/mol. It may inhibit the self-assembly and replication of TMV particles and have an anti-TMV effect, which supports its potential usefulness as an antiviral agent.

Antifungal Activity and Action Mechanism Study of Coumarins from Cnidium monnieri Fruit and Structurally Related Compounds

The increasing resistance of plant diseases caused by phytopathogenic fungi highlights the need for highly effective and environmentally benign agents. The antifungal activities of Cnidium monnieri fruit extracts and five isolated compounds as well as structurally related coumarins against five plant pathogenic fungi were evaluated. The acetone extract, which contained the highest amount of five coumarins, showed strongest antifungal activity. Among the coumarin compounds, we found that 4-methoxycoumarin exhibited stronger and broader antifungal activity against five phytopathogenic fungi, and was more potent than osthol. Especially, it could significantly inhibit the growth of Rhizoctonia solani mycelium with an EC₅₀ value of 21 μg mL^-1 . Further studies showed that 4-methoxycoumarin affected the structure and function of peroxisomes, inhibited the β-oxidation of fatty acids, decreased the production of ATP and acetyl coenzyme A, and then accumulated ROS by damaging MMP and the mitochondrial function to cause the cell death of R. solani mycelia. 4-Methoxycoumarin presented antifungal efficacy in a concentration- dependent manner in vivo and could be used to prevent the potato black scurf. This study laid the foundation for the future development of 4-methoxycournamin as an alternative and friendly biofungicide.

Novel Pyrazolo[3,4-d]pyrimidin-4-one Derivatives as Potential Antifungal Agents: Design, Synthesis, and Biological Evaluation

Plant pathogenic fungi seriously threaten agricultural production. There is an urgent need to develop novel fungicides with low toxicity and high efficiency. In this study, we designed and synthesized 44 pyrazolo[3,4-d]pyrimidin-4-one derivatives and evaluated them for their fungicidal activities. The bioassay data revealed that most of the target compounds possessed moderate to high in vitro antifungal activities. Especially compound g22 exhibited remarkable antifungal activity against Sclerotinia sclerotiorum with an EC₅₀ value of 1.25 mg/L, close to that of commercial fungicide boscalid (EC₅₀ = 0.96 mg/L) and fluopyram (EC₅₀ = 1.91 mg/L). Moreover, compound g22 possessed prominent protective activity against S. sclerotiorum in vivo for 24 h (95.23%) and 48 h (93.78%), comparable to positive control boscalid (24 h (96.63%); 48 h (93.23%)). Subsequent studies indicated that compound g22 may impede the growth and reproduction of S. sclerotiorum by affecting the morphology of mycelium, destroying cell membrane integrity, and increasing cell membrane permeability. In addition, the application of compound g22 did not injure the growth or reproduction of Italian bees. This study revealed that compound g22 is expected to be developed for efficient and safe agricultural fungicides.

Novel Pyrazole-4-acetohydrazide Derivatives Potentially Targeting Fungal Succinate Dehydrogenase: Design, Synthesis, Three-Dimensional Quantitative Structure-Activity Relationship, and Molecular Docking

Succinate dehydrogenase inhibitors (SDHIs) have emerged in fungicide markets as one of the fastest-growing categories that are widely applied in agricultural production for crop protection. Currently, the structural modification focusing on the flexible amide link of SDHI molecules is being gradually identified as one of the innovative strategies for developing novel highly efficient and broad-spectrum fungicides. Based on the above structural features, a series of pyrazole-4-acetohydrazide derivatives potentially targeting fungal SDH were constructed and evaluated for their antifungal effects against Rhizoctonia solani, Fusarium graminearum, and Botrytis cinerea. Strikingly, the in vitro EC₅₀ values of constructed pyrazole-4-acetohydrazides 6w against R. solani, 6c against F. graminearum, and 6f against B. cinerea were, respectively, determined as 0.27, 1.94, and 1.93 μg/mL, which were obviously superior to that of boscalid against R. solani (0.94 μg/mL), fluopyram against F. graminearum (9.37 μg/mL), and B. cinerea (1.94 μg/mL). Concurrently, the effects of the substituent steric, electrostatic, hydrophobic, and hydrogen-bond fields on structure-activity relationships were elaborated by the reliable comparative molecular field analysis and comparative molecular similarity index analysis models. Subsequently, the practical value of pyrazole-4-acetohydrazide derivative 6w as a potential SDHI was ascertained by the relative surveys on the in vivo anti-R. solani preventative efficacy, inhibitory effects against fungal SDH, and molecular docking studies. The present results provide an indispensable complement for the structural optimization of antifungal leads potentially targeting SDH.

Fabrication of Versatile Pyrazole Hydrazide Derivatives Bearing a 1,3,4-Oxadiazole Core as Multipurpose Agricultural Chemicals against Plant Fungal, Oomycete, and Bacterial Diseases

Developing multipurpose agricultural chemicals is appealing in crop protection, thus eventually realizing the reduction and efficient usage of pesticides. Herein, an array of versatile pyrazole hydrazide derivatives bearing a 1,3,4-oxadiazole core were initially synthesized and biologically evaluated the antifungal, antioomycetes, and antibacterial activities. In addition, the pyrazole ring was replaced by the correlative pyrrole, thiazole, and indole scaffolds to extend the molecular diversity. The results showed that most of these hybrid compounds were empowered with multifunctional bioactivities, which are exemplified by compounds a1-a6, b1-b3, b7, b10, b13, and b18. For the antifungal activity, the minimal EC₅₀ values could afford 0.47 (a2), 1.05 (a2), 0.65 (a1), and 1.32 μg/mL (b3) against the corresponding fungi Gibberella zeae (G. z.), Fusarium oxysporum, Botryosphaeria dothidea, and Rhizoctonia solani. In vivo pot experiments against corn scab (caused by G. z.) revealed that the compound a2 was effective with protective and curative activities of 90.2 and 86.3% at 200 μg/mL, which was comparable to those of fungicides boscalid and fluopyram. Further molecular docking study and enzymatic activity analysis (IC₅₀ = 3.21 μM, a2) indicated that target compounds were promising succinate dehydrogenase inhibitors. Additionally, compounds b2 and a4 yielded superior anti-oomycete and antibacterial activities toward Phytophora infestins and Xanthomonas oryzae pv. oryzae with EC₅₀ values of 2.92 and 8.43 μg/mL, respectively. In vivo trials against rice bacterial blight provided the control efficiency within 51.2-55.3% (a4) at 200 μg/mL, which were better than that of bismerthiazol. Given their multipurpose characteristics, these structures should be positively explored as agricultural chemicals.

Photostable 1-Trifluoromethyl Cinnamyl Alcohol Derivatives Designed as Potential Fungicides and Bactericides

In the current work, a series of 1-trifluoromethyl cinnamyl alcohol derivatives were designed and synthesized and their antifungal activities were evaluated. The bioassay result showed that most compounds exhibited excellent antifungal activity in vitro at 10 μg mL^-1. Next, photostable and easily synthesized compound 2 with broad-spectrum antifungal activity in vitro was selected as a potential candidate to evaluate its antibacterial and antifungal activities. The EC₅₀ values of compound 2 against eight fungal plant pathogens in vitro ranged from 3.806 to 17.981 μg mL^-1; at the same time, compound 2 could effectively control Podosphaera xanthii, Odium heveae Steinm, Puccinia striiformis West, and Puccinia sorghi in pot experiments. In addition, compound 2 exhibited excellent antibacterial activities in vitro and in vivo against Xanthomonas oryzae pv. oryzae. Furthermore, the absorption and translocation of compound 2 in wheat plants were determined by the high-performance liquid chromatography method. The result showed that compound 2 could be translocated acropetally as well as basipetally in wheat plants. Finally, it was found that compound 2 had no cross-resistance with carbendazim, azoxystrobin, and boscalid.

Phytostilbenes as agrochemicals: biosynthesis, bioactivity, metabolic engineering and biotechnology

Covering: 1976 to 2020. Although constituting a limited chemical family, phytostilbenes represent an emblematic group of molecules among natural compounds. Ever since their discovery as antifungal compounds in plants and their ascribed role in human health and disease, phytostilbenes have never ceased to arouse interest for researchers, leading to a huge development of the literature in this field. Owing to this, the number of references to this class of compounds has reached the tens of thousands. The objective of this article is thus to offer an overview of the different aspects of these compounds through a large bibliography analysis of more than 500 articles. All the aspects regarding phytostilbenes will be covered including their chemistry and biochemistry, regulation of their biosynthesis, biological activities in plants, molecular engineering of stilbene pathways in plants and microbes as well as their biotechnological production by plant cell systems.

Discovery of γ-Lactam Alkaloid Derivatives as Potential Fungicidal Agents Targeting Steroid Biosynthesis

Biological control of plant pathogens is considered as one of the green and effective technologies using beneficial microorganisms or microbial secondary metabolites against plant diseases, and so microbial natural products have played important roles in the research and development of new and green agrochemicals. To explore the potential applications for natural γ-lactam alkaloids and their derivatives, 26 γ-lactams that have flexible substituent patterns were synthesized and characterized, and their in vitro antifungal activities against eight kinds of plant pathogens belonging to oomycetes, basidiomycetes, and deuteromycetes were fully evaluated. In addition, the high potential compounds were further tested using an in vivo assay against Phytophthora blight of pepper to verify a practical application for controlling oomycete diseases. The potential modes of action for compound D1 against Phytophthora capsici were also investigated using microscopic technology (optical microscopy, scanning electron microscopy, and transmission electron microscopy) and label-free quantitative proteomics analysis. The results demonstrated that compound D1 may be a potential novel fungicidal agent against oomycete diseases (EC₅₀ = 4.9748 μg·mL^-1 for P. capsici and EC₅₀ = 5.1602 μg·mL^-1 for Pythium aphanidermatum) that can act on steroid biosynthesis, which can provide a certain theoretical basis for the development of natural lactam derivatives as potential antifungal agents.

Bioassay-guided isolation of two antifungal compounds from Magnolia officinalis, and the mechanism of action of honokiol

Magnolia officinalis, as a well-known herb worldwide, has been widely used to treat multiple diseases for a long time. In this study, the petroleum ether extract from M. officinalis showed effective antifungal activity against seven plant pathogens (particularly against R. solani with an inhibition rate of 100.00% at 250 μg/mL). Honokiol and magnolol, isolated by the bioassay-guided method, exhibited greater antifungal activity than tebuconazole (EC₅₀ = 3.07 μg/mL, p ≤ 0.001) against R. solani, which EC₅₀ values were 2.18 μg/mL and 3.48 μg/mL, respectively. We used transcriptomics to explore the mechanism of action of honokiol against R. solani. Results indicated that honokiol may exert antifungal effects by blocking the oxidative phosphorylation metabolic pathway. Further studies indicated that honokiol induced ROS overproduction, disrupted the mitochondrial function, affected respiration, and blocked the TCA cycle, which eventually inhibited ATP production. Besides, honokiol also damaged cell membranes and caused morphological changes. This study demonstrated that the lignans isolated from M. officinalis possess the potential to be developed as botanical fungicides.

Synthesis of novel 18β-glycyrrhetinic piperazine amides displaying significant in vitro and in vivo antibacterial activities against intractable plant bacterial diseases

BACKGROUND

The limited amount of agrochemicals targeting plant bacterial diseases has motivated us to study innovative antibacterial surrogates with fresh modes of action. Notably, fabrication of violent apoptosis inducers to control the reproduction of pathogenic bacteria should be a feasible way to control plant bacterial diseases. To achieve this aim, we constructed a series of novel 18β-glycyrrhetinic piperazine amides based on the natural bioactive ingredient 18β-glycyrrhetinic acid to evaluate the in vitro and in vivo antibacterial activity and induced apoptosis behaviors on tested pathogens.

RESULTS

Screening results suggested that these designed compounds were extremely bioactive against two notorious pathogens, Xanthomonas oryzae pv. oryzae and X. axonopodis pv. citri. This conclusion was highlighted by the biological effects of compounds A₃ and B₁ , affording the related EC₅₀ values of 2.28 and 0.93 μg mL^-1 . In vivo trials confirmed the prospective application for managing rice bacterial blight disease with control efficiency within 50.57-53.70% at 200 μg mL^-1 . In particular, target compounds could induce the generation of excessive reactive oxygen species (ROS) in tested pathogens, subsequently leading to a strong apoptotic effect at a very low drug concentration (≤ 10 μg mL^-1 ). This finding was consistent with the observed ROS-enhanced fluorescent images and morphological changes of pathogens from scanning electron microscopy patterns.

CONCLUSION

Given these features, we anticipate that these novel piperazine-tailored 18β-glycyrrhetinic hybrids can provide an perceptible insight for fighting bacterial infections by activation of the apoptosis mechanism. Novel 18β-glycyrrhetinic piperazine amides were reported to have excellent antibacterial efficacy toward phytopathogens Xanthomonas oryzae pv. oryzae and X. axonopodis pv. citri. A possible apoptosis mechanism was proposed from the remarkable apoptotic behaviors triggered by target compounds. © 2020 Society of Chemical Industry.

Sulfur-containing natural hinduchelins derivatives as potential antifungal agents against Rhizoctonia solani

Aryl-oxazole alkaloids are an important class of heterocyclic natural products, and which has been demonstrated to exhibit broad biological functions. During the course of our research for highly active compounds from natural products, the natural hinduchelins A-D with typical aryl-oxazole unit have been synthesized and investigated. So, in order to develop highly potential functional molecules, a series of novel sulfur-containing aryl-oxazole compounds derived from natural hinduchelins was designed and synthesized, and their in vitro fungicidal activities against four common plant pathogenic fungi (oomycetes Phytophthora capsici, ascomycetes Sclerotinia sclerotiorum, deuteromycetes Botrytis cinerea and basidiomycetes Rhizoctonia solani) were evaluated, the results demonstrated that compounds 7b and 7c displayed good selectivity and specificity in vitro against basidiomycetes R. solani. In addition, the in vivo antifungal activities also indicated compounds 7b and 7c can protect the horsebean against infection by R. solani, and the possible mechanism of antifungal action for these compounds has also been investigated.

Novel 1,3,4-Oxadiazole-2-carbohydrazides as Prospective Agricultural Antifungal Agents Potentially Targeting Succinate Dehydrogenase

A novel simple 1,3,4-oxadiazole-2-carbohydrazide was reported to discover low-cost and versatile antifungal agents. Bioassay results suggested that a majority of the designed compounds were extremely bioactive against four types of fungi and two kinds of oomycetes. This extreme bioactivity was highlighted by the applausive inhibitory effects of compounds 4b, 4h, 5c, 5g, 5h, 5i, 5m, 5p, 5t, and 5v against Gibberella zeae, affording EC₅₀ values ranging from 0.486 to 0.799 μg/mL, which were superior to that of fluopyram (2.96 μg/mL) and comparable to those of carbendazim (0.947 μg/mL) and prochloraz (0.570 μg/mL). Meanwhile, compounds 4g, 5f, 5i, and 5t showed significant actions against Fusarium oxysporum with EC₅₀ values of 0.652, 0.706, 0.813, and 0.925 μg/mL, respectively. Pharmacophore exploration suggested that the N'-phenyl-1,3,4-oxadiazole-2-carbohydrazide pattern is necessary for the bioactivity. Molecular docking of 5h with succinate dehydrogenase (SDH) indicated that it can completely locate the inside of the binding pocket via hydrogen-bonding and hydrophobic interactions, revealing that this novel framework might target SDH. This result was further verified by the significant inhibitory effect on SDH activity. In addition, scanning electron microscopy patterns were performed to elucidate the anti-G. zeae mechanism. Given these features, this type of framework is a suitable template for future exploration of alternative SDH inhibitors against plant microbial infections.