Bioactivity-Guided Synthesis Accelerates the Discovery of 3-(Iso)quinolinyl-4-chromenones as Potent Fungicide Candidates

Design, synthesis, and mechanism study of novel tetrahydroisoquinoline derivatives as antifungal agents

In screening for natural-derived fungicides, a series of 32 novel tetrahydroisoquinoline derivatives were designed and synthesized based on tetrahydroisoquinoline alkaloids. Their structures were verified by 1H NMR, 13C NMR, HRMS, and single X-ray crystal diffraction analysis. Most of the target products exhibited medium to excellent antifungal activity against 6 phytopathogenic fungi in vitro at a concentration of 50 mg/L. Interestingly, compounds A13 and A25 with EC50 values of 2.375 and 2.251 mg/L against A. alternate were similar to boscalid (EC50 = 1.195 mg/L). The in vivo experiments revealed that A13 presented 51.61 and 70.97% protection activities against A. alternate at the dosage of 50 and 100 mg/L, respectively, which were equal to that of boscalid (64.52 and 77.42%). SDH enzyme assays and molecular docking studies indicated that compound A13 may act on SDH. In addition, the SEM analysis showed that compound A13 could strongly damage the mycelium morphology. These results revealed that A13 may be a promising lead compound for the development of natural-derived fungicides.

Design, Synthesis, and Fungicidal Activity of α-Methylene-γ-Butyrolactone Derivatives Bearing a Diphenyl Ether Moiety

The γ-butyrolactone scaffold, commonly present in natural products and bioactive compounds, has played a crucial role in the development of novel pesticides. In this study, a series of α-methylene-γ-butyrolactone derivatives containing a diphenyl ether moiety were designed and synthesized using the scaffold splicing strategy. Bioassays revealed that several target compounds demonstrated potent fungicidal activities, particularly against Phytophthora capsici and Valsa mali. Notably, compound B7 (EC50 = 0.809 mg/L) exhibited the highest antioomycete activity against P. capsici, outperforming famoxadone (EC50 = 41.0 mg/L) but being less effective than dimethomorph (EC50 = 0.180 mg/L). Meanwhile, compound C22 (EC50 = 1.47 mg/L) showed the strongest antifungal activity against V. mali, which was higher than those of famoxadone (EC50 = 1.80 mg/L) and dimethomorph (EC50 = 13.6 mg/L). In vivo experiments confirmed that compound B7 has satisfactory protective and curative effects against P. capsici, which were better than those of famoxadone. Additionally, compound B7 was found to inhibit sporangia formation, zoospore release, and cystospore germination of P. capsici at 10 mg/L. Physiological and biochemical studies indicated that compound B7 can induce changes in the mycelial morphology of P. capsici, increase cell membrane permeability, and modulate respiratory metabolism. Furthermore, both in vitro enzymatic inhibition assays and molecular docking analysis suggested that the primary mechanism of action of compound B7 may involve binding to complex III on the respiratory chain. This work provides valuable insights for the development of α-methylene-γ-butyrolactone derivatives incorporating a diphenyl ether moiety as novel agricultural fungicidal agents.

Novel flavonol derivatives containing benzoxazole as potential antiviral agents: design, synthesis, and biological evaluation

A series of flavonol derivatives containing benzoxazole were designed and synthesized, and the structures of all the target compounds were determined by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). The structure of X2 was further confirmed by single crystal X-ray diffraction analysis. The results of the bioactivity tests showed that some of the target compounds possessed excellent antiviral activity against tobacco mosaic virus (TMV) in vivo. In particular, the median effective concentration (EC50) values for the curative and protective activities of X17 against TMV were 127.6 and 101.2 μg/mL, respectively, which were superior to those of ningnanmycin (320.0 and 234.6 μg/mL). The results of preliminary mechanism study indicated that X17 had a strong binding affinity for TMV coat protein (TMV-CP), which might hinder the self-assembly and replication of TMV particles. In addition, X17 was able to effectively inhibit tobacco leaf membrane lipid peroxidation and facilitate the removal of O2- from the body, thereby improving the disease resistance of tobacco plants. Therefore, the design and synthesis of flavonol derivatives containing benzoxazole provides value for the development of new antiviral drugs.

Development and Biological Evaluation of New Diphenyl Ether Formylhydrazide Compounds as Potent Inhibitors of Succinate Dehydrogenase

Succinate dehydrogenase (SDH), also recognized as succinate ubiquinone oxidoreductase (SQR), is considered one of the most promising targets for fungicide development, garnering significant international interest. We have focused on the development of highly effective, broad-spectrum-targeted SDH inhibitors. Using an active scaffold combining strategy, we designed and synthesized a series of novel diphenyl ether formylhydrazine derivatives, and most compounds have demonstrated broad-spectrum antifungal activity. Notably, compound M8 exhibited antifungal activity of more than 93% against four tested pathogen types at a concentration of 10 μg/mL, with an EC50 value below 0.3 μg/mL for each pathogen, outperforming boscalid. Additionally, compound M8 exhibited a control efficacy of 83% against Sclerotinia sclerotiorum on rapeseed leaves at a concentration of 200 μg/mL and demonstrated an 87% efficacy in controlling Fusarium graminearum on wheat ears when applied at 400 μg/mL. Structure-activity relationship research suggested that para-substituted benzene rings are more effective, offering stronger and more extensive antifungal potency. Further investigation, including enzyme inhibition assays, mycelial morphology observations, and molecular docking studies, suggests that the antifungal potency of M8 is due to the inhibition of its SDH activity. Therefore, our research positions compound M8 as a highly promising lead compound with broad-spectrum antifungal properties, potentially introducing a new class of fungicide.

I2-Mediated [3 + 3] Annulation for the Construction of Indole-Pyrimidine-Pyrazole-Fused Tetracyclic Heteroarenes

An I2-mediated annulation of 3-aminopyrazoles with indole-3-carboxaldehydes has been demonstrated for the first time. This tandem strategy allows the facile construction of indole-pyrimidine-pyrazole-fused tetracyclic heteroarenes that are otherwise inaccessible by the existing methods. These fused heterocycles exhibited enhanced antifungal activities against Valsa mali and Botryosphaeria dothidea compared with commercial Xemium fungicide.

Discovery, Optimization, and Biological Evaluation of Novel Pyrazol-5-yl-phenoxybenzamide Derivatives as Potent Succinate Dehydrogenase Inhibitors

The diphenyl ether molecular pharmacophore has played a significant role in the development of fungicidal compounds. In this study, a variety of pyrazol-5-yl-phenoxybenzamide derivatives were synthesized and evaluated for their potential to act as succinate dehydrogenase inhibitors (SDHIs). The bioassay results indicate certain compounds to display a remarkable and broad-spectrum in their antifungal activities. Notably, compound 12x exhibited significant in vitro activities against Valsa mali, Gaeumannomyces graminis, and Botrytis cinerea, with EC50 values of 0.52, 1.46, and 3.42 mg/L, respectively. These values were lower or comparable to those of Fluxapyroxad (EC50 = 12.5, 1.93, and 8.33 mg/L, respectively). Additionally, compound 12x showed promising antifungal activities against Sclerotinia sclerotiorum (EC50 = 0.82 mg/L) and Rhizoctonia solani (EC50 = 1.86 mg/L), albeit lower than Fluxapyroxad (EC50 = 0.23 and 0.62 mg/L). Further in vivo experiments demonstrated compound 12x to possess effective protective antifungal activities against V. mali and S. sclerotiorum at a concentration of 100 mg/L, with inhibition rates of 66.7 and 89.3%, respectively. In comparison, Fluxapyroxad showed inhibition rates of 29.2 and 96.4% against V. mali and S. sclerotiorum, respectively. Molecular docking analysis revealed that compound 12x interacts with SDH through hydrogen bonding, π-cation, and π-π interactions, providing insights into the probable mechanism of action. Furthermore, compound 12x exhibited greater binding energy and SDH enzyme inhibitory activity than Fluxapyroxad (ΔGcal = -46.8 kcal/mol, IC50 = 1.22 mg/L, compared to ΔGcal = -41.1 kcal/mol, IC50 = 8.32 mg/L). Collectively, our results suggest that compound 12x could serve as a promising fungicidal lead compound for the development of more potent SDHIs for crop protection.

Design, Synthesis, Bioactivity, and Tentative Exploration of Action Mode for Benzyl Ester-Containing Derivatives

The active splicing strategy has witnessed improvement in bioactivity and antifungal spectra in pesticide discovery. Herein, a series of simple-structured molecules (Y1-Y53) containing chloro-substituted benzyl esters were designed using the above strategy. The structure-activity relationship (SAR) analysis demonstrated that the fatty acid fragment-structured esters were more effective than those containing an aromatic acid moiety or naphthenic acid part. Compounds Y36 and Y41, which featured a thiazole-4-acid moiety and trifluoromethyl aliphatic acid part, respectively, exhibited excellent in vivo curative activity (89.4%, 100 mg/L Y36) and in vitro fungicidal activity (EC50 = 0.708 mg/L, Y41) against Botrytis cinerea. Determination of antifungal spectra and analysis of scanning electron microscopy (SEM), membrane permeability, cell peroxidation, ergosterol content, oxalic acid pathways, and enzymatic assays were performed separately here. Compound Y41 is cost effective due to its simple structure and shows promise as a disease control candidate. In addition, Y41 might act on a novel target through a new pathway that disrupts the cell membrane integrity by inducing cell peroxidation.

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.

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

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

Synthesis, antifungal activity and mechanism of action of novel chalcone derivatives containing 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole

A series of chalcone derivatives containing 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole was designed and synthesized. Structures of all compounds were characterized by 1H NMR, 13C NMR, 19F NMR, and HRMS. The biological activities of the compounds were determined with the mycelial growth rate method, and further studies showed that some compounds had good antifungal activities at the concentration of 100 μg/mL. The EC50 value of compound L31 was 15.9 μg/mL against Phomopsis sp., which were better than that of azoxystrobin (EC50 value was 69.4 μg/mL). In addition, the mechanism of action of compound L31 shown that compound can affect mycelial growth by disrupting membrane integrity against Phomopsis sp., and that the higher the concentration of the compound is, the greater the disruption of membrane integrity is.

Discovery of Cadinane-Type Sesquiterpenoids from the Infected Stems of Hibiscus tiliaceus as Potential Agrochemical Fungicides

Ten new cadinane-type sesquiterpenoids, named hibisceusins I-R (1-10), along with 14 known sesquiterpenoids (11-24), were acquired from the tainted stems of Hibiscus tiliaceus. Their structures were identified via spectroscopic analysis, one-dimensional (1D) and two-dimensional (2D) NMR, and computer-assisted structure elucidation techniques, including infrared (IR) and mass spectrometry (MS) data. Additionally, subsequent DP4/DP4+ probability methods were used to resolve 3's relative configurations by comparing their experimental values to the predicted NMR data. The absolute configurations of compounds 1-4 were measured through electronic circular dichroism (ECD) spectra. The ability of all isolates to inhibit the growth of five phytopathogenic fungi (Rhizopus stolonifer, Verticillium dahliae Kleb., Thanatephorus cucumeris, Fusarium oxysporum Schltdl., and F. oxysporum HK-27) was evaluated. Aldehydated sesquiterpenoids (1, 6-9, 11, 12, and 22) and a known sesquiterpenoid quinine (18) exhibited significant inhibitory activities against V. dahliae, T. cucumeris, F. oxysporum, and F. oxysporum HK-27 with minimum inhibitory concentration (MIC) values of 2.5-50 μg/mL, but all isolates remained inactive against R. stolonifer. Moreover, the effects of the isolates on the mycelial morphology were watched through scanning electron microscopy. This study revealed that aldehydated cadinane-type sesquiterpenoids could be used as novel antifungal molecules to develop agrochemical fungicides in plant protection.

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 Antifungal Activity of N-(alkoxy)-Diphenyl Ether Carboxamide Derivates as Novel Succinate Dehydrogenase Inhibitors

Succinate dehydrogenase (SDH, EC 1.3.5.1) is one of the most promising targets for fungicide development and has attracted great attention worldwide. However, existing commercial fungicides targeting SDH have led to the increasingly prominent problem of pathogen resistance, so it is necessary to develop new fungicides. Herein, we used a structure-based molecular design strategy to design and synthesize a series of novel SDHI fungicides containing an N-(alkoxy)diphenyl ether carboxamide skeleton. The mycelial growth inhibition experiment showed that compound M15 exhibited a very good control effect against four plant pathogens, with inhibition rates of more than 60% at a dose of 50 μg/mL. A structure-activity relationship study found that N-O-benzyl-substituted derivatives showed better antifungal activity than others, especially the introduction of a halogen on the benzyl. Furthermore, the molecular docking results suggested that π-π interactions with Trp35 and hydrogen bonds with Tyr33 and Trp173 were crucial interaction sites when inhibitors bound to SDH. Morphological observation of mycelium revealed that M15 could inhibit the growth of mycelia. Moreover, in vivo and in vitro tests showed that M15 not only inhibited the enzyme activity of SDH but also effectively protected rice from damage due to R. solani infection, with a result close to that of the control at a concentration of 200 μg/mL. Thus, the N-(alkoxy)diphenyl ether carboxamide skeleton is a new starting point for the discovery of new SDH inhibitors and is worthy of further investigation.

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.

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.

Design, Synthesis, and Antifungal Activity of Novel 2-Ar-1,2,3-Triazole Derivatives

Triazoles are crucial molecular frameworks in the development of fungicidal compounds. Although there has been extensive research on triazole derivatives for fungicide discovery, the investigation of 2-Ar-substituted-1,2,3-triazoles remains in progress. This study reports the synthesis and evaluation of the fungicidal activity of 27 distinct 2-Ar-substituted-1,2,3-triazole derivatives. These derivatives were synthesized from anilines through a three-step process, with the key step being the Cu(II)-catalyzed annulation reaction of readily accessible alkyl 3-aminoacrylates with aryldiazonium salts. All derivatives were novel, and their structures were characterized using 1H NMR, 13C NMR, and high-resolution mass spectrometry. Their antifungal activity was tested against five phytopathogenic fungi. Twelve of the target compounds exhibited better performance than the positive control hymexazol in the fungal test. Notably, compound 6d demonstrated the most potent inhibition against Botryosphaeria dothidea with an EC50 value of 0.90 mg/L. The structure-activity relationships are also discussed in this paper. Preliminary studies on the antifungal mechanism of compound 6d revealed that it inhibits ergosterol synthesis and alters the morphology and ultrastructure of the B. dothidea mycelium. These results suggest that the designed 2-Ar-substituted-1,2,3-triazole-containing hydrazone derivatives warrant further investigation as potential lead compounds for novel antifungal agents.

Application of Quinoline Ring in Structural Modification of Natural Products

Natural compounds are rich in pharmacological properties that are a hot topic in pharmaceutical research. The quinoline ring plays important roles in many biological processes in heterocycles. Many pharmacological compounds, including saquinavir and chloroquine, have been marketed as quinoline molecules with good anti-viral and anti-parasitic properties. Therefore, in this review, we summarize the medicinal chemistry of quinoline-modified natural product quinoline derivatives that were developed by several research teams in the past 10 years and find that these compounds have inhibitory effects on bacteria, viruses, parasites, inflammation, cancer, Alzheimer's disease, and others.

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

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

Exploration of Fungicidal Activity and Mode of Action of Ferimzone Analogs

Lead discovery and molecular target identification are important for developing novel pesticides. Scaffold hopping, an effective approach of modern medicinal and agrochemical chemistry for a rational design of target molecules, is aiming to design novel molecules with similar structures and similar/better biological performance. Herein, 24 new ferimzone derivatives were designed and synthesized by a scaffold-hopping strategy. In vitro bioassays indicated that compound 5o showed similar potency to ferimzone against Cercospora arachidicola and 2-fold higher potency than ferimzone against Alternaria solani. Compounds 5q, 6a, and 6d displayed fungicidal activity with EC₅₀ values ranging from 1.17 to 3.84 μg/mL against Rhizoctonia solani, and compounds 5q and 6a displayed 1.6-1.8-fold higher activity than ferimzone against Fusarium graminearum. The in vivo bioassays at 200 μg/mL indicated that compound 5q was more potent than ferimzone against Pyricularia oryzae (90% vs 70% efficacy, respectively). Density functional theory (DFT) calculations elucidated the structure-energy relationship. Although the mode of action of ferimzone is still unclear, studies suggested that compound 5q significantly inhibited the growth and reproduction of R. solani, and its energy metabolism pathways (e.g., starch, sucrose, lipids, and glutathione) were seriously downregulated after a 5q treatment.

Novel Camphor Sulfonohydrazide and Sulfonamide Derivatives as Potential Succinate Dehydrogenase Inhibitors against Phytopathogenic Fungi/Oomycetes

To discover novel fungicidal agrochemicals for treating wheat scab, 39 novel camphor sulfonohydrazide/sulfonamide derivatives 4a-4t and 6a-6s were designed and synthesized. In the in vitro antifungal/antioomycete assay, compounds 4g, 4n, and 4o displayed significant inhibitory activities against Fusarium graminearum, Botryosphaeria dothidea, and Phytophthora capsici. Among them, 4n exhibited the best antifungal activity against F. graminearum with an EC₅₀ value of 0.41 mg/L, which was at the same level as that of pydiflumetofen. The in vivo experiment revealed that 4n presented excellent protective and curative efficacy toward F. graminearum. In the antifungal mechanism study, 4n could increase the cell membrane permeability and reduce the exopolysaccharide and ergosterol content of F. graminearum. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed that 4n could significantly damage the surface morphology and the cell ultrastructure of mycelia to interfere with the growth of F. graminearum. Furthermore, 4n exhibited potent succinate dehydrogenase (SDH) inhibitory activity in vitro with an IC₅₀ value of 3.94 μM, which was equipotent to pydiflumetofen (IC₅₀ = 4.07 μM). The molecular dynamics simulation and docking study suggested that compound 4n could well occupy the active site and form strong interactions with the key residues of SDH. The above-mentioned results demonstrated that the title camphor sulfonohydrazide/sulfonamide derivatives could be promising lead compounds for further succinate dehydrogenase inhibitor (SDHI) fungicide development.

Sustainable synthesis of azobenzenes, quinolines and quinoxalines via oxidative dehydrogenative couplings catalysed by reusable transition metal oxide–Bi(iii) cooperative catalysts

Heterogeneous catalytic oxidative dehydrogenative processes for N-heterocycles are presented, which enable waste-minimized (additive-, oxidant-, base-free), efficient cyclisations/couplings via transition metal oxide–Bi(iii) cooperative catalysis.

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

A series of pyrazol-5-yl-benzamide derivatives containing the oxazole group were designed and synthesized as potential SDH inhibitors. According to the results of the bioassays, most target compounds displayed moderate-to-excellent in vitro antifungal activities against Valsa mali, Sclerotinia scleotiorum, Alternaria alternata, and Botrytis cinerea. Among them, compounds C13, C14, and C16 exhibited more excellently inhibitory activities against S. sclerotiorum than boscalid (EC₅₀ = 0.96 mg/L), with EC₅₀ values of 0.69, 0.26, and 0.95 mg/L, respectively. In vivo experiments on rape leaves and cucumber leaves showed that compounds C13 and C14 exhibited considerable protective effects against S. sclerotiorum than boscalid. SEM analysis indicated that compounds C13 and C14 significantly destroyed the typical structure and morphology of S. scleotiorum hyphae. In the respiratory inhibition effect assays, compounds C13 (28.0%) and C14 (33.9%) exhibited a strong inhibitory effect on the respiration rate of S. sclerotiorum mycelia, which was close to boscalid (30.6%). The results of molecular docking indicated that compounds C13 and C14 could form strong interactions with the key residues TRP O:173, ARG P:43, TYR Q:58, and MET P:43 of the SDH. Furthermore, the antifungal mechanism of these derivatives was demonstrated by the SDH enzymatic inhibition assay. These results demonstrate that compounds C13 and C14 can be developed into novel SDH inhibitors for crop protection.

Rational Design, Synthesis, and Biological Evaluation of Fluorine- and Chlorine-Substituted Pyrazol-5-yl-benzamide Derivatives as Potential Succinate Dehydrogenase Inhibitors

To develop novel succinate dehydrogenase inhibitors (SDHIs), two series of novel N-4-fluoro-pyrazol-5-yl-benzamide and N-4-chloro-pyrazol-5-yl-benzamide derivatives were designed and synthesized, and their antifungal activities were evaluated against Valsa mali, Sclerotinia sclerotiorum, FusaHum graminearum Sehw, Physalospora piricola, and Botrytis cinerea. The bioassay results showed that some of the target compounds exhibited good antifungal activities in vitro against V. mali and S. sclerotiorum. Remarkably, compound 9Ip displayed good in vitro activity against V. mali with an EC₅₀ value of 0.58 mg/L. This outcome was 21-fold greater than that of fluxapyroxad (12.45 mg/L) and close to that of the commercial fungicide tebuconazole (EC₅₀ = 0.36 mg/L). In addition, in vivo experiments proved that compound 9Ip has good protective fungicidal activity with an inhibitory rate of 93.2% against V. mali at 50 mg/L, which was equivalent to that of the positive control tebuconazole (95.5%). The results of molecular docking indicated that there were obvious hydrogen bonds and p-π interactions between compound 9Ip and succinate dehydrogenase (SDH), which could explain the probable action mechanism. In addition, the SDH enzymatic inhibition assay was carried out to further prove its mode of action. Our studies suggest that compound 9Ip could be a fungicidal lead to discover more potent SDHIs for crop protection.

Novel N-(1H-Pyrazol-5-yl)nicotinamide Derivatives: Design, Synthesis and Antifungal Activity

To discover more effective antifungal agents, twenty N-(1H-pyrazol-5-yl)nicotinamide derivatives were designed, synthesized, and structurally confirmed by ¹ H-NMR, ¹³ C-NMR, and ESI-MS. All target compounds were evaluated for their antifungal activities by mycelia growth inhibition. Preliminary screening results displayed that many of these compounds had good fungicidal activity to S. sclerotiorum and V. mali. Compound B4 exhibited antifungal activity against S. sclerotiorum and V. mali with EC₅₀ values of 10.35 and 17.01 mg/L, respectively. The experiment in vivo identified that compound B4 was effective for suppressing rape sclerotinia rot caused by S. sclerotiorum at 50 mg/L. The molecular docking study and scanning electron microscopy preliminary clarified the possible antifungal mechanism of compound B4.

Bioactivity-Guided Synthesis Accelerates the Discovery of Evodiamine Derivatives as Potent Insecticide Candidates

Pests threaten worldwide food security by decreasing crop yields and damaging their quality. Natural product-based molecular design and structural optimization have been one of the most effective ways to innovate pesticides for integrated insect management. To continue our previous studies on the discovery of insecticidal lead, a series of evodiamine derivatives were designed, synthesized, and evaluated for their insecticidal activities. The bioassay results demonstrated that compounds Ian and Iao exhibited 90 and 80% insecticidal activities against Mythimna separata at 2.5 mg/L, respectively, which were superior to evodiamine (10% at 10 mg/L), matrine (45% at 600 mg/L), and rotenone (30% at 200 mg/L). Compounds Ian-Iap showed 90% insecticidal activities against Plutella xylostella at 1.0 mg/L, far more potent than those of evodiamine, matrine, and rotenone. Compound Ian displayed 60% insecticidal activity against Helicoverpa armigera at 5.0 mg/L, while evodiamine, matrine, and rotenone showed very poor activities. The study on the insecticidal mechanism of action by a calcium imaging experiment indicated that the insect ryanodine receptors (RyRs) could be the potential target of Ian. Furthermore, the molecular docking indicated that Ian anchored in the binding site of the RyR of P. xylostella. The above results manifested the potential of evodiamine derivatives as potent insecticide candidates.

Revisiting pesticide pollution: The case of fluorinated pesticides

Fluorinated pesticides acquired a significant market share in the agrochemical sector due to the surge of new fluoroorganic ingredients approved in the last two decades. This growing trend has not been accompanied by a comprehensive scientific and regulatory framework entailing all their potential negative impacts for the environment, especially when considering the hazardous properties that may result from the incorporation of fluorine into organic molecules. This review aims to address the safe/hazardous dichotomy associated with fluorinated pesticides by providing an updated outlook on their relevancy in the agrochemical sector and how it leads to their role as environmental pollutants. Specifically, the environmental fate and distribution of these pesticides in the ecosystems is discussed, while also analysing their potential to act as toxic substances for non-target organisms.

Isoflavonoids Modified with Azole Heterocycles with Three Heteroatoms

Heterocycle modified chromones are attracting increasing attention as novel potential therapeutic agents due to their effective bioactivities and low toxicity. This review describes all strategies and versatile synthons that have been developed for the synthesis of isoflavone heterocyclic analogs containing isolated 5-member heterocyclic rings with three identical or different heteroatoms. Their biological activity is also presented.

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...

Design, Synthesis, and Antifungal Activity of Novel Thiophene/Furan-1,3,4-Oxadiazole Carboxamides as Potent Succinate Dehydrogenase Inhibitors

Succinate dehydrogenase (SDH) is known as an ideal target for the investigations of fungicides. To develop novel SDH inhibitors, 30 novel thiophene/furan-1,3,4-oxadiazole carboxamide derivatives were designed and synthesized. In the in vitro antifungal assay, a majority of the target compounds demonstrated fair to potent antifungal activity against seven tested phytopathogenic fungi. Compounds 4b, 4g, 4h, 4i, and 5j showed remarkable antifungal activity against Sclerotinia sclerotiorum, affording EC50 values ranging from 0.1∼1.1 mg/L. In particular, compound 4i displayed the most potent activity against S. sclerotiorum (EC₅₀ = 0.140 ± 0.034 mg/L), which was superior to that of boscalid (EC₅₀ = 0.645 ± 0.023 mg/L). A further morphological investigation revealed the abnormal mycelia and damaged cell structures of compound 4i-treated S. sclerotiorum by scanning electron microscopy. Furthermore, the in vivo antifungal assay against S. sclerotiorum revealed that compounds 4g and 4i were effective for suppressing rape Sclerotinia rot at a dosage of 200 mg/L. In the SDH inhibition assay, compounds 4g and 4i also presented significant inhibitory activity with IC₅₀ values of 1.01 ± 0.21 and 4.53 ± 0.19 μM, respectively, which were superior or equivalent to that of boscalid (3.51 ± 2.02 μM). Molecular docking and molecular dynamics simulation of compound 4g with SDH revealed that compound 4g could form strong interactions with the key residues of the SDH. These results indicated that this class of derivatives could be a promising scaffold for the discovery and development of novel SDH inhibitors.

Synthesis, Antifungal Activity, DFT Study and Molecular Dynamics Simulation of Novel 4-(1,2,4-Oxadiazol-3-yl)-N-(4-phenoxyphenyl)benzamide Derivatives

In order to find novel potential antifungal agrochemicals, a series of new 4-(1,2,4-oxadiazol-3-yl)-N-(4-phenoxyphenyl)benzamide derivatives 3a-j were designed, synthesized and characterized by their ¹ H-, ¹³ C-NMR and HRMS spectra. The preliminary antifungal assay in vitro revealed that compounds 3a-j exhibited moderate to good antifungal activity against five plant pathogenic fungi. Especially, compound 3e presented significant antifungal activity against Alternaria solani, Botrytis cinerea and Sclerotinia sclerotiorum, superior to positive control boscalid. In the in vivo antifungal assay on tomato plants and cucumber leaves, compound 3e presented good inhibition rate against B. cinerea at 200 mg/L. Molecular dynamics simulation revealed that compound 3e could bind with the active site of class II histone deacetylase (HDAC).

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.

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.

Discovery of Novel Pyrazole Carboxylate Derivatives Containing Thiazole as Potential Fungicides

Inspired by commercially established fluxapyroxad as the lead compound of novel efficient antifungal ingredients, novel pyrazole carboxylate derivatives containing a flexible thiazole backbone were successfully designed, synthesized, and detected for their in vitro and in vivo biological activities against eight agricultural fungi. The antifungal bioassay results showed that compound 24 revealed excellent bioactivities against Botrytis cinerea and Sclerotinia sclerotiorum, with median effective concentrations (EC₅₀) of 0.40 and 3.54 mg/L, respectively. Compound 15 revealed remarkable antifungal activity against Valsa mali, with an EC₅₀ value of 0.32 mg/L. For in vivo fungicide control against B. cinerea and V. mali, compounds 3 and 24 at 25 mg/L, respectively, displayed prominent efficacy on cherry tomatoes and apple branches. Molecular docking results demonstrated that compound 15 could form an interaction with several crucial residues of succinate dehydrogenase (SDH), and the in vitro enzyme assay indicated that the target compound 15 displayed an inhibitory effect toward SDH, with an IC₅₀ value of 82.26 μM. The experimental results indicated that phenyl pyrazole carboxylate derivatives displayed a weak antifungal property and low activity compared to the other title substituent pyrazole carboxylate derivatives. Compounds 3, 15, and 24 are promising antifungal candidates worthy of further fungicide development due to their prominent effectiveness.

Synthesis and Biological Activity of Novel Pyrazol-5-yl-benzamide Derivatives as Potential Succinate Dehydrogenase Inhibitors

To promote the discovery and development of new fungicides, a series of novel pyrazol-5-yl-benzamide derivatives were designed, synthesized by hopping and inversion of amide groups of pyrazole-4-carboxamides, and evaluated for their antifungal activities. The bioassay data revealed that compound 5IIc exhibited an excellent in vitro activity against Sclerotinia sclerotiorum with an EC₅₀ value of 0.20 mg/L, close to that of commercial fungicide Fluxapyroxad (EC₅₀ = 0.12 mg/L) and Boscalid (EC₅₀ = 0.11 mg/L). For Valsa mali, compound 5IIc (EC₅₀ = 3.68 mg/L) showed a significantly higher activity than Fluxapyroxad (EC₅₀ = 12.67 mg/L) and Boscalid (EC₅₀ = 14.83 mg/L). In addition, in vivo experiments proved that compound 5IIc has an excellent protective fungicidal activity with an inhibitory rate of 97.1% against S. sclerotiorum at 50 mg/L, while the positive control Fluxapyroxad showed a 98.6% inhibitory effect. The molecular docking simulation revealed that compound 5IIc interact with TRP173, SER39, and ARG43 of succinate dehydrogenase (SDH) through a hydrogen bond and p-π interaction, which could explain the probable mechanism of the action between compound 5IIc and target protein. Also, the SDH enzymatic inhibition assay was carried out to further validate its mode of action. These results demonstrate that compound 5IIc could be a promising fungicide candidate and provide a valuable reference for further investigation.