Discovery of Novel Benzoxaborole-Containing Streptochlorin Derivatives as Potential Antifungal Agents

Investigation of the Antifungal Activity and Preliminary Mode of Action of Novel 2-(1H-Indol-2-yl)-1,3,4-oxadiazole Derivatives against Botrytis cinerea

The discovery of novel leads and new targets is an important approach to address the issue of fungicide resistance by new fungicide development. The indole skeleton has been widely utilized in agrochemicals due to its unique biological activity. YZK-C22 is a potent pyruvate kinase inhibitor with high antifungal activity. Several novel fungicide leads were developed based on YZK-C22. Inspired by these, the [1,2,4]triazino[4,5-a]indol-1(2H)-one derivatives were designed using a skeleton hopping strategy; however, these compounds exhibited moderate fungicidal activity. Unexpectedly, 2-(1H-indol-2-yl)-1,3,4-oxadiazole derivatives formed under controlled reaction conditions showed significantly higher fungicidal activity. Compounds 6c, 6d, 6f, and 6j exhibited excellent antifungal activity in vitro, with EC50 values ranging from 0.120 to 0.310 μg/mL against Botrytis cinerea, more potent than commercial fungicide pyrimethanil (EC50 = 0.990 μg/mL). In the field trials at 540 and 720 g of active ingredient (ai)/hm2, compound 6c exhibited 81.46 and 86.58% efficacy against B. cinerea, higher than that of pyrimethanil at a rate of 540 g of ai/hm2 (70.46%). The affinity constants of compounds 6c and 6d to pyruvate kinase from B. cinerea were lower than that of YZK-C22. Higher field efficacy but lower affinity to pyruvate kinase implies that these compounds may work as prodrugs or have a different mode of action. Thus, 2-(1H-indol-2-yl)-1,3,4-oxadiazole derivatives are worth being further investigated.

Synthesis and Fungicidal Activity Evaluation of Novel Triazole Thione/Thioether Derivatives Containing a Pyridylpyrazole Moiety

Compounds containing N-pyridylpyrazole motif have aroused interest and brought about research hotspots due to their highly-efficient insecticidal activity. The fungicidal potential of N-pyridylpyrazole derivatives has gradually been disclosed in recent years. To discover new agrochemicals with poly-heterocyclic features, a series of novel triazole thione/thioether derivatives containing pyridylpyrazole motif (8-11) was synthesized. The new compounds were identified by melting point, 1H-NMR, 13C NMR, 19F NMR, HRMS, and elemental analysis. The bioassays showed that most of the pyridylpyrazole-containing triazole thione Mannich bases possessed favorable in vitro fungicidal activity toward pathogenic fungi, such as Magnaporthe oryzae, Sclerotinia sclerotiorum, Botrytis cinerea and Fusarium verticillioides, and were comparable with those of the contrast compounds A and triadimefon. Some of them exhibited moderate to good in vivo fungicidal activity against S. sclerotiorum at 0.2 mg/mL (e. g. 8f control efficacy: 60.9±3.2 %). The SEM observation displayed that 8f might cause disruption of cell membrane and wall of S. sclerotiorum. Compounds 8a, 8c, 8f-8h, 8p and 9b can serve as promising new fungicidal agents to make further structural optimization. The findings in this article provide useful clue and guidance for the design and development of new poly-heterocyclic agrochemicals.

Dual-Target Inhibitors─Discovery of Novel Diphenyl-(Thio)ether-Containing Benzoxaborole Derivatives as Potential Antifungal and Herbicidal Agents

LeuRS and PPO are important targets in the development of green pesticides; novel diphenyl-(thio)ether-containing benzoxaborole derivatives were designed and synthesized as novel dual-target enzyme inhibitors; their antifungal activities against six kinds of common plant pathogens in vitro and their herbicidal activities against purslane and barnyard grass were studied. Most of the target compounds showed excellent antifungal activity against six kinds of plant pathogenic fungi in vitro, and this is highlighted by compounds 6c and 6h, both displayed 100.0% inhibition effects against three kinds of the tested plant pathogenic fungi under the concentrations of 50.0 μg/mL, and the EC50 value of compound 6r against Rhizoctonia solani was 0.763 μg/mL, significantly lower than that of boscalid (1.20 μg/mL). In addition, compound 6c was also used in negative control experiments, and the results revealed that compound 6c had no significant effect on the growth of noninfected plants. Meanwhile, most of the compounds also demonstrated promising herbicidal activity, as compounds 6b, 6h, 6m, and 7e showed effective control on purslane and barnyard grass. Beyond that, compound 6s demonstrated certain safety against rape. Enzymatic inhibition experiments further confirmed that compound 7e exhibited remarkable inhibitory activity against NtPPO. Moreover, the molecular docking results between 6c and 7g and tLeuRS and NtPPO further revealed the mechanisms of action for their biological activities. In summary, compounds 6b, 6c, 6h, 7e, and 7g showed excellent antifungal and herbicidal activities and can be further studied as new antifungal and herbicidal agents in the next step.

Design, Synthesis, and Biological Evaluation of Novel Aryl Sulfonamide Derivatives as Potential Succinate Dehydrogenase Inhibitors Targeting Phytopathogenic Fungi

In our pursuit of novel succinate dehydrogenase inhibitor (SDHI) fungicides for agriculture, we replaced the traditional amide structure with a sulfonamide framework and introduced various heterocyclic and aromatic rings at the sulfonamide's termini. This strategy yielded 30 synthesized compounds, which were screened for antifungal activity against eight phytopathogenic fungi. The biological assay results demonstrated that several target compounds exhibited significant in vitro antifungal activity. Notably, compound 2f showed remarkable antifungal activity against Valsa mali with an EC50 value of 0.56 mg/L, outperforming Boscalid (EC50 = 1.79 mg/L). In vivo experiments revealed that compound 2f provided significant protection to apple fruits, comparable to Boscalid. SEM analysis of compounds 2f and 3e showed that compound 2f disrupted the structure and morphology of fungal hypha analysis, which suggested that the terminal polyhalogen-substituted pyridine moieties might be pivotal regions influencing their antifungal efficacy. Molecular docking analysis revealed that compound 2f and Boscalid exhibited a comparable binding mode to SDH. Furthermore, detailed SDH inhibition assays confirmed the potential of 2f (IC50 = 2.51 μM) as prospective SDH inhibitors. RNA transcriptomic analysis indicated that the application of compound 2f could influence gene expression in fungi, thereby exerting a defensive effect against plant pathogenic fungi. Consequently, compound 2f shows promise for developing a novel and efficient agrochemical fungicide.

Rational design and discovery of novel hydrazide derivatives as potent succinate dehydrogenase inhibitors inspired by natural d/l-camphor

BACKGROUND

Succinate dehydrogenase inhibitors (SDHIs) have rapidly become one of the fastest-growing categories of fungicides used against plant pathogenic fungi. Recent research advancements have emphasized that structural modifications of SDHIs using naturally sourced scaffolds represent an innovative strategy for developing new, highly effective, broad-spectrum fungicides. A novel series of d/l-camphorhydrazide derivatives potentially targeting fungal succinate dehydrogenase (SDH) were designed, synthesized and evaluated for their antifungal effects against Rhizoctonia solani, Fusarium graminearum, Valsa mali and Botrytis cinerea.

RESULTS

Amongst them, compounds A1-7 (d-camphor) and A2-7 (l-camphor) displayed excellent in vitro activity against R. solani with median effective concentration (EC50) values of 0.38 and 0.48 μg mL-1, which were obviously superior to that of boscalid (0.87 μg mL-1). A2-5 (l-camphor, EC50 = 3.27 μg mL-1) exhibited good activity against V. mali. A2-7 (2.13 μg mL-1), A2-21 (5.2 μg mL-1) and A1-5 (5.15 μg mL-1) showed good antifungal activity against F. graminearum with EC50 values below that of boscalid (5.85 μg mL-1). Preliminary mechanistic studies, using scanning and transmission electron microscopy, indicated that compound A1-7 induced disordered entanglement of hyphae, shrinkage of hyphal surfaces, and vacuole swelling and rupture, which disrupted normal hyphal growth. Additionally, compound A1-7 induced the production and accumulation of reactive oxygen species, disrupted mitochondrial membrane potential, and effectively inhibited the germination and formation of sclerotia in R. solani. Moreover, the molecular docking results and SDH enzyme assays yielded promising outcomes.

CONCLUSION

In this study, the designed and optimized compounds A1-7 and A2-7 emerged as promising candidates for SDH-targeting fungicides, demonstrating strong antifungal activity. These compounds hold potential as new antifungal agents for further research. © 2024 Society of Chemical Industry.

Natural and synthetic 5-(3'-indolyl)oxazoles: Biological activity, chemical synthesis and advanced molecules

5-(3'-Indolyl)oxazole moiety is a privileged heterocyclic scaffold, embedded in many biologically interesting natural products and potential therapeutic agents. Compounds containing this scaffold, whether from natural sources or synthesized, have demonstrated a wide array of biological activities. This has piqued the interest of synthetic chemists, leading to a large number of reported synthetic approaches to 5-(3'-indolyl)oxazole scaffold in recent years. In this review, we comprehensively overviewed the different biological activities and chemical synthetic methods for the 5-(3'-indolyl)oxazole scaffold reported in the literatures from 1963 to 2024. The focus of this study is to highlight the significance of 5-(3'-indolyl)oxazole derivatives as the lead compounds for the lead discovery of anticancer, pesticidal, antimicrobial, antiviral, antioxidant and anti-inflammatory agents, to summarize the synthetic methods for the 5-(3'-indolyl)oxazole scaffold. In addition, the reported mechanism of action of 5-(3'-indolyl)oxazoles and advanced molecules studied in animal models are also reviewed. Furthermore, this review offers perspectives on how 5-(3'-indolyl)oxazole scaffold as a privileged structure might be exploited in the future.

Design, synthesis and antimicrobial activity of novel berberine derivatives

BACKGROUND

The threats to the safety of humans and the environment and the resistance of agricultural chemicals to plant pathogenic fungi and bacteria highlight an urgent need to find safe and efficient alternatives to chemical fungicides and bactericides. In this study, a series of Berberine (BBR) derivatives were designed, synthesized and evaluated for in vitro and in vivo antimicrobial activity against plant pathogenic fungi and bacteria.

RESULTS

Bioassay results indicated that compounds A11, A14, A20, A21, A22, A25, A26, E1, E2, E3, Z1 and Z2 showed high inhibitory activity against Sclerotinia sclerotiorum and Botrytis cinerea. Especially, A25 showed a broad spectrum and the highest antifungal activity among these compounds. Its EC50 value against Botrytis cinerea was 1.34 μg mL-1. Compound E6 possessed high inhibitory activity against Xanthomonas oryzae and Xanthomonas Campestris, with MIC90 values of 3.12 μg mL-1 and 1.56 μg mL-1. A Topomer CoMFA model was generated for 3D-QSAR studies based on anti-B. cinerea effects, with high predictive accuracy, showed that the addition of an appropriate substituent group at the para-position of benzyl of BBR derivatives could effectively improve the anti-B. cinerea activity. In addition, compound A25 could significantly inhibit the spore germination of Botrytis cinerea at low concentration, and compound F4 exhibited remarkable curative and protective efficiencies on rice bacterial leaf blight.

CONCLUSION

This study indicates that the BBR derivatives are hopeful for further exploration as the lead compound with novel antimicrobial agents. © 2024 Society of Chemical Industry.

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

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

Design, Synthesis, Antifungal Evaluation, and Three-Dimensional Quantitative Structure-Activity Relationship of Novel 5-Sulfonyl-1,3,4-thiadiazole Flavonoids

Plant pathogenic fungi frequently disrupt the normal physiological and biochemical functions of plants, leading to diseases, compromising plant health, and ultimately reducing crop yield. This study aimed to address this challenge by identifying antifungal agents with innovative structures and novel mechanisms of action. We designed and synthesized a series of flavonoid derivatives substituted with 5-sulfonyl-1,3,4-thiadiazole and evaluated their antifungal activity against five phytopathogenic fungi. Most flavonoid derivatives demonstrated excellent antifungal activity against Botrytis cinerea (B. cinerea), Alternaria solani (A. solani), Rhizoctorzia solani (R. solani), Fusarium graminearum (F. graminearum), and Colletotrichum orbiculare (C. orbiculare). Specifically, the EC50 values of 38 target compounds against R. solani were below 4 μg/mL, among which the compounds C13 (EC50 = 0.49 μg/mL), C15 (EC50 = 0.37 μg/mL), and C19 (EC50 = 0.37 μg/mL) had the most prominent antifungal activity, superior to that of the control drug carbendazim (EC50 = 0.52 μg/mL). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the cellular ultrastructures of R. solani mycelia and cells after treatment with the compound C19 revealed sprawling growth of hyphae, a distorted outline of their cell walls, and reduced mitochondrial numbers. Studying the 3D-QSAR between the molecular structure and antifungal activity of 5-sulfonyl-1,3,4-thiadiazole-substituted flavonoid derivatives could significantly improve conventional drug molecular design pathways and facilitate the development of novel antifungal leads.

3D-QSAR-Directed Synthesis of Halogenated Coumarin-3-Hydrazide Derivatives: Unveiling Their Potential as SDHI Antifungal Agents

The pursuit of new succinate dehydrogenase (SDH) inhibitors is a leading edge in fungicide research and development. The use of 3D quantitative structure-activity relationship (3D-QSAR) models significantly enhances the development of compounds with potent antifungal properties. In this study, we leveraged the natural product coumarin as a molecular scaffold to synthesize 74 novel 3-coumarin hydrazide derivatives. Notably, compounds 4ap (0.28 μg/mL), 6ae (0.32 μg/mL), and 6ah (0.48 μg/mL) exhibited exceptional in vitro effectiveness against Rhizoctonia solani, outperforming the commonly used fungicide boscalid (0.52 μg/mL). Furthermore, compounds 4ak (0.88 μg/mL), 6ae (0.61 μg/mL), 6ah (0.65 μg/mL), and 6ak (1.11 μg/mL) showed significant activity against Colletotrichum orbiculare, surpassing both the SDHI fungicide boscalid (43.45 μg/mL) and the broad-spectrum fungicide carbendazim (2.15 μg/mL). Molecular docking studies and SDH enzyme assays indicate that compound 4ah may serve as a promising SDHI fungicide. Our ongoing research aims to refine this 3D-QSAR model further, enhance molecular design, and conduct additional bioactivity assays.

Ethynyl-substituted benzosiloxaboroles: the role of C(π)⋯B interactions in their crystal packing and use in Cu(i)-catalyzed 1,3-dipolar cycloaddition

The synthesis and characterization of two novel 6-ethynyl-7-halogen substituted benzosiloxaboroles (Hal = F, Cl) is reported. The crystal structures of these compounds show a unique type of supramolecular assembly dictated by distinctive C(π)⋯B interactions resulting in the formation of columnar networks involving alternating ethynyl groups and boron atoms. The QTAIM, NBO and NCI analyses were performed in order to obtain a deeper quantitative insight into the nature of these interactions including energy and charge density distribution. The fluoro derivative 1c was used as a starting material in Cu-catalyzed 1,3-dipolar cycloaddition reactions with substituted benzenesulfonyl azides giving rise to benzosiloxaboroles with pendant 1-(arylsulfonyl)-1,2,3-triazole-4-yl functionalities or analogous ionic species, i.e., 1,2,3-triazolium arylsulfonates. Screening of antimicrobial activity of obtained derivatives against a wide selection of Gram-positive and Gram-negative bacteria as well as fungi strains was performed and the obtained results were compared with the data obtained previously for related benzosiloxaborole derivatives.

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

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