Natural Alkaloid Waltherione F-Derived Hydrazide Compounds Evaluated in an Agricultural Fungicidal Field

Discovery of α-Methylene-γ-Butyrolactone Derivatives with Hydrazide Moieties as Novel Fungicidal Agents

To discover novel fungicides with unique structures, a series of α-methylene-γ-butyrolactone derivatives were designed and synthesized by incorporating a flexible amide or hydrazide chain through active substructure splicing and linker modification strategies. Bioassay assessments demonstrated that certain hydrazide-containing compounds have potent fungicidal efficacy. Notably, compound 7IIj exhibited broad-spectrum antifungal activity, with EC50 values as low as 0.179, 0.301, 0.647, 0.549, and 0.789 mg/L against Rhizoctonia solani, Physalospora piricola, Botrytis cinerea, Gaeumanomyces graminis, and Valsa mali, respectively. In vivo experiments confirmed the effective fungicidal activity of compound 7IIj, showing an inhibitory rate of 69.7% against V. mali on apple twigs at 200 mg/L. Additionally, at a concentration of 100 mg/L, compound 7IIj demonstrated significant protective and curative effects against R. solani on rice plants. Research on the mechanism of action revealed that compound 7IIj could disrupt hyphal morphology, induce reactive oxygen species (ROS) accumulation, affect mitochondrial membrane potential (MMP), and interfere with respiratory metabolism by binding to complex II. Molecular docking analysis showed significant interactions of compound 7IIj with TRP 173, TYR 58, and ARG 43 in the succinate dehydrogenase (SDH) binding site, resembling the binding mode of fluxapyroxad. These findings suggest that compound 7IIj holds potential as an SDH inhibitor for agricultural disease control.

Evaluation of natural l-phenylalanine-derived Amidohydrazide derivatives in ensuring agriculture production against phytopathogenic fungi†

BACKGROUND

Ensuring food security is fundamental to national security and an important guarantee for global peace and development. The use of fungicides represents an effective strategy in safeguarding sufficient food supply against phytopathogenic fungi; however, given the escalating pathogen resistance, there is an urgent need to develop new, highly efficient, and environmentally friendly green fungicides.

RESULTS

In this study, 24 novel amidohydrazide derivatives were designed and synthesized by incorporating the bioactive amide and hydrazide groups into natural l-phenylalanine. The bioassays revealed that certain compounds exhibited remarkable inhibitory activity against agricultural pathogenic fungi, with compound A21 particularly displaying exceptional in vitro and in vivo fungicidal activity against Rhizoctonia solani. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that treatment with compound A21 induced significant morphological changes in R. solani mycelia, including the cell membrane contraction. Transcriptomic analysis indicated that differentially expressed genes (DEGs) in R. solani treated with compound A21 were significantly enriched in pathways related to the carbohydrate metabolism and lipid metabolism, and the relative expression of representative DEGs was further validated by quantitative real-time polymerase chain reaction (qRT-PCR). The increase in ergosterol content suggested that R. solani may counteract the drug stress of amidohydrazide compounds by enhancing ergosterol biosynthesis. Toxic assessment demonstrated that zebrafish exposed to compound A21 had survival rates of 90% at 1 μg mL-1 and 60% at 10 μg mL-1 within 72 h. Additionally, hydrolysis behavior in different pH buffers indicated that these compounds displayed rapid hydrolysis rates in the pH 9.18 buffer, while maintaining relatively high stability in the pH 4.01 and 6.86 buffers.

CONCLUSION

Amidohydrazide compounds have exhibited excellent fungicidal efficacy and hold great promise as a bioactive pharmacophore for the development of new environmentally friendly fungicides, thereby ensuring food supply and security. © 2025 Society of Chemical Industry.

Competitive Affinity-Based Protein Profiling Reveals Potential Antifungal Targets of 1,2,3-Triazole Hydrazide in Fusarium graminearum

In previous research, 1,2,3-triazole hydrazide NAU-6ad exhibited remarkable broad-spectrum antifungal activity. However, the specific targets of NAU-6ad remained unknown. Initially, we excluded three targets─succinate dehydrogenase, laccase, and ergosterol synthase─commonly associated with hydrazide derivatives mentioned in the literature. Subsequently, we developed two types of photoprobes: one incorporating diazirine (DA) and the other phenyl tetrazole (TZ), both featuring terminal alkynes for bioorthogonal reactions. Using these two sets of probes, a total of 52 potential targets were identified through competitive affinity-based proteome profiling. Notably, Ndufs6 and I1RC94 were consistently identified by both sets. The overexpression or knockout of Ndufs6, a subunit of complex I, led to significant changes in sensitivity to NAU-6ad in F. graminearum. Similarly, the knockout of other subunits of complex I, specifically Ndufs2, Ndufv1, and Ndufa9, altered the sensitivity of F. graminearum to NAU-6ad, indicating that NAU-6ad might act upon complex I. Further validation was provided by enzyme activity tests, ATP content assays, pyruvate addition assays, and molecular docking, collectively reinforcing the hypothesis that NAU-6ad might function as a complex I inhibitor.

Discovery of Novel Quinazolinone-2-carbohydrazide Derivatives as Effective Succinate Dehydrogenase Inhibitors and Biosafety Assessment on Rice and Zebrafish

To develop potent and safe antifungal agents in agriculture, a total of 48 novel quinazolinone-2-carbohydrazide derivatives were designed and synthesized based on the pharmacophore hybridization method. The bioassay results demonstrated that many compounds exhibited powerful and broad-spectrum inhibition activities in vitro against the tested fungi. For instance, compounds E23 and F23 possessed EC50 (half-maximal effective concentration) values of 0.41 and 0.47 μg/mL against Rhizoctonia solani, comparable to that of the commercial fungicide Boscalid (EC50 = 0.49 μg/mL). Additionally, compound E23 also demonstrated pronounced antifungal effects against Verticillium dahliae, Alternaria solani, and Colletotrichum gloeosporioides with EC50 values of 0.27, 1.15, and 0.27 μg/mL, respectively. In vivo assays on rice plants revealed that this compound at 200 μg/mL exhibited nearly equipotent curative and protective effects against R. solani, as compared with the positive controls Boscalid and Carbendazim. Moreover, compound E23 had an obvious inhibition activity against fungal succinate dehydrogenase (SDH) from R. solani with the half-maximal inhibition concentration (IC50) of 11.76 μM, and the interactions between compound E23 and SDH enzyme were further confirmed by molecular docking studies. Furthermore, the presence of compound E23 also triggered obvious morphological changes of fungal mycelia and increased the conductivity and permeability of fungal cell membranes. Interestingly, the built three-dimensional quantitative structure-activity relationship (3D-QSAR) models showed that the electrostatic effect played a more important role in maintaining anti-R. solani effects of target compounds than other effects. Finally, the biosafety assessment of compound E23 demonstrated its safety toward rice and zebrafish.

Evaluation of Novel Pyridine-Based Compounds Integrating Bioactive Amide and Hydrazide Groups as a Potential Fungicide Agent

A series of novel pyridine-based compounds integrating bioactive amide and hydrazide groups were designed and synthesized through an active group splicing strategy. The fungicidal bioassays indicated that several compounds showed remarkable and broad-spectrum inhibitory activity. Notably, compound A5 displayed satisfactory in vitro fungicidal activity against Fusarium graminearum, Magnaporthe oryzae, Rhizoctonia solani, Colletotrichum gloeosporioides, Botrytis cinerea, Sclerotinia sclerotiorum, Alternaria sp., and Physalospora piricola, with EC50 values of 2.53, 2.84, 1.64, 7.59, 4.67, 5.50, and 2.84 μg mL-1, respectively. Additionally, A5 also showed promising in vivo preventive efficiency against F. graminearum and R. solani at 100 μg mL-1. Preliminary investigation of the fungicidal mechanism demonstrated that the differentially expressed genes and differential metabolites in R. solani treated with A5 at 10 μg mL-1 exhibited notable enrichment in pathways associated with lipid metabolism, potentially linking to the plasma membrane contraction observed by TEM. Furthermore, to assess the environmental compatibility of compound A5, its toxicity to zebrafish, hydrolysis rates in different pH buffers, and effects on the growth of wheat seedlings were evaluated. These findings will provide substantial theoretical guidance for the development of new environmentally friendly fungicides.

Design, Synthesis, and Biological Activity Evaluation of 5-Aryl-cyclopenta[c]pyridine Derivatives

Taking the natural product cerbinal as the lead compound, 30 novel 5-aryl-cyclopenta[c]pyridine derivatives were designed and synthesized based on the previous bioactivity studies of the cyclopenta[c]pyridines. The modification of the position-5 of compound 2 was achieved by amination, bromination, and cross coupling using cerbinal as the raw material. The results of the bioactivity tests demonstrated that partial compounds exhibited superior activity against plant viruses compared to compound 2. Compounds 4g and 4k showed higher anti-TMV activity levels than commercial varieties of ribavirin at concentrations of 500 and 100 μg/mL. In particular, compound 4k, which contained a m-methoxyphenyl substitution, displayed the most potent anti-TMV activity in vivo (inactivation effect 51.1 ± 1.9%, curative effect 50.7 ± 3.6%, protection effect 53.8 ± 2.8% at 500 μg/mL) The toxicological experiments also revealed that compound 4k exhibited low toxicity to zebrafish. Additionally, molecular docking results indicated that access to the benzene ring enhanced the binding affinity of these derivatives for TMV receptor proteins. Furthermore, studies on the insecticidal and fungicidal activities of these derivatives showed that most of the compounds exhibited good larvicidal efficacy against Plutella xylostella and broad-spectrum fungicidal activities. Notably, compound 4i (3,4,5-trifluorophenyl) displayed an outstanding inhibition ratio of 91.9% against Sclerotinia sclerotiorum, 75% against Botrytis cinerea, and 62.5% against Phytophthora infestans at a concentration of 50 μg/mL. These results suggest that 5-aryl-cyclopenta[c]pyridine derivatives could serve as promising candidate agents for antiviral, insecticidal, and fungicidal applications in agricultural production.

Alkaloids from Waltheria spp. (Malvaceae): Chemosystematic Aspects, Biosynthesis, Total Synthesis, and Biological Activities

Waltheria, a genus within the Malvaceae family, is abundantly distributed in tropical and subtropical areas worldwide. Many species of this genus are widely utilized in various ways, including chewing, in folk medicine, acting as an anti-inflammatory agent, and treating gastrointestinal disorders, rheumatism, and asthma, among other conditions. These applications are largely due to their secondary metabolites, primarily quinolone alkaloids and cyclopeptides. Several biological activities have been reported for Waltheria species, including antifungal, anticancer, trypanocidal, acetylcholinesterase inhibitory, potential anti-HIV, antinociceptive, analgesic, anti-inflammatory, antibacterial, antioxidant, and leishmanicidal activities. This review not only presents information on isolated alkaloids and their biological activities but also delves into biosynthetic, chemosystematic, medicinal chemistry, and total synthesis aspects. Additionally, the manuscript highlights other applications of alkaloids of the genus, such as a study on their herbicidal activity, which shows significant potential for agricultural use.

Dual actions of chloroinconazide on pepper blight in Capsicum annuum: disruption of Phytophthora capsici mycelium and activation of CaCNGC9-mediated SA signaling

BACKGROUND

Pepper blight, caused by Phytophthora capsici, is a devastating disease that seriously threatens pepper production worldwide. With the emergence of resistance in P. capsici against conventional fungicides, there is an urgent need to explore novel alternatives for pepper blight management. This study aims to assess the inhibitory effect of chloroinconazide (CHI), a compound synthesized from tryptophan, against pepper blight, and to explore its potential mechanisms of action.

RESULTS

The results demonstrated that CHI effectively targeted P. capsici, disrupting its growth and mycelial structure, which resulted in the release of dissolved intracellular substances. Additionally, CHI significantly inhibited the sporangium formation, zoospores release, and zoospores germination, thereby reducing the re-infection of P. capsici. In contrast, the commercial pesticide methylaxyl only inhibited mycelial growth and had limited effect on re-infection, while azoxystrobin inhibited re-infection but had a weak inhibitory effect on mycelial growth. Furthermore, CHI activated the salicylic acid (SA) signaling pathway-mediated immune response to inhibit P. capsici infection in pepper, with this activation being contingent upon cyclic nucleotide-gated ion channel CaCNGC9.

CONCLUSION

CHI exhibited potent dual inhibitory effects on P. capsici by disrupting mycelial structure and activating the CaCNGC9-mediated SA signaling pathway. These dual mechanisms of action suggested that CHI could serve as a promising alternative chemical fungicide for the effective management of pepper blight, offering a new approach to control this devastating disease. Our findings highlighted the potential of CHI as a sustainable and efficient solution to combat the increasing resistance of P. capsici to conventional fungicides, ensuring better crop protection and yield. © 2024 Society of Chemical Industry.

l-Isoleucine-Derived Amide-hydrazide Compounds Evaluated as a Novel Potential Agricultural Fungicide

Building upon previous structure-activity relationships about the fungicidal amide and hydrazide lead structures, 24 novel amide-hydrazide compounds were designed and synthesized with L-isoleucine as the initial skeleton to explore the impact of substituents in the hydrazide bridge on the fungicidal activity. Among these compounds, A5 exhibited excellent and broad spectrum inhibitory activity, along with satisfactory in vivo protective efficiency against R. solani at concentrations of 200 and 50 μg·mL-1. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that compound A5 induced significant morphological changes in the R. solani mycelium coupled with vacuole rupture and cytoplasmic inhomogeneity in cellular structures. Transcriptomic and metabolomic analyses indicated that, following A5 treatment, the differentially expressed genes and metabolites were significantly enriched in carbohydrate metabolism-related pathways as well as in lipid metabolism-associated pathways, including glycerophospholipid metabolism, steroid biosynthesis, arachidonic acid metabolism, and sphingolipid metabolism. Additionally, compound A5 demonstrated low toxicity to zebrafish, with survival rates of 100% and 60% at concentrations of 1 and 10 μg·mL-1, respectively, over a period of 7 days. The above results provide theoretical guidance for the development of novel green hydrazide fungicidal candidates.

Design, Synthesis, and Nematocidal Evaluation of Waltherione A Derivatives: Leveraging a Structural Simplification Strategy

Southern root-knot nematodes are among the most pernicious phytoparasites; they are responsible for substantial yield losses in agricultural crops worldwide. The limited availability of nematicides for the prevention and control of plant-parasitic nematodes necessitates the urgent development of novel nematicides. Natural products have always been a key source for the discovery of pesticides. Waltherione A, an alkaloid, exhibits potent nematocidal activity. In this study, we designed and synthesized a series of quinoline and quinolone derivatives from Waltherione A, leveraging a strategy of structural simplification. Bioassays have revealed that the quinoline derivatives exhibit better activity than quinolone derivatives in terms of both nematocidal and fungicidal activities. Notably, compound D1 demonstrated strong nematocidal activity, with a 72 h LC50 of 23.06 μg/mL, and it effectively controlled the infection of root-knot nematodes on cucumbers. The structure-activity relationship suggests that the quinoline moiety is essential for the nematocidal efficacy of Waltherione A. Additionally, compound D1 exhibited broad-spectrum fungicidal activity, with an EC50 of 2.98 μg/mL against Botrytis cinerea. At a concentration of 200 μg/mL, it significantly inhibited the occurrence of B. cinerea on tomato fruits, with an inhibitory effect of 96.65%, which is slightly better than the positive control (90.30%).

Design, Synthesis, Antifungal Activity, and Mechanism of Action of New Piperidine-4-carbohydrazide Derivatives Bearing a Quinazolinyl Moiety

A series of new piperidine-4-carbohydrazide derivatives bearing a quinazolinyl moiety were prepared and evaluated for their fungicidal activities against agriculturally important fungi. Among these derivatives, the chemical structure of compound A45 was clearly verified by X-ray crystallographic analysis. The antifungal bioassays revealed that many compounds in this series possessed good to excellent inhibition effects toward the tested fungi. For example, compounds A13 and A41 had EC50 values of 0.83 and 0.88 μg/mL against Rhizoctonia solani in vitro, respectively, superior to those of positive controls Chlorothalonil and Boscalid (1.64 and 0.96 μg/mL, respectively). Additionally, the above two compounds also exhibited notable inhibitory activities against Verticillium dahliae (with EC50 values of 1.12 and 3.20 μg/mL, respectively), far better than the positive controls Carbendazim and Chlorothalonil (19.3 and 11.0 μg/mL, respectively). More importantly, compound A13 could potently inhibit the proliferation of R. solani in the potted rice plants, showing good in vivo curative and protective efficiencies of 76.9% and 76.6% at 200 μg/mL, respectively. Furthermore, compound A13 demonstrated an effective inhibition of succinate dehydrogenase (SDH) activity in vitro with an IC50 value of 6.07 μM. Finally, the molecular docking study revealed that this compound could be well embedded into the active pocket of SDH via multiple noncovalent interactions, involving residues like SER39, ARG43, and GLY46.

Design, Synthesis, Antifungal Activity, and 3D-QSAR Study of Novel Quinoxaline-2-Oxyacetate Hydrazide

Plant pathogenic fungi pose a major threat to global food security, ecosystem services, and human livelihoods. Effective and broad-spectrum fungicides are needed to combat these pathogens. In this study, a novel antifungal 2-oxyacetate hydrazide quinoxaline scaffold as a simple analogue was designed and synthesized. Their antifungal activities were evaluated against Botrytis cinerea (B. cinerea), Altemaria solani (A. solani), Gibberella zeae (G. zeae), Rhizoctonia solani (R. solani), Colletotrichum orbiculare (C. orbiculare), and Alternaria alternata (A. alternata). These results demonstrated that most compounds exhibited remarkable inhibitory activities and possessed better efficacy than ridylbacterin, such as compound 15 (EC50 = 0.87 μg/mL against G. zeae, EC50 = 1.01 μg/mL against C. orbiculare) and compound 1 (EC50 = 1.54 μg/mL against A. alternata, EC50 = 0.20 μg/mL against R. solani). The 3D-QSAR analysis of quinoxaline-2-oxyacetate hydrazide derivatives has provided new insights into the design and optimization of novel antifungal drug molecules based on quinoxaline.

Environmental Evaluation on Toxicity, Toxic Mechanism, and Hydrolysis Behavior of Potential Acethydrazide Fungicide Candidates

The evaluation of toxicity and environmental behavior of bioactive lead molecules is helpful in providing theoretical support for the development of agrochemicals, in line with the sustainable development of the ecological environment. In previous work, some acethydrazide structures have been demonstrated to exhibit excellent and broad-spectrum fungicidal activity; however, its environmental compatibility needs to be further elucidated if it is to be identified as a potential fungicide. In this project, the toxicity of fungicidal acethydrazide lead compounds F51, F58, F72, and F75 to zebrafish was determined at 10 μg mL-1 and 1 μg mL-1. Subsequently, the toxic mechanism of compound F58 was preliminarily explored by histologic section and TEM observations, which revealed that the gallbladder volume of common carp treated with compound F58 increased, accompanied by a deepened bile color, damaged plasma membrane, and atrophied mitochondria in gallbladder cells. Approximately, F58-treated hepatocytes exhibited cytoplasmic heterogeneity, with partial cellular vacuolation and mitochondrial membrane rupture. Metabolomics analysis further indicated that differential metabolites were enriched in the bile formation-associated steroid biosynthesis, primary bile acid biosynthesis, and taurine and hypotaurine metabolism pathways, as well as in the membrane function-related glycerophospholipid metabolism, linolenic acid metabolism, α-linolenic acid metabolism, and arachidonic acid metabolism pathways, suggesting that the acethydrazide F58 may have acute liver toxicity to common carp. Finally, the hydrolysis dynamics of F58 was investigated, with the obtained half-life of 5.82 days. The above results provide important guiding significance for the development of new green fungicides.