Natural products: a strategic lead generation approach in crop protection discovery

Accessing the specialized metabolome of actinobacteria from the bulk soil of Paullinia cupana Mart. on the Brazilian Amazon: a promising source of bioactive compounds against soybean phytopathogens

The Amazon rainforest, an incredibly biodiverse ecosystem, has been increasingly vulnerable to deforestation. Despite its undeniable importance and potential, the Amazonian microbiome has historically received limited study, particularly in relation to its unique arsenal of specialized metabolites. Therefore, in this study our aim was to assess the metabolic diversity and the antifungal activity of actinobacterial strains isolated from the bulk soil of Paullinia cupana, a native crop, in the Brazilian Amazon Rainforest. Extracts from 24 strains were subjected to UPLC-MS/MS analysis using an integrative approach that relied on the Chemical Structural and Compositional Similarity (CSCS) metric, GNPS molecular networking, and in silico dereplication tools. This procedure allowed the comprehensive understanding of the chemical space encompassed by these actinobacteria, which consists of features belonging to known bioactive metabolite classes and several unannotated molecular families. Among the evaluated strains, five isolates exhibited bioactivity against a panel of soybean fungal phytopathogens (Rhizoctonia solani, Macrophomina phaseolina, and Sclerotinia sclerotiorum). A focused inspection led to the annotation of pepstatins, oligomycins, hydroxamate siderophores and dorrigocins as metabolites produced by these bioactive strains, with potentially unknown compounds also comprising their metabolomes. This study introduces a pragmatic protocol grounded in established and readily available tools for the annotation of metabolites and the prioritization of strains to optimize further isolation of specialized metabolites. Conclusively, we demonstrate the relevance of the Amazonian actinobacteria as sources for bioactive metabolites useful for agriculture. We also emphasize the importance of preserving this biome and conducting more in-depth studies on its microbiota.

Development of natural perfume as potential fungicide candidates: construction and biological evaluation of vanillin analogs bearing the 1,3,4-oxadiazole/1,3-thiazolidin-4-one fragments

Two series of vanillin derivatives containing 1,3,4-oxadiazole and 1,3-thiazolidin-4-one scaffolds were prepared and evaluated for their antifungal activity. The results revealed that compounds 6j (29.73 μg/ml) and 7a (38.15 μg/ml) displayed excellent inhibitory activity against the spore of Fusarium solani. The inhibitory activity of compound 7d (10.53 μg/ml) against the spore of Alternaria solani was more than 42-fold that of vanillin. Compound 7a (37.54 μg/ml) showed better antifungal activity against the spore of B. cinerea than positive controls. The cytotoxicity assay confirmed that compounds 6k, 7a, and 7d showed good selectivity and less toxicity to normal mammalian cells.

Plant Protease Inhibitors as Emerging Antimicrobial Peptide Agents: A Comprehensive Review

Antimicrobial peptides (AMPs) are important mediator molecules of the innate defense mechanisms in a wide range of living organisms, including bacteria, mammals, and plants. Among them, peptide protease inhibitors (PPIs) from plants play a central role in their defense mechanisms by directly attacking pathogens or by modulating the plant's defense response. The growing prevalence of microbial resistance to currently available antibiotics has intensified the interest concerning these molecules as novel antimicrobial agents. In this scenario, PPIs isolated from a variety of plants have shown potential in inhibiting the growth of pathogenic bacteria, protozoans, and fungal strains, either by interfering with essential biochemical or physiological processes or by altering the permeability of biological membranes of invading organisms. Moreover, these molecules are active inhibitors of a range of proteases, including aspartic, serine, and cysteine types, with some showing particular efficacy as trypsin and chymotrypsin inhibitors. In this review, we provide a comprehensive analysis of the potential of plant-derived PPIs as novel antimicrobial molecules, highlighting their broad-spectrum antimicrobial efficacy, specificity, and minimal toxicity. These natural compounds exhibit diverse mechanisms of action and often multifunctionality, positioning them as promising molecular scaffolds for developing new therapeutic antibacterial agents.

Novel Cyclopenta[c]pyridine Derivatives Based on Natural Cerbinal as Potential Agrochemical Anti-TMV Agents and Insecticides

Based on natural cerbinal, a series of novel 4-bit modified cyclopenta[c]pyridine derivatives containing a substituted amide or ester moiety were designed and synthesized for the first time. Their structures were systematically characterized by NMR and high-resolution mass spectra (HRMS). The anti-TMV activities, such as protection, inactivation, and curative effects in vivo, were evaluated methodically. The lethal activities of the target compounds against the agriculturally common pests Plutella xylostella larvae and Aphis laburni kaltenbach were evaluated by the immersion method. The bioassay results indicated that most of the target compounds exhibited good to excellent anti-TMV activity levels, good lethal activity against P. xylostella larvae at 600 μg/mL, and greater insecticidal activities against A. laburni Kaltenbach compared to the plant-derived insecticide rotenone. The binding mode of cerbinal and cyclopenta[c]pyridine derivatives 4b, 4p, and 4v with the TMV protein was studied with a molecular docking method, which indicated that the functional group of the 2- and 4-positions is vital for anti-TMV activity. The systematic research provides strong evidence that these novel 4-bit modified cyclopenta[c]pyridine derivatives could become potential agrochemical insecticides and anti-TMV agents.

Identification of Lydicamycins as Main Antioomycete Compounds from the Biocontrol Agent Streptomyces sp. NEAU-S7GS2

Oomycetes are well-known phytopathogens that seriously threaten many important crops worldwide. In this study, the endophytic actinobacterium Streptomyces sp. NEAU-S7GS2 demonstrated significant antagonistic activity against Phytophthora and Pythium and showed a potent biocontrol effect on suppression of soybean phytophthora root rot and pepper phytophthora blight. Two compounds were subsequently isolated as the main active components by bioassay-guided fractionation and identified as lydicamycins A and B. These two compounds showed high antioomycete activity against Phytophthora and Pythium with EC50 values of 0.73-2.67 μg/mL, which are equal to or lower than those of commercialized drug metalaxyl. In vivo bioassay using detached leaves demonstrated that lydicamycin A had a better control efficiency against soybean phytophthora root rot than metalaxyl. Taken together, these results suggest that the biocontrol agent Streptomyces sp. NEAU-S7GS2 and lydicamycins have the potential to be developed as promising pesticides to control diseases caused by oomycetes.

Novel Evodiamine-Based Sulfonamide Derivatives as Potent Insecticide Candidates Targeting Insect Ryanodine Receptors

Pests represent an important impediment to efficient agricultural production and pose a threat to global food security. On the basis of our prior research focused on identifying insecticidal leads targeting insect ryanodine receptors (RyRs), we aimed to identify evodiamine scaffold-based novel insecticides. Thus, a variety of evodiamine-based derivatives were designed, synthesized, and assessed for their insecticidal activity against the larvae of Mythimna separata (M. separata) and Plutella xylostella (P. xylostella). The preliminary bioassay results revealed that more than half of the target compounds exhibited superior activity compared to evodiamine, matrine, and rotenone against M. separata. Among these, compound 21m displayed the most potent larvicidal efficiency, with a remarkable mortality rate of 93.3% at 2.5 mg/L, a substantial improvement over evodiamine (10.0% at 10 mg/L), matrine (10.0% at 200 mg/L), and rotenone (30.0% at 200 mg/L). In the case of P. xylostella, compounds 21m and 21o displayed heightened larvicidal activity, boasting LC50 values of 9.37 × 10-2 and 0.13 mg/L, respectively, surpassing that of evodiamine (13.41 mg/L), matrine (291.78 mg/L), and rotenone (18.39 mg/L). A structure-activity relationship analysis unveiled that evodiamine-based derivatives featuring a cyclopropyl sulfonyl group at the nitrogen atom of the B ring and a fluorine atom in the E ring exhibited more potent larvicidal effects. This finding was substantiated by calcium imaging experiments and molecular docking, which suggested that 21m could target insect RyRs, including resistant mutant RyRs of P. xylostella (G4946E and I4790M), with higher affinity than chlorantraniliprole (CHL). Additionally, cytotoxicity assays highlighted that the potent compounds 21i, 21m, and 21o displayed favorable selectivity and low toxicity toward nontarget organisms. Consequently, compound 21m emerges as a promising candidate for further development as an insecticide targeting insect RyRs.

Toxicity assessment of carvacrol and its acetylated derivative in early staged zebrafish (Danio rerio): Safer alternatives to fipronil-based pesticides?

Fipronil is a broad-spectrum pesticide presenting high acute toxicity to non-target organisms, particularly to aquatic species. Natural compounds stand out as promising alternatives to the use of synthetic pesticides such as fipronil. Thus, our study aimed to compare the toxicity of carvacrol (natural), acetylcarvacrol (semisynthetic), and fipronil (synthetic) to early staged zebrafish. We conducted a series of toxicity assays at concentrations ranging from 0.01 μM to 25 μM for fipronil and 0.01 μM to 200 μM for carvacrol and acetylcarvacrol, depending on the assay, after 7-days post-fertilization (dpf). The potency (EC50) of fipronil was ∼1 μM for both deformities and mortality at 7 dpf, whereas EC50 was >50 μM for carvacrol and >70 μM for acetylcarvacrol. Fipronil at 0.1 and 1 μM caused a decrease in body length and swim bladder area of larvae at 7dpf, but no difference was observed for either carvacrol or acetylcarvacrol. Based upon the visual motor response test, fipronil induced hypoactivity in larval zebrafish at 1 μM and acetylcarvacrol induced hyperactivity at 0.1 μM. Anxiolytic-type behaviors were not affected by any of these chemicals. All chemicals increased the production of reactive oxygen species at 7 dpf, but not at 2 dpf. Genes related to swim bladder inflation, oxidative stress, lipid metabolism, and mitochondrial activity were measured; only fipronil induced upregulation of atp5f1c. There were no changes were observed in oxygen consumption rates of fish and apoptosis. Taken together, our data suggest that carvacrol and its derivative may be safer replacements for fipronil due to their lower acute toxicity.

Design, Synthesis, and Antifungal Activity of Some Novel Phenylthiazole Derivatives Containing an Acylhydrazone Moiety

Crop fungal diseases pose a serious threat to global crop production and quality. Developing new and efficient fungicides is an important measure to control crop diseases. Phenylthiazole was found to be an excellent antifungal skeleton based on our previous study on the structural optimization and biological activity of the natural product thiasporine A. To find new fungicides, 45 phenylthiazole derivatives containing an acylhydrazone moiety were designed and synthesized by the principle of active substructure splicing. Forty-two of the forty-five compounds are novel, except for compounds E1, E14, and E33. Their structures were structurally characterized by 1H NMR, 13C NMR, and HRMS. The antifungal activities of the target compounds against Magnaporthe oryzae Colletotrichum camelliaet, Bipolaris maydis, and Sclerotinia sclerotiorum were evaluated at 25 μg/mL. The bioassay results revealed that most of these compounds exhibited excellent antifungal activities against M. oryzae and C. camelliaet at 25 μg/mL. In particular, compounds E4, E10, E14, E17, E23, E26, and E27 showed the inhibition rate of more than 80% against M. oryzae, with EC50 values of 1.66, 2.01, 2.26, 1.45, 1.50, 1.29, and 2.65 μg/mL, respectively, which were superior to that of the commercial fungicides Isoprothiolane (EC50 = 3.22 μg/mL) and Phenazine-1-carboxylic acid (EC50 = 27.87 μg/mL). The preliminary structure-activity relationship (SAR) results suggested that introducing methyl, halogen, or methoxy at the ortho-position of R1 and the para-position of R2 can endow the final structure with excellent antifungal activity against M. oryzae. The current results provide useful data for developing phenylthiazole derivatives as new fungicides for controlling rice blast caused by M. oryzae.

C-Alkylated flavonoids from the whole plants of Desmodium caudatum and their anti-TMV activity

BACKGROUND

Natural products are important sources of biopesticides to control plant virus, and flavonoids are identified as promising anti-tobacco mosaic virus (TMV) agents. Since Desmodium caudatum is a rich source of flavonoids, this study focuses on the discovery of the new anti-TMV active flavonoids from D. caudatum and their possible mode of action.

RESULTS

Three new (compounds 1-3) and nine known (compounds 4-12) C-alkylated flavonoids were isolated from D. caudatum. To the best of our knowledge, the framework of 1-3 was reported in natural products for the first time. In addition, 1-3, 5, and 6 showed notable anti-TMV activity with inhibition rates in the range of 35.8-64.3% at a concentration of 50 μg/mL, and these rates are higher than that of positive control (with inhibition rates of 34.6% ± 2.8). In addition, the structure-activity relationship study revealed that the (pyrrol-2-yl)methyl moiety on flavone can significantly increases the activity. This result is helpful to find new anti-TMV inhibitors.

CONCLUSION

C-Alkylated flavonoids showed potent activities against TMV with multiple modes of actions. The increase of defense-related enzyme activities, up-regulate the expression of defense related genes, down-regulate the expression of Hsp70 protein by inhibiting the related Hsp genes that are involved in tobacco resistance to TMV. By the actions mentioned earlier, the infection of TMV was influenced, thereby achieving the effects of control of TMV. The successful isolation of the earlier-mentioned flavonoids provide the new source of biopesticides to TMV proliferation, and also contribute to the utilization of D. caudatum. © 2023 Society of Chemical Industry.

Design, synthesis and antifungal evaluation of phenylthiazole-1,3,4-oxadiazole thione (ketone) derivatives inspired by natural thiasporine A

BACKGROUND

Plant pathogenic fungal infections have become a severe threat to the yield and quality of agricultural products, and new green antifungal agents with high efficiency and low toxicity are needed. In this study, a series of thiasporine A derivatives containing phenylthiazole-1,3,4-oxadiazole thione (ketone) structures were designed and synthesized, and their antifungal activities against six invasive and highly destructive phytopathogenic fungi were evaluated.

RESULTS

The results found that all compounds showed moderate to potent antifungal activity against six phytopathogenic fungi, and most of the E series compounds showed remarkable antifungal activity against Sclerotinia sclerotiorum and Colletotrichum camelliaet. In particular, compounds E1-E5, E7, E8, E13, E14, E17, and E22 showed more significant antifungal activity against S. sclerotiorum, with half-maximal effective concentration (EC50 ) values of 0.22, 0.48, 0.56, 0.65, 0.51, 0.39, 0.60, 0.56, 0.60, 0.63, and 0.45 μg mL-1 , respectively, which were superior to that of carbendazim (0.70 μg mL-1 ). Further activity studies showed that compound E1 possessed superior curative activities against S. sclerotiorum in vivo and better inhibitory effects on sclerotia germination and the formation of S. sclerotiorum compared with those of carbendazim.

CONCLUSIONS

This study indicates that these thiasporine A derivatives containing phenylthiazole-1,3,4-oxadiazole thione structures might be used as antifungal agents against S. sclerotiorum. © 2023 Society of Chemical Industry.

Natural Product-Based Crop Protection Compounds─Origins and Future Prospects

The continuing need to protect food and fiber production to address the demands of an expanding global population requires new pest management tools for crop protection. Natural products (NPs) have been and continue to be a key source of inspiration for new active ingredients (AIs) for crop protection, accounting for 17% of all crop protection AIs. However, potentially 50% of all crop protection compounds have or could have a NP origin if NP synthetic equivalents (NPSEs, synthetic compounds discovered by other approaches but for which a NP model also happens to exist) are also considered. The real and hypothetical NPs have their greatest impact as insight for new classes of crop protection compounds. Among the different product areas, NPs have their largest influence on the discovery of new insecticides, while herbicides have been the least affected by mining NPs for new AIs. While plants have historically been the largest (60% of the total) source of NPs of AIs for crop protection, in the last 30 years, bacterial NPs have become the largest source (42% of the total) of new classes (first in class) of NP-inspired crop protection AIs. Interest in NPs for crop protection continues, an aspect that is highlighted by the notable rise in the numbers of publications and patents on this topic, especially in the last 20 years. The present analysis further illustrates the continuing interest and value in NPs as sources of and inspiration for new classes of crop protection compounds.

Structure-Based Virtual Screening of Natural Products and Optimization for the Design and Synthesis of Novel CeCht1 Inhibitors as Nematicide Candidates

Nematode chitinases are critical components of the nematode life cycle, and CeCht1 is a potential target for developing novel nematicides. Herein, lunidonine, a natural quinoline alkaloid, was first discovered to have inhibitory activity against CeCht1, which was acquired from a library of over 16,000 natural products using a structure-based virtual screening methodology. A pocket-based lead optimization strategy was employed based on the predicted binding mode of lunidonine. Subsequently, a series of benzo[d][1,3]dioxole-5-carboxylate derivatives were designed and synthesized, and their inhibitory activities against CeCht1 as well as in vitro nematicidal activities against Caenorhabditis elegans were assessed. The analysis of structure-activity relationship and inhibitory mechanisms provided insights into their interactions with the CeCht1 active site, which could facilitate future research in improving the potency of the inhibitory activity. Especially, compound a12 interacted well with CeCht1 and exhibited excellent in vitro nematicidal activity against C. elegans with a LC₅₀ value of 41.54 mg/L, suggesting that it could be a promising candidate for a novel chemical nematicide targeting CeCht1. The known binding modes and structural features of these inhibitors will contribute to the design of stronger CeCht1-based nematicides to control nematodes in agriculture.

Preparation and Biological Evaluation of Novel Osthole-Derived N-Benzoylthioureas as Insecticide Candidates

To discover novel natural-product-based insecticide candidates, herein, a variety of osthole-derived N-benzoylthioureas were synthesized and assessed for their insecticidal activities against three insect pests. An insecticidal assay showed that most of the target osthole-derived N-benzoylthioureas displayed a more potent and broad-spectrum insecticidal effect than the parent osthole after the introduction of N-benzoylthioureas on the C-3' position of osthole. Compound B24 displayed the most potent growth inhibitory (GI) effect on Mythimna separata Walker, with a final corrected mortality rate of 82.1% when treated with a concentration of 1 mg/mL, which was 1.64- and 1.53-fold higher in comparison to osthole and the botanical insecticide toosendanin, respectively. Compounds B22, B23, and B25 displayed a more promising aphicidal effect on Myzus persicae Sulzer, and their LD₅₀ values were 0.015, 0.017, and 0.019 μg/larvae, respectively, superior to the commercially available insecticide rotenone (0.024 μg/larvae). Derivatives B19, B20, B23, and B25 displayed more potent larvicidal activity against Plutella xylostella Linnaeus, with LC₅₀ values of 0.22, 0.26, 0.15, and 0.30 mg/mL, respectively, exceeding that of rotenone (0.37 mg/mL). Furthermore, both compounds B19 and B23 against P. xylostella were found to be more effective than rotenone in a control efficacy assay under greenhouse conditions. The structure-activity relationship (SAR) suggested that osthole-derived N-benzoylthioureas are more active in most cases when the R group is an electron-withdrawing group than when it is an electron-donating group, especially for halogenated groups. Additionally, the potent compounds B19 and B23 possessed good selectivity and were less toxic to non-target organisms. This study suggests that these osthole-derived N-benzoylthioureas could be further studied in depth as eco-friendly natural product pesticides in crop protection.

Synthesis and Antifungal Activity of New butenolide Containing Methoxyacrylate Scaffold

In order to improve the antifungal activity of new butenolides containing oxime ether moiety, a series of new butenolide compounds containing methoxyacrylate scaffold were designed and synthesized, based on the previous reports. Their structures were characterized by ¹H NMR, ¹³C NMR, HR-MS spectra, and X-ray diffraction analysis. The in vitro antifungal activities were evaluated by the mycelium growth rate method. The results showed that the inhibitory activities of these new compounds against Sclerotinia sclerotiorum were significantly improved, in comparison with that of the lead compound 3-8; the EC₅₀ values of V-6 and VI-7 against S. sclerotiorum were 1.51 and 1.81 mg/L, nearly seven times that of 3-8 (EC₅₀ 10.62 mg/L). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation indicated that compound VI-3 had a significant impact on the structure and function of the hyphal cell of S. sclerotiorum mycelium and the positive control trifloxystrobin. Molecular simulation docking results indicated that the introduction of methoxyacrylate scaffold is beneficial to improving the antifungal activity of these compounds against S. sclerotiorum, which can be used as the lead for further structure optimization.

Insecticidal Triterpenes in Meliaceae: Plant Species, Molecules, and Activities: Part II (Cipadessa, Melia)

Plant-originated triterpenes are important insecticidal molecules. Research on the insecticidal activity of molecules from Meliaceae plants has always been a hotspot due to the molecules from this family showing a variety of insecticidal activities with diverse mechanisms of action. In this paper, we discussed 116 triterpenoid molecules with insecticidal activity from 22 plant species of five genera (Cipadessa, Entandrophragma, Guarea, Khaya, and Melia) in Meliaceae. In these genera, the insecticidal activities of plants from Entandrophragma and Melia have attracted substantial research attention in recent years. Specifically, the insecticidal activities of plants from Melia have been systemically studied for several decades. In total, the 116 insecticidal chemicals consisted of 34 ring-intact limonoids, 31 ring-seco limonoids, 48 rearranged limonoids, and 3 tetracyclic triterpenes. Furthermore, the 34 ring-intact limonoids included 29 trichilin-class chemicals, 3 azadirone-class chemicals, and 1 cedrelone-class and 1 havanensin-class limonoid. The 31 ring-seco limonoids consisted of 16 C-seco group chemicals, 8 B,D-seco group chemicals, 4 A,B-seco group chemicals, and 3 D-seco group chemicals. Furthermore, among the 48 rearranged limonoids, 46 were 2,30-linkage group chemicals and 2 were 10,11-linkage group chemicals. Specifically, the 46 chemicals belonging to the 2,30-linkage group could be subdivided into 24 mexicanolide-class chemicals and 22 phragmalin-class chemicals. Additionally, the three tetracyclic triterpenes were three protolimonoids. To sum up, 80 chemicals isolated from 19 plant species exhibited antifeedant activity toward 14 insect species; 18 chemicals isolated from 17 plant species exhibited poisonous activity toward 10 insect species; 16 chemicals isolated from 11 plant species possessed growth-regulatory activity toward 8 insect species. In particular, toosendanin was the most effective antifeedant and insect growth-regulatory agent. The antifeedant activity of toosendanin was significant. Owing to its high effect, toosendanin has been commercially applied. Three other molecules, 1,3-dicinnamoyl-11-hydroxymeliacarpin, 1-cinnamoyl-3-methacryl-11-hydroxymeliacarpin, and 1-cinnamoyl-3-acetyl-11-hydroxymeliacarpin, isolated from Meliaazedarach, exhibited a highly poisonous effect on Spodoptera littoralis; thus, they deserve further attention.

The search for new herbicide mechanisms of action: Is there a 'holy grail'?

New herbicide modes of action (MOAs) are in great demand because of the burgeoning evolution of resistance of weeds to existing commercial herbicides. This need has been exacerbated by the almost complete lack of introduction of herbicides with new MOAs for almost 40 years. There are many highly phytotoxic compounds with MOAs not represented by commercial herbicides, but neither these compounds nor structural analogues have been developed as herbicides for a variety of reasons. Natural products provide knowledge of many MOAs that are not being utilized by commercial herbicides. Other means of identifying new herbicide targets are discussed, including pharmaceutical target sites and metabolomic and proteomic information, as well as the use of artificial intelligence and machine learning to predict herbicidal compounds with new MOAs. Information about several newly discovered herbicidal compounds with new MOAs is summarized. The currently increased efforts of both established companies and start-up companies are likely to result in herbicides with new MOAs that can be used in herbicide resistance management within the next decade. © 2021 Society of Chemical Industry.

Afidopyropen, a novel insecticide originating from microbial secondary extracts

Afidopyropen, a novel insecticide, is a derivative of pyripyropene A, which is produced by the filamentous fungus Penicillium coprobium. Afidopyropen has strong insecticidal activity against aphids and is currently used as a control agent of sucking pests worldwide. In this study, we summarized the biological properties and field efficacies of its derivatives against agricultural pests using official field trials conducted in Japan. Afidopyropen showed good residual efficacies against a variety of aphids, whiteflies and other sucking pests under field conditions. Furthermore, toxicological studies revealed its safety profiles against nontarget organisms, such as the honeybee, natural enemies and other beneficial insects, as well as mammals. Thus, afidopyropen is a next-generation agrochemical for crop protection that has a low environmental impact.

Impact of natural products on discovery of, and innovation in, crop protection compounds

Natural products (NPs) have long been an important source of, and inspiration for, developing novel compounds to control weeds, pathogens and insect pests. In this review, we use a dataset of 800 historic, current and emerging crop protection compounds to explore the influence of NPs on the introduction of new crop protection compounds (fungicides, herbicides, insecticides) as a function of time. NPs, their semisynthetic derivatives (NPDs) and compounds inspired by NPs (NP mimics, NPMs) account for 17% of all crop protection compounds. NPs, NPDs, and NPMs have been a fairly constant source of new agrochemicals over the past 70 years. NP synthetic equivalents (NPSEs) is a fourth group of NP-related crop protection compounds composed of synthetic compounds which by chance also happen to have an NP model (but are not involved in the discovery). If NPSE compounds are also included, then 50% of all crop protection compounds hypothetically could have had a NP origin. Similar trends also hold true for the impact of NPs on the discovery of new modes of action (MoA) or innovation in crop protection compounds as measured by the number of first-in-class compounds. NPs have had the largest impact on the numbers and global sales (2018 USD) of insecticides compared to fungicides and herbicides. The present analysis highlights NPs as a long-standing and continuing source of new chemistry, new MoAs and innovation in crop protection compound discovery. © 2021 Society of Chemical Industry.

Design, Synthesis, and Antifungal Evaluation of Luotonin A Derivatives against Phytopathogenic Fungi

Crop diseases caused by fungi threaten food security and exacerbate the food crisis. Inspired by the application of fungicide candidates from natural products in agrochemical discovery, a series of luotonin A derivatives were designed, synthesized, and evaluated for their antifungal activities against five plant fungi. Most of these compounds exhibited significant fungicidal activity against Botrytis cinerea in vitro with EC₅₀ values less than 1 μg/mL. Among them, compounds w7, w8, w12, and w15 showed superior antifungal activity against B. cinerea with EC₅₀ values of 0.036, 0.050, 0.042, and 0.048 μg/mL, respectively, which were more potent than boscalid (EC₅₀ = 1.790 μg/mL). Preliminary mechanism studies revealed that compound w7 might pursue its antifungal activity by disrupting the fungal cell membrane and cell wall. Moreover, in vivo bioassay also indicated that compound w7 could be effective for the control of B. cinerea. The above results evidenced the potential of luotonin A derivatives as novel and promising candidate fungicides.

Challenges, Advances and Opportunities in Exploring Natural Products to Control Arboviral Disease Vectors

Natural products constitute an important source of molecules for product development. However, despite numerous reports of compounds and active extracts from biodiversity, poor and developing countries continue to suffer with endemic diseases caused by arboviral vectors, including dengue, Zika, chikungunya and urban yellow fever. Vector control remains the most efficient disease prevention strategy. Wide and prolonged use of insecticides has resulted in vector resistance, making the search for new chemical prototypes imperative. Considering the potential of natural products chemistry for developing natural products-based products, including insecticides, this contribution discusses the general aspects and specific characteristics involved in the development of drug leads for vector control. Throughout this work, we highlight the obstacles that need to be overcome in order for natural products compounds to be considered promising prototypes. Moreover, we analyze the bottlenecks that should be addressed, together with potential strategies, to rationalize and improve the efficiency of the drug discovery process.

Preparation and Anti-Tobacco Mosaic Virus Activities of Crocetin Diesters

The development of antiviral agents with an original structure and noticeable effect is always in great need. Natural products are important lead compounds in the development of new pesticides. Crocin-1 and crocin-2 were effectively isolated from Gardeniae fructus and found to have higher anti-tobacco mosaic virus (TMV) activity levels than ribavirin. A series of the crocetin diester derivatives were synthesized with separated crocetin-1 as material and evaluated for their anti-TMV activities. They could be dissolved in common organic solvents as dichloromethane, ethyl acetate, tetrahydrofuran, and methanol. Compounds 5, 9, 13, 14, and 15 displayed higher activities in vivo than ribavirin. Compound 14 with significantly higher antiviral activities than lead compounds (crocin-1 and crocin-2) emerged as a new antiviral candidate.

Design, Synthesis, and Biological Activity of Novel Ferulic Amide Ac5c Derivatives

A total of 34 novel ferulic amide Ac5c derivatives were designed and synthesized and their antipest activities were investigated. The results showed that some compounds exhibited excellent in vitro antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc), such as compounds 4q and 5n demonstrated excellent in vitro activity against Xoo, with EC₅₀ values of 4.0, and 1.9 μg/mL, respectively. Compounds 4c, 4h, 4m, 4p, 4q, and 5a had significant in vitro activities against Xoc, with EC₅₀ values of 12.5, 13.9, 9.8 15.0, 9.2, and 19.8 μg/mL, respectively. Moreover, the antibacterial activity in vivo against rice bacterial leaf blight was also evaluated. Scanning electron microscopy (SEM) showed that compound 5n significantly reduced the cell membrane of Xoo, and resulted in cell surface wilting, deformation, breakage, and increased porous attributes. In addition, some of the target compounds also showed moderate biological activity against fungi and acted as potential insecticides.

Potential of Ficus carica extracts against Euschistus heros: Toxicity of major active compounds and selectivity against beneficial insects

BACKGROUND

Using plant-based extracts and their constituents has been suggested as an alternative tool to replace or integrate with the synthetic compounds used to manage insect pests. Here, we evaluated the potential of extracts obtained from Ficus carica Linn (Moraceae) branches and leaves against the Neotropical brown stink bug, Euschistus heros, one of the most prevalent insect pests in soybean fields. We further isolated and evaluated the toxicity of the extracts' major components against E. heros. Additionally, by using computational docking analysis and toxicological approaches, we assessed the physiological basis for the selectivity of these extracts against beneficial insects such as pollinator bees (i.e. Apis mellifera and the Neotropical stingless bee Partamona helleri), ladybeetles (Eriopis connexa and Coleomegilla maculata), and lacewings (Chrysoperla externa).

RESULTS

Our results demonstrate that branch (LC50  = 5.9 [4.7-7.1] mg mL-1 ) and leaf (LC50  = 14.1 [12.5-15.4] mg mL-1 ) extracts exhibited similar toxicity against E. heros. Our phytochemical analysis revealed psoralen and bergapten furanocoumarins as the major components of the extract. Based on our computational predictions, these molecules' differential abilities to physically interact with the acetylcholinesterases of E. heros and beneficial insects play relevant roles in their selectivity actions. The estimated LC90 values of branch (30.0 mg mL-1 ) and leaf (30.0 mg mL-1 ) extracts killed less than 12% of the beneficial insects.

CONCLUSION

Overall, our findings revealed that furanocoumarin-rich extracts obtained from F. carica extracts have the potential to be used as alternative tools in the integrated management of stink bug pests. © 2021 Society of Chemical Industry.

The cys-loop ligand-gated ion channel gene superfamilies of the cockroaches Blattella germanica and Periplaneta americana

BACKGROUND

Cockroaches are serious urban pests that can transfer disease-causing microorganisms as well as trigger allergic reactions and asthma. They are commonly managed by pesticides that act on cys-loop ligand-gated ion channels (cysLGIC). To provide further information that will enhance our understanding of how insecticides act on their molecular targets in cockroaches, we used genome and reverse transcriptase polymerase chain reaction (RT-PCR) data to characterize the cysLGIC gene superfamilies from Blattella germanica and Periplaneta americana.

RESULTS

The B. germanica and P. americana cysLGIC superfamilies consist of 30 and 32 subunit-encoding genes, respectively, which are the largest insect cysLGIC superfamilies characterized to date. As with other insects, the cockroaches possess ion channels predicted to be gated by acetylcholine, γ-aminobutyric acid, glutamate and histamine, as well as orthologues of the drosophila pH-sensitive chloride channel (pHCl), CG8916 and CG12344. The large cysLGIC superfamilies of cockroaches are a result of an expanded number of divergent nicotinic acetylcholine receptor subunits, with B. germanica and P. americana, respectively, possessing eight and ten subunit genes. Diversity of the cockroach cysLGICs is also broadened by alternative splicing and RNA A-to-I editing. Unusually, both cockroach species possess a second glutamate-gated chloride channel as well as another CG8916 subunit.

CONCLUSION

These findings on B. germanica and P. americana enhance our understanding of the evolution of the insect cysLGIC superfamily and provide a useful basis for the study of their function, the detection and management of insecticide resistance, and for the development of improved pesticides with greater specificity towards these major pests. © 2020 Society of Chemical Industry.

The spinosyns, spinosad, spinetoram, and synthetic spinosyn mimics - discovery, exploration, and evolution of a natural product chemistry and the impact of computational tools

Natural products (NPs) have long been a source of insecticidal crop protection products. Like many macrolide NPs, the spinosyns originated from a soil inhibiting microorganism (Saccharopolyspora spinosa). More than 20 years after initial registration, the spinosyns remain a unique class of NP-based insect control products that presently encompass two insecticidal active ingredients, spinosad, a naturally occurring mixture of spinosyns, and spinetoram, a semi-synthetic spinosyn product. The exploration and exploitation of the spinosyns has, unusually, been tied to an array of computational tools including artificial intelligence (AI)-based quantitative structure activity relationship (QSAR) and most recently computer-aided modeling and design (CAMD). The AI-based QSAR directly lead to the discovery of spinetoram, while the CAMD studies have recently resulted in the discovery and building of a series of synthetic spinosyn mimics. The most recent of these synthetic spinosyn mimics show promise as insecticides targeting lepidopteran insect pests as demonstrated by field studies wherein the efficacy has been shown to be comparable to spinosad and spinetoram. These and a range of other aspects related to the exploration of the spinosyns over the past 30 years are reviewed herein. © 2020 Society of Chemical Industry.

Pine Rosin as a Valuable Natural Resource in the Synthesis of Fungicide Candidates for Controlling Fusarium oxysporum on Cucumber

To improve the effect of pine rosin in plant fungicides, four series of dehydroabietyl-1,3,4-thiadiazole derivatives from the natural product rosin were synthesized. Based on the evaluation of the in vitro antifungal activity against Sclerotinia sclerotiorum, Botrytis cinerea, Fusarium oxysporum, and Magnaporthe oryzae, rosin-based 1,3,4-thiadiazole compounds containing thiophene heterocycles were screened. Notably, compound 3e [dehydroabietyl-(1,3,4-thiadiazol-2-yl)-5-nitrothiophene-2-carboxamide] exhibited excellent antifungal property against F. oxysporum with an EC₅₀ of 0.618 mg/L, which was lower than that of the positive control carbendazim (0.649 mg/L). The in vivo antifungal activity results showed that 3e exerted a protective effect on cucumber plants. Physiological and biochemical studies showed that the primary mechanism of action of compound 3e on F. oxysporum was it changed the mycelial morphology, increased the cell membrane permeability, and inhibited the synthesis of ergosterol in the mycelia. Furthermore, the quantitative structure-activity relationship studies revealed that the frontier orbital energy in the molecule had a key role in the antifungal activity through the conjugation and electrostatic interaction between compound 3e and the receptors of the target. Thus, the present study highlighted the application of rosin-based fungicidal candidates and exploited efficient plant pesticides for sustainable crop production.

Review: Allelochemicals as multi-kingdom plant defence compounds: towards an integrated approach

The capability of synthetic pesticides to manage weeds, insect pests and pathogens in crops has diminished due to evolved resistance. Sustainable management is thus becoming more challenging. Novel solutions are needed and, given the ubiquity of biologically active secondary metabolites in nature, such compounds require further exploration as leads for novel crop protection chemistry. Despite improving understanding of allelochemicals, particularly in terms of their potential for use in weed control, their interactions with multiple biotic kingdoms have to date largely been examined in individual compounds and not as a recurrent phenomenon. Here, multi-kingdom effects in allelochemicals are introduced by defining effects on various organisms, before exploring current understanding of the inducibility and possible ecological roles of these compounds with regard to the evolutionary arms race and dose-response relationships. Allelochemicals with functional benefits in multiple aspects of plant defence are described. Gathering these isolated areas of science under the unified umbrella of multi-kingdom allelopathy encourages the development of naturally-derived chemistries conferring defence to multiple discrete biotic stresses simultaneously, maximizing benefits in weed, insect and pathogen control, while potentially circumventing resistance. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Synthesis and Anti-Tobacco Mosaic Virus/Fungicidal/Insecticidal/Antitumor Bioactivities of Natural Product Hemigossypol and Its Derivatives

To further study the structure-activity relationship of gossypol, hemigossypol (1) and its derivatives (2-23) were successfully designed via structure simplification and chemically synthesized. The anti-tobacco mosaic virus (TMV), fungicidal, and insecticidal activities of them were tested systematically. Most of these derivatives exhibited excellent anti-TMV activity. Furthermore, these compounds also exhibited broad-spectrum fungicidal activities against 14 kinds of phytopathogenic fungi. In particular, hemigossypol acid lactone (7) was stable in the air. In terms of biological activity, it not only showed anti-TMV activity (inhibitory rates of 70.3, 65.4 and 72.4% at 500 μg/mL for inactivation, curative, and protection activity in vivo, respectively) comparable to ningnanmycin but also exhibited higher insecticidal activity against mosquito larvae (60%/0.25 mg/kg) than the commercial species rotenone. None of hemigossypol and the tested derivatives showed antitumor activities.

Biocontrol ability and action mechanism of dihydromaltophilin against Colletotrichum fructicola causing anthracnose of pear fruit

BACKGROUND

Anthracnose caused by Colletotrichum fructicola is one of the most important diseases in pear fruit, resulting in huge economic losses. Public awareness of protecting the environment and food safety, together with pathogen resistance to many key fungicides have led to an urgent need to develop alternative strategies for controlling fruit diseases. Here, the antifungal activity of a natural product, dihydromaltophilin [heat-stable antifungal factor (HSAF)], against C. fructicola in vitro and in vivo was investigated to determine its efficacy for anthracnose management.

RESULTS

HSAF exhibited pronounced antifungal activity against in vitro mycelial growth of C. fructicola, with a half-inhibition concentration of 0.43 mg L^-1 . Hyphae treated with HSAF showed defects such as hyperbranching, swelling and depolarized growth. Conidia germination in the pathogen was inhibited by HSAF in a dose-dependent manner. In the presence of 4 mg L^-1 HSAF, conidia germination was significantly delayed, and germ tube growth was inhibited. HSAF at 8 mg L^-1 completely blocked conidia germination in C. fructicola. In addition, HSAF disrupted coordination of cytokinesis with growth and nuclear division, induced reactive oxygen species production in conidia, and damaged the integrity of the conidia cell wall. Moreover, an in vivo test confirmed that 50 mg L^-1 HSAF significantly reduced the development of anthracnose decay in pear fruit caused by C. fructicola.

CONCLUSION

HSAF was highly effective in reducing pear anthracnose caused by C. fructicola and has great potential to become a new type of fruit preservative.

Teratogenic, Oxidative Stress and Behavioural Outcomes of Three Fungicides of Natural Origin (Equisetum arvense, Mimosa tenuiflora, Thymol) on Zebrafish (Danio rerio)

The improper use of synthetic fungicides has raised public concerns related to environmental pollution and animal health. Over the years, plant-derived antifungals have been investigated as safer alternatives, although little scientific evidence of its neurodevelopmental effects exist. The main objective of this study was to explore the effects of three alternative natural extracts (Equisetum arvense, Mimosa tenuiflora, Thymol) with antifungal properties during the early development of zebrafish by evaluating different teratogenic, oxidative stress and behavioural outcomes. Following the determination of the 96 h-LC₅₀, exposure to sublethal concentrations showed the safety profile of both E. arvense and M. tenuiflora. However, following 96-h exposure to Thymol, increased lethality, pericardial oedema, yolk and eye deformations, and decreased body length were observed. The reduced and oxidized glutathione (GSH:GSSG) ratio was increased, and the glutathione-s-transferase activity in the group exposed to the highest Thymol concentration. Overall, these results support a more reducing environment associated with possible effects at the cellular proliferation level. In addition, the disruption of behavioural states (fear- and anxiety-like disorders) were noted, pointing to alterations in the c-Jun N-terminal kinase developmental signalling pathway, although further studies are required to explore this rationale. Notwithstanding, the results provide direct evidence of the teratogenic effects of Thymol, which might have consequences for non-target species.

4-Ethylphenol, A Volatile Organic Compound Produced by Disease-Resistant Soybean, Is a Potential Botanical Agrochemical Against Oomycetes

Oomycetes, represented by Phytophthora, are seriously harmful to agricultural production, resulting in a decline in grain quality and agricultural products and causing great economic losses. Integrated management of oomycete diseases is becoming more challenging, and plant derivatives represent effective alternatives to synthetic chemicals as novel crop protection solutions. Biologically active secondary metabolites are rapidly synthesized and released by plants in response to biotic stress caused by herbivores or insects, as well as pathogens. In this study, we identified groups of volatile organic compounds (VOCs) from soybean plants inoculated with Phytophthora sojae, the causal agent of soybean root rot. 4-Ethylphenol was present among the identified VOCs and was induced in the incompatible interaction between the plants and the pathogen. 4-Ethylphenol inhibited the growth of P. sojae and Phytophthora nicotianae and had toxicity to sporangia formation and zoospore germination by destroying the pathogen cell membrane; it had a good control effect on soybean root rot and tobacco black shank in the safe concentration range. Furthermore, 4-Ethylphenol had a potent antifungal activity against three soil-borne phytopathogenic fungi, Rhizoctonia solani, Fusarium graminearum, and Gaeumannomyces graminis var tritici, and four forma specialis of Fusarium oxysporum, which suggest a potential to be an eco-friendly biological control agent.

Water Dipping of Auxin Coated Chrysanthemum Cuttings Confers Protection against Insect Herbivores

Simple Summary

Cultivated chrysanthemums are one of the most economically important ornamental greenhouse crops worldwide. Classical breeding programs have mainly focused on improving aesthetic characteristics to meet the continuous increasing customer demands for new flower varieties. Consequently, commercial cultivars often lack insect resistance traits. Among the most important production constraints are biotic foes, in particular thrips and leaf miner infestations form a prominent hazard during its vegetative state. To maintain the desired aesthetic characteristics, clonal commercial propagation is aided by the use of auxin hormones for root promotion. This study aims to evaluate the potential of root promoting auxins in antiherbivore defenses. We demonstrate that water dipping of unrooted basal cut ends, coated with the commercial rooting hormone indole-3-butyric acid (IBA), conferred protection in chrysanthemum against thrips and leaf miner. Our findings add an interesting twist to the traditional role of auxins. We advocate a new twist of auxins beyond its traditional role in rooting in order to maximize plant yield by reducing herbivory through feasible, cost-effective water dipping treatments.

Abstract

Auxins are commonly used for commercial propagation of chrysanthemums by stem cuttings. Recent studies imply that these root-promoting hormones also affect plant defense responses. The underlying motive of this study stems from the serendipitous observation that water dipping of auxin-coated cuttings beneficially affected thrips herbivory. Therefore, the primary objective of this investigation was to explore the role of indole-3-butyric acid (IBA) in relation to herbivore susceptibility in chrysanthemum. We observed contrasting findings concerning the physical presence of IBA and it’s role in promoting susceptibility of cuttings to thrips, which may in part be explained by the phenotypical variations of cuttings generated from mother plants. Nonetheless, we repeatedly demonstrated considerable protection, in some experiments up to 37%, against thrips and leaf miner upon water dipping of IBA-coated cuttings. Assessment of polyphenol oxidase activity (PPO), 14 days after dipping treatment, suggests that neither direct induction nor priming of plant defenses are involved. Future experiments aimed at understanding the early signaling events may help to explain the underlying mechanisms involved in conferring herbivore protection. We propose a dual role for auxins in early integrated pest management strategies to maximize plant development and minimize herbivory through feasible, cost-effective water dipping treatments.

Natural Compound-derived Cytochrome bc1 Complex Inhibitors as Antifungal Agents

The high incidence of fungal pathogens has become a global issue for crop protection. A promising strategy to control fungal plant infections is based on the use of nature-inspired compounds. The cytochrome bc1 complex is an essential component of the cellular respiratory chain and is one of the most important fungicidal targets. Natural products have played a crucial role in the discovery of cytochrome bc1 inhibitors, as proven by the development of strobilurins, one of the most important classes of crop-protection agents, over the past two decades. In this review, we summarize advances in the exploration of natural product scaffolds for the design and development of new bc1 complex inhibitors. Particular emphasis is given to molecular modeling-based approaches and structure-activity relationship (SAR) studies performed to improve the stability and increase the potency of natural precursors. The collected results highlight the versatility of natural compounds and provide an insight into the potential development of nature-inspired derivatives as antifungal agents.

Recent advances in biodegradable matrices for active ingredient release in crop protection: Towards attaining sustainability in agriculture

Climate changes, emerging species of plant pests, and deficits of clean water and arable land have made availability of food to the ever-increasing global population a challenge. Excessive use of synthetic pesticides to meet ever-increasing production needs has resulted in development of resistance in pest populations, as well as significant ecotoxicity, which has directly and indirectly impacted all life-forms on earth. To meet the goal of providing safe, sufficient, and high-quality food globally with minimal environmental impact, one strategy is to focus on targeted delivery of pesticides using eco-friendly and biodegradable carriers that are derived from naturally available materials. Herein, we discuss some of the recent approaches to use biodegradable matrices in crop protection, while exploring their design and efficiency. We summarize by discussing associated challenges with the existing approaches and future trends that can lead the world to more sustainable agricultural practices.

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Providing food safety and security is critical for the growing global population.

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Crop yield is affected by various biotic and abiotic factors.

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Targeted/sustained delivery of agrochemicals reduces excessive use of pesticides.

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Nature-derived biodegradable materials curtail plant health and environmental harm.

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Biodegradable matrices hold promise for sustainable crop protection.

Natural Product Cerbinal and Its Analogues Cyclopenta[c]pyridines: Synthesis and Discovery as Novel Pest Control Agents

Owing to the changing needs of agriculture, the exploration of new pest control agents remains as critical as ever. The analogues 3a-3v of the natural product cerbinal were synthesized from genipin by an efficient and practical method under additive-free conditions. The antiviral and insecticidal effects of cerbinal and these cyclopenta[c]pyridines (3a-3v) were evaluated systematically. Most of the synthesized compounds exhibited higher anti-TMV activities than the lead compound cerbinal. Compound 3s (2-(4-methoxyphenyl)) had the most promising inhibitory activities against TMV (inactivation effect 49.0 ± 0.8%, curative effect 41.2 ± 4.3%, and protection effect 51.5 ± 2.7% at 500 μg/mL). Among the synthesized compounds, only 3v (2-(2-chloro-4-(trifluoromethoxy)phenyl)) reached the activity level of cerbinal against Plutella xylostella. This suggested that the cyclopenta[c]pyridines obtained by modifications of cerbinal at position 2 are very significant for the anti-TMV activity, and yet were exceptionally less active for the insecticidal activities.