Construction, Pesticidal Activities, Control Effects, and Detoxification Enzyme Activities of Osthole Ester/Amide Derivatives

Structural Optimization of Natural Plant Products: Construction, Pesticidal Activities, and Toxicology Study of New 2-Isopropanol-4-methoxy-7-alkyl/aryloxycarbonyl-(E)-vinyl-2,3-dihydrobenzofurans

Recently, the structural optimization of natural bioactive products has been one of the important ways to discover new pesticide candidates. Based on osthole as a lead compound, herein, a series of new 2-isopropanol-4-methoxy-7-alkyl/aryloxycarbonyl-(E)-vinyl-2,3-dihydrobenzofuran derivatives were synthesized. Steric configurations of compounds 3, 4, 6, 9, 11, 29, and 31 were confirmed by X-ray monocrystallography. Notably, an efficient method for preparation of 2-isopropanol-2,3-dihydrobenzofurans from osthole by the epoxidation and rearrangement reactions was developed. Against Plutella xylostella Linnaeus, compound 31 (R = CH2CH2Ph; LC50: 0.759 mg/mL) displayed a 1.9-fold insecticidal activity compared to that of osthole; against Tetranychus cinnabarinus Boisduval, compound 34 (R = (CH2)9CH3; LC50: 0.401 mg/mL) exhibited a 3.3-fold acaricidal activity and good control effects compared to those of osthole. By the scanning electron microscope (SEM) imaging method, it was demonstrated that the acaricidal activity of compound 34 may be related to the damage of the cuticle layer crest of T. cinnabarinus. Compound 34 could be further studied as a potential acaricide.

Plant natural product-based pesticides in crop protection: semi-synthesis, mono-crystal structures and agrochemical activities of osthole ester derivatives, and study of their toxicology against Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Owing to large amounts of synthetic pesticides being extensively and unreasonably used for crop protection, currently, resistance and negative impacts on human health and environment safety have appeared. Therefore, development of potential pesticide candidates is highly urgent. Herein, a series of ester derivatives of osthole were designed and synthesized as pesticidal agents.

RESULTS

Six spatial configurations of 4'-(p-toluenoyloxy)osthole (4b), 4'-(m-fluorobenzoyloxy)osthole (4f), 4'-(p-fluorophenylacetyloxy)osthole (4m), 4'-(3'',4''-methylenedioxybenzoyloxy)osthole (4q), 4'-formyloxyosthole (4u) and 4'-acetyloxyosthole (4v) were determined by X-ray mono-crystal diffraction. Compounds 4b, 4'-(p-chlorobenzoyloxy)osthole (4g), 4'-(m-chlorobenzoyloxy)osthole (4h), 4'-(p-bromobenzoyloxy)osthole (4i) and 4'-(2''-chloropyridin-3''-ylcarbonyloxy)osthole (4p) showed higher insecticidal activity than toosendanin against Mythimna separata Walker; notably, compound 4b displayed 1.8 times insecticidal activity of the precursor osthole. Against Tetranychus cinnabarinus Boisduval, compounds 4g and 4h showed 3.3 and 2.6 times acaricidal activity of osthole, and good control effects in the glasshouse. Scanning electron microscopy assay demonstrated that compound 4g can damage the cuticle layer of T. cinnabarinus resulting in death.

CONCLUSION

Compounds 4g and 4h can be further studied as lead pesticidal agents for the management of M. separata and T. cinnabarinus. These results will pave the way for application of osthole derivatives as agrochemicals. © 2024 Society of Chemical Industry.

Recent Advances of Coumarin-Type Compounds in Discovery of Pesticides

Coumarin, a naturally occurring active ingredient with various biological activities in pesticides, is commonly found in plants belonging to the Rutaceae and Apiaceae families. Thanks to its unique structural properties and natural benefits, coumarin and its derivatives exhibit a wide range of physiological activities, including insecticidal, antifungal, antibacterial, herbicidal, and antiviral properties. These compounds have attracted considerable interest in the field of pesticide development, although there is a lack of comprehensive reviews on their use in pesticides. This Review aims to provide a detailed overview of the applications of coumarin and its derivatives in pesticides, covering biological activities, structure-activity relationship analyses, and mechanisms of action. It is hoped that this Review will offer new insights into the discovery and mechanisms of these compounds in pesticide development.

Semi-Preparation and X-ray Single-Crystal Structures of Sophocarpine-Based Isoxazoline Derivatives and Their Pesticidal Effects and Toxicology Study

Recently, research and development of novel pesticides from natural plant products have received much attention. To accelerate the application of sophocarpine as the agrochemical candidate, a series of novel sophocarpine-based isoxazoline derivatives were prepared by the 1,3-dipolar [2 + 3] cycloaddition reaction of sophocarpine with different chloroximes. Their structures were well characterized by high-resolution mass spectra, infrared spectra, and proton/carbon-13 nuclear magnetic resonance spectra. Eight steric configurations of compounds 5a, 5e', 5f, 5g, 5h, 5i, 5r, and 5u' were further determined by X-ray single-crystallography. Against Aphis citricola Van der Goot, compounds 5n (LD50: 0.032 μg/nymph) and 5o (LD50: 0.024 μg/nymph) exhibited greater than 3.7- and 4.9-fold potent aphicidal activity compared to sophocarpine (LD50: 0.118 μg/nymph). Against Tetranychus cinnabarinus Boisduval, derivative 5g displayed the most promising acaricidal activity with the LC50 value of 0.247 mg/mL, which was 14.2-fold that of sophocarpine. Compounds 5d and 5g also exhibited good control efficacy against T. cinnabarinus. Scanning electron microscopy images indicated that compound 5g can destroy the mite cuticle layer. These results will provide the foundation for the structural modification and use of sophocarpine derivatives as agrochemicals in the future.

Overexpression of SmUGGT1 Confers Imidacloprid Resistance to Sitobion miscanthi (Takahashi)

Sitobion miscanthi, the main species of wheat aphids, is one kind of harmful pest. Chemical insecticides are the important agrochemical products to effectively control wheat aphids. However, the broad application has led to serious resistance of pests to several insecticides, and understanding insecticide resistance mechanisms is critical for integrated pest management. In this study, SmUGGT1, a new uridine diphosphate (UDP)-glycosyltransferase (UGT) gene, was cloned and more strongly expressed in the SM-R (the resistant strain to imidacloprid) than in the SM-S (the susceptible strain to imidacloprid). The increased susceptibility to imidacloprid was observed after silencing SmUGGT1, indicating that it can be related to the resistance to imidacloprid. Subsequently, SmUGGT1 regulated post-transcriptionally in the coding sequences (CDs) by miR-81 was verified and involved in the resistance to imidacloprid in S. miscanthi. This finding is crucial in the roles of UGT involved in insecticide resistance management in pests.

Recent Advances and Outlook of Benzopyran Derivatives in the Discovery of Agricultural Chemicals

Scaffold structures, new mechanisms of action, and targets present enormous challenges in the discovery of novel pesticides. The discovery of new scaffolds is the basis for the continuous development of modern agrochemicals. Identification of a good scaffold such as triazole, carbamate, methoxy acrylate, pyrazolamide, pyrido-pyrimidinone mesoionic, and bisamide often leads to the development of a new series of pesticides. In addition, pesticides with the same target, including the inhibitors of succinate dehydrogenase (SDH), oxysterol-binding-protein, and p-hydroxyphenyl pyruvate dioxygenase (HPPD), may have the same or similar scaffold structure. Recent years have witnessed significant progress in the discovery of new pesticides using natural products as scaffolds or bridges. In recent years, there have been increasing reports on the application of natural benzopyran compounds in the discovery of new pesticides, especially osthole and coumarin. A systematic and comprehensive review of benzopyran active compounds in the discovery of new agricultural chemicals is helpful to promote the discussion and development of benzopyran active compounds. Therefore, this work systematically reviewed the research and application of benzopyran derivatives in the discovery of agricultural chemicals, summarized the antiviral, herbicidal, antibacterial, fungicidal, insecticidal, nematicidal and acaricidal activities of benzopyran active compounds, and discussed the structural-activity relationship and mechanism of action. In addition, some active fragments were recommended to further optimize the chemical structure of benzopyran active compounds based on reference information.

Discovery of Pesticide Candidates from Natural Plant Products: Semisynthesis and Characterization of Andrographolide-Based Esters and Study of Their Pesticidal Properties and Toxicology

To explore the use of nonfood plant-derived secondary metabolites for plant protection, a series of ester derivatives for controlling the major migratory agricultural pests were obtained by structural modification of andrographolide, a labdane diterpenoid isolated from Andrographis paniculata. Compound Id showed good insecticidal activity against the fall armyworm Spodoptera frugiperda Smith. Compounds IIa (LC50: 0.382 mg/mL) and IIIc (LC50: 0.563 mg/mL), the acaricidal activities of which were, respectively, 13.1 and 8.9 times that of andrographolide (LC50: 4.996 mg/mL), exhibited strong acaricidal and control effects against Tetranychus cinnabarinus Boisduval. Against Aphis citricola Van der Goot, compounds IIIc and IVb displayed 3.9- and 3.7-fold pronounced aphicidal activity of andrographolide. Effects of compound Id on three protective enzymes (superoxide dismutase, peroxidase, and catalase) of S. frugiperda were also observed. The obvious differences of epidermal cuticle structures of mites treated with compound IIa were determined by scanning electron microscopy. Structure-activity relationships indicated that 14-ester derivatives of andrographolide showed potential insecticidal/acaricidal activities and can be further utilized as lead compounds.

Osthole, a Coumarin from Cnidium monnieri: A Review on Its Pharmacology, Pharmacokinetics, Safety, and Innovative Drug Delivery Platforms

Osthole, a coumarin compound mainly derived from Cnidium monnieri (L.), has attracted much interest from the scientific community owing to its multiple therapeutic properties. However, its pharmacological mechanism, pharmacokinetics, and toxicological effects are far from clear. Furthermore, the potential drug delivery platforms of osthole remain to be comprehensively delineated. The present review aimed to systematically summarize the most up-to-date information related to pharmacology, pharmacokinetics, and safety issues related to osthole, and discuss the investigations of novel drug delivery platforms. The information herein discussed was retrieved from authoritative databases, including PubMed, Web of Science, Google Scholar, Chinese National Knowledge Infrastructure (CNKI) and so on, reviewing information published up until February of 2024. New evidence shows that osthole induces a sequence of therapeutic actions and has a moderate absorption rate and rapid metabolic characteristics. In addition, this phytoconstituent possesses potential hepatotoxicity, and caution should be exercised against the risk of the drug combination. Furthermore, given its needy solubility in aqueous medium and non-organizational targeting, novel drug delivery methods have been designed to overcome these shortcomings. Given the properties of osthole, its therapeutic benefits ought to be elucidated in a greater array of comprehensive research studies, and the molecular mechanisms underlying these benefits should be explored.

Discovery of 3-Formyl-N-(un)Substituted Benzylindole Pyrimidines as an Acaricidal Agent and Their Mechanism of Action

To discover the pronounced acaricide candidate, herein, a series of 3-formyl-N-(un)substituted benzylindole pyrimidines were prepared by structural modification of indoles at the N-1 and C-3 positions via the successive Vilsmeier-Haack-Arnold (VHA), aldol condensation, and cyclization reactions. The steric structures of nine compounds were undoubtedly confirmed by X-ray single-crystallography. Against Tetranychus cinnabarinus Boisduval, compounds V-15, V-31, V-34, V-42, V-44, and V-60 exhibited promising acaricidal activity with LC50 values of 0.299-0.481 mg/mL. In particular, compound V-34 displayed 4.2 times the acaricidal activity of its precursor 6-methylindole. Scanning electron microscopy (SEM) imaging revealed that the construction of the cuticle layer of V-34-treated T. cinnabarinus was seriously destroyed. Furthermore, RNA-Seq analysis indicated that compound V-34 could regulate the homeostasis metabolism of T. cinnabarinus through arachidonic acid and linoleic acid metabolism and lysosome pathways. These results suggested that compound V-34 can be further studied as a lead acaricidal agent.

Molecular mechanism of Osthole against chitin synthesis of Ustilaginoidea virens based on combined transcriptome and metabolome analyses

Rice false smut, caused by the fungus Ustilaginoidea virens, is a destructive grain disease in rice-producing areas worldwide. To reveal the action mechanism of osthole against U. virens, the mycelial morphology, differential genes and metabolites of osthole-treated U. virens were determined using electron microscopy and multi-omics, respectively. The hyphae of osthole-treated U. virens were severely wrinkled and distorted with rough cell walls, uneven thickness, and protoplast aggregation. Calcium fluorescent white staining showed that osthole affected chitin synthesis in U. virens. The differential genes and metabolites in U. virens were significantly enriched in amino sugar and nucleotide sugar metabolism pathway. The expression of the acetylglucosamine phosphate mutase (AGM) gene (UvAGM1) and UDP-N-acetylglucosamine was significantly down regulated. The AGM of osthole-treated U. virens was 133.43 ng/mL, which was significantly lower than that of the control group (205.67 ng/mL). Osthole combined with the amino acid residue THR334 of AGM via hydrogen bonding. These results indicate that UvAGM1 may be a key candidate gene of osthole against U. virens. Overall, the results provide valuable information for the application of osthole to control rice false smut.

Optimization of Osthole in the Lactone Ring as an Agrochemical Candidate: Synthesis, Characterization, and Pesticidal Activities of Osthole Amide/Ester Derivatives and Their Effects on Morphological Changes of Mite Epidermis

Structural modification of natural products is one of the important ways in the discovery of novel pesticides. Based on a diversity-oriented synthesis strategy, herein, two series of amide/ester derivatives (52 compounds) were obtained by opening the lactone of osthole. Interestingly, the effect of different concentrations of aq. sodium hydroxide on the ratio of two isomers (cis- and trans-2) was investigated, and a magical phenomenon of ultraviolet (UV) light irradiation on intertransformation of two isomers (cis- and trans-2) was observed. Against Mythimna separata, when compared with the precursor osthole, compounds 4b, 4l, 5l, 5m, 7h, 7l, and 7m displayed more pronounced growth inhibitory activity with the final mortality rates of 62.0-68.9%. Compounds 4b, 4i, and 5m showed 5.7-6.6 times stronger acaricidal activity against Tetranychus cinnabarinus than osthole, and notably, control effects of compounds 4i and 5m were 2.4- and 2.7-fold that of osthole in the management of T. cinnabarinus in the greenhouse. Scanning electron microscopy (SEM) images of the epidermis of 5m-treated T. cinnabarinus indicated that compound 5m can destroy the mite cuticle layer. Compounds 4b and 5m can be used as leads to further explore more promising pesticidal agents.

Synthesis of Piperine-Based Ester Derivatives with Diverse Aromatic Rings and Their Agricultural Bioactivities against Tetranychus cinnabarinus Boisduval, Aphis citricola Van der Goot, and Eriosoma lanigerum Hausmann

Exploration of plant secondary metabolites or by using them as leads for development of new pesticides has become one of the focal research topics nowadays. Herein, a series of new ester derivatives of piperine were prepared via the Vilsmeier−Haack−Arnold (VHA) reaction, and their structures were characterized by infrared spectroscopy (IR), melting point (mp), proton nuclear magnetic resonance spectroscopy (1H NMR), and carbon nuclear magnetic resonance spectroscopy (13C NMR). Notably, the steric configurations of compounds 6 and 7 were confirmed by single-crystal analysis. Against T. cinnabarinus, compounds 9 and 11 exhibited 47.6- and 45.4-fold more pronounced acaricidal activity than piperine. In particular, compounds 9 and 11 also showed 2.6-fold control efficiency on the fifth day of piperine. In addition, compound 6 (>10−fold higher than piperine) displayed the most potent aphicidal activity against A. citricola. Furthermore, some derivatives showed good aphicidal activities against E. lanigerum. Moreover, the effects of compounds on the cuticles of T. cinnabarinus were investigated by the scanning electron microscope (SEM) imaging method. This study will pave the way for future high value added application of piperine and its derivatives as botanical pesticides.

High Value-Added Application of Natural Plant Products in Crop Protection: Construction and Pesticidal Activities of Piperine-Type Ester Derivatives and Their Toxicology Study

To discover new potential pesticide candidates, recently, structural modification of natural bioactive products has received much attention. In this work, a series of new piperine-type ester derivatives were regio- and stereoselectively synthesized based on a natural alkaloid piperine isolated from Piper nigrum. Their structures were characterized by IR, mp, ¹H NMR (¹³C NMR), and high-resolution mass spectrometry (HRMS). Against Tetranychus cinnabarinus Boisduval (Acari: Tetranychidae), compounds 4e, 4f, 4u, and 4v displayed the most significant acaricidal activity with LC₅₀ values of 0.155, 0.117, 0.177, and 0.164 mg/mL, respectively. Particularly, compound 4f showed >120-fold higher acaricidal activity than piperine (LC₅₀: 14.198 mg/mL). Notably, the acaricidal activity of 4f was equivalent to that of the commercial acaricide spirodiclofen (LC₅₀: 0.115 mg/mL). Additionally, against Eriosoma lanigerum Hausmann (Hemiptera: Aphididae), compounds 4w and 4b' showed 1.8-fold aphicidal activity of piperine. Furthermore, via the scanning electron microscope (SEM) imaging method, the obvious destruction of the construction of the cuticle layer of 4f-treated T. cinnabarinus was observed. Compound 4f could be further studied as a lead acaricidal agent.