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

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.

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.