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

Synthesis and Pesticidal Activities of Ester Derivatives of the Labdane Diterpenoid Andrographolide at the C-3 Position Containing the Isoxazoline Fragment and Their Toxicology Study against Tetranychus cinnabarinus Boisduval

Due to the long-term overuse of chemical pesticides, serious resistance and negative problems on human health and the ecological environment have appeared. To develop plant-product-based pesticide candidates, a series of novel andrographolide ester derivatives containing the isoxazoline skeleton were prepared at the C-3 position. Their pesticidal activities were evaluated against three typical pests such as Mythimna separata Walker, Aphis citricola Van der Goot, and Tetranychus cinnabarinus Boisduval. Against M. separata, compounds Ik, IIf, IIg, and IIk showed 1.6-1.8 times insecticidal activity compared to that of andrographolide; against A. citricola, compounds 6, Ih, and IIh possessed 3.7-3.9-fold aphicidal activity compared to that of andrographolide; against T. cinnabarinus, compounds Ib, Ig, and IIk exhibited 7.4-9.1-fold promising acaricidal activity compared to that of andrographolide. It is worth mentioning that effects of IIk on morphological changes of the treated mite cuticle layer structures were observed by the scanning electron microscope imaging method. Compound IIk can be studied as a pesticidal lead for further structural modification.

Construction and Single-Crystal Structures of N-Isoxazolin-5-ylcarbonylindole Derivatives, and Their Pesticidal Activities and Toxicology Study

To explore natural product-based pesticide candidates, a series of indole derivatives containing the isoxazoline skeleton at the N-1 position were synthesized by 1,3-dipolar [2 + 3] cycloaddition reaction. Their structures were characterized by melting points (mp), infrared (IR) spectra, proton nuclear magnetic resonance spectra (1H NMR), carbon-13 nuclear magnetic resonance spectra (13C NMR), and high resolution mass spectrometry (HRMS). The single-crystal structures of five compounds were presented. Against Tetranychus cinnabarinus Boisduval, compound 3b showed greater than 3.8-fold acaricidal activity of indole and good control effects under glasshouse conditions. Against Aphis citricola Van der Goot, compounds 3b and 3q exhibited 48.3- and 36.8-fold aphicidal activity of indole and 6-methylindole, respectively. Particularly, compound 3b showed good bioactivities against T. cinnabarinus and A. citricola. Against Eriosoma lanigerum Hausmann, compound 3h and 3i showed 2.1 and 1.9 times higher aphicidal activity compared to indole. Furthermore, the construction of the epidermal cuticle layer of 3b-treated carmine spider mites was distinctly damaged, which ultimately led to their death.

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.

Piperine: Chemistry and Biology

Piperine is a plant-derived promising piperamide candidate isolated from the black pepper (Piper nigrum L.). In the last few years, this natural botanical product and its derivatives have aroused much attention for their comprehensive biological activities, including not only medical but also agricultural bioactivities. In order to achieve sustainable development and improve survival conditions, looking for environmentally friendly pesticides with low toxicity and residue is an extremely urgent challenge. Fortunately, plant-derived pesticides are rising like a shining star, guiding us in the direction of development in pesticidal research. In the present review, the recent progress in the biological activities, mechanisms of action, and structural modifications of piperine and its derivatives from 2020 to 2023 are summarized. The structure-activity relationships were analyzed in order to pave the way for future development and utilization of piperine and its derivatives as potent drugs and pesticides for improving the local economic development.

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.

Exploration of Synergistic Pesticidal Activities, Control Effects and Toxicology Study of a Monoterpene Essential Oil with Two Natural Alkaloids

With the increasing development of pest resistances, it is not easy to achieve satisfactory control effects by using only one agrochemical. Additionally, although the alkaloid matrine (MT) isolated from Sophora flavescens is now utilized as a botanical pesticide in China, in fact, its pesticidal activities are much lower in magnitude than those of commercially agrochemicals. To improve its pesticidal activities, here, the joint pesticidal effects of MT with another alkaloid oxymatrine (OMT) (isolated from S. flavescens) and the monoterpene essential oil 1,8-cineole (CN) (isolated from the eucalyptus leaves) were investigated in the laboratory and greenhouse conditions. Moreover, their toxicological properties were also studied. Against Plutella xylostella, when the mass ratio of MT and OMT was 8/2, good larvicidal activity was obtained; against Tetranychus urticae, when the mass ratio of MT and OMT was 3/7, good acaricidal activity was obtained. Especially when MT and OMT were combined with CN, the significant synergistic effects were observed: against P. xylostella, the co-toxicity coefficient (CTC) of MT/OMT (8/2)/CN was 213; against T. urticae, the CTC of MT/OMT (3/7)/CN was 252. Moreover, the activity changes over time of two detoxification enzymes, carboxylesterase (CarE) and glutathione S-transferase (GST) of P. xylostella treated with MT/OMT (8/2)/CN, were observed. In addition, by scanning electron microscope (SEM), the toxicological study suggested that the acaricidal activity of MT/OMT (3/7)/CN may be related to the damage of the cuticle layer crest of T. urticae.