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 <b>4e</b>, <b>4f</b>, <b>4u</b>, and <b>4v</b> displayed the most significant acaricidal activity with LC₅₀ values of 0.155, 0.117, 0.177, and 0.164 mg/mL, respectively. Particularly, compound <b>4f</b> showed >120-fold higher acaricidal activity than piperine (LC₅₀: 14.198 mg/mL). Notably, the acaricidal activity of <b>4f</b> was equivalent to that of the commercial acaricide spirodiclofen (LC₅₀: 0.115 mg/mL). Additionally, against Eriosoma lanigerum Hausmann (Hemiptera: Aphididae), compounds <b>4w</b> and <b>4b′</b> showed 1.8-fold aphicidal activity of piperine. Furthermore, <i>via</i> the scanning electron microscope (SEM) imaging method, the obvious destruction of the construction of the cuticle layer of <b>4f-</b>treated T. cinnabarinus was observed. Compound <b>4f</b> could be further studied as a lead acaricidal agent.