Discovery of Cholesterol-Type Oxime Ester/Ether Derivatives as Aphicidal Candidates against Aphis citricola Van der Goot and Hyalopterus arundimis Fabricius.

The exploration of natural bioactive products as leads for high-value-added applications in crop protection has emerged as one of the prominent research focuses. Based on cholesterol as a lead molecule, herein oxime ester/ether derivatives of cholesterol at the C-3 position were semisynthesized via five successive chemical reactions. The steric configuration of derivative Ip was determined by a single-crystal analysis. Against Aphis citricola Van der Goot (Hemiptera: Aphididae), compounds Id, Iq-Is, Iv, Iw, Iy, IIb, IIc, IIf, and IIi (LC50: 0.074-0.171 mg/mL) exhibited better aphicidal activity compared with cholesterol. Notably, derivative IIc displayed 130.2-fold aphicidal activity compared to cholesterol and good control efficiency on the fifth day in the field. Against Hyalopterus arundimis Fabricius (Homoptera: Aphididae), compounds Ii, Im, IId, and IIg depicted 59.2-66.7 times aphicidal activity compared to that of cholesterol. In addition, it demonstrated that the hydroxyl at the C-3 position of cholesterol is a vital modification site. Furthermore, the severe destruction of the superficial layers of treated A. citricola and H. arundimis was unveiled by scanning electron microscope (SEM). Hopefully, these results can lay the foundation for further optimization of cholesterol-type compounds as resultful aphicides.