Discovery of Novel (+)-Nootkatone-Based Amine Derivatives as Potential Insecticide Candidates

To discover novel natural product-based insecticides, a series of (+)-nootkatone-based amine derivatives 3a-t were prepared and evaluated for their insecticidal activities against Mythimna separata Walker, Myzus persicae Sulzer, and Plutella xylostella Linnaeus. Insecticidal assays showed that most of the title (+)-nootkatone derivatives exhibited stronger insecticidal activities against three insect pests than the precursor (+)-nootkatone after the introduction of amine groups on the parent (+)-nootkatone. Compounds 3a, 3d, 3h, 3m, 3n, 3p, and 3r displayed more promising growth inhibitory (GI) effect against M. separata than the commercially available botanical insecticide toosendanin. Compound 3o exhibited the most potent aphicidal activity with an LD₅₀ value of 0.011 μg/larvae, which was 2.09-fold higher than the positive control rotenone. Additionally, compounds 3g and 3n showed more promising larvicidal activity against P. xylostella with LC₅₀ values of 260 and 230 mg/L, respectively, superior to that of rotenone (460 mg/L). Moreover, derivatives 3g and 3n exhibited better control efficacy toward P. xylostella than rotenone under greenhouse conditions. Preliminary mechanistic studies revealed that derivative 3n could inhibit the activity of glutathione S-transferase (GST) in P. xylostella and thus exerted larvicidal activity, and molecular docking further demonstrated that 3n could interact well with some amino acid residues of GST. Finally, the toxicity assay suggested that derivatives 3g and 3n were relatively less toxic to nontarget organisms. These findings will provide insights into the development of (+)-nootkatone derivatives as green pesticides.