Novel Pesticide Candidates Inspired by Natural Neolignan: Preparation and Insecticidal Investigation of Honokiol Analogs Containing 2-Aminobenzoxazole-Fused Core Scaffold

Abstract

As a continuation of our efforts to develop new agrochemicals with typical architecture and efficient bioactivity from plant natural products, natural neolignan honokiol was used as a lead compound to prepare novel analogs bearing the core 2-aminobenzoxazole scaffold. Their insecticidal potency against two representative agricultural pests, Plutella xylostella Linnaeus and Mythimna separata (Walker), were evaluated in vivo. The pesticide bioassay results revealed that compounds 7″a, 9, 10d, and 10j exhibited prominent larvicidal activity against the larvae of P. xylostella (LC₅₀ = 7.95, 11.85, 15.51, and 12.06 μg/mL, respectively), superior to the precursor honokiol (LC₅₀ = 43.35 μg/mL) and two botanical insecticides, toosendanin (LC₅₀ = 26.20 μg/mL) and rotenone (LC₅₀ = 23.65 μg/mL). Compounds 7d, 10d, and 10j displayed a more pronounced nonchoice antifeedant effect (AFC₅₀ = 9.48, 9.14, and 12.41 μg/mL, respectively) than honokiol (AFC₅₀ = 54.81 μg/mL) on P. xylostella. Moreover, compounds 7b, 7″a, 9, 10d, 10f, and 10j showed better growth inhibitory activity against M. separata (LC₅₀ = 0.36, 0.34, 0.28, 0.16, 0.26, and 0.11 mg/mL, respectively) than honokiol, toosendanin, and rotenone (LC₅₀ = 1.48, 0.53, and 0.46 mg/mL, respectively). A potted plant assay under greenhouse conditions illustrated that compounds 10d and 10j continued to provide good control efficacy against P. xylostella and an apparent protective effect on plants. Further cytotoxicity assay revealed that the aforementioned potent compounds showed relatively moderate toxicity and a good safety profile for non-target mammalian cells. Overall, the current work provides valuable insight into the agrochemical innovation of honokiol-derived analogs for use as natural-inspired pesticides in agricultural pest management.