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.