Diterpenoid Alkaloids from Two Aconitum Species with Antifeedant Activity against Spodoptera exigua

Twenty-five diterpenoid alkaloids were isolated from the roots of two Aconitum species. The structures of seven new C₁₉-diterpenoid alkaloids, apetaldines A-G (1-7), and 10 known alkaloids (8-17) from Aconitum apetalum and eight known alkaloids (18-25) from Aconitum franchetii var. villosulum were elucidated via HRESIMS, IR, and NMR data. Alkaloids 1-10, 15, 16, and 18-25 were screened for their antifeedant activity. Among the compounds tested, chasmanthinine (19) showed highly potent antifeedant activity with an effective concentration for 50% feeding reduction (EC₅₀) at 0.07 mg/cm². The antifeedant structure-activity relationship of the diterpenoid alkaloids is also discussed.