Defensive Sesquiterpenoids from Leaves of Eupatorium adenophorum

The invasive plant Eupatorium adenophorum Spreng has caused great economic loss in China, and is gravely threatening the native biodiversity and ecosystem. The plant has been phytochemically investigated for the defensive chemical substances in its leaves. Three active sesquiterpenoids were isolated and identified, which include a new sesquiterpenoid (1), and two known sesquiterpenoids (2, 3). Their structures were established by spectroscopic studies such as 1D‐ and 2D‐NMR and MS analyses. Meanwhile, the antifeedant activities of these compounds against two generalist plant‐feeding insects, Helicoverpa armigera and Spodoptera exigua, were carried out. Compound 1 showed significant antifeedant activity against S. exigua with EC50=7.46 µg/cm2, while compounds 2 and 3 were more active against H. armigera (EC50=2.57 and 3.04 µg/cm2 respectively). These findings suggest a defensive role of sesquiterpenoids in E. adenophorum against herbivores.