Secondary metabolites from Solanum rostratum and their antifeedant defense mechanisms against Helicoverpa armigera.

Solanum rostratum is a worldwide malignant invasive weed, causing serious harm to ecological environment and biodiversity. Strong chemical defense against herbivorous insects is supposed to be one of the successful invasive mechanisms of this exotic plant. However, the real defense components, their action mechanisms and distributions are still unknown. To address these problems, we bioassay-guided isolated compounds from the aerial part of S. rostratum, and determined their structures using HR-ESIMS, NMR, together with ECD calculation. One new and seven known compounds were identified, and all the isolates exhibited different levels of antifeedant activities, especially compounds 1 and 4. Consistently, compounds 1 and 4 displayed potent inhibitory effects on antifeedant related enzymes (AchE and CarE). The action mechanisms of active compounds 1 and 4 were revealed by molecular docking and molecular dynamics simulation studies. Furthermore, the distributions of the active compounds in leaves, stems and flowers were also analyzed by LC-MS.