Flavonolignans from Elymus natans L. and Phytotoxic Activities

Elymus natans, a perennial gramineous grass, plays an important role in animal husbandry and environmental sustenance in the Qinghai–Tibet plateau as a result of its high forage quality and good adaptability to the local environment. A bioassay showed that the extracts of green grasses of E. natans (GG) exhibited stronger phytotoxic activities than withered grasses (WG) against crops and grasses. In view of the secondary metabolites, which may be responsible for the resistance of the plant, the chemical components of GG were investigated. The flavone tricin, E1, and 10 flavonolignans, E2–E11, including three new flavonolignans, E2, E10, and E11, were isolated and identified. As far as we know, this is the first report on the chemical constitutions of the plant until now. The contents of compounds E1 and E4–E7 in GG were significantly higher than those in WG in high-performance liquid chromatography analysis, and they also showed observably phytotoxic activities against lettuce and Festuca arundinacea.