Phytotoxic Lignans from Artemisia arborescens

A systematic bioassay-guided fractionation of methylene chloride extracts of the aerial part of Artemisia arborescens was performed in order to identify its phytotoxic compounds. Two lignans were isolated, sesamin and ashantin, that inhibited growth of Agrostis stolonifera (bentgrass), a monocot, and Lactuca sativa (lettuce), a dicot, at 1 mg mL−1. In a dose-response screening of these lignans for growth inhibition against Lemna paucicostata (duckweed), ashantin was the most active with an IC50 of ca. 224 μM. The mode of action of these compounds is still unknown. In mosquito larvicidal bioassays the pure compounds sesamin and ashantin did not cause mortality at the highest dose of 125 mg/L against 1-d-old Aedes aegypti larvae. In bioautography bioassays for antifungal activity using Botrytis cinerea, Fusarium oxysporum, Colletotrichum fragariae, Colletotrichum acutatum, and Colletotrichum gloeosporioides, ashantin and sesamin were inactive at 5 μg and were therefore not subjected to additional screening in secondary antifungal assays.