PHYTOTOXIC IRIDOID GLUCOSIDES FROM THE ROOTS OF VERBASCUM-THAPSUS

The iridoid glucosides lateroside 1, harpagoside 2, ajugol 3, and aucu bin 4 were isolated from an ethanolic extract of the roots of the weed Verbascum thapsus that exhibits antigermination activity on seeds of barley (Hordeum vulgare). Bioassays indicated that at 3 mM concentrati on, compounds 1, 2, and 4 showed moderate inhibition of seed germinati on. These compounds also reduced root length when they were assayed on pregerminated seeds at 1 mM to 0.001 mM concentration range. Of all c ompounds tested, aucubin 4 was the most active against root elongation . Compound 3 showed no activity in the bioassays.