POTENTIAL ALLELOPATHIC SESQUITERPENE LACTONES FROM SUNFLOWER LEAVES

Isolation, structure elucidation and allelopathic bioassays of 13 sesq uiterpene lactones, four of them new, from the sunflower cultivar VYP( R) are described. Structures of the lactone assigned as 1,2-anhydrido- 4,5-dihydroniveusin A, previously isolated from capitate glandular tri chomes of Helianthus annuus and of annuithrin are corrected. The effec t of a series of aqueous solutions at 10(-4)-10(-9) M of the sesquiter pene lactones was studied on the root and shoot lengths of Lactuca sat iva var. nigra, Lepidium sativum, Lycopersicon esculentum, seedlings ( dicotyledons) and Hordeum vulgare and Triticum estivum (monocotyledons ). The guaianolides generally had no effect on the germination and gro wth of L. sativum and L. esculentum, except for C-10 epimers 8 beta-an geloyloxycumambranolide and annuolide G where inhibitory effects were found on the shoot length of L. esculentum. Both exhibit similar activ ity profiles, the most persistenty active compound on dilution was 8 b eta-angeloyloxycumambranolide with an alpha-orientated hydroxyl group at C-10. The conformational changes due to functionalization within ge rmacranolides influence principally root and shoot growth. Heliangolid es have greater effect on root and shoot length of dicotyledon species , presumably due to conformational flexibility and the presence of ele ctrophylic groups. Copyright (C) 1996 Elsevier Science Ltd