The genus Eupatorium L. (Asteraceae, tribe Eupatorieae) is comprised of some 38 perennial species that occur mainly in eastern North America and eastern South America (). From this center of distribution, however, species of Eupatorium have reached parts of Europe and Asia as well. Eupatorium cannabinum L. (commonly known as hemp agrimony) is frequently found in moist woods and meadows in northern and central Europe where it often grows along streams (). It is a perennial which reaches a height of ca. 0.5-1.5 m. The flowering heads are pink in color.
Eupatorium cannabinum was used as a medicinal plant by the Greeks and Romans, as well as in medieval times to aid digestion and prevent constipation (). The roots of E. cannabinum are especially known to possess cholagogic properties and are also used in the treatment of liver diseases (). No information on the bioactive constituents from Eupatorium cannabinum, however, has been available so far, since phytochemical studies on E. cannabinum have been sparse and were mainly limited to the study of toxic pyrrolizidine alkaloids from aerial parts of this species (). In the course of our continued interest in biologically active chromenes and benzofurans from the Asteraceae we have recently isolated for the first time a series of benzofurans from roots of Eupatorium cannabinum that are absent in the aerial parts of this species (). Benzofurans are known to exhibit interesting biological activities, e.g., they are bacteriostatic and piscicidal, photoxic against several bacteria and yeasts, and cytostatic (). In spite of these documented bioactivities, very little has been known so far of the biogenetic origin of this group of natural products in the Asteraceae. We have now for the first time established a root culture of Eupatorium cannabinum and have found it to be a suitable and easy accessible in vitro system for studies on the accumulation and biogenesis of benzofuran derivatives.
The biosynthesis of benzofurans from E. cannabinum in regard to its C6C2-part as elucidated in this study shows similarities to that of pungenine (3,4-dihydroxy-acetophenone), the major acetophenone derivative present in needles of Picea pungens (Pinaceae). Following feeding of 14C-labeled tracers to needles of P. pungens L-14C-phenylalanine, 14C-cinnamic acid and 14C-caffeic acid were effectively incorporated into pungenine, whereas 14C-acetate was not (). In a previous study on the biogenetic origin of the acetophenone moiety of benzofurans in leaves of Eupatorium rugosum, the authors reported acetate as being the precursor of the C6-C2 part of the benzofuran dehydrotremetone (6-desoxyeuparin; euparin = 1) (). The incorporation of 14C-acetate into dehydrotremetone, however, was only 0.06% of the applied dose, which is two orders of magnitude smaller than the incorporation of the 14C-phenylalanine obtained in this study using root cultures of the related species E. cannabinum. The close systematic relationship of the two Eupatorium species studied, as well as the close similarity of the benzofurans euparin (1) and dehydrotremetone, calls for a reinves-tigation of the biosynthesis of dehydrotremetone.
Selections from the book: “Medicinal and Aromatic Plants IV”, 1993.