Vorkommen und biologische Bedeutung von Benzopyranen (Chromenen) und Benzofuranen in denAsteraceae

Abstract

Benzopyrans (chromenes) and benzofurans are characteristic natural products of theAsteraceae and are found together with their biogenetic precursors primarily in the tribesAnthemideae, Astereae, Eupatorieae, Heliantheae, Inuleae, andSenecioneae. The accumulation of benzopyrans and benzofurans supports an arrangement of the tribes of theAsteraceae into two groups as suggested recently based on morphological characters. The methods for analysing this class of natural products are demonstrated with the American genusEncelia. Experiments on the localization of benzopyrans and benzofurans inEncelia species indicate that these compounds are stored in resin ducts. Several benzopyrans and benzofurans are biologically active and are repellent as well as toxic towards herbivorous insects. Experiments on structure — activity relationships indicate the biological activities as being influenced by the heterocycle (pyranvs. furan) as well as by the substituents of the aromatic ring. In addition, several tested compounds showed phototoxic activities.