Sesquiterpene coumarins

Plants have a long history as therapeutic tools in the treatment of human diseases and have been used as a source of medicines for ages. In search of new biologically active natural products, many plants and herbs used in traditional medicine are screened for natural products with pharmacological activity. In this paper, we present a group of natural products, the sesquiterpene coumarins isolated from plants, and describe their wide range of biological activity. Sesquiterpene coumarins are found in some plants of the families Apiaceae (Umbelliferae), Asteraceae (Compositae) and Rutaceae. The coumarin moiety is often umbelliferone (7-hydroxycoumarin) but scopoletin (7-hydroxy-6-methoxycoumarin) and isofraxidin (7-hydroxy-6,8-dimethoxycoumarin) are also found. These coumarins are linked to a C-15 terpene moiety through an ether linkage. Another group of sesquiterpene coumarins is the prenylated 4-hydroxycoumarins where the link between the coumarin and the C15 terpene moiety is a C-C-bond at carbon 3 of the coumarin moiety. Finally, the prenyl-furocoumarin-type sesquiterpenoids are a separate group of sesquiterpene coumarins based on the suggested biosynthetic pathway. Our relatively limited knowledge on the biosynthesis of sesquiterpene coumarins is reviewed.