Biosynthetic Studies on Coumarins

Coumarins, a group of naturally occurring phenylpropanoid lactones exerting a wide range of physiological effects, are elaborated by many plants and in a few microbial species. Early studies on the biosynthetic reactions leading to the simple coumarins in plants demonstrated derivation from the shikimic acid pathway via cinnamic acid and either ortho– or para –hydroxycinnamic acid. Radiotracer experiments later indicated that the furan ring of the furanocoumarins, found chiefly in the Rutaceae and Umbelliferae, is constructed on the coumarin nucleus following attachment of a mevalonate–derived side–chain to umbelliferone, and cyclization to dihydrofuranocoumarin intermediates. These findings have been substantiated and extended by the isolation and characterization of several of the enzymes participating in the biosynthetic pathway.