Biosynthesis of 6,7-dihydroxycoumarin in Cichorium intybus

Abstract

Labelled 7-hydroxycoumarin (umbelliferone) was converted efficiently to 6,7-dihydroxycoumarin (aesculetin), the aglycone of the glucoside cichoriin, in Cichorium intybus L., and earlier studies contraindicating caffeic acid as a precursor were confirmed. Umbelliferone, which occurs in this species, is thus indicated to be a natural intermediate in aesculetin biosynthesis. Administered umbelliferone was readily converted to its 7-O-glucoside, skimmin, an observation consistent with participation of skimmin in the biosynthetic pathway to cichoriin. This evidence for derivation of aesculetin from umbelliferone provides further support for the theory that polyoxygenated coumarins are, in general, elaborated by additional oxygenation of umbelliferone. Implications of this concept for the evolution of the biosynthesis of coumarins are discussed.