Über die Lactonringbildung des Cumarins

Abstract

Tracer experiments with 14C have shown that p-coumaric acid is over 70 times less efficient than cinnamic acid as a precursor of coumarin in Hierochloe odorata, and that tyrosine is over 60 times less efficient than phenylalanine. The results show that in this species the reaction sequence postulated by HAWORTH, in which coumarins are formed from p-coumaric acid, is not significantly involved in the biosynthesis of coumarin itself. It is suggested that, in higher plants, cinnamic acid (or an “activated“ form of it) is a common precursor of all coumarins, and that ortho- or para-hydroxylation of this compound leads subsequently to the formation of coumarin and the 7-hydroxycoumarins, respectively. Different enzyme systems may be required for the formation of the lactone ring of coumarin and the 7-hydroxycoumarins.