BIOSYNTHESIS OF THE COUMARINS. TRACER STUDIES ON COUMARIN FORMATION IN HIEROCHLOË ODORATA AND MELILOTUS OFFICINALIS

Abstract

Coumarin formation has been studied with C¹⁴ in the perennial grass, Hierochloë odorata, and in yellow sweet clover, Melilotus officinalis. In general the latter species yielded inconsistent data. In Hierochloë, o-coumaric, cinnamic, and shikimic acids and L-phenylalanine were the best of 10 compounds tested as coumarin precursors, the first two at least being incorporated with little randomization of C¹⁴. Acetate was more poorly utilized. It was concluded that the aromatic ring of coumarin arises via the shikimic acid pathway in preference to acetate condensation. When the time of metabolism was varied, o-coumaryl glucoside and free o-coumaric acid rapidly acquired high specific activities from cinnamic acid-C¹⁴, but coumarin and melilotic acid became active much more slowly. A lag in the acquisition of C¹⁴ by coumarin for the first 6 to 8 hours was followed by a rectilinear increase until at least 24 hours. Much the greatest accumulation of C¹⁴ was found in o-coumaryl glucoside during this entire period. Furthermore, this compound when fed to Hierochloë is comparable to cinnamic acid as a coumarin precursor. These findings suggest a possible function for o-coumaryl glucoside or a derivative in coumarin biosynthesis.