BIOSYNTHESIS OF THE COUMARINS: III. THE ROLE OF GLYCOSIDES IN THE FORMATION OF COUMARIN BY HIEROCHLOE ODORATA

Abstract

Coumarinic acid β-glucoside has been identified in Hierochloe odorata. Carbon dioxide-C14was administered to this species, and the plants were allowed to metabolize for periods up to 31 days. "Free" coumarin was recovered by simple extraction, and additional coumarin and o-coumaric acid were recovered after hydrolysis of the corresponding glucosides with emulsin. The total C14in o-coumaric acid reached a maximum in about 4 days and then declined, but the peak in the total C14of coumarin was not reached until 8 to 17 days after activation. o-Coumaryl glucoside and coumarin are thus both metabolic intermediates rather than end products, and the glucoside is formed first. This supports the orthohydroxylation theory of coumarin biosynthesis. The specific activity of coumarin liberated by emulsin hydrolysis from the glucoside was consistently lower than that of "free" coumarin. This is irreconcilable with the proposed formation of free coumarin from coumarinic acid glucoside as a major pathway in vivo unless separate pools of the glucoside exist in the plant. Indirect evidence is presented that free coumarin can exist in Hierochloe.