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In sweetclover (Melilotus alba Desr.) the cis- and trans-isomers of o-hydroxycinnamic acid occur primarily as the respective, β-D-glucosides. Available evidence indicates that these glucosides are formed via the following pathway: phenylalanine (formed from shikimic acid) → trans-cinnamic acid → o-coumaric acid (trans-o-hydroxycinnamic acid) → o-coumaryl glucoside (trans-β-D-glucosyl-o-hydroxycinnamic acid) → coumarinyl glucoside (cis-β-D-glucosyl-o-hydroxycinnamic acid). In tissues that are disrupted, coumarinyl glucoside is rapidly hydrolyzed by the action of endogenous β-glucosidase to yield coumarinic acid, which lactonizes spontaneously to form coumarin. The cu gene influences the content of the glucosides, apparently by controlling the o-hydroxylation of cinnamic acid, while the b gene is associated with loss of β-glucosidase activity.