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Fresh leaves of deer's tongue contain large quantities (more than 10% of the dry weight, in some cases) of o-hydroxycinnamic acid (o-HCA). Both cis- and trans-o-HCA are present, and both isomers exist in the fresh tissue predominantly as glucosides. Cured deer's tongue leaves contain relatively high levels of coumarin and lower amounts of o-HCA glucosides. It is probable that during the curing process cis-o-HCA glucoside is hydrolyzed by an endogenous g-glucosidase, and that the liberated cis-o-HCA lactonizes spontaneously to form coumarin.