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The biogenesis of rosmarinic acid (alpha-O-caffeoyl-3,4-dihydroxyphenyl-lactic acid), the second most common ester of caffeic acid in the plant kingdom, was studied in Mentha arvense and Mentha piperita. Administration of (14)C-labelled compounds showed that, whereas the caffeoyl moiety was formed from phenylalanine via cinnamic acid and p-coumaric acid, the 3,4-dihydroxyphenyl-lactic acid moiety was formed from tyrosine and 3,4-dihydroxyphenylalanine. Time-course studies and the use of labelled rosmarinic acid showed that endogenous rosmarinic acid had a low turnover rate. The caffeoyl moiety did not appear to contribute to the formation of insoluble polymers, as has been suggested for chlorogenic acid in other plants.
Ellis et al. (Mon,) studied this question.