Pulcaffeate, a Trimeric Caffeic Acid Derivative from Bourreria pulchra

The trimeric caffeic acid derivative pulcaffeate (1) was isolated from the organic crude extract of the roots of Bourreria pulchra (Boraginaceae). The biosynthesis of 1 appears to involve an intramolecular Diels-Alder reaction between a cyclohexa-1,3-diene intermediate, generated by the oxidation of the aromatic ring of a cinnamic acid unit, and the conjugated double bond of a caffeic acid unit. The structure of the new metabolite was elucidated through a detailed analysis of its 1H and 13C NMR spectroscopic data. This is the first report of a trimeric metabolite occurring in B. pulchra.