The structures and absolute configurations of macrophyllic acids A–E, five new rearranged eudesmane sesquiterpene acids from the bark of Inula macrophylla

Macrophyllic acids A–E, five novel sesquiterpene acids with a new rearranged carbon skeleton, have been isolated from the bark of Inula macrophylla. Their structures were determined on the basis of spectral evidence (especially by HREIMS and 2D NMR) as well as chemical transformations. The structure of macrophyllic acid A was finally confirmed by an X-ray analysis. The absolute configuration of macrophyllic acid A was determined by appropriate chemical conversion and the means of PGME. The possible biosynthetic pathway for macrophyllic acids A–E is also discussed.