Macrophyllols A and B, two unusual novel sesquiterpene and monoterpene dimers from the bark of Inula macrophylla

[GRAPHICS] Two novel sesquiterpene and monoterpene dimers, macrophyllols A (1) and B (2), were isolated from the bark of Inula macrophylla, Their structures were determined on the basis of spectral evidence (especially HREIMS and 2D NMR) as well as chemical transformation. The structure of macrophyllol A (1) was confirmed by X-ray analysis. The possible biosynthetic pathways of macrophyllols A (1) and B (2) are discussed.