Vielopsides A-E, five new guaiane-type sesquiterpenoid dimers from Xylopia vielana.

Five new guaiane-type sesquiterpenoid dimers vielopsides A-E, connecting patterns through two direct CC bonds (C-2 to C-2', C-4 to C-1'), were isolated from the roots of Xylopia vielana. Their absolute configurations were established by NOE analysis, the Cu Kα X-ray crystallographic and circular dichroism (CD) experiment. Among them, compound 5 showed moderate activity IC50 values of 33.8 µM on NO production in RAW 264.7 macrophages.