Xylopins A–F, six rare guaiane dimers with three different connecting modes from Xylopia vielana

Six rare guaiane-type sesquiterpene dimers xylopins A-F, having three different connecting modes through two direct C-C bonds, were isolated from the roots of Xylopia vielana. Their absolute configurations were established by NOESY analysis, Cu Kα X-ray crystallography, and experimental and calculated electronic circular dichroism spectra. Flow cytometry demonstrated the fact that compound 6 arrested the cell cycle at G2 phase and concentration-dependently induced apoptosis of DU145 cells. Furthermore, the EPT2-TGC cell model, zebrafish study and western blot analysis illustrated compound 6 could induce apoptosis by efficiently inhibiting the Wnt/β-catenin signaling pathway via decreasing the expression of β-catenin.