Terpene−Shikimate conjugated meroterpenoids from the endophytic fungus Guignardia mangiferae

Nine undescribed shikimate-conjugated meroterpenes, as well as nine known compounds, were isolated from solid cultures of the fungus Guignardia mangiferae, an endophyte obtained from the leaves of Dendrobium nobile. The structures of these undescribed compounds were characterized by analyses of their 1D and 2D NMR and HRESIMS data, and their absolute configurations were assigned by single-crystal X-ray crystallography, electronic circular dichroism (ECD) calculations, modified Mosher's method, and Mo2(OCOCH3)4-induced ECD experiments. Of these compounds, mangnardone A represents the first example of terpene–shikimate-conjugated meroterpenoid with a hydroxy group at C-5. In addition, the X-ray diffraction analysis of mangnardone I is the first example to confirm the structure of bicycloalternarene (BCA) meroterpenoid by single-crystal data. Nine undescribed meroterpenes inhibited nitric oxide (NO) production in LPS-induced RAW 264.7 cells with IC50 values in the range of 4.7–40.0 μM.