Rhinoclactones A-E, Resorcylic Acid Analogs from Desert Plant Endophytic Fungus Rhinocladiella similis

Seven resorcylic acid lactones (RALs) including five new analog rhinoclactones, A-E (1, 2, 4-6), were isolated from an endophytic fungus Rhinocladiella similis in the plant Agriophyllum squarrosum collected from the Tengger Desert of the Ningxia Province, China. The structures of these new compounds were determined by HR-ESI-MS (High Resolution Electrospray Ionization Mass Spectrometry), NMR data, modified Mosher's method, and X-ray diffraction experiments. All compounds isolated from this fungus possessed the 16-OMe/14-OH, not the common 16-OH/14-OH or 16-OH/14-OMe groups on the aromatic ring, which are rarely found in nature. Compound 7 displayed cytotoxic activities against HCT116 and HeLa cancer cell lines. The possible biosynthesis of 1-7 is suggested, and the potential ecological roles of these fungal secondary metabolites is discussed.