Four New Cytotoxic Arborinane-Type Triterpenes from the Endolichenic Fungus Myrothecium inundatum

Two new arborinane-type triterpenes, myrotheols A ( 1 ) and B ( 2 ), two new arborinane-type glycosides, myrothesides C ( 3 ) and D ( 4 ), together with four known diterpenes ( 5  –  8 ) were isolated from the ethyl acetate extract of the endolichenic fungus Myrothecium inundatum . The structures of new compounds 1  –  4 were elucidated by NMR and MS analyses. The absolute configuration of 1 was assigned by a single-crystal X-ray diffraction experiment. Compounds 3 and 4 represent the first two natural 4-O-methyl- α -D-mannosides. Compounds 1  –  8 exhibited cytotoxicity against K562 and RKO human cancer cell lines.