Trichoderones A and B: Two Pentacyclic Cytochalasans from the Plant Endophytic Fungus Trichoderma gamsii

Two new cytochalasans, trichoderones A ( 1 ) and B ( 2 ), and three known analogues, aspochalasins D ( 3 ), J ( 4 ), and I ( 5 ), were isolated from the endophytic fungus Trichoderma gamsii . Their structures were determined by analysis of their spectroscopic data. The absolute configurations of 1 and 2 were established by quantum chemical electronic circular dichroism calculations. Compounds 3 and 4 displayed cytotoxic activity against the HeLa cell line. Trichoderone A ( 1 ) possesses an unprecedented 7/6/6/5/5 pentacyclic system, whereas trichoderone B ( 2 ) contains the rare 6/5/6/6/5 pentacyclic skeleton with a 12‐oxatricyclo [6.3.1.0 2,7 ] moiety.