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 [6.3.1.02,7] moiety.