Dioxatricyclic and Oxabicyclic Polyketides from Trichocladium opacum

Five new polyketides, trichocladinols D–H (1–5) with dioxatricyclic (1–3) and oxabicyclic (4 and 5) skeletons, and the known massarilactone C (6) were isolated from the solid-substrate fermentation cultures of the ascomycete fungus Trichocladium opacum. The structures of 1–5 were determined mainly by NMR experiments, and 1, 3, and 4 were confirmed by X-ray crystallography. The absolute configurations of 1 and 3 were assigned by X-ray crystallography using Cu Kα radiation, whereas that of C-5 in 2 and 4 was deduced via the circular dichroism (CD) data. Compounds 2–4 showed weak cytotoxicity against the human tumor cell lines A549, HCT116, and SW480.