Pentacyclic Cytochalasins and Their Derivatives from the Endophytic Fungus sp. xz-18.

Eight new cytochalasins - and ten known analogs - were isolated from the endophytic fungus Phomopsis sp. xz-18. The planar structures of the cytochalasins were determined by HR-ESI-MS and NMR analysis. Compounds , , and were 5/6/6/7/5-fused pentacyclic cytochalasins; compounds and had conjugated diene structures in the macrocycle; and compound had a β,γ-unsaturated ketone. The absolute configuration of 6 was confirmed for the first time by the octant rule. The acid-free purification process proved that the pentacyclic system was a natural biosynthetic product and not an acid-mediated intramolecular cyclized artifact. The new compounds did not exhibit activities against human cancer cell lines in cytotoxicity bioassays or antipathogenic fungal activity, but compounds , and showed moderate antibacterial activity in disk diffusion assays.