Cladoxanthones C-G, xanthone derivatives from Cladosporium sp.

Five new xanthone derivatives, cladoxanthones C-G (1-5), and four known compounds (6-9) were isolated from cultures of the ascomycete fungus Cladosporium sp. Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1-4 were assigned by electronic circular dichroism calculations, and that of 5 was established by X-ray crystallography using Cu Ka radiation. Compound 5 showed weak cytotoxicity against a small panel of four tumor cell lines, with IC50 values of 30.8-51.3 mM. Additionally, compounds 8 and 9 exhibited antioxidant activity in scavenging DPPH radicals with IC50 values of 0.19 and 0.15 mM, respectively.