Heptaketides from Corynespora sp. inhabiting the cavern beard lichen, Usnea cavernosa: first report of metabolites of an endolichenic fungus

Abstract

Two new heptaketides, corynesporol (1) and 1-hydroxydehydroherbarin (2), along with herbarin (3) were isolated from an endolichenic fungal strain, Corynespora sp. BA-10763, occurring in the cavern beard lichen Usnea cavernosa. The structures of 1-3 were elucidated from their spectroscopic data. Aerial oxidation of corynesporol (1) yielded herbarin (3). Acetylation of 1 afforded the naphthalene derivative 4, whereas acetylation of 3 gave the corresponding naphthoquinone 6 and dehydroherbarin (5). All compounds were evaluated for their cytotoxicity and ability to inhibit migration of human metastatic breast and prostate cancer cell lines MDA-MB-231 and PC-3M, respectively. Dehydroherbarin (5) inhibited migration of both cell lines at concentrations not toxic to these cell lines. This is the first report of metabolites from an endolichenic fungus.