New Bioactive β-Resorcylic Acid Derivatives from the Alga-Derived Fungus KMM 4685.

Five new β-resorcylic acid derivatives, 14-hydroxyasperentin B (), β-resoantarctines A-C (, , ) and 8-dehydro-β-resoantarctine A (), together with known 14-hydroxyasperentin (5'-hydroxyasperentin) (), were isolated from the ethyl acetate extract of the fungus KMM 4685 associated with the brown alga . The structures of the compounds were elucidated by spectroscopic analyses and modified Mosher's method, and the biogenetic pathways for compounds - were proposed. For the very first time, the relative configuration of the C-14 center of a known compound was assigned via analyses of magnitudes of the vicinal coupling constants. The new metabolites - were biogenically related to resorcylic acid lactones (RALs); however, they did not possess lactonized macrolide elements in their structures. Compounds , and exhibited moderate cytotoxic activity in LNCaP, DU145 and 22Rv1 human prostate cancer cells. Moreover, these metabolites could inhibit the activity of p-glycoprotein at their noncytotoxic concentrations and consequently synergize with docetaxel in p-glycoprotein-overexpressing drug-resistant cancer cells.