Spiro-Phthalides and Isocoumarins Isolated from the Marine-Sponge-Derived Fungus Setosphaeria sp. SCSIO41009

Abstract

Fourteen new polyketides classified as four phthalides, setosphalides A and B, 5- O-desmethylcolletotrialide, and ( S)-colletotrialide (1-4), three isocoumarin derivatives, exserolides I-K (5-7), four pyrones, setosphapyrones A-D (8-11), one furanone (12), and two depsidones (13 and 14), along with 17 known polyketides were isolated from cultures of the sponge-derived fungus Setosphaeria sp. SCSIO41009. The structures and absolute configurations of these new compounds (1-14) were determined by spectroscopic analyses, X-ray diffraction, chiral-phase HPLC analysis, modified Mosher's method, and comparison of ECD spectra to calculations. Setosphalides A (1) and B (2) are the first examples possessing a 5,5 spiroketal skeleton in phthalide derivatives. Botryorhodines I (13) and J (14) showed moderate antifungal activities against the phytopathogenic fungi Colletotrichum asianum and Colletotrichum acutatum. Compound 18 (7- O-demethylmonocerin) exhibited potent radical scavenging activity against DPPH.