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

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.