Asperolides A–C, Tetranorlabdane Diterpenoids from the Marine Alga-Derived Endophytic Fungus Aspergillus wentii EN-48

Bioassay-guided fractionation of the culture extract of Aspergillus wentii EN-48, an endophytic fungus isolated from an unidentified marine brown algal species of the genus Sargassum, led to the isolation of three new tetranorlabdane diterpenoids, asperolides A–C (1–3), and five related derivatives (4–8). The structures of these compounds were established on the basis of spectroscopic interpretation, and compound 1 was confirmed by X-ray crystallographic analysis. The absolute configuration of 1 was determined by application of the modified Mosher’s method. An X-ray structure for wentilactone B (6) is also reported. Compounds 1–8 were evaluated for cytotoxic and antibacterial activities.