Annularins A−H: New Polyketide Metabolites from the Freshwater Aquatic Fungus Annulatascus triseptatus

Eight new polyketide metabolites, annularins A−H (1−8), along with the known compound (−)-(S)-p-hydroxyphenyllactic acid, were isolated from the organic extracts of the freshwater fungus Annulatascus triseptatus. Compounds 1−6 are 3,4,5-trisubstituted α-pyrones, and the fused bicyclic pyrone−furanone system in annularin F (6) has not been reported previously among natural products. Compounds 7 and 8 are 3,4-disubstituted α,β-unsaturated γ-lactones. Annularins A (1), B (2), C (3), and F (6) exhibited antibacterial activity.