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 alpha-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 alpha,beta-unsaturated gamma-lactones. Annularins A (1), B (2), C (3), and F (6) exhibited antibacterial activity.