Curvularin‐Type Metabolites from the Fungus <i>Curvularia </i>sp. Isolated from a Marine Alga

Abstract

Abstract Two new curvularin‐type macrolides, curvulone A ( 1 ) and B ( 2 ), and two known ones ( 3a , 4 ) of the rare 15 R series have been isolated from the fungus Curvularia sp., which has been isolated from the marine alga Gracilaria folifera . Their structures were determined by extensive 2D NMR experiments and supported by the single‐crystal X‐ray analysis of 1 . The structural elucidation of 1 , which has a benzo[ b ]furanone moiety as part of a 12‐membered macrolactone, has led to a revision of the structure of the previously reported (11 S ,15 S )‐11β‐hydroxy‐12‐oxocurvularin. The absolute configuration of curvulone A was established independently by the solid‐state TD‐DFT ECD method and by measuring the anomalous dispersion effect. The absolute configuration of curvulone B was determined by TD‐DFT ECD calculations on the computed solution conformers. Two different solid‐state conformers of 4 were identified by X‐ray analysis of the single crystals obtained from different solvents; TD‐DFT ECD calculations were performed to reproduce the experimental ECD spectra. All four metabolites were biologically active against fungal, bacterial and algal test organisms.