Insecticidal Cyclodepsipeptides from <i>Beauveria felina</i>

A novel cyclodepsipeptide, iso-isariin B (<b>1</b>), and the known isaridin E (<b>2</b>) were isolated from the entomopathogenic fungus <i>Beauveria felina.</i> Their structures were elucidated using MS/MS fragmentation and extensive 2D-heteronuclear NMR. The X-ray structure of isaridin E was obtained, showing two potent intramolecular H bonds and a type-VI turn with the HyLeu<sup>1</sup>-Pro<sup>2</sup> amide bond in a <i>cis</i> conformation. Iso-isariin B (<b>1</b>) was active against the pest-insect <i>Sitophilus</i> spp. with an LD<sub>50</sub> value of 10 μg/mL. This observation also gives some clues for ecological interpretation of cyclodepsipeptide production by <i>B. felina</i>.