Insecticidal Cyclodepsipeptides from Beauveria felina

A novel cyclodepsipeptide, iso-isariin B (1), and the known isaridin E (2) were isolated from the entomopathogenic fungus Beauveria felina. 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(1)-Pro(2) amide bond in acts conformation. Iso-isariin B (1) was active against the pest-insect Sitophilus spp. with an LD50 value of 10 mu g/mL. This observation also Oyes some dues for ecological interpretation of cyclodesipeptide production by B. felina.