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 HyLeu¹-Pro² amide bond in a cis conformation. Iso-isariin B (1) was active against the pest-insect Sitophilus spp. with an LD₅₀ value of 10 μg/mL. This observation also gives some clues for ecological interpretation of cyclodepsipeptide production by B. felina.