Roseabol A, a New Peptaibol from the Fungus Clonostachys rosea

A new 11 amino acid linear peptide named roseabol A (1) and the known compound 13-oxo-trans-9,10-epoxy-11(E)-octadecenoic acid (2) were isolated from the fungus Clonostachys rosea. Combined NMR and MS analysis revealed that roseabol A (1) contained amino acid residues characteristic of the peptaibol family of peptides such as isovaline, α-aminoisobutyric acid, hydroxyproline, leucinol, and an N-terminal isovaleric acid moiety. The amino acid sequence was established by a combination of NMR studies and tandem MS fragmentation analyses, and the absolute configurations of the constituent amino acids of 1 were determined by the advanced Marfey's method. Compound 2 showed inhibitory activity against Merkel cell carcinoma, a rare and difficult-to-treat type of skin cancer, with an IC₅₀ value of 16.5 μM.