Cycloforskamide, a Cytotoxic Macrocyclic Peptide from the Sea Slug <i>Pleurobranchus forskalii</i>

Abstract

A macrocylic dodecapeptide, cycloforskamide, was isolated from the sea slug <i>Pleurobranchus forskalii</i>, collected off Ishigaki Island, Japan. Its planar structure was deduced by extensive NMR analyses and was further confirmed by MS/MS fragmentation analyses. Finally, the absolute configuration was determined by total hydrolysis and chiral-phase gas chromatographic analysis. This novel dodecapeptide contains three d-amino acids and three thiazoline heterocycles and exhibits cytotoxicity against murine leukemia P388 cells, with an IC₅₀ of 5.8 μM