The structure of ulithiacyclamide B. Antitumor evaluation of cyclic peptides and macrolides from Lissoclinum patella.

The major cytotoxic metabolites of Lissoclinum patella from Pohnpei have been isolated and identified. Most of the cytotoxicity is attributed to a new cyclic peptide, ulithiacyclamide B [4], which is closely related to ulithiacyclamide [1]. The proposed structure of 4 is based on spectroscopic analysis and chemical degradation. Compound 4 exhibits an IC50 of 17 ng/ml against the KB cell line but does not show selective cytotoxicity against solid tumor cells in the Corbett assay.