Euryjanicins E–G, poly-phenylalanine, and poly-proline cyclic heptapeptides from the Caribbean sponge Prosuberites laughlini

A new investigation of the active sponge extracts of Prosuberites laughlini collected off the West coast of Puerto Rico has yielded three new cyclic heptapeptides, namely euryjanicins E (1)–G (3), containing multiple phenylalanine and proline residues. In CDCl3 solution, each euryjanicin F (2) and G (3) exists as an inseparable complex mixture of conformational isomers. The molecular structures of 1–3 were elucidated by a combination of chemical degradation, extensive ESI-MS/MSn analyses, and 2D NMR methods. The elucidation of the absolute configuration was achieved by HPLC following analysis of the acid hydrolysates after derivatization with Marfeyʹs reagent. When assayed against the National Cancer Institute 60 tumor cell line panel, the new cyclic peptides did not display significant in vitro cytotoxicity.