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

Abstract

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/MS ⁿ analyses, and 2D NMR methods. The elucidation of the absolute configuration was achieved by HPLC following analysis of the acid hydrolysates after derivatization with Marfey's reagent. When assayed against the National Cancer Institute 60 tumor cell line panel, the new cyclic peptides did not display significant in vitro cytotoxicity.

Keywords: Caribbean sponge; Cyclic peptides; Cytotoxicity; Peptides; Prosuberites laughlini.

Fig. 1

Key HMBC (C→H) and ROESY correlations (dashed arrows) for euryjanicin E (1) and euryjanicin F (2).