Proline-Containing Cyclopeptides from the Marine Sponge Phakellia fusca

Four new cyclopeptides, phakellistatins 15-18 (2-5), together with five known cyclopeptides, phakellistatin 13 (1), hymenistatin I, and hymenamides G, H, and J, were isolated from the South China Sea sponge Phakellia fusca. Their structures were elucidated by HR-ESIMS, NMR, and MALDI-TOF/TOF sequence analysis. The absolute configurations of the amino acid residues of 2-5 were assigned to be L by enantioselective HPLC analysis.