Gombamide A, a Cyclic Thiopeptide from the Sponge <i>Clathria gombawuiensis</i>

A new peptide, gombamide A (<b>1</b>), was isolated from the marine sponge <i>Clathria gombawuiensis</i>, collected from Korean waters. On the basis of the results of combined spectroscopic analyses, the structure of this compound was determined to be a cyclic C-terminally modified thiohexapeptide containing the unusual amino acid residues <i>para</i>-hydroxystyrylamide (<i>p</i>HSA) and pyroglutamic acid (pyroGlu). The absolute configurations of all amino acid residues were determined to be l by advanced Marfey’s analysis. The new compound exhibited weak cytotoxicity against A549 and K562 cell lines as well as moderate inhibitory activity against Na⁺/K⁺-ATPase