Bistratamides M and N Oxazole-Thiazole Containing Cyclic Hexapeptides Isolated from Lissoclinum bistratum Interaction of Zinc (II) with Bistratamide K

摘要

Two novel oxazole-thiazole containing cyclic hexapeptides, bistratamides M (>1) and N (>2) have been isolated from the marine ascidian Lissoclinum bistratum (L. bistratum) collected in Raja Ampat (Papua Bar, Indonesia). The planar structure of >1 and >2 was assigned on the basis of extensive 1D and 2D NMR spectroscopy and mass spectrometry. The absolute configuration of the amino acid residues in >1 and >2 was determined by the application of the Marfey’s and advanced Marfey’s methods after ozonolysis followed by acid-catalyzed hydrolysis. The interaction between zinc (II) and the naturally known bistratamide K (>3), a cyclic hexapeptide isolated from a different specimen of Lissoclinum bistratum, was monitored by ¹H and ¹³C NMR. The results obtained are consistent with the proposal that these peptides are biosynthesized for binding to metal ions. Compounds >1 and >2 display moderate cytotoxicity against four human tumor cell lines with GI50 values in the micromolar range.