Metal binding of Lissoclinum patella metabolites. Part 1: Patellamides A, C and ulithiacyclamide A

Abstract Studies on three Thz, and Oxn containing cyclic peptides, patellamide A and C ( 1 , 3 ) and ulithiacyclamide A ( 9 ) isolated from the Indo-Pacific ascidian (seasquirt) Lissoclinum patella have delineated their metal binding selectivity. Patellamide C ( 3 ) shows extreme selectivity for Cu 2+ even in the presence of an excess of Zn 2+ and shows no binding at all to Co 2+ , Ni 2+ and Hg 2+ . Patellamide A ( 1 ) is less selective for Cu 2+ , whereas ulithiacyclamide A ( 9 ) shows selectivity similar to that of patellamide C ( 3 ). The selectivity was studied by circular dichroism spectroscopy and mass spectrometry. The CD spectra obtained whilst patellamide C was slowly titrated with Cu 2+ show one isosbestic point indicating the Cu 2+ binding involves only two conformations. These studies indicate that Cu 2+ , not Zn 2+ is the biologically relevant metal for these compounds and point towards a potential ecological function of these complexes.