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

Studies on three Thz, and Oxn containing cyclic peptides, patellamide A and C (1, 3) and ulithiacyclamide A (9) isolated from the Indo-Pacific ascidia n (seasquirt) Lissoclinum patella have delineated their metal binding selec tivity. Patellamide C (3) shows extreme selectivity for Cu2+ even in the pr esence of an excess of Zn2+ and shows no binding at all to Co2+, Ni2+ and H g2+. Patellamide A (1) is less selective for Cu2+, whereas ulithiacyclamide A (9) shows selectivity similar to that of patellamide C (3). The selectiv ity was studied by circular dichroism spectroscopy and mass spectrometry. T he CD spectra obtained whilst patellamide C was slowly titrated with CU2+ s how one isosbestic point indicating the CU2+ binding involves only two conf ormations. These studies indicate that CU2+, not Zn2+ is the biologically r elevant metal for these compounds and point towards a potential ecological function of these complexes. (C) 2001 Elsevier Science Ltd. All rights rese rved.