Influence of the position of two dehydro-amino acids residues in the oligopeptide sequence on the binding ability towards Cu(II) ions Justyna Brasun a, * , Maciej Makowski b , Anna Janicka c , Jolanta Swiatek-Kozlowska a a Department of Basic Medical Sciences, Medical University, Kochanowskiego 14, 51601 Wroclaw, Poland b Department of Organic Chemistry, University of Opole, 45052 Opole, Poland c Faculty of Chemistry, University of Wroclaw, Wroclaw, Poland Received 16 March 2005; accepted 9 May 2005 Available online 19 August 2005 Abstract Studies on the binding ability of bis-dehydro-hexa- and pentapeptides have shown that the hexapeptides bind Cu +2 with similar efficacy as pentapeptides. The increase of distance between two dehydro-amino acid residues in the peptide backbone has no impact on the efficacy in metal ion binding. The type of isomeration [(Z) or (E)] has an influence on the coordination of the metal ion only to the first amide nitrogen. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Dehydro-peptides; Complex; Copper(II) 1. Introduction The a, b-dehydro-amino acids are analogues of a-amino acids with a double bond between a- and b-car- bon atoms. Dehydro-amino acids occur in nature as constituents of several peptides, enzymes and hormones [1,2]. Peptides containing dehydro-phenyloalanine can oc- cur in two isomers: Z and E. It depends on the loca- tion of the aromatic ring in relation to the amino group. The insertion of (Z) or (E) isomers into the peptide backbone have a strong impact on the biolog- ical activity of the peptides. The (Z) isomers are much more common and they are found, e.g., in antibiotics [3]. Our recent work concerning the coordination abil- ity of dehydro-peptides has shown that insertion of a dehydro-amino acid residue into a peptide backbone makes it more effective in metal ion binding than the parent peptide [4–6]. The type of isomeration has a strong impact on the efficiency in metal ion binding. The (Z) isomer is usually more effective in metal ion coordination than its (E) analogue [7]. Insertion of a second dehydro-amino acid residue into a peptide molecule makes the ligand more effective in Cu(II) ion binding [8]. In this work the binding of Cu 2+ ions to dehydro- hexa- and pentapeptides with two dehydro-amino acid residues in their sequence is discussed. Using the potentiometric and spectroscopic data the impact of the position of the dehydro-amino acid residue is evaluated. 0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2005.05.016 Abbreviations: Boc, tert-butyloxycarbonyl; TEA, triethylamine; ACN, acetonitrile; DMT-MM, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4- methyl-morpholinium chloride; TBTU, O-benzotriazol-1-yl-N,N,N 0 , N 0 -tetramethyluronium tetrafluoroborate; i-PrOH, iso-propyl alcohol; THF, tetrahydrofuran; TFA, trifluoroacetic acid. * Corresponding author. Tel.: +48 71 348 6024; fax: +48 71 347 9211. E-mail address: jbrasun@basmed.am.wroc.pl (J. Brasun). www.elsevier.com/locate/poly Polyhedron 24 (2005) 1929–1936