Cyclotetrapeptide Complexes of Nickel(II) and Palladium(II) by Template Synthesis from Dipeptide Esters with Functionalized Side Chains − Crystal Structure of [(cyclo‐Gly‐β‐Ala‐Gly‐β‐Ala‐4H⁺)Cu](PPN)₂

Abstract

The cyclocondensations of dipeptide esters [Gly‐L‐Asp(OMe)2, Gly‐L‐Glu(OMe)2, L‐AspOMe‐β‐AlaOMe, β‐Ala‐L‐Lys(ψ‐N‐Boc,OMe), β‐Ala‐L‐Orn(ψ‐N‐Boc,OMe)] at nickel(II), palladium(II), and copper(II) templates give dianionic square‐planar complexes of deprotonated cyclotetrapeptides that contain functional groups in the side chains. The complexes with 14‐ or 16‐membered rings were isolated as [Ph3PNPPh3]+ salts. Hydrolysis of {[cyclo‐Gly‐Asp(OMe)‐Gly‐Asp(OMe)‐4H+]Pd}2− affords the tetraanionic complex [{cyclo‐Gly‐Asp(O−)‐Gly‐Asp(O−)‐4H+}Pd]4−(Li+)2(PNP+)2. The crystal structure of [(cyclo‐Gly‐β‐Ala‐Gly‐β‐Ala‐4H+)Cu](PPN)2 is also reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Impact of ring size on the copper(II) coordination abilities of cyclic tetrapeptides

“…Insertion of one more carbon atom into the peptide cycle causes that the oxidation of the copper is observed [10]. For the peptides with greater than 13-membered rings the formation of the complex with the {4 Â N À } binding mode is preferred [8,9,11].…”

“…The previous studies on the binding abilities of cyclopeptides towards Cu(II) ions [5][6][7][8][9][10][11] showed that His-containing cyclopeptides are able to bind copper(II) tightly through imidazole as well as amide nitrogens. The pH and the peptide ring size have a great impact on the kind of the coordinated nitrogens.…”

Metal Complexes of Biologically Important Ligands, CLXXVI.[1] Formation of Peptides within the Coordination Sphere of Metal Ions and of Classical and Organometallic Complexes and Some Aspects of Prebiotic Chemistry

“…Cyclocondensation of various non activated dipeptide esters (also those with functionalized side chains) could be achieved at Ni II , Pd II , or Cu II templates to give dianonic square‐planar complexes of deprotonated cyclotetrapeptides 7 47,48 (Scheme ). From steric reasons these template reactions proceed favorably with dipeptide esters, which contain α‐ and β‐amino acids to give finally complexes with a 14 membered cyclopeptide (e.g.…”

“…The dianionic tetrapeptide palladium complex from Gly‐ L ‐Asp(OMe) 2 was hydrolyzed to give the tetraanionic complex [Pd(cyclo‐Gly‐Asp‐Gly‐Asp‐6H + )] 4– . Also cyclopeptide complexes from the dipeptide esters β‐Ala‐l‐Lys(ω‐NBoc)OMe and β‐Ala‐ L ‐Orn(ω‐NBoc)OMe were synthesized 48. The free cyclo‐tetrapeptides can be cleaved from the metal ion by HCl in methanol.…”

Selective complexation of α-amino acids and simple peptides via their carboxylate groups

“…23 The affinity of Ni for dipeptide esters can be utilized in the metal-ion templated synthesis of cyclotetrapeptides. 24 Our group is interested in the coordination chemistry of dinuclear nickel complexes supported by the hexaaza-dithiophenolato macrocycle (L) 2− ( Fig. 1).…”