title: Synthetic analogue approach to metallobleomycins: syntheses, structure and properties of mononuclear and tetranuclear gallium(III) complexes of a ligand that resembles the metal-binding site of bleomycin.
abstract: As part of our interest into the bioinorganic chemistry of gallium, gallium(III) complexes of the peptide ligand N-(2-(4-imidazolyl)ethyl)pyridine-2-carboxamide (pypepH2) resembling a fragment of the metal-binding domain of bleomycins (BLMs), have been isolated. Reaction of pypepH2 with (Et4N)[GaCl4] and Ga(acac)3 [acac- is the acetylacetonate(-1) ion] affords the mononuclear complex [Ga(pypepH)2]Cl.2H2O (1) and the tetranuclear complex [Ga4(acac)4(pypep)4].4.4H2O (2), respectively. Both complexes were characterized by single-crystal X-ray crystallography, IR spectroscopy and thermal decomposition data. The pypepH- ion in 1 behaves as a N(pyridyl), N(deprotonated amide), N(pyridine-type imidazole) chelating ligand. The doubly deprotonated pypep2- ion in 2 behaves as a N(pyridyl), N(deprotonated amide), N(imidazolate), N'(imidazolate) mu2 ligand and binds to one Ga(III) atom at its pyridyl, amide and one of the imidazolate nitrogens, and to a second metal ion at the other imidazolate nitrogen; a chelating acac- ligand completes six coordination at each Ga(III) centre. The IR data are discussed in terms of the nature of bonding and known structures. The 1H NMR spectrum of 1 suggests that the cation of the complex maintains its integrity in dimethylsulfoxide (DMSO) solution. Complexes 1 and 2 are the first synthetic analogues of metallobleomycins with gallium(III).
authors.affiliation: Department of Chemistry, University of Patras, GR 265 04 Patras, Greece.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Manessi
authors.forename: Giannis S
authors.initials: GS
authors.lastname: Papaefstathiou
authors.forename: Catherine P
authors.initials: CP
authors.lastname: Raptopoulou
authors.forename: Aris
authors.initials: A
authors.lastname: Terzis
authors.forename: Theodoros F
authors.initials: TF
authors.lastname: Zafiropoulos
mesh_terms: D001665:Binding Sites; D001761:Bleomycin / Q000031:analogs & derivatives* / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005708:Gallium / Q000737:chemistry*; D006860:Hydrogen Bonding; D007287:Inorganic Chemicals / Q000737:chemistry; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D007287:Inorganic Chemicals; D008024:Ligands; D009942:Organometallic Compounds; D001761:Bleomycin; D005708:Gallium