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

摘要

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 (pypepH(2)) 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 . 2H(2)O (1) and the tetranuclear complex [Ga-4(acac)(4)(pypeP)(4)] . 4.4H(2)O (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 pypep(2-) ion in 2 behaves as a N(pyridyl), N(deprotonated amide), N(imidazolate), N'(imidazolate) mu(2) ligand and binds to one Gain 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 H-1 NMR spectrum of I 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). (C) 2004 Elsevier Inc. All rights reserved.