Structural study of copper(I)-bleomycin.

Previous NMR studies on Cu(I)-bleomycin have suggested that this adduct has a geometry distinct from Fe(II)BLM. The coordination chemistry of this bleomycin derivative has been investigated through the extension of the NMR data reported previously, and the use of molecular dynamics calculations. The data collected from the NMR experiments support the coordination to the metal center of the primary and secondary amines in beta-aminoalanine and the pyrimidine ring. The detection in the NMR spectra of the signal derived from the amide hydrogen in beta-hydroxyhistidine indicates that this amide is protonated in Cu(I)-bleomycin, precluding participation of the pyrimidinyl carboxamide nitrogen in the coordination of Cu(I), as previously reported. Three-dimensional solution structures compatible with the NMR data have been assayed for Cu(I)-bleomycin for the first time by way of molecular dynamics calculations, and two models showing four and five coordination have been found to be those that better fit the experimental data. In both models the primary amine in beta-aminoalanine is coordinated such that it is located on the same side, with respect to the coordination cage, as the peptide linker fragment. This result seems important for the favored models to be compatible with either their possible oxidation to become one of the reported structures for Cu(II)BLM, or their transformation into Fe(II) adducts able to cause DNA damage.