Identification of the internal axial ligand of HO2-cobalt(III)-bleomycin:: 1H{15N} HSQC NMR investigation of bleomycin, deglycobleomycin, and their hydroperoxide-cobalt(III) complexes

The identity of the axial ligand contributed by the drug in hydroperoxide-Co(III)-bleomycin and hydroperoxide-Co(III)-deglycobleomycin has been in doubt. With each structure, a combination of H-1{N-15} HSQC and HMBC and H-1 COSY and NOESY NMR spectroscopy was used to observe and completely assign the nonaromatic N-15 chemical shifts of natural abundance bleomycin in the two hydroperoxide-Co(III) structures. Together with the N-15 assignments from a published ID N-15 spectrum, the results permitted the assignment of the primary amine nitrogen to an axial ligand position in both structures.