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 (1)H[(15)N] HSQC and HMBC and (1)H COSY and NOESY NMR spectroscopy was used to observe and completely assign the nonaromatic (15)N chemical shifts of natural abundance bleomycin in the two hydroperoxide-Co(III) structures. Together with the (15)N assignments from a published 1D (15)N spectrum, the results permitted the assignment of the primary amine nitrogen to an axial ligand position in both structures.