STUDIES OF THE SOLUTION STRUCTURE OF THE BLEOMYCIN-A2 IRON(II) CARBON-MONOXIDE COMPLEX BY MEANS OF 2-DIMENSIONAL NMR-SPECTROSCOPY AND DISTANCE GEOMETRY CALCULATIONS

As part of our program to delineate the solution structure of bleomycin-metal complexes and the DNA complexes thereof, we studied the bleomycin-iron(II)-carbon monoxide complex. With aid of various 2D NMR techniques we were able to assign the 1H and 13C NMR spectra of this complex completely. Vicinal coupling constant analysis, 13C chemical shift information, and NOE data revealed the active participation of five iron binding sites in the bleomycin molecule, namely, the secondary amine function of the β-aminoalanine fragment, the aromatic pyrimidine, the amide and imidazole group of the β-hydroxyhistidine residue, and the carbamoyl group of the mannose sugar. A study of the 13C NMR spectrum of the corresponding enriched iron-57 complex enabled us to establish the carbon monoxide as the sixth iron binding site via a 30-Hz coupling constant between iron-57 and the carbon monoxide carbon-13 atom. Subsequently, NOE data and the five iron coordination sites in the bleomycin molecule were used as interpoint distances in distance geometry calculations. In this way, several acceptable structures were generated that represent the first three-dimensional structure of the bleomycin-iron(11)-carbon monoxide complex in solution. Also, a discussion is presented of some aspects of the structure-activity relationship. © 1990, American Chemical Society. All rights reserved.