[Structure of an oligonucleotide of bleomycin A5 from 13C-NMR data]

The localization of the covalent bond in the conjugates of bleomycin A5 and oligonucleotides was established by 13C NMR using the bleomycin derivative of uridine-5'-phosphate synthesized as a model compound. The phosphate group of the nucleotide was shown to form a phosphamide bond with the primary amino group of the spermidine moiety of bleomycin A5. The formation of the P-N bond causes the downfield shift of the signals of the neighboring carbon atoms of the spermidine fragment by 1.8 and 4.2 ppm and the splitting of the signal of the C-2 atom of the spermidine fragment with J 6.8 Hz due to vicinal spin-spin coupling with the phosphorous atom.