[Direct breaks in a single-stranded DNA fragment by a bleomycin-derived oligonucleotide]

A method for coupling bleomycin to oligonucleotides is suggested. The reaction was carried out between the amino group of the spermidine residue of the bleomycin A5 Cu(II)-complex (Cu(II)Blm-RH) and the 5'-phosphate group of the oligonucleotide pd(CCAAACA) (I) activated with a mixture of triphenylphosphine and 2,2'-dipyridyldisulphide in the presence of 4-N,N-dimethylaminopyridine-1-oxide. The resultant compound (Ia) (yield 70%) forms more stable complementary complexes than the parent oligonucleotide (delta Tm = 11 degrees C). When Cu(II) ion was removed from (Ia), compound (Ib) formed which effectively (80%) cleaved pd(TGTTTGGCGAAGGA). Neither pd(TCCTTCG) nor the oligonucleotide tail of the reagent (Ib) were destroyed under the cleavage conditions. Free Blm-RH and bleomycin bound in the reagent (Ib) damage different regions of the target.