Osmium-labeled Polynucleotides: Reaction of Osmium Tetraoxide, with Poly-1,N6-Ethenoadenylic Acid

Osmium tetraoxide, in the presence of ligands such as pyridine and bipyridine, adds across the etheno bridge of 1N⁶-etheno-9-methyladenine and poly-1 N⁶-ethenoadenylic acid. The Os:P ratio in the labeled polynucleotide was 1 when bipyridine was used as the stabilizing ligands. A similar study with polycytidylic acid, which had been partially modified with chloroacetaldehyde so that some bases were converted to 3 N⁴-ethenocytosine, gave an Os:P ration of 1.3. Calf-thymus DNA, in which the adenine and cytosine bases were modified by chloroacetaldehyde, gave an Os:P ratio of 1 after 24 h. These results suggest that 3 N⁴-ethenocytosine will add two Os labels.