Covalent labeling of nucleosides with VIII- and VI-valent osmium complexes

Osmium tetroxide complexes with nitrogen ligands [Os(VIII)L] have been widely applied as probes of the DNA structure and as electroactive labels of DNA. Here we describe the electrochemical behavior of Os(VIII)2,2-bipyridine (Os, bipy)-base-labeled nucleosides. We show that electroactive label can be introduced also in the nucleoside ribose residues using six-valent osmium complex. Cyclic voltammograms of sugar-Os (VI) -modified ribosides are similar but not identical to those of the base-modified ribosides. Our results showing the electroactivity of sugar modified ribosides pave the way to facile end-labeling of RNA.