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.