Vicinal Diol-Tethered Nucleobases as Targets for DNA Redox Labeling with Osmate Complexes

Six-valent osmium (osmate) complexes with nitrogenous ligands have previously been used for the modification and redox labeling of biomolecules involving vicinal diol moieties (typically, saccharides or RNA). In this work, aliphatic (3,4-dihydroxybutyl and 3,4-dihydroxybut-1-ynyl) or cyclic (6-oxo-6-(cis-3,4-dihydroxypyrrolidin-1-yl)hex-2-yn-1-yl, PDI) vicinal diols are attached to nucleobases to functionalize DNA for subsequent redox labeling with osmium(VI) complexes. The diol-linked 2′-deoxyribonucleoside triphosphates were used for the polymerase synthesis of diol-linked DNA, which, upon treatment with K₂OsO₃ and bidentate nitrogen ligands, gave the desired Os-labeled DNA, which were characterized by means of the gel-shift assay and ESI-MS. Through ex situ square-wave voltammetry at a basal plane pyrolytic graphite electrode, the efficiency of modification/labeling of individual diols was evaluated. The results show that the cyclic cis-diol (PDI) was a better target for osmylation than that of the flexible aliphatic ones (alkyl- or alkynyl-linked). The osmate adduct-specific voltammetric signal obtained for Os^VI-treated DNA decorated with PDI showed good proportionality to the number of PDI per DNA molecule. The Os^VI reagents (unlike OsO₄) do not attack nucleobases; thus offering specificity of modification on the introduced glycol targets.