The epigenetic modification 5-methylcytosine plays a vital role in development, cell specific gene expression and disease states. The selective chemical modification of the 5-methylcytosine methyl group is challenging. Currently, no such chemistry exists. Direct functionalisation of 5-methylcytosine would improve the detection and study of this epigenetic feature. We report a xanthone-photosensitised process that introduces a 4-pyridine modification at a C(sp3)-H bond in the methyl group of 5-methylcytosine. We propose a reaction mechanism for this type of reaction based on density functional calculations and apply transition state analysis to rationalise differences in observed reaction efficiencies between cyanopyridine derivatives. The reaction is initiated by single electron oxidation of 5-methylcytosine followed by deprotonation to generate the methyl group radical. Cross coupling of the methyl radical with 4-cyanopyridine installs a 4-pyridine label at 5-methylcytosine. We demonstrate use of the pyridination reaction to enrich 5-methylcytosine-containing ribonucleic acid.
Selective functionalisation of the C(sp3)−H bond in the methyl group of 5‐methylcytosine is achieved by xanthone‐catalysed photoredox catalysis. The specific nature of the functionalisation of 5‐methylcytosine on ribonucleic acid (RNA) was used to install a Halo‐Tag reactive handle which enabled the chemical enrichment of 5‐methylcytosine containing RNA.
Keywords: C−H Functionalization; Nucleic Acids; Photocatalysis; Radicals; Reaction Mechanisms.
© 2023 The Authors. Angewandte Chemie published by Wiley-VCH GmbH.