Selective Arylation of RNA 2'-OH Groups via S_NAr Reaction with Trialkylammonium Heterocycles

Small-molecule reactions at the 2'-OH groups of RNA enable useful applications for transcriptome technology and biology. To date, all reactions have involved carbonyl acylation and mechanistically related sulfonylation, limiting the types of modifications and properties that can be achieved. Here we report that electron-deficient heteroaryl species selectively react with 2'-OH groups of RNA in water via S_NAr chemistry. In particular, trialkyl-ammonium (TAA)-activated aromatic heterocycles, prepared in one step from aryl chloride precursors, give high conversions to aryl ether adducts with RNAs in aqueous buffer in ~2-3 h. Remarkably, a TAA triazine previously used only for reaction with carboxylic acids, shows unprecedented selectivity for RNA over water, reacting rapidly with 2'-OH groups while exhibiting a half-life in water of >10 days. We further show that a triazine aryl species can be used as a probe at trace-level yields to map RNA structure in vitro. Finally, we prepare a number of functionalized trialkylammonium triazine reagents and show that they can be used to covalently label RNA efficiently for use in vitro and in living cells. This direct arylation chemistry offers a simple and distinct structural scaffold for post-synthetic RNA modification, with potential utility in multiple applications in transcriptome research.