42 We considered this reagent promising to tolerate the functionalities present in RNA. To reach this goal, our attention was caught by a recently published diazotizing reagent, fluorosulfuryl azide (FSO 2N 3), originally designed to provide rapid access to azido libraries of small organic compounds. tRNAs, aminoacyl-RNAs, synthetic RNA-peptide conjugates, etc.) currently suffer from a lack of suitable methods that allow for selective chemical transformation into azide functionalities without affecting the nucleobase NH 2 groups (B NH2). RNA with primary aliphatic amino group modifications of natural or synthetic origin (e.g. azide-alkyne cycloadditions (Click) 33- 38 or Staudinger ligations 39- 41). 9 The transformation of their primary amines into azides would deliver a well-behaved reactive handle that allows the application of high-yielding bioorthogonal conjugation reactions (e.g. Finding such a conversion reaction would open new avenues for RNA labeling, for the preparation of RNA-peptide conjugates, and for the selective isolation and identification of cellular RNAs with nucleotide modifications, such as 3-(3-amino-3-carboxypropyl)uridine (acp 3U), 31 lysidine (k 2C), 32 5-aminomethyl-2-thiouridine (mn 5s 2U), 9 and many others (Supporting Figure S1). In the present work, we have searched for a solution to convert an RNA containing a primary amino group into the corresponding azide-modified RNA, leaving the nucleobase amines unaffected (Figure 1). Reactive handles can also be generated through metabolic labeling of RNA 14- 21 or by RNA solid-phase synthesis. RNA containing such modifications is endowed with functional groups that are distinct from the repetitive nucleotide pattern of RNA, and therefore, they can serve as handle for specific and selective transformations. 9- 13 A broad spectrum of modifications is encountered, ranging from simple methylations to very complex nucleotides containing tricyclic nucleobases (wybutosine), deazanucleobases with sugar moieties attached (queuosine), or amino acid conjugated nucleobases (e.g. The functionalities of RNA are more diverse when one considers naturally occurring RNA with more than 140 modifications known to date, most of them found in tRNA, and also in rRNA, mRNA and non-coding RNAs. fluorophores, biotin, etc.) by reductive amination reactions.
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Most prominent is the utilization of the diol moiety for labeling of native RNA through periodate cleavage to the corresponding dialdehyde and subsequent attachment of reporter groups (e.g.
![anime conv anime conv](https://i.pinimg.com/736x/23/dc/e0/23dce038924166bf300d0a86f074d70c.jpg)
1- 5 With only four building blocks (A, C, G, U), RNA is structurally rather uniform and only offers the primary alcohol of the 5′ terminal ribose, and the diol at the 3′-terminal ribose (2′-OH, 3′-OH) as unique structural features for direct selective chemical transformations. Ribonucleic acid (RNA) is a fragile molecule that does not survive harsh reaction conditions and thus makes selective modification by synthetic organic chemistry challenging. Our approach therefore adds a new dimension to the targeted chemical manipulation of diverse RNA species.
![anime conv anime conv](https://i.ytimg.com/vi/mX5y3rxnMOU/maxresdefault.jpg)
We exemplify the robustness of this approach for the synthesis of peptidyl-tRNA mimics and for the pull-down of 3-(3-amino-3-carboxypropyl)uridine (acp 3U)- and lysidine (k 2C)-containing tRNAs of an Escherichia coli tRNA pool isolated from cellular extracts. The obtained azido-RNA can then be further processed utilizing well-established bioortho-gonal reactions, such as azide-alkyne cycloadditions (Click) or Staudinger ligations. The reaction provides the corresponding azide-modified RNA in nearly quantitatively yields without affecting the nucleobase amino groups.
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Here, we introduce metal-free diazotransfer on native RNA containing an aliphatic primary amino group using the diazotizing reagent fluorosulfuryl azide (FSO 2N 3). A major challenge in the field of RNA chemistry is the identification of selective and quantitative conversion reactions on RNA that can be used for tagging and any other RNA tool development.