Azide‐Modified Nucleosides as Versatile Tools for Bioorthogonal Labeling and Functionalization

Abstract

Azide‐modified nucleosides are important building blocks for RNA and DNA functionalization by click chemistry based on azide‐alkyne cycloaddition. This has put demand on synthetic chemistry to develop approaches for the preparation of azide‐modified nucleoside derivatives. We review here the available methods for the synthesis of various nucleosides decorated with azido groups at the sugar residue or nucleobase, their incorporation into oligonucleotides and cellular RNAs, and their application in azide‐alkyne cycloadditions for labelling and functionalization.

Click chemistry: A fascinating, Nobel-winning method for the improvement of biological activity

“…Moreover, thanks to their tolerance for typical biological conditions and almost all functional groups along with hydrogen bonding capacity based high solubility in aqueous solutions, 1,2,3triazole compounds are targeted in the synthesis of various polymeric carrier systems and dendrimers, crosslinking of micelles and the syntheses on modifying the surfaces of various nanoparticle carrier systems [23][24][25][26][27] . The stability of those compounds makes the reaction in which they are synthesized extremely ideal for bioconjugation, and so as a result, the binding of oligonucleotides, proteins, polysaccharides, viruses and bacteria such as E. coli to various substrates is successfully accomplished using this approach [28][29][30][31][32][33] .…”

Robust synthesis of 2′-azido modified RNA from 2′-amino precursors by diazotransfer reaction

“…1-5 †). Thereby, the 5 nt long RNA (2-5) without any secondary structure (single strand) showed much faster reaction progress than the 10 nt hairpin (6)(7)(8)(9) or the 8 nt palindrome (1, 10-12) that exhibits defined secondary structures (double helices). A summary of the diazotransfer on the 10 nt hairpin for all canonical 2′-NH 2 modified RNAs (6-9) is shown in Fig.…”

“…5,6 In all these approaches, a covalent linkage of the azido group to a reporter molecule, fluorescent dye, affinity tag or transporter unit is formed by either Staudinger ligation, Cu(I)-catalyzed azidealkyne cycloaddition (CuAAC), strain-promoted [3 + 2] cycloaddition (SPAAC), or photo-click chemistry, with the RNA azido group being located at the ribose, the termini, the phosphate backbone or the nucleobase. [4][5][6][7][8][9] For chemical biology, 2′-azido modified RNA is an upcoming tool whose physicochemical properties have been reported earlier. [10][11][12] The 2′-N 3 modification favours the RNA C3′-endo sugar pucker, only causes a slight decrease in base pairing stabilities, and hardly influences the overall RNA structure.…”

“…5,6 In all these approaches, a covalent linkage of the azido group to a reporter molecule, fluorescent dye, affinity tag or transporter unit is formed by either Staudinger ligation, Cu( i )-catalyzed azide–alkyne cycloaddition (CuAAC), strain-promoted [3 + 2] cycloaddition (SPAAC), or photo-click chemistry, with the RNA azido group being located at the ribose, the termini, the phosphate backbone or the nucleobase. 4–9…”

Pathways of the Dissociative Electron Attachment Observed in 5- and 6-Azidomethyluracil Nucleosides: Nitrogen (N2) Elimination vs Azide Anion (N3–) Elimination

“…Azido-modified nucleosides have been of interest for over six decades and the finding that 3′-azido-3′-deoxythymidine (AZT or 3′-AZT) is a therapeutic agent , for acquired immunodeficiency syndrome (AIDS) has sparked interest in their chemistry. The synthesis of azidonucleosides, their reactions, and biological activities have been the subject of several comprehensive reviews. , Azidonucleosides have been mainly explored as substrates for the (a) synthesis of amino nucleosides, (b) click chemistry, (c) bioconjugation and ligation, (d) enzyme inhibitions including ribonucleotide reductases (RNR), , among others. Recently, our group is employing azidonucleosides to augment the radiation-induced damage (i.e., radiosensitization) in cancer cells to improve the efficacy of tumor radiotherapy .…”