Nitrone dipoles in bioorthogonal chemistry applications

Bioorthogonal chemistry is commonly used in chemical biology for the ligation of biomolecules and exogenous probes. The traditional copper(I)-catalyzed azide-alkyne cycloaddition and strain-promoted azide-alkyne cycloaddition remain key methods of ligating molecules, driven by transition metal catalysis in the former case and by built-in ring strain in the latter. While these 1,3-dipolar cycloadditions famously employ azides to react with alkynes, an alternative reaction partner is found in nitrones, which provide corresponding copper(I)-catalyzed and strain-promoted alkyne-nitrone cycloadditions. The latter are known to achieve faster kinetics than the corresponding azide reactions. Nitrones are also opportune for synthetically accessible electronic tuning of reaction rates, making them ideal for the design of mutually orthogonal labeling approaches. Our lab has demonstrated the versatility of alkyne-nitrone cycloadditions and developed straightforward workflows for the use of copper(I)-catalyzed and strain-promoted ligation reactions for bacterial labeling, including mutually orthogonal dual-labeling schemes. This chapter provides a sample of these methods, which may be easily adapted to suit the specific needs of a given system, for investigators seeking to take advantage of these simple and high-speed bioconjugation reactions.