Strain-promoted cycloadditions involving nitrones and alkynes--rapid tunable reactions for bioorthogonal labeling.

The development and applications of strain-promoted alkyne-nitrone cycloaddition (SPANC) reactions have brought about new tools for rapid and specific functionalization of biomolecules in different settings. While a number of strain-promoted reactions have been successfully developed, SPANC reactions offer high reactivity with bimolecular rate constants of k2 that are as fast as 60M(-1)s(-1). SPANC reactions also offer stability of starting materials, particularly in the case of endocyclic nitrones, as well as stereoelectronic tunability of the nitrone moiety to optimize reactivity towards different alkyne reaction partners. Herein we discuss recent advances in the development of SPANC reactions and their applications in bioorthogonal labeling.