Diazo Groups Endure Metabolism and Enable Chemoselectivity in Cellulo

Abstract

We introduce a stabilized diazo group as a reporter for chemical biology. ManDiaz, which is a diazo derivative of N-acetylmannosamine, is found to endure cellular metabolism and label the surface of a mammalian cell. There, its diazo group can undergo a 1,3-dipolar cycloaddition with a strained alkyne, providing a signal comparable to that from the azido congener, ManNAz. The chemoselectivity of diazo and alkynyl groups enables dual labeling of cells that is not possible with azido and alkynyl groups. Thus, the diazo group, which is approximately half the size of an azido group, provides unique opportunities for orthogonal labeling of cellular components.

Rapid cycloaddition of a diazo group with an unstrained dipolarophile

“…Through a computational distortion/interaction analysis, we conclude that the enhanced reactivity results from the development of strong interactions in the transition state, including an N–H···F–C hydrogen bond and hyperconjugation. Diazo compounds can complement azides as biological probes, 7 and the insights herein could inspire the de novo design of dipolarophiles tailored for rapid reaction with a diazo group. 25 …”

“…7 Nevertheless, the use and development of diazo compounds in chemical biology are constrained by a paucity of chemoselective reactions. Most confounding is the overlapping reactivity of the diazo group with that of the azido group in strain-promoted azide–alkyne cycloadditions (SPAACs).…”

“…Most confounding is the overlapping reactivity of the diazo group with that of the azido group in strain-promoted azide–alkyne cycloadditions (SPAACs). 7,8 …”

Decreasing Distortion Energies without Strain: Diazo-Selective 1,3-Dipolar Cycloadditions

“…3 Though azido groups have been the most prevalent reactant, their diazo congeners can likewise participate in 1,3-dipolar cycloadditions, and both dipoles survive cellular metabolism. 4 …”

“…11 Owing to the inherent conjugation to its pendant carbon, the diazo group is well-suited for optimization. Such optimization might allow for dual-labeling strategies, 4,9b,12 which require orthogonal reactions that remain chemoselective in the presence of biological moieties. 3 The small size, high stability, and cycloaddition-reactivity of azido and diazo groups make them attractive chemical reporters for such applications.…”