Novel Rhenium(I) Tricarbonyl Polypyridine Sydnone Complexes for Phosphorogenic Bioorthogonal Labeling of Live Cells

Bioorthogonal chemistry has allowed for selective labeling in living systems, through the introduction of a biomolecule modified with a chemical reporter and the subsequent specific reaction with a bioorthogonal probe. Notably, the development of bioorthogonal smart probes (turn-on probes) has received great attention. Past works on luminogenic bioorthogonal probes have mainly utilized phosphine, azide, and tetrazine ligation. Due to the youth of the field, there is an increasing demand for new bioorthogonal reactions to expand the chemical biology toolbox. Hence, we report the synthesis, characterization, and photophysical studies of three novel phosphorogenic rhenium(I) tricarbonyl polypyridine sydnone complexes as bioorthogonal probes for live cells. These complexes were weakly or non-emissive and exhibited significant emission enhancement upon strain-promoted sydnone-alkyne cycloaddition. These complexes were used to study the intracellular distribution of bicyclo[6.1.0]non-4-yne (BCN) derivatives in live cells by laser-scanning confocal microscopy.