Synthesis of a Novel Fluorescent Ruthenium Complex with an Appended Ac₄GlcNAc Moiety by Click Reaction

The -linked β- -acetylglucosamine ( -GlcNAc) modification is an abundant post-translational modification in eukaryotic cells, which plays a fundamental role in the activity of many cells and is associated with pathologies like type II diabetes, Alzheimer’s disease or some cancers. However, the precise connexion between -GlcNAc-modified proteins and their function in cells is largely undefined for most cases. Confocal microscopy is a powerful and effective tool for in-cell elucidation of the function of biological molecules. Chemical labeling of non-ultraviolet or non-fluorescent carbohydrates with fluorescent tag is an essential step that makes intra-cellular microscopic inspection possible. Here we report a strategy based on the 1,3-dipolar cycloaddition, called click chemistry, between unnatural -acetylglucosamine (GlcNAc) analogues Ac₄GlcNAc (substituted with an azido group) and the corresponding fluorescent tag Ru(bpy)₂(Phen-alkyne)Cl₂ ( ) to synthesize the fluorescent dye Ru(bpy)₂(Phen-Ac₄GlcNAc)Cl₂ ( ) under mild and neutral reaction conditions. Moreover, showed good stability, desirable fluorescence characteristics, and exhibited rather low levels of cytotoxicity against sensitive MCF-7 cells. Additionally, we have achieved successful fluorescent imaging of transported in living MCF-7 cells. Cell images displayed that proteins are potentially labelled with in the cytoplasm.