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

TheO-linked β-N-acetylglucosamine (O-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 betweenO-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 unnaturalN-acetylglucosamine (GlcNAc) analogues Ac4GlcNAc (substituted with an azido group) and the corresponding fluorescent tag Ru(bpy)2(Phen-alkyne)Cl2(4) to synthesize the fluorescent dye Ru(bpy)2(Phen-Ac4GlcNAc)Cl2(5) under mild and neutral reaction conditions. Moreover,5showed good stability, desirable fluorescence characteristics, and exhibited rather low levels of cytotoxicity against sensitive MCF-7 cells. Additionally, we have achieved successful fluorescent imaging of5transported in living MCF-7 cells. Cell images displayed that proteins are potentially labelled with5in the cytoplasm.Keywords:O-GlcNAc;click chemistry;cell imaging;fluorescent labeling;living cells