One-pot fluorescent labeling of saccharides with fluorescein-5-thiosemicarbazide for imaging polysaccharides transported in living cells

A simple and efficient procedure for the fluorescent labeling of saccharides is a prerequisite step for imaging the transport of polysaccharides in living cells. We report a one-pot strategy for the fluorescent labeling of saccharides with fluorescein-5-thiosemicarbazide (FTSC), which introduces the thiosemicarbazide group of FTSC to the aldehyde group at the reducing end of saccharides to form stable amino derivatives via reductive amination. The Glc-FTSC derivative was characterized by HPLC–MS, HRESIMS and NMR spectroscopy. Saccharides were quantitatively labeled with FTSC at 75 °C for 1 h under optimum reaction conditions. Fluorescence studies illustrated that the conjugation of FTSC to saccharides did not change its florescence properties (λ_ex = 495 nm, λ_em = 517 nm), presenting desirable compatibility with commonly used fluorescence equipment. Polysaccharide AAG-FTSC derivatives exhibited rather low levels of cytotoxicity against rat thymus cells, and the fluorescent labeling procedure had slight impact on their anti-tumor activity. Results indicate that the assay neither introduces discernible cytotoxicity against living cells nor obviously alters the functional activities of polysaccharides, and provides a convenient, highly efficient fluorescent labeling approach for imaging the transport of polysaccharides in living cells.