Glycerol-Based Contrast Agents: A Novel Series of Dendronized Pentamethine Dyes

The synthesis of water-soluble dyes, which absorb and emit in the range between 650 and 950 nm and display high extinction coefficients (e) as well as high fluorescence quantum yields (Φf), is still a demand for optical imaging. We now present a synthetic route for the preparation of a new group of glycerol-substituted cyanine dyes from dendronized indole precursors that have been functionalized as N-hydroxysuccinimide (NHS) esters. High Φf values of up to 0.15 and extinction coefficients of up to 189 000 L mol–1 cm–1 were obtained for the pure dyes. Furthermore, conjugates of the new dendronized dyes with the antibody cetuximab (ctx) that were directed against the epidermal growth factor receptor (EGFR) of tumor cells could be prepared with dye to protein ratios between 0.3 and 2.2 to assess their potential as imaging probes. For the first time, ctx conjugates could be achieved without showing a decrease in Φf and with an increasing labeling degree that exceeded the value of the pure dye even at a labeli...