Synthesis and labeling of α-(2,9)-trisialic acid with cyanine dyes for imaging of glycan-binding receptors on living cells.

A sugar epitope, α-(2,9)-trisialic acid, was synthesized and labeled by cyanine dyes through Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The cyanine tagged oligosialic acid can be utilized as an efficient fluorescent probe to image the glycan-binding receptors on PC-12 cells. The distribution of Sia-binding immunoglobulin-like lectins (Siglecs) for α-(2,9)-trisialic acid was visualized by Cy3/Cy5 or FRET channel fluorescence imaging.