Capturing Sialyl‐glycan on Live Cancer Cells by Tailored Boronopeptide**

Boronic acid-containing molecules are substantially popularized in chemical biology and medicinal chemistry due to the broad spectrum of covalent conjugations as well as interaction modules offered by the versatile boron atom. Apparently, the WGA peptide (wheat germ agglutinin, 62-73), which shows a considerably low binding affinity to sialic acid, turned into a selective and >5 folds potent binder with the aid of a suitable boronic acid probe installed chemoselectively. In silico studies prompted us to install BA probes on the cysteine residue, supposedly located in close proximity to the bound sialic acid. In vitro studies revealed that the tailored boronopeptides show enhanced binding ability due to the synergistic recognition governed by selective non-covalent interactions and cis-diol boronic acid conjugation. The intense binding is observed even in 10 % serum, thus enabling profiling of sialyl-glycan on cancer cells, as compared with the widely used lectin, Sambucus nigra. The synergistic binding mode between the best boronopeptide (P3) binder and sialic acid was analyzed via