Azidocoumarin Glycan Probes for Photoinduced Cross-Linking and In Situ Fluorescent Labeling

Photoinduced affinity labeling for cross-linking biomolecules in close spatial proximity has become a powerful strategy in life science studies to identify interaction partners in fundamental research as well as biomarkers in applied studies. Next-generation photo-cross-linkers additionally provide inducible fluorogenic properties to enable a visual read-out. Azido-substituted coumarin is nonfluorescent, but UV irradiation initiates the formation of a highly reactive nitrene radical that can act as a cross-linker while restoring the fluorescence activity of the coumarin chromophore. In this study, we present a 7-azidocoumarin derivative that is used as a suitable building block for solid-phase synthesis and demonstrates easy access to a variety of glycan-based photo affinity probes. Applications of photo-cross-linkers for glycans and their respective binding proteins are still rare. We show several azidocoumarin glycan-presenting probes and their selective targeting and covalent linking to lectins, accompanied by a turn-on fluorescence activity of the coumarin fluorophore. Selective recognition of specific target lectins from the presented glycan photo affinity probes is further demonstrated in complex biological environments, which now open opportunities for identifying and localizing both known and previously unidentified glycan receptors in cells, tissues, or patient samples.