Molecular reporters for mammalian sugars via hydrogen bonding auxiliaries.

Glycans are essential transmitters of biological information. However, their complex and dynamic structures remain difficult to characterize, posing a major barrier to fully understanding their biological functions. Here, we demonstrate that hydrogen bonding auxiliaries positioned adjacent to the boron site of turn-on fluorogenic phenylboronic acid reporters serve as key modulators of sensitivity to mammalian sugars, providing a new design principle analogous to the hydrogen bonding networks found in lectin binding pockets. We show that these auxiliaries tune sensitivity both globally and for individual mammalian sugars and reveal a striking differential turn-on response between the anomeric forms of monosaccharides. The versatility of these selective and reversible molecular reporters is demonstrated through in-gel glycoprotein imaging, flow cytometry, and cell-surface visualization, establishing them as a generalizable chemical platform for interrogating mammalian glycans.