<i>De Novo</i> Boronic Acid-Containing Macrocyclic Peptides That Selectively Bind a Sialylated <i>N</i> -Glycan

Glycan-mediated molecular recognition is central to many diseases, yet designing selective synthetic glycan binders is difficult due to the limited functional group diversity of carbohydrates. Boronic acids can form reversible covalent bonds with cis -diols but typically lack selectivity. To address this, we developed conformationally constrained macrocyclic peptides incorporating boronic acid-containing amino acids using genetic code reprogramming and the RaPID system. Screening against the N -linked biantennary sialylated glycan N -A2G2S2 yielded de novo macrocycles with single-digit micromolar affinities. The lead peptide, A2–17, showed remarkable selectivity for N -A2G2S2 and formed a reversible boronate ester with the glycan, as confirmed by competition assays and mass spectrometry. Fluorescence microscopy and flow cytometry demonstrated that A2–17 recognizes cell-surface glycans containing N -A2G2S2, highlighting the potential of this platform for discovering selective glycan-binding peptides.