HAAC Ligation-Enabled Hierarchical Assembly: Deciphering the Synergy of α-Hydroxyl Aldehydes and 2-Aminooxazoles

We report α-hydroxyl aldehyde-2-aminooxazole conjugation (HAAC), a bioorthogonal ligation platform that enables selective biomolecular labeling and functional modulation under physiological conditions (pH 7.0, 37 °C). HAAC chemistry supports: (1) multiplexed fluorescent labeling of proteins (demonstrated with BSA), (2) targeted cell-surface engineering through αHA-functionalized cetuximab for precision EGFR engagement, and (3) spatially controlled regulation of β-amyloid levels in HEK293T cells via small-molecule triggers (e.g., tetra-N-butylammonium fluoride, TBAF). Leveraging this tunable reactivity, we developed a chemoproteomic workflow for system-wide profiling of sialoglycoproteins, identifying ANK3 and FBXL22 as novel sialylated effectors through SA (sialic acid)-specific mass spectra detection. As the first chemical biology strategy to directly interrogate SA (sialic acid)-modified proteomes, α-hydroxyl aldehydes and 2-aminooxazoles conjugation (HAAC) uniquely bridges prebiotic reaction principles with contemporary biomedical applications. This platform establishes a versatile paradigm for precision glycoproteomics, targeted protein degradation, and dynamic control of biological systems.