L-Azidonorleucine (hydrochloride) is widely used in chemical biology and protein engineering for site-specific labeling and modification of biomolecules. Its azide functional group enables efficient conjugation with alkyne-containing compounds via click chemistry, particularly the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. This property makes it valuable for tagging proteins, peptides, and other biomolecules with fluorescent dyes, affinity tags, or other functional groups for imaging, tracking, or purification purposes. Additionally, it is incorporated into proteins during translation using engineered tRNA/synthetase systems, allowing for precise modification of specific amino acid residues. This chemical is also utilized in proteomics studies to investigate protein-protein interactions, post-translational modifications, and cellular localization.