N-(3-azidopropyl)-5-((3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl)pentanamide is a biotin derivative functionalized with an azide group. It is a bifunctional crosslinking reagent that combines the high-affinity binding of biotin to streptavidin/avidin with the bioorthogonal reactivity of an azide group, which can undergo strain-promoted or copper-catalyzed azide-alkyne cycloaddition (SPAAC or CuAAC) with alkynes. This compound is primarily used in chemical biology and proteomics research for labeling, pull-down assays, and affinity purification. The biotin moiety allows for strong immobilization or detection via streptavidin-conjugated systems, while the azide handle enables site-specific conjugation to alkyne-modified biomolecules, surfaces, or fluorophores. It is a key tool for constructing probes for studying protein-protein interactions, post-translational modifications, and cellular localization. Furthermore, its bifunctional nature makes it relevant in the development of advanced therapeutic modalities. It can serve as a component in the design of PROTACs (Proteolysis Targeting Chimeras) and other bifunctional molecules, acting as a linker to connect a target protein ligand to an E3 ubiquitin ligase recruiter, facilitating targeted protein degradation.