Fmoc-L-Lys(4-N3-Z)-OH is a chemical reagent characterized by its azide group. This compound serves as a lysine building block in solid-phase peptide synthesis (SPPS) with azide functionality, useful as a bioorthogonal handle, an infrared probe, and a photoaffinity label. It undergoes strain-promoted 1,3-dipolar cycloaddition facilitated by trans-cyclooctene decarboxylation. Additionally, Fmoc-L-Lys(4-N3-Z)-OH functions as a click chemistry reagent, enabling copper-catalyzed azide-alkyne cycloaddition reactions (CuAAc) with molecules containing alkyne groups. Moreover, it can participate in strain-promoted alkyne-azide cycloaddition reactions (SPAAC) with molecules that possess DBCO or BCN groups.