L-Azidohomoalanine-1,2,3,4- 13 C 4 (hydrochloride) is the 13 C- and 15 N-labeled L-Azidohomoalanine hydrochloride. L-Azidohomoalanine hydrochloride is an alkyl chain-based PROTAC linker that can be used in the synthesis of PROTACs. L-Azidohomoalanine-1,2,3,4-13C4 (hydrochloride) is a click chemistry reagent, it contains an Azide group and can undergo copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with molecules containing Alkyne groups. It can also undergo strain-promoted alkyne-azide cycloaddition (SPAAC) reactions with molecules containing DBCO or BCN groups.