Lenalidomide-C4-NH2 hydrochloride is a PROTAC linker that can be used to construct small-molecule linkers or PROTAC molecules to induce the degradation or regulation of target proteins. Lenalidomide-C4-NH2 hydrochloride acts as a ligand for the E3 ubiquitin ligase CRBN and is used to study protein degradation, signaling pathway regulation, and pharmacological mechanisms.