Azido-PEG4-CH2-Boc is a four-unit cleavable polyethylene glycol (PEG) linker compound employed in the synthesis of antibody-drug conjugates (ADCs)[1] and PROTACs[2]. This linker is characterized by its azide functional group and PEG backbone, facilitating the conjugation of drugs to antibodies in ADC development and enabling the synthesis of PROTACs utilizing PEG and alkyl ether moieties.