H2N-PEG2-CH2COOH belongs to a polyethylene glycol (PEG) linker covalently bound to E3 Ligase binding group (E3LB) and protein binding group (PB). H2N-PEG2-CH2COOH is a PEG derivative containing an amino group with a terminal carboxylic acid. The amino group is reactive with carboxylic acids, activated NHS esters, carbonyls (ketone, aldehyde) etc. The terminal carboxylic acid can be reacted with primary amine groups in the presence of activators (e.g. EDC, or DCC) to form a stable amide bond. PEG Linkers may be useful in the development of antibody drug conjugates and PROTACs.