COOH-PEG5-COOMe

COOH-PEG5-COOMe is a polyethylene glycol-based bifunctional linker designed for assembling PROTACs that require controlled spacing and improved solubility between a targeting ligand and an E3 ligase binder. Its flexible ether-rich backbone helps accommodate conformational demands during ternary complex formation, while the two distinct carboxyl-derived termini enable reliable conjugation strategies. The following sections describe the linker’s structural features and practical reactivity considerations for PROTAC construction in research workflows.

Structure: The linker contains a flexible PEG chain composed of repeating ether units, terminating in carboxylic acid and methyl ester functionalities. It features ester and carboxyl groups capable of hydrogen bonding and ionic interactions, with ether oxygen atoms that enhance polarity and aqueous compatibility.

Reactivity: PROTAC assembly typically uses carboxyl-derivatives through amide bond formation or ester-to-acid activation. The methyl ester can be hydrolyzed to the corresponding acid under standard aqueous base conditions, then converted to an activated intermediate (for example, via carbodiimide coupling) to react with amine-bearing partners. Alternatively, orthogonal protection/activation enables stepwise conjugation, using commonly employed coupling reagents and polar solvents to maintain solubility.