Hydroxy-PEG4-propionic acid

Hydroxy-PEG4-propionic acid is a polyethylene glycol-based linker building block designed to support PROTAC assembly by providing a hydrophilic, flexible spacer and a terminal functional handle for conjugation. Its ether-rich backbone can enhance aqueous solubility and reduce steric constraints between the target-binding ligand and the E3 ligase recruiter. The following points describe the structure and the practical reactivity considerations for constructing PROTACs using this linker.

Structure: This linker comprises a short PEG chain featuring repeating ether units, terminating in a hydroxy group and a propionic acid functionality. It contains ether linkages and oxygen-bearing groups that confer flexibility, hydrogen-bonding capacity, and improved water compatibility, making it suitable for spacer roles in bifunctional degraders.

Reactivity: The propionic acid group enables amide or ester formation under standard coupling chemistries commonly used in PROTAC synthesis, typically via activation of the carboxylic acid followed by nucleophilic substitution with an appropriate amine or alcohol on a ligand. The terminal hydroxy group can also be leveraged for derivatization to introduce reactive handles. Mild, moisture-tolerant conditions and compatible coupling reagents are generally selected to preserve sensitive ligands and maintain linker integrity.