Hydroxy-PEG8-propionic acid

Hydroxy-PEG8-propionic acid is a polyethylene glycol–based linker building block designed to support PROTAC assembly by providing a hydrophilic, conformationally flexible spacer and a functional handle for conjugation. Its ether-rich backbone can improve solubility and reduce nonspecific interactions, while the terminal hydroxy and carboxylic acid enable robust coupling strategies to ligands and warheads. The following sections describe its structure and the practical considerations for using it in PROTAC linker construction.

Structure: The molecule consists of a PEG chain terminated by a hydroxy group and a propionic acid moiety. Its repeating ether units provide flexible C–O–C linkages, while the carboxylic acid offers a polar, ionizable functionality. Overall, it exhibits strong hydrophilicity and hydrogen-bonding capacity.

Reactivity: The carboxylic acid is suitable for amide or ester formation under standard peptide-coupling conditions, typically using carbodiimide-based coupling reagents with an activating additive and a polar aprotic solvent. The hydroxy group can be leveraged for ether or ester linkage formation depending on the electrophile and activation chemistry. In PROTAC synthesis, these transformations enable modular attachment of the linker to ligand-bearing amines or activated alcohol/acid partners, preserving linker flexibility and minimizing steric constraints.