N-(Azido-PEG3)-N-(PEG2-amine)-PEG3-acid

This azido-functional PEG-based linker is designed for modular PROTAC assembly by enabling efficient conjugation to ligands and subsequent installation of reactive handles for targeted protein degradation workflows. Its flexible, hydrophilic polymer segments support favorable solubility and reduced steric bias at the junctions, while the azide group provides a chemically orthogonal site for bioorthogonal coupling. The detailed structural and synthetic considerations are provided below.

Structure: The linker consists of multiple polyethylene glycol segments connected through ether linkages, terminating in an azide-bearing amine functionality and a terminal carboxylic acid. It contains an azide substituent suitable for click-type transformations and an amide-forming amine for ligand attachment. Overall, it is highly flexible and water-compatible.

Reactivity: The azide group enables copper-catalyzed azide–alkyne cycloaddition or strain-promoted azide–alkyne coupling, depending on the partner functionality. PROTAC construction typically proceeds by first coupling the amine to a ligand-bearing activated ester or activated carboxylate, followed by azide-based conjugation to an alkyne-functional moiety. Reactions are commonly performed in polar aprotic or aqueous/organic mixtures under conditions compatible with PEG stability and amide formation, using appropriate catalysts for click chemistry when required.