Azido-PEG3-acetic acid

Azido-PEG3-acetic acid is a PEG-based bifunctional linker that incorporates an azide handle for bioorthogonal conjugation and a carboxylic acid for coupling to PROTAC warheads or ligands. Its flexible ether-rich scaffold can improve solubility and provide spatial separation between binding elements, which is often beneficial for efficient ternary complex formation and targeted protein degradation workflows. The following points describe its structure and practical reactivity considerations for PROTAC assembly.

Structure: The linker features an azide functional group attached to a short polyethylene glycol segment terminated by a carboxylic acid. It contains ether linkages within the PEG chain, a terminal aliphatic carboxyl group, and an organic azide suitable for click-type transformations. Overall, it is a flexible, polar, water-compatible scaffold.

Reactivity: The azide group is commonly used in copper-catalyzed azide–alkyne cycloaddition or related bioorthogonal conjugation strategies to connect the linker to alkyne-bearing partners under mild, compatibility-focused conditions. The carboxylic acid can be activated for amide or ester bond formation using standard coupling chemistries (for example, carbodiimide-based activation with appropriate additives) in polar aprotic or aqueous-organic solvent systems. Reaction design should consider maintaining azide integrity and preserving functional-group compatibility during PROTAC synthesis.