Azido-PEG5-propionic acid

Azido-PEG5-propionic acid is a PEG-based bifunctional linker designed for modular PROTAC assembly, enabling efficient conjugation between a targeting ligand and an E3 ligase binder. Its flexible ethylene glycol spacer improves solubility and spatial presentation, while the azide handle supports chemoselective “click” coupling to complementary alkynes. The resulting PROTAC constructs can benefit from reduced steric interference and tunable linker length, and the detailed structural and reactivity features are described below.

Structure: The linker comprises an azide-functional group attached to a poly(ethylene glycol) chain terminated by a propionic acid moiety. It contains ether linkages within the PEG segment, an aliphatic carboxylic acid, and an organic azide suitable for bioorthogonal reactions. Overall, it is a polar, water-compatible scaffold.

Reactivity: The azide group participates in copper-catalyzed azide–alkyne cycloaddition with terminal alkynes to form stable triazole linkages, a widely used strategy in PROTAC synthesis. Coupling is typically performed under mild conditions using copper catalysts and appropriate ligands to control reactivity, often in polar solvents compatible with biomolecule conjugation. The terminal carboxylic acid can be activated for amide or ester formation using standard coupling chemistries.