Azido-PEG5-CH2COOH

Azido-PEG5-CH2COOH is a polyethylene glycol-based bifunctional linker designed for modular assembly of PROTACs. The azide handle enables chemoselective conjugation to complementary partners, while the terminal carboxylic acid supports coupling and controlled attachment strategies. Its PEG character promotes solubility and provides spatial flexibility between ligands, which can improve productive ternary complex formation. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains an azide functionality attached to a PEG chain terminating in a carboxylic acid, connected through a methylene spacer. It features ether-rich PEG segments, a terminal carboxyl group, and an azide moiety, offering polar, hydrogen-bonding capability and conformational flexibility.

Reactivity: The azide group is suited for click-type conjugation with alkynes under copper-catalyzed or copper-free azide–alkyne cycloaddition conditions, enabling selective formation of triazole linkages. The carboxylic acid can be activated for amide or ester bond formation using standard coupling chemistries (e.g., carbodiimide-based activation with an amine nucleophile) in compatible polar solvents. Reaction design should preserve azide integrity and avoid harsh conditions that can degrade PEG linkers.