Azido-PEG2-t-butyl ester

Azido-PEG2-t-butyl ester is a polyethylene glycol-based PROTAC linker building block that incorporates an azide handle for bioorthogonal conjugation and a protected carboxylate for controlled coupling. Its PEG spacer supports favorable solubility and conformational flexibility, which can improve effective proximity between target-binding ligands and the recruited E3 ligase. The azide functionality enables modular assembly of degraders, while the ester protection facilitates stepwise synthesis. Detailed structural and reactivity considerations are provided below.

Structure: The molecule is an azide-functionalized PEG spacer capped with a tert-butyl ester, featuring ether linkages within the PEG chain and a terminal azide substituent. The tert-butyl ester provides a stable, protected carboxylate, while the PEG segment contributes hydrophilicity and conformational mobility.

Reactivity: The azide group is commonly used in copper-catalyzed or strain-promoted azide–alkyne cycloaddition to connect PROTAC fragments under mild, compatible conditions. The tert-butyl ester can be deprotected using acid to reveal a carboxylic acid for subsequent amide or ester bond formation. Typical coupling steps employ activated carboxylic acid chemistries with appropriate bases and coupling reagents, using solvents compatible with both linker stability and downstream ligands.