Azide-PEG9-amido-C8-Boc

This linker is designed for modular PROTAC assembly, providing an azide handle for orthogonal conjugation and a PEG-based spacer to tune solubility and effective linker length between the targeting ligand and the E3-ligase recruiter. Its amide-containing connectivity and protected functionality support synthetic flexibility and controlled deprotection steps. The following sections describe its structure and the practical reactivity considerations for constructing PROTACs using this scaffold.

Structure: The molecule incorporates an azide-bearing terminus connected through a polyethylene glycol spacer, with an amide linkage that provides polarity and hydrogen-bonding capability. A tert-butyl ester-protected carboxyl group supports stability during earlier coupling steps and enables subsequent controlled deprotection. Overall, it is a flexible, ether-rich linker with a terminal azide.

Reactivity: The azide group is suitable for bioorthogonal conjugation strategies commonly used in PROTAC synthesis, including copper-catalyzed azide–alkyne cycloaddition with a terminal alkyne or strain-promoted azide–alkyne cycloaddition (SPAAC) with a strained alkyne such as DBCO or BCN, depending on the partner fragment. Coupling is typically performed under inert conditions with appropriate base and solvent systems compatible with peptide-like ligands. The tert-butyl ester is generally cleaved using standard acidolysis conditions to reveal the carboxylic acid for subsequent activation and coupling, enabling stepwise PROTAC construction.