Azido-PEG4-amido-PEG4-Boc

Azido-PEG4-amido-PEG4-Boc is a polyethylene glycol-based PROTAC linker designed to combine flexible spacing with orthogonally addressable functional handles. The azide enables reliable bioorthogonal conjugation chemistry, while the amide-containing PEG segments support solubility and conformational adaptability between targeting ligands and the recruited E3 ligase binder. The Boc-protected functionality provides a protected reactive site that can be unmasked under controlled conditions during linker assembly. Detailed structural and reactivity considerations for PROTAC construction are provided below.

Structure: The linker comprises two PEG segments connected through an amide linkage, incorporating an azide-bearing terminus and a Boc-protected group at the other end. It contains ether oxygen atoms from PEG, amide carbonyl and nitrogen, and an azide functional group, yielding a flexible, polar, and water-compatible scaffold.

Reactivity: The azide group is suitable for copper-catalyzed azide–alkyne cycloaddition or strain-promoted azide–alkyne cycloaddition, enabling conjugation to alkyne-functional partners under conditions compatible with sensitive biomolecular ligands. The Boc group can be removed using standard acid-mediated deprotection to reveal an amine for subsequent amide coupling. Linker assembly typically employs amide-forming coupling chemistries in polar aprotic solvents, with base and coupling reagents selected to match the functional-group tolerance of the chosen ligands.