Aminooxy-PEG5-azide

Aminooxy-PEG5-azide is a bifunctional PROTAC linker designed to connect targeting ligands and enable efficient conjugation through orthogonal reactive handles. The aminooxy group supports oxime-formation chemistry, while the azide functionality enables bioorthogonal attachment via azide–alkyne cycloaddition. Its PEG-based segment provides aqueous compatibility and conformational flexibility, which can improve conjugate solubility and reduce steric constraints in ternary-complex formation. Detailed structural and synthetic considerations are provided below.

Structure: The linker contains an aminooxy moiety and an azide group separated by a polyethylene glycol chain, providing a flexible, hydrophilic scaffold. It features ether linkages within the PEG backbone and reactive functional-group termini suitable for selective conjugation under mild conditions.

Reactivity: Conjugation can be performed by reacting the aminooxy group with carbonyl-bearing partners to form stable oxime linkages, typically using mildly acidic conditions and an appropriate aqueous/organic solvent mixture. Alternatively, the azide group can undergo copper-catalyzed or strain-promoted azide–alkyne cycloaddition with alkyne-functional ligands or handles. Reaction progress is commonly monitored by chromatographic or spectroscopic methods, and purification should remove residual catalysts when applicable.