Azido-PEG8-NHS ester

Azido-PEG8-NHS ester is a bifunctional polyethylene glycol linker designed for modular PROTAC synthesis, combining an NHS ester for efficient amide-bond formation with an azide handle for orthogonal bioorthogonal conjugation. Its PEG-based spacer improves aqueous solubility and can reduce steric constraints between targeting ligands and the recruited E3 ligase moiety. The azide functionality enables click-type attachment strategies, while the NHS ester supports rapid coupling to primary amines. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a terminal azide group and an activated N-hydroxysuccinimide ester attached to a PEG chain, providing a flexible, hydrophilic spacer. Key functional groups include an NHS ester for acyl transfer and an azide suitable for azide–alkyne cycloaddition. The molecule is stable under appropriate storage conditions but reactive toward nucleophiles at the NHS ester.

Reactivity: The NHS ester reacts with primary amines to form stable amide bonds via nucleophilic acyl substitution, typically under mildly basic aqueous or mixed solvent conditions while minimizing hydrolysis. For PROTAC assembly, the resulting azide-bearing intermediate can be carried into azide-specific conjugation, most commonly copper-catalyzed or copper-free azide–alkyne cycloaddition depending on the sensitivity of other components. Use dry, amine-free solvents for coupling steps, and buffer systems compatible with NHS ester stability; catalysts and ligands should be selected to preserve functional groups during the click reaction.