Azido-PEG3-NHS ester

Azido-PEG3-NHS ester is a versatile PROTAC linker building block that combines an NHS-activated ester for efficient amide coupling with a terminal azide handle for orthogonal bioorthogonal conjugation. Its PEG spacer improves aqueous solubility and provides conformational flexibility, which can help tune the geometry between ligand moieties in targeted protein degradation constructs. Detailed structural and synthetic considerations are provided below to support robust linker installation in PROTAC workflows.

Structure: The molecule contains a polyethylene glycol spacer terminating in an azide group and an N-hydroxysuccinimide ester for activated acyl transfer. It features an ether-rich PEG backbone, an ester linkage, and an azide functional group suitable for click-type reactions. Overall, it is designed for water-compatible conjugation chemistry.

Reactivity: The NHS ester reacts with primary amines under mildly basic aqueous or mixed solvent conditions to form stable amide bonds, typically using buffering bases and controlled stoichiometry to minimize hydrolysis. The azide enables orthogonal conjugation via azide–alkyne cycloaddition or related azide-compatible chemistries, often requiring copper catalysts or catalyst-free variants depending on substrate compatibility. Purification is commonly performed after coupling to remove hydrolyzed NHS byproducts.