Azido-PEG7-NHS ester

Azido-PEG7-NHS ester is a heterobifunctional polyethylene glycol linker designed for constructing PROTACs and related targeted protein degradation conjugates. It combines an NHS ester handle for efficient amide-bond formation with a terminal azide for orthogonal bioorthogonal labeling and subsequent conjugation. The PEG segment improves aqueous solubility and can help modulate linker flexibility and accessibility of the recruited ligands. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a polyethylene glycol chain terminating in an azide group and an activated N-hydroxysuccinimide ester at the other end. It features ether linkages characteristic of PEG, an NHS-activated carboxylate for acyl transfer, and a stable azide suitable for click-type transformations.

Reactivity: The NHS ester reacts with primary amines to form stable amide bonds under mild, aqueous-compatible conditions, typically using buffered, slightly basic media to promote nucleophilic acyl substitution while minimizing hydrolysis. The azide enables orthogonal conjugation via azide–alkyne cycloaddition or related azide-based chemistries, often requiring appropriate copper-free or copper-assisted catalytic systems depending on sensitivity of the PROTAC components.