Bromo-PEG4-NHS ester

Bromo-PEG4-NHS ester is a PEG-based bifunctional linker designed for building PROTACs and related targeted protein degradation constructs. Its NHS ester enables efficient coupling to primary amines on ligands, while the bromo handle supports subsequent functionalization or installation of complementary fragments through nucleophilic substitution. The flexible polyethylene glycol scaffold helps tune solubility and spatial presentation of binding elements, facilitating robust synthesis and downstream conjugation. Detailed structural and reactivity considerations are provided below.

Structure: The linker comprises a PEG oligomer bearing an NHS ester for acyl transfer chemistry and a terminal bromo group for halide displacement. It contains an activated carboxylate, ether-rich repeating units, and an alkyl bromide, providing conformational flexibility and improved aqueous compatibility.

Reactivity: The NHS ester reacts with primary amines under mildly basic conditions to form stable amide bonds, typically using polar aprotic or buffered organic solvents while minimizing hydrolysis. The bromo group can undergo nucleophilic substitution with suitable nucleophiles to install the next PROTAC fragment, following standard SN-type reactivity principles. Common approaches use anhydrous handling, controlled pH, and inert atmosphere when feasible to preserve linker integrity.