Propargyl-PEG2-NHS ester

Propargyl-PEG2-NHS ester is a bifunctional polyethylene glycol (PEG) linker designed for PROTAC assembly, enabling efficient conjugation between a PEG-based spacer and amine-containing ligands. Its NHS ester provides a reliable handle for forming stable amide bonds, while the terminal propargyl group supports orthogonal click-type coupling. This combination improves modular synthesis, linker flexibility, and conjugation control, and the molecule will be described in detail below.

Structure: The linker contains a PEG-based ether chain providing conformational flexibility, coupled to an N-hydroxysuccinimide ester for acyl transfer. A terminal propargyl (alkyne) functionality offers a chemically distinct reactive site. The molecule features an amide-forming acyl ester, ether linkages, and a carbon–carbon triple bond.

Reactivity: The NHS ester reacts with primary amines to form amide bonds via nucleophilic acyl substitution, typically under mildly basic aqueous buffer conditions with controlled pH to preserve the ester. The propargyl group is suitable for copper-catalyzed azide–alkyne cycloaddition or related alkyne-based coupling strategies, using standard click chemistry reagents and appropriate solvent systems. Reaction order and stoichiometry are commonly optimized to minimize hydrolysis of the NHS ester.