Benzyl-PEG2-CH2COOH

This PEG-based PROTAC linker, Benzyl-PEG2-CH2COOH, provides a flexible hydrophilic spacer terminating in a carboxylic acid handle for controlled conjugation to ligands. Its ether-rich chain supports favorable solubility and spatial presentation of reactive groups, which can improve productive ternary complex formation in targeted protein degradation workflows. The points below describe its structure and practical reactivity considerations for PROTAC assembly.

Structure: The linker contains a benzyl group connected to a short poly(ethylene glycol) segment through ether linkages, followed by a methylene spacer terminating in a carboxylic acid. It features flexible C–O and C–C bonds, an aliphatic acid functionality, and overall amphiphilic character that enhances aqueous compatibility.

Reactivity: The terminal carboxylic acid enables standard PROTAC coupling strategies such as amide bond formation with amine-bearing ligand fragments using peptide-coupling chemistries. Typical approaches rely on activating the acid (for example, via carbodiimide or uronium-type activators) in polar aprotic solvents with base to promote nucleophilic acyl substitution. Reaction conditions should minimize ester hydrolysis and preserve ligand integrity, and the acid can also be converted to activated esters for controlled conjugation.