Cl-C6-PEG4-O-CH2COOH

Cl-C6-PEG4-O-CH2COOH, is designed to provide a flexible polyethylene glycol (PEG) spacer coupled to a functional handle for conjugation. Its ether-rich architecture supports solubility and conformational adaptability, which are advantageous for tuning ternary complex formation in targeted protein degradation workflows. The following sections describe the structure and the practical reactivity considerations for assembling PROTAC constructs using this linker.

Structure: The linker contains a PEG-based polyether chain terminating in an ether-linked chlorinated aromatic substituent and a terminal carboxymethyl group. It features ether linkages, an aliphatic methylene spacer, and a carboxylic acid functionality, with polarity that promotes aqueous compatibility and reduced aggregation.

Reactivity: The terminal carboxylic acid is suitable for standard PROTAC conjugation strategies that form amide or related acyl linkages with compatible nucleophiles on warheads or ligands. Typical approaches use carboxyl-activation chemistry under mild, anhydrous conditions, often employing coupling reagents and base in polar aprotic solvents; the mechanism proceeds via formation of an activated ester or acyl intermediate followed by nucleophilic substitution.