Bis-PEG4-acid

Bis-PEG4-acid, is designed to provide a flexible, hydrophilic spacer that supports efficient conjugation between targeting and recruiting ligands in targeted protein degradation constructs. Its PEG-based architecture helps reduce steric constraints and can improve solubility and maintain productive ternary complex formation. The following sections describe its structure-related features and practical considerations for linker incorporation into PROTAC assemblies.

Structure: Bis-PEG4-acid contains two PEG-derived chains terminated with carboxylic acid functionalities. The linker is characterized by repeating ether units, providing conformational flexibility, and by stable carbon–oxygen and carbon–carbon connectivity. The presence of carboxyl groups supports salt formation and amide or ester bond formation under standard coupling chemistries.

Reactivity: The carboxylic acid termini enable PROTAC synthesis via activation to form amide or ester linkages with amine- or alcohol-bearing ligands. Common approaches include carbodiimide-mediated coupling with additives to suppress side reactions, or activated ester strategies using suitable coupling reagents. Reactions are typically performed under anhydrous or low-water conditions in polar aprotic solvents, with base to promote nucleophilic attack and controlled pH to preserve ligand integrity.