Bis-PEG3-sulfonic acid

Bis-PEG3-sulfonic acid is a polyethylene glycol (PEG)-based, water-soluble PROTAC linker building block designed to support efficient spatial organization between a ligand and an E3-recruiting moiety. Its anionic sulfonate functionality and flexible PEG scaffold help tune solubility, reduce nonspecific aggregation, and maintain productive linker conformations in targeted protein degradation constructs. The detailed structural and reactivity considerations are provided below.

Structure: The linker contains a PEG-based flexible chain featuring ether linkages and terminal sulfonic acid groups. These strongly polar, ionizable sulfonates promote high hydrophilicity and ionic interactions, while the ether-rich backbone provides conformational flexibility. The molecule is typically handled as an acidic, water-compatible component.

Reactivity: Sulfonic acid groups are generally stable under standard coupling conditions but can be used to support salt formation and aqueous compatibility. For PROTAC assembly, this linker is commonly incorporated through complementary functional handles on partner ligands (for example, via established amide, sulfonamide, or ether-forming chemistries depending on the reactive groups present). Mild, aqueous or mixed-solvent conditions are often selected to preserve sensitive ligands and maintain solubility, with coupling reagents and bases chosen according to the specific partner functional group chemistry.