Thiol-C9-PEG4-acid

Thiols are widely used in PROTAC linker chemistry to enable modular assembly of bifunctional degraders. Thiol-C9-PEG4-acid provides a PEG-based, carboxylic-acid–terminated tether bearing a reactive thiol handle, supporting conjugation strategies that preserve solubility and facilitate controlled attachment to targeting ligands. Its flexible, hydrophilic architecture is advantageous for maintaining productive ternary-complex formation in targeted protein degradation workflows. Detailed structural and reactivity considerations are provided below.

Structure: This linker combines a PEG-rich, flexible polyether segment with a terminal carboxylic acid and a thiol functionality. The scaffold contains ether linkages that enhance hydrophilicity and conformational freedom, while the thiol and acid groups provide chemically addressable sites for coupling. Overall, it is designed to behave as a stable, polar tether in aqueous PROTAC assembly.

Reactivity: The thiol group can participate in thiol–maleimide or thiol–activated ester coupling, enabling formation of thioether or related stable linkages under mild, typically aqueous or mixed-solvent conditions. The carboxylic acid can be converted to activated intermediates (for example, acid chlorides or coupling-agent–mediated esters/amides) to connect to amine-containing ligands. Careful pH control and thiol protection/handling are important to minimize oxidation and side reactions during synthesis.