mPEG9-thiol

This mPEG9-thiol linker is designed to provide a polyethylene glycol–based handle for constructing PROTACs and related targeted degradation conjugates. Its PEG-rich scaffold enhances solubility and offers a convenient thiol functionality for controlled coupling strategies. The thiol group enables site-selective attachment to electrophilic partners, supporting modular PROTAC assembly and optimization. Detailed structural and reactivity considerations for practical synthesis and conjugation are provided below.

Structure: The linker comprises a methoxy-terminated PEG chain terminating in a thiol group. It contains ether linkages along the PEG backbone and a terminal sulfur functionality. Overall, it behaves as a flexible, hydrophilic polymeric linker with reduced steric constraints and favorable aqueous compatibility.

Reactivity: The terminal thiol can participate in nucleophilic coupling to activated electrophiles commonly used in PROTAC linker chemistry, including maleimide-containing or haloacetamide-type partners, typically via Michael addition or substitution mechanisms. Thiol reactivity is sensitive to oxidation; therefore, inert atmosphere handling and freshly prepared thiol solutions are often employed. Mild bases and polar aprotic solvents are frequently used to promote coupling while minimizing side reactions.