m-PEG5-sulfonic acid

m-PEG5-sulfonic acid is a polyethylene glycol-based linker designed to support PROTAC assembly by providing aqueous compatibility, conformational flexibility, and a reliable handle for conjugation. Its sulfonic acid functionality enables strong, water-soluble behavior and can facilitate robust coupling strategies with suitable protein-binding ligands. These properties can help maintain productive ternary complex formation by reducing steric constraints and improving solubility during synthesis and biochemical evaluation. Detailed structural and reactivity considerations are provided below.

Structure: The linker comprises a short, linear PEG chain terminated by a meta-positioned sulfonic acid group. It contains repeating ether linkages that confer flexibility and hydrophilicity, and a sulfonic acid moiety that is strongly polar and typically present as an anion under neutral to basic conditions.

Reactivity: For PROTAC construction, this linker is commonly used in conjugation workflows that exploit sulfonate/sulfonic acid chemistry. Suitable approaches include activating the sulfonic acid for nucleophilic substitution or coupling to complementary electrophiles on partner ligands under mild, water-compatible conditions. Reaction design should account for the acid’s strong polarity, selecting appropriate bases and solvents to maintain solubility and suppress undesired side reactions.