Tos-PEG2-O-CH2COOH

Tos-PEG2-O-CH2COOH, is designed to provide a flexible polyethylene glycol (PEG) spacer that can improve solubility and help tune the spatial relationship between a targeting ligand and an E3 ligase recruiter. Its terminal carboxylic acid enables robust conjugation strategies commonly used in targeted protein degradation workflows. The flexible ether-rich backbone and functional group compatibility make it well suited for constructing degraders, where controlled linker length and reactivity are critical.

Structure: The linker contains a PEG-based ether chain (polyethylene glycol) capped with a tosyl-protecting group and terminated by a carboxylic acid. It features ether linkages, aromatic sulfonyl functionality, and a primary carboxymethyl moiety, yielding a polar, hydrogen-bonding capable scaffold.

Reactivity: The terminal carboxylic acid can be activated for amide or ester formation under standard coupling conditions used for PROTAC synthesis. Typical approaches rely on carboxyl activation with coupling reagents and base in compatible organic solvents, followed by nucleophilic acyl substitution with amine-containing ligands. The tosyl group can serve as a leaving group or protecting/activation handle depending on the synthetic sequence, enabling controlled stepwise assembly.