Tos-PEG3-O-CH2COOH

Tos-PEG3-O-CH2COOH is a PEG-based PROTAC linker component designed to provide conformational flexibility and a chemically addressable terminal carboxyl group for controlled conjugation. Its ether-rich backbone helps tune linker length, solubility, and linker–ligand presentation, which are key determinants of ternary complex formation and targeted protein degradation performance. The detailed structural and synthetic considerations for PROTAC construction are provided below.

Structure: This linker contains a PEG chain featuring repeating ether linkages, terminated by an O-CH2 substituent bearing a carboxylic acid. A tosyl (Ts) group provides a sulfonate functionality that can serve as a leaving group or protective handle depending on synthetic context. The molecule is polar and hydrogen-bonding.

Reactivity: The terminal carboxylic acid enables standard PROTAC conjugation routes such as amide bond formation via activated carboxyl intermediates. Typical strategies include coupling with amines using carbodiimide-based activation or acid-activated ester formation, often under mild base in polar aprotic solvents. The tosyl-associated functionality can be leveraged in substitution or deprotection workflows to install the linker onto targeting ligands while preserving PEG integrity.