Cl-PEG4-acid

Cl-PEG4-acid is a polyethylene glycol-based PROTAC linker bearing a chloro substituent and a terminal carboxylic acid, designed to support efficient conjugation between targeting ligands and E3-recruiting modules. Its PEG character promotes aqueous solubility and conformational flexibility, which can help maintain productive ternary complex formation. The chloro handle enables controlled functionalization, while the acid group supports stable amide or ester coupling strategies. The following sections describe its structure and the practical reactivity considerations for PROTAC assembly in detail below.

Structure: The linker comprises a PEG chain terminated by a carboxylic acid and a chloro-functional site. It contains ether linkages within the PEG backbone, a terminal aliphatic acid functionality, and a carbon–chlorine bond suitable for substitution chemistry. The overall polarity supports water compatibility and flexible spacer behavior.

Reactivity: The carboxylic acid can be activated for amide-bond formation using standard coupling chemistries (for example, carbodiimide-based systems with additives) under mild base conditions. The chloro site is typically exploited for nucleophilic substitution or related functionalization after appropriate activation or under conditions that promote substitution. Common solvents include polar aprotic media, and reactions are generally performed to minimize hydrolysis and side reactions.