Mal-amido-PEG4-propionic acid

Mal-amido-PEG4-propionic acid, is designed to provide a flexible hydrophilic PEG-based spacer terminating in a reactive carboxylic acid for controlled conjugation. Its amide linkage and polyethylene glycol segment support favorable solubility and spatial presentation of warhead and E3-ligand moieties, which can improve effective ternary complex formation. The following sections describe its structure and practical reactivity considerations for PROTAC assembly.

Structure: The linker contains a polyethylene glycol chain that confers conformational flexibility and hydrophilicity, connected through an amide to a maleimide-derived functionality and bearing a terminal carboxylic acid. It features stable covalent amide and ether linkages, with a maleimide-type electrophilic alkene suitable for selective coupling.

Reactivity: The terminal carboxylic acid can be activated for amide-bond formation with amine-bearing partners using standard coupling chemistries such as carbodiimide-based systems with an appropriate additive. The maleimide electrophile enables thiol–maleimide conjugation under mild, aqueous-compatible conditions, typically preserving maleimide reactivity while avoiding strong nucleophiles and conditions that promote hydrolysis. Reaction setup should be optimized for buffer pH and thiol availability to ensure chemoselective attachment.