Mal-PEG6-PFP ester

Mal-PEG6-PFP ester, is designed to connect a targeting ligand to an E3-recruiting moiety through a hydrophilic polyethylene glycol spacer, improving solubility and conformational flexibility. The activated PFP ester enables efficient conjugation to primary amines under mild conditions, supporting modular PROTAC assembly workflows. The structure and reactivity characteristics are described in detail below to guide experimental design and coupling strategy.

Structure: The linker comprises a maleimide functional group coupled to a polyethylene glycol chain and terminated with a pentafluorophenyl (PFP) ester. It contains an activated carboxylate, ether-rich PEG segments, and electrophilic aromatic ester functionality, providing a balance of hydrophilicity, spacing, and controlled reactivity for bioconjugation.

Reactivity: The PFP ester is well suited for nucleophilic acyl substitution with primary amines, typically using buffered aqueous or mixed solvent systems that maintain amine nucleophilicity while limiting hydrolysis. Conjugation proceeds via formation of a tetrahedral intermediate followed by displacement of pentafluorophenol. No special catalysts are required; however, reaction temperature, pH, and water content should be optimized to minimize competing hydrolysis.