Mal-PEG5-PFP ester

Mal-PEG5-PFP ester is a bifunctional PEG-based linker designed for constructing PROTACs through efficient coupling between a primary amine–bearing ligand and a thiol- or amine-reactive partner. Its malemide handle enables reliable conjugation chemistry, while the PFP ester provides a complementary electrophile for rapid formation of stable amide linkages under mild conditions. These features make it well suited for assembling targeted protein degradation constructs with controlled linker length and improved solubility. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a PEG spacer that confers hydrophilicity and conformational flexibility, coupled to a maleimide moiety and a pentafluorophenyl (PFP) ester. It features an electrophilic maleimide double bond and an activated aromatic ester, enabling selective bioconjugation via nucleophilic addition and acyl substitution.

Reactivity: The PFP ester reacts with primary amines to form amide bonds via nucleophilic acyl substitution, typically using mildly basic aqueous buffers to preserve protein-ligand integrity. The maleimide undergoes conjugation through Michael-type addition with thiols, often in the presence of controlled pH and reduced nucleophile conditions to minimize side reactions. Common solvents include aqueous buffer systems with limited organic co-solvent when needed for solubility.