Fmoc-N-amido-PEG4-propionic acid

Fmoc-N-amido-PEG4-propionic acid, provides a polyethylene glycol–based spacer bearing an Fmoc-protected amide functionality and a carboxylic acid handle for conjugation. Its flexible, hydrophilic scaffold is well suited for constructing bifunctional degraders that require controlled spatial separation between ligand-binding modules, supporting efficient ternary complex formation. The following sections describe its structure and practical reactivity considerations in linker assembly for PROTAC synthesis.

Structure: The linker contains an Fmoc-protected amide connected to a PEG-based chain and terminates in a carboxylic acid. It features stable amide and ether linkages, with conformational flexibility typical of PEG spacers. The combination yields a hydrophilic, polar scaffold that enhances solubility and reduces nonspecific aggregation.

Reactivity: The carboxylic acid enables amide-bond formation with amine-bearing partners under standard peptide-coupling conditions, commonly using coupling reagents and base in polar aprotic solvents. The Fmoc group can be removed using mild base to reveal a reactive amine for subsequent coupling steps. Mechanistically, nucleophilic acyl substitution proceeds via an activated carboxylate intermediate; careful control of pH, stoichiometry, and protecting-group compatibility is recommended to maintain chemoselectivity during PROTAC assembly.