NH-(mPEG4)2

NH-(mPEG4)2, is designed to provide a hydrophilic, sterically tunable spacer that can improve solubility and modulate the effective distance and presentation between a target-binding ligand and an E3 ligase recruiter. Its polyethylene glycol–based character supports aqueous compatibility and can help mitigate aggregation and nonspecific interactions in linker–conjugate assemblies. The detailed structural and reactivity considerations for constructing PROTACs using this linker are provided below.

Structure: The linker contains an amide-bearing connection to a bis-mPEG architecture, featuring repeating ethylene glycol units that confer strong hydrogen-bonding capacity and high polarity. Ether linkages within the PEG segments dominate the conformational flexibility, while the terminal amide functionality provides a defined attachment point for conjugation chemistry.

Reactivity: For PROTAC assembly, the linker is typically used as a functionalized PEG spacer that can be coupled to ligands via amide-forming or related condensation strategies, depending on the complementary reactive handle on the partner molecule. Common approaches rely on activating carboxylic acids (or amine equivalents) under mild base conditions in polar aprotic solvents, with coupling reagents such as carbodiimides or uronium-type activators to drive formation of stable amide bonds while preserving PEG integrity.