N-(Boc-PEG3)-N-bis(PEG3-acid)

N-(Boc-PEG3)-N-bis(PEG3-acid), is designed to provide a hydrated, flexible spacer that can improve solubility and reduce steric bias between the target-binding ligands and the recruited E3 ligase moiety. Its poly(ethylene glycol)-based architecture supports efficient conjugation strategies commonly used in targeted protein degradation workflows. The following sections describe its structure and practical reactivity considerations for PROTAC assembly in detail.

Structure: The linker comprises a Boc-protected amine integrated with multiple PEG segments and terminal carboxylic acid functionalities. It contains ether linkages characteristic of PEG, an amide-bearing connection to the protected nitrogen, and carboxyl groups suitable for coupling. Overall, it is a hydrophilic, conformationally flexible scaffold.

Reactivity: The Boc group enables controlled amine deprotection under standard acid-mediated conditions to reveal a reactive amine for subsequent amide-forming coupling. The terminal PEG carboxylic acids are compatible with peptide-coupling chemistries (e.g., carbodiimide-based activation with coupling additives) to form stable amide bonds with ligand amines. Reactions are typically performed in polar aprotic solvents under conditions that minimize PEG degradation and preserve functional group integrity.