HO-PEG5-CH2-COOH
CAS No.: 52026-48-9
Cat No.: BP-501430
Purity: ≥95%
4.5 
HO-PEG5-CH2-COOH is a heterobifunctional hydroxy-PEG-acid linker bearing a terminal hydroxyl group and a terminal carboxylic acid, providing a flexible hydrophilic chain of five ethylene glycol units and a methylene spacer to the acid. In PROTAC construction, this linker is used to spatially tune the relative positioning of the two binding elements by acting as a solvent-exposed “molecular spacer,” which can reduce steric clashes and help maintain productive geometry for ternary complex formation. The carboxyl group enables straightforward conjugation to amine-containing ligands or to activated intermediates (e.g., via amide-bond formation), while the hydroxyl terminus can be used for further functionalization depending on the synthetic route. Such PEG linkers are widely employed in targeted protein degradation research to improve solubility and to modulate linker length and flexibility, thereby supporting systematic optimization of degradation potency and selectivity.
Structure of 52026-48-9
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HO-PEG5-CH2-COOH is a polyethylene glycol (PEG) based PROTAC linker fragment designed to provide solubility, conformational flexibility, and a practical attachment handle for assembling targeted protein degradation constructs. Its ether-rich chain and terminal functional groups support robust conjugation strategies commonly used in PROTAC synthesis, enabling efficient formation of bifunctional molecules that can recruit an E3 ligase and engage a target protein. Detailed structural and reaction considerations are provided below.
Structure: HO-PEG5-CH2-COOH consists of a PEG ether backbone bearing a terminal hydroxyl and a terminal methylene-linked carboxylic acid. The molecule features repeating C–O ether bonds, a flexible polyether chain, and a carboxylate-capable functional group suitable for amide or ester formation.
Reactivity: The carboxylic acid end is typically activated for coupling to amines or alcohols to form amide or ester linkages used in PROTAC architectures. Common approaches include carbodiimide-mediated activation with an appropriate coupling additive, or acid-derivative activation under anhydrous conditions. Solvents such as polar aprotic media and controlled pH buffering are generally employed to maintain functional-group compatibility and minimize side reactions, while the PEG ether chain remains stable under standard coupling conditions.
* Our calculator is based on the following equation:
Concentration (start) x Volume (start) = Concentration (final) x Volume (final)
It is commonly abbreviated as: C1V1 = C2V2
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