Carboxy-PEG4-sulfonic acid
CAS No.: 1817735-25-3
Cat No.: BP-500469
Purity: ≥95%
4.5 
Carboxy-PEG4-sulfonic acid is a heterobifunctional polyethylene glycol linker bearing a terminal carboxylic acid and a sulfonic acid group, providing a short PEG chain that imparts aqueous solubility, conformational flexibility, and reduced nonspecific hydrophobic interactions. The PEG4 segment acts as a hydrophilic spacer between PROTAC-relevant moieties, helping to improve effective reach and minimize steric hindrance at the junctions where ligands are conjugated. In targeted protein degradation designs, the carboxyl group can be used for amide or ester coupling to connect to one binding element (e.g., an E3 ligase ligand or a target-binding ligand), while the sulfonic acid functionality enables additional chemical handles or ionic stabilization depending on the synthetic strategy. This linker is particularly valuable for constructing soluble, well-behaved PROTACs and for tuning linker length and polarity to optimize ternary complex formation and cellular degradation performance.
Structure of 1817735-25-3
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Carboxy-PEG4-sulfonic acid is a polyethylene glycol-based linker designed to support efficient conjugation in targeted protein degradation workflows. Its hydrophilic PEG segment improves solubility and helps tune linker flexibility, while the dual functional handles enable robust attachment to ligands used in PROTAC architectures. The molecule is commonly applied in linker assembly strategies, where detailed structural and synthetic considerations below guide experimental design for reliable PROTAC construction.
Structure: The linker contains a PEG chain bearing a terminal carboxylic acid and a sulfonic acid group, providing strongly polar, ionizable functionality. It is composed of ether linkages within the PEG backbone and acidic groups capable of hydrogen bonding and salt formation under aqueous conditions.
Reactivity: The carboxylic acid can be activated for amide bond formation with primary or secondary amines using standard coupling chemistries, typically under mildly basic conditions. The sulfonic acid generally remains stable and can enhance aqueous compatibility. For PROTAC assembly, sequential functionalization of the carboxyl handle is commonly used to connect ligand fragments, while maintaining conditions that preserve amine reactivity and avoid side reactions such as hydrolysis during activation.
* 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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