Carboxy-PEG4-phosphonic acid
CAS No.: 1623791-69-4
Cat No.: BP-501504
Purity: ≥95%
4.5 
Carboxy-PEG4-phosphonic acid is a heterobifunctional PEG-based linker featuring a terminal carboxylic acid and a phosphonic acid group separated by a short, flexible polyethylene glycol chain. The PEG4 segment provides conformational flexibility and aqueous solubility, while the carboxylate and phosphonate functionalities enable orthogonal attachment strategies to PROTAC components. In targeted protein degradation constructs, such linkers are commonly used to connect or spatially tune the geometry between a ligand-bearing moiety (e.g., a warhead or binding element) and a second component that engages an E3 ligase, helping to maintain productive ternary complex formation. The phosphonic acid can participate in strong coordination or surface/chelator-compatible conjugation chemistries, and the carboxylic acid supports standard amide coupling for modular synthesis. This linker is valuable for researchers seeking reproducible, water-compatible conjugation and for optimizing linker length and polarity to improve degradation efficiency and experimental robustness.
Structure of 1623791-69-4
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Carboxy-PEG4-phosphonic acid is a versatile PROTAC linker component designed to integrate a PEG-based spacer with a phosphonic acid handle and a carboxyl functionality. Its hydrophilic, flexible architecture can help tune linker solubility and conformational freedom in targeted protein degradation constructs. The phosphonic acid and carboxyl groups provide practical chemical handles for conjugation strategies, enabling efficient assembly of degraders. The following sections describe its structure and reactivity considerations in detail.
Structure: The linker contains a poly(ethylene glycol) chain providing conformational flexibility and water compatibility, flanked by a carboxylic acid and a phosphonic acid group. These functionalities enable strong hydrogen-bonding and ionic interactions, while the carbon–oxygen and phosphorus–oxygen bond networks support stable, polar linkages under typical organic synthesis conditions.
Reactivity: The carboxyl group is suitable for amide or ester formation using standard coupling chemistries such as carbodiimide-based activation, optionally with additives that suppress side reactions. The phosphonic acid can participate in phosphorylation-type coupling or be used as a reactive anchor after appropriate activation. Linker assembly is commonly performed in polar aprotic or mixed solvent systems under conditions that preserve PEG integrity and avoid phosphonate degradation; mild bases and controlled pH are often used to maintain functional-group compatibility.
* 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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