SPDP-PEG9-acid
Cat No.: BP-502047
4.5 
SPDP-PEG9-acid is a heterobifunctional polyethylene glycol linker featuring a terminal carboxylic acid for conjugation or surface attachment and a protected thiol-reactive disulfide functionality (SPDP-derived) that enables formation of stable thioether bonds after thiol exchange. The PEG9 chain provides a flexible, hydrophilic spacer that helps reduce steric hindrance and improves the accessibility of the two functional ends, which is particularly valuable when linking bulky ligands in targeted protein degradation constructs. In PROTAC design workflows, this linker is used to connect an amine- or thiol-bearing recognition element (e.g., a ligand for a target protein or an E3 ligase binder) to the complementary partner, while maintaining sufficient conformational freedom to support productive ternary-complex formation. Its carboxyl handle also facilitates downstream coupling strategies and analytical derivatization, making it a practical tool for constructing and optimizing degraders and related conjugates in mechanistic and structure–function studies.
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* For research and manufacturing use only. Not for human or clinical use.
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SPDP-PEG9-acid is a PEG-based, heterobifunctional linker designed to support targeted protein degradation workflows by enabling efficient conjugation between a ligand-bearing targeting module and a thiol-reactive handle. Its PEG spacer provides conformational flexibility and improved aqueous compatibility, which can help preserve binding interactions during PROTAC assembly. The linker’s functional groups are well suited for stepwise coupling strategies; detailed structural and reactivity considerations are provided below.
Structure: SPDP-PEG9-acid contains a polyethylene glycol spacer terminating in a carboxylic acid and a thiol-reactive disulfide-containing group. The molecule features ether linkages within the PEG chain and a disulfide moiety for reversible conjugation, along with a terminal carboxyl group enabling amide or ester formation under standard coupling conditions.
Reactivity: The thiol-reactive disulfide functionality is commonly used to form stable thioether-linked conjugates via nucleophilic attack by a free thiol, proceeding through a disulfide exchange mechanism. PROTAC linker installation is typically performed under mild, aqueous-compatible conditions using appropriate buffers that maintain thiol availability while minimizing premature reduction. Carboxylic acid functionality can be leveraged for amide bond formation with amine-bearing partners using carbodiimide-based coupling reagents and suitable activators in compatible solvents.
* 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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