Mal-PEG5-COOtBu
CAS No.: 2250216-91-0
Cat No.: BP-501069
Purity: ≥95%
4.5 
Mal-PEG5-COOtBu is a bifunctional polyethylene glycol (PEG) linker bearing a maleimide group and a protected carboxylate (tert-butyl ester). The PEG chain length provides aqueous solubility and conformational flexibility, while the maleimide electrophile enables selective conjugation to thiols through a stable thioether linkage, a widely used strategy for attaching PROTAC components or other targeting ligands under mild conditions. The tert-butyl ester functionality serves as a handle for subsequent deprotection and controlled introduction of a carboxylate-bearing attachment point, supporting modular assembly of degraders and facilitating optimization of linker polarity and geometry. In targeted protein degradation research, such PEG–maleimide linkers help tune the effective distance and orientation between the recruiting ligand and the E3 ligase-binding moiety, often improving conjugation efficiency and preserving bioactive conformations. This product is therefore valuable for constructing chemically defined PROTACs and for systematic linker optimization in degradation assays.
Structure of 2250216-91-0
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* For research and manufacturing use only. Not for human or clinical use.
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Mal-PEG5-COOtBu is a maleimide-terminated polyethylene glycol (PEG) linker designed for efficient conjugation in targeted protein degradation workflows, including PROTAC assembly. Its maleimide functionality enables selective coupling to thiol-bearing ligands, while the PEG spacer supports solubility and adaptable linker length to tune ternary complex formation. The subsequent points describe the linker’s structural features and practical reactivity considerations for experimental use.
Structure: The linker contains a maleimide electrophile for Michael-type addition, a PEG-based hydrophilic spacer, and a protected carboxyl group presented as a tert-butyl ester. It features conjugated carbon–carbon double bonds within the maleimide ring, ether linkages in the PEG chain, and ester carbonyl functionality.
Reactivity: Maleimide groups typically react with accessible thiols under mild aqueous or mixed aqueous conditions via nucleophilic addition to the activated double bond, forming a stable thioether adduct. For PROTAC construction, thiol-functionalized warheads or intermediate conjugates are commonly used as nucleophiles. Reaction performance depends on pH control, thiol availability, and avoidance of strong competing nucleophiles; inert atmosphere and gentle mixing can help preserve maleimide integrity. The tert-butyl ester is compatible with standard ester deprotection strategies when downstream carboxyl functionality is required.
* 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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