Mal-PEG6-COOtBu
CAS No.: 518044-37-6
Cat No.: BP-501217
Purity: ≥95%
4.5 
Mal-PEG6-COOtBu is a maleimide-terminated polyethylene glycol linker bearing a protected carboxylic acid (t-butyl ester) at the distal end. Structurally, it provides a flexible, hydrophilic PEG chain of moderate length that spaces reactive groups and reduces steric interference, while the maleimide moiety enables selective conjugation to thiols via a stable thioether linkage under mild aqueous conditions. In PROTAC design and related targeted degradation constructs, this linker can be used to connect a thiol-bearing ligand (e.g., a cysteine-derivatized binding moiety or a thiol-releasing handle) to a second component after functionalization of the terminal carboxyl group for subsequent coupling or activation. Its value lies in improving solubility and tuning linker length to optimize ternary complex formation, thereby supporting systematic evaluation of how conjugation geometry influences target engagement and degradation efficiency in experimental workflows.
Structure of 518044-37-6
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Mal-PEG6-COOtBu is a maleimide-terminated, PEG-based PROTAC linker designed to enable efficient conjugation to thiol-bearing ligands and to support robust, water-compatible linker architectures in targeted protein degradation workflows. Its flexible polyethylene glycol segment can improve solubility and presentation of binding motifs, while the protected carboxylate functionality provides a handle for subsequent coupling strategies. The following points describe its structure and practical reactivity features in detail.
Structure: The linker contains a maleimide electrophile for selective thio-Michael addition, paired with a polyethylene glycol spacer that imparts conformational flexibility and hydrophilicity. A tert-butyl ester-protected carboxylate provides a masked acidic group, enabling controlled deprotection and downstream functionalization.
Reactivity: Maleimide groups typically react with cysteine or other thiol-containing building blocks via a thio-Michael addition under mildly basic, aqueous-compatible conditions, often using buffering systems that preserve thiol nucleophilicity. The PEG segment generally supports homogeneous conjugation in solution. The tert-butyl ester can be unmasked using acid-mediated deprotection to regenerate a carboxylate for coupling reactions, commonly enabling amide or related bond formation with activated carboxyl derivatives.
* 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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