Mal-PEG4-t-butyl ester
CAS No.: 518044-36-5
Cat No.: BP-501386
Purity: ≥95%
4.5 
Mal-PEG4-t-butyl ester is a maleimide-terminated polyethylene glycol linker bearing a protected carboxylic acid as a tert-butyl ester, providing a versatile bifunctional scaffold for PROTAC and related targeted degradation constructs. The maleimide group enables efficient, chemoselective conjugation to thiol-containing ligands (e.g., cysteine residues or thiol-functionalized targeting moieties) via a stable thioether linkage, while the PEG4 segment provides aqueous solubility and conformational spacing to reduce steric interference between the binding and recruitment components. Upon deprotection of the tert-butyl ester under appropriate conditions, the resulting carboxylate can be used for further coupling or for installing additional handles required for assembling multicomponent degraders. In targeted protein degradation research, such linkers help tune effective distance and orientation between ligands, improving the probability of productive ternary complex formation and thereby supporting systematic optimization of PROTAC performance.
Structure of 518044-36-5
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Mal-PEG4-t-butyl ester is a PEG-based PROTAC linker building block designed to support efficient conjugation chemistry while providing beneficial solubility and conformational flexibility for targeted protein degradation workflows. Its maleimide functionality enables selective coupling to thiol-bearing ligands, and the protected carboxylate supports controlled downstream derivatization. Researchers use this linker to assemble bifunctional degraders that bring an E3 ligase binder into proximity with a target protein, with subsequent sections describing its structure and reactivity in detail below.
Structure: The molecule combines a maleimide electrophile with a polyethylene glycol spacer and a tert-butyl ester-protected carboxylate. It contains conjugated unsaturated imide functionality, ether linkages within the PEG chain, and ester carbonyl connectivity, contributing to enhanced aqueous compatibility and stable handling prior to deprotection.
Reactivity: The maleimide group undergoes thiol–Michael addition under mild aqueous or mixed solvent conditions, typically requiring a suitable pH to maintain thiol nucleophilicity while minimizing maleimide hydrolysis. The tert-butyl ester is designed for acid-mediated deprotection to reveal a carboxylate for subsequent amide or ester coupling. Common approaches use standard coupling reagents and inert atmosphere when appropriate to limit side reactions.
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Concentration (start) x Volume (start) = Concentration (final) x Volume (final)
It is commonly abbreviated as: C1V1 = C2V2
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