Thiol-PEG4-t-butyl ester
CAS No.: 564476-33-1
Cat No.: BP-500652
Purity: >95%
4.5 
Thiol-PEG4-t-butyl ester is a heterobifunctional PEG-based linker designed for PROTAC and targeted protein degradation workflows, featuring a terminal thiol handle and a protected carboxylate ester that can be selectively deprotected or activated for subsequent conjugation. Structurally, it provides a short, flexible polyethylene glycol spacer (approximately four ethylene glycol units) that helps reduce steric interference between the ligand-binding moieties and the recruited E3 ligase or target-binding ligand. The thiol functionality enables chemoselective coupling strategies commonly used in PROTAC assembly, including maleimide or thiol-reactive chemistries, while the t-butyl ester offers protection during synthesis and can be converted to a reactive acid for amide or ester formation. In targeted degradation research, such linkers are valuable for tuning spatial arrangement, improving solubility, and optimizing degradation potency by facilitating productive ternary-complex formation while maintaining chemical stability during multistep synthesis.
Structure of 564476-33-1
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Thiol-PEG4-t-butyl ester is a bifunctional PEG linker containing a free thiol and an acid-labile tert-butyl-protected carboxyl group. The PEG spacer provides flexible separation between conjugated components, while the two distinct terminal functionalities support sequential derivatization in PROTAC and related conjugate synthesis. The following sections describe its structural features and relevant reactivity.
Structure: Thiol-PEG4-t-butyl ester consists of a PEG4-based chain bearing a free terminal thiol and a carboxylic acid protected as a tert-butyl ester. The ether-rich spacer contributes polarity and conformational flexibility. Importantly, the tert-butyl ester protects the carboxyl group rather than the thiol.
Reactivity: The free thiol can directly participate in chemoselective conjugation with maleimides, vinyl sulfones, haloalkyl groups, and other suitable thiol-reactive electrophiles. Separately, the tert-butyl ester can be removed under acidic conditions to reveal a carboxylic acid, which may then be activated for amide or ester formation with a complementary coupling partner. Oxygen-limited handling may be used when necessary to minimize oxidation of the thiol to disulfide species.
* 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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