AcS-PEG3-t-butyl ester
CAS No.: 1818294-27-7
Cat No.: BP-500611
Purity: ≥95%
4.5 
AcS-PEG3-t-butyl ester is a PEG-based PROTAC linker building block featuring an acetylthio (AcS) capping group, a short three-unit poly(ethylene glycol) spacer, and a terminal tert-butyl ester that can serve as a protected carboxyl functionality. Structurally, the PEG segment provides aqueous solubility and conformational flexibility, while the tert-butyl ester enables controlled derivatization or subsequent deprotection to reveal a reactive carboxyl handle for amide or ester coupling to targeting ligands or E3-recruiting moieties. In PROTAC design, this type of linker supports productive spatial positioning between the two binding partners, helping to maintain effective ternary complex formation by reducing steric constraints and improving hydrophilicity. The AcS and protected ester features are particularly useful for stepwise synthesis workflows, allowing researchers to assemble conjugates under mild conditions and then generate coupling-ready intermediates for targeted protein degradation studies.
Structure of 1818294-27-7
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AcS-PEG3-t-butyl ester is a bifunctional PEG linker containing an S-acetyl-protected thiol and an acid-labile tert-butyl-protected carboxyl group. The PEG3 spacer provides a flexible, polar connection between conjugated components, while the two protected termini support controlled, stepwise functionalization in PROTAC and related conjugate synthesis.
Structure: The linker comprises a PEG3-based chain bearing an S-acetyl group at one terminus and a carboxylic acid protected as a tert-butyl ester at the other. The S-acetyl group masks a thiol, helping limit premature thiol oxidation or side reactions during handling and intermediate synthesis. Ether linkages within the PEG segment contribute polarity and conformational flexibility.
Reactivity: Removal of the S-acetyl group under suitable thiol-deprotection conditions releases a free thiol for conjugation with maleimides, vinyl sulfones, haloalkyl groups, and other thiol-reactive electrophiles. Independently, acid-mediated cleavage of the tert-butyl ester exposes the corresponding carboxylic acid, which can be activated for amide or ester formation with a complementary coupling partner. Deprotection order and reaction conditions should be selected to preserve the second protected terminus and minimize oxidation of the liberated thiol.
* 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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