AcS-PEG4-t-butyl ester
CAS No.: 1818294-26-6
Cat No.: BP-501070
Purity: ≥95%
4.5 
AcS-PEG4-t-butyl ester is a PEG-based PROTAC linker featuring an acetylthio (AcS) terminus and a terminal tert-butyl ester that provides a protected carboxyl functionality. Structurally, it comprises a short polyethylene glycol chain that confers aqueous solubility and flexibility, while the AcS group is a thioacetate-protected thiol that can be deacetylated to release a free thiol for subsequent thiol-selective conjugation. In targeted protein degradation constructs, such linkers are selected to spatially separate a ligand-binding moiety from an E3-recruiting or effector element, thereby improving productive ternary complex formation and reducing steric mismatch. The PEG segment also helps maintain favorable conformational dynamics across linker length, which is critical for efficient ubiquitination. As a building-block reagent, AcS-PEG4-t-butyl ester is valuable for preparing degraders where orthogonally protected thiol and carboxylic acid functionalities are required for subsequent functionalization and final conjugate synthesis.
Structure of 1818294-26-6
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AcS-PEG4-t-butyl ester is a PEG-based PROTAC linker designed to provide a flexible, water-compatible spacer between targeting and recruiting ligands. Its S-acetyl-protected thiol and tert-butyl ester functionality enable controlled chemical coupling strategies commonly used in targeted protein degradation workflows, supporting synthesis of well-defined conjugates with improved solubility and conformational adaptability. The following sections describe the linker’s structure and the practical reactivity considerations for PROTAC assembly.
Structure: The linker comprises a poly(ethylene glycol) segment bearing an S-acetyl thioester at one end and a tert-butyl ester at the other. It contains ether linkages within the PEG chain, an S-acetyl thioester that serves as a protected thiol, and a tert-butyl ester protecting a carboxylic acid.
Reactivity: The tert-butyl ester can be removed by acid-promoted deprotection to reveal a carboxylic acid for amide-bond formation, while the S-acetyl thioester can be deacetylated to expose a free thiol for thiol-selective conjugation. Typical PROTAC linker installation relies on carboxyl activation chemistry (e.g., carbodiimide-mediated coupling) under anhydrous conditions with appropriate bases, followed by purification to remove coupling byproducts. Reaction design should account for PEG stability and solvent compatibility to maintain solubility of intermediates.
* 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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