Tos-PEG2-COOtBu
CAS No.: 1309666-78-1
Cat No.: BP-501477
Purity: ≥95%
4.5 
Tos-PEG2-COOtBu is a heterobifunctional polyethylene glycol linker bearing a tosyl (tosylate) leaving group for efficient nucleophilic substitution and a protected carboxylate terminus (tert-butyl ester) that can be selectively deprotected to reveal a reactive acid for subsequent amide coupling. Structurally, it comprises a short PEG chain of two ethylene glycol units that provides aqueous solubility, conformational flexibility, and a defined spacer between the two functional ends, while the tosyl group enables attachment to nucleophiles such as amines or thiols under standard linker-conjugation conditions. In PROTAC and targeted protein degradation workflows, such PEG-based linkers are used to connect ligands (e.g., an E3-recruiting moiety and a target-binding ligand) while minimizing steric clashes and tuning effective intramolecular geometry to promote formation of the ternary complex. This linker is valuable for constructing modular degradation agents, enabling systematic variation of linker length and attachment chemistry to optimize degradation potency and selectivity in experimental studies.
Structure of 1309666-78-1
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Tos-PEG2-COOtBu is a PEG-based PROTAC linker building block designed to provide a flexible, hydrophilic spacer that can connect a ligand to a reactive functional handle for subsequent conjugation. Its polyethylene glycol character supports improved solubility and conformational adaptability in targeted protein degradation constructs, helping maintain productive geometry for ternary complex formation. The structure and reactivity considerations for assembling PROTACs using this linker are described in detail below.
Structure: The linker comprises a PEG segment terminating in a carboxylate protected as a tert-butyl ester, paired with a tosyl-type leaving group. It contains ether linkages characteristic of PEG, an ester carbonyl, and an aromatic sulfonyl aryl group, providing a balance of polarity, stability, and controlled reactivity.
Reactivity: Tosyl-activated handles are commonly used for nucleophilic substitution or for enabling ligand installation under standard organic synthesis conditions. The tert-butyl ester can be selectively deprotected using acid-mediated conditions to reveal a carboxylic acid for amide or ester coupling, typically employing coupling reagents and bases in compatible solvents. Mechanistically, substitution proceeds via displacement at the activated site, while ester deprotection follows acid-catalyzed cleavage to generate the free acid for downstream PROTAC assembly.
* 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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