Tos-PEG5-CH2COOtBu

Tos-PEG5-CH2COOtBu is a polyethylene glycol-based PROTAC linker building block designed to provide aqueous compatibility, flexible spacing, and efficient conjugation handles for targeted protein degradation constructs. Its PEG segment supports favorable solubility and conformational adaptability, while the protected carboxylate enables controlled functional-group transformations during linker assembly. The molecule is well suited for constructing bifunctional degraders by connecting an E3 ligase ligand to a target-binding moiety through robust, experimentally tractable synthetic steps.

Structure: The linker combines a tosyl-protected PEG chain with a terminal methylene carboxylate bearing a tert-butyl ester. It contains ether linkages characteristic of PEG, aromatic tosyl functionality, and an ester carbonyl, providing a polar, flexible scaffold with a protected carboxyl group for downstream coupling.

Reactivity: The tosyl group can serve as an activated leaving group for substitution reactions to install nucleophiles at the PEG terminus, enabling attachment of PROTAC fragments. The tert-butyl ester is compatible with ester-stabilized handling and can be deprotected under standard acid conditions to reveal a carboxylic acid for amide or related coupling. Typical PROTAC assembly employs nucleophilic substitution and carboxyl-activation/coupling strategies using common bases, coupling reagents, and polar organic solvents.