Hydroxy-PEG5-t-butyl ester

Hydroxy-PEG5-t-butyl ester is a PEG-based PROTAC linker designed to provide a hydrophilic, conformationally flexible spacer between ligand moieties while incorporating an acid-labile t-butyl ester handle for controlled functionalization. Its ether-rich backbone supports solubility and reduces nonspecific interactions, which is advantageous for targeted protein degradation workflows. The sections below describe the linker’s structure and the practical reactivity considerations relevant to PROTAC assembly.

Structure: The linker contains a hydroxy-terminated poly(ethylene glycol) segment connected through an ester linkage to a tert-butyl group. Its repeating ether units confer flexibility, while the ester introduces a chemically addressable functional group for downstream conjugation. Overall, it is an amphiphilic, water-compatible scaffold.

Reactivity: The tert-butyl ester can be selectively cleaved under mild acid conditions to generate a carboxylic acid suitable for amide coupling or other acyl-transfer reactions. PROTAC construction commonly uses standard carbodiimide or activated ester strategies to couple the resulting acid to amine-bearing ligands. The PEG ether backbone is typically compatible with aqueous/organic mixed solvents, and reaction design should minimize strong nucleophiles that could disrupt ester integrity prior to deprotection.