Bromo-PEG5-phosphonic acid diethyl ester

Bromo-PEG5-phosphonic acid diethyl ester is a PEG-based, bromo-functional linker designed to support modular PROTAC assembly by enabling reliable attachment to ligand scaffolds and subsequent coupling strategies. Its ether-rich PEG segment imparts conformational flexibility and aqueous compatibility, while the phosphonate diethyl ester provides a protected handle that can be manipulated under controlled conditions. The bromo terminus supports electrophilic substitution or cross-coupling workflows, facilitating efficient construction of targeted protein degraders. Detailed structure and reactivity guidance are provided below.

Structure: This linker contains a brominated terminus connected to a polyethylene glycol chain, providing ether-rich flexibility. A phosphonate center bearing diethyl ester groups offers a protected, tetrahedral phosphorus motif. The molecule features C–Br, C–O, and P–O ester linkages, contributing to stability and controlled reactivity.

Reactivity: The bromo functionality is suitable for nucleophilic substitution or palladium-catalyzed cross-coupling approaches, depending on the partner nucleophile or coupling partner. The phosphonic acid diethyl ester can be retained during coupling steps and later converted to the corresponding phosphonic acid under standard deprotection conditions. Typical PROTAC linker synthesis uses inert or controlled atmospheres, polar aprotic solvents for coupling, and base/acid conditions selected to preserve ether integrity and avoid unwanted PEG cleavage.