Bromo-PEG3-C2-phosphonic acid

Bromo-PEG3-C2-phosphonic acid is a functionalized PEG-based linker designed for modular assembly of PROTACs, enabling efficient conjugation between a ligand-bearing “warhead” and an E3-recruiting element. Its brominated handle supports controlled electrophilic substitution, while the phosphonic acid provides a strongly polar, metal-coordinating motif that can influence solubility and linker presentation. The subsequent points describe the linker’s structure and practical reactivity considerations for PROTAC synthesis.

Structure: The molecule combines a short PEG chain with a bromo-terminated electrophile and a C2 phosphonic acid functionality. It contains ether linkages within the PEG segment, a carbon–bromine bond for substitution, and a phosphonic acid group capable of forming hydrogen bonds and coordinating metal ions.

Reactivity: The bromo group is suitable for nucleophilic substitution with ligand-derived nucleophiles under standard alkylation conditions, typically using polar aprotic solvents and controlled base selection to promote SN-type reactivity while minimizing side reactions. The phosphonic acid can be handled as an acid or protected derivative during coupling, and its coordination behavior may be leveraged or mitigated by adjusting solvent polarity and base strength during PROTAC linker installation.