Bromo-PEG3-t-butyl ester

Bromo-PEG3-t-butyl ester is a PEG-based, bromo-functional linker designed for modular construction of PROTACs, enabling efficient conjugation between a ligand and an E3-recruiting module or target-binding moiety. Its polyethylene glycol segment provides conformational flexibility and improved solubility, while the bromo handle supports reliable electrophilic substitution strategies. The tert-butyl ester offers a protected carboxyl functionality that can be selectively unmasked when required. Detailed structural and reactivity considerations are provided below.

Structure: The linker comprises a polyethylene glycol chain bearing a terminal bromide and a tert-butyl ester group. It contains ether linkages within the PEG backbone, an alkyl bromide electrophile, and an ester carbonyl, providing a balance of polarity, flexibility, and chemical stability under standard organic conditions.

Reactivity: The bromo terminus is suitable for nucleophilic substitution reactions with appropriate nucleophiles (for example, amines or carboxylates) to form C–N or C–O bonds during PROTAC assembly. The tert-butyl ester can be used as a protected carboxyl equivalent and later converted to the free acid under established deprotection conditions. Typical coupling sequences employ polar aprotic solvents and base-mediated activation, while maintaining compatibility with sensitive ligands.