Br-PEG1-COOtBu

This Br-PEG1-COOtBu linker is designed for modular PROTAC synthesis, providing a polyethylene glycol spacer that can tune solubility and enable efficient conjugation between a ligand and a reactive handle. The bromide-bearing terminus supports controlled functionalization, while the protected carboxylate enables subsequent coupling strategies. Its balanced polarity and chemical stability make it well-suited for constructing targeted protein degraders, with detailed structural and reactivity considerations provided below.

Structure: The linker combines a short PEG segment with a terminal bromide substituent and a tert-butyl-protected carboxylate. It contains ether linkages characteristic of PEG, an alkyl bromide for electrophilic substitution, and an ester-like tert-butyl carboxylate that can be deprotected under appropriate conditions.

Reactivity: The bromide terminus is compatible with nucleophilic substitution to install PROTAC-building fragments, typically using nucleophiles such as amines or organometallic reagents under standard coupling conditions. The tert-butyl carboxylate supports protected-carboxyl chemistry, enabling deprotection followed by carboxyl activation for amide or related bond formation. Common approaches use base-mediated deprotection and coupling reagents in polar aprotic solvents with inert atmosphere when required.