Propargyl-PEG4-Br

This Propargyl-PEG4-Br linker is designed to provide a PEG-based spacer terminating in a propargyl handle and a bromide leaving group, enabling modular assembly of targeted protein degradation (PROTAC) constructs. Its flexible ether-rich backbone can improve solubility and presentation of reactive termini, while the propargyl functionality supports orthogonal conjugation strategies. The bromide enables efficient linkage to nucleophilic partners, facilitating controlled synthesis of PROTACs and related bifunctional degraders. Detailed structural and reactivity considerations are provided below.

Structure: The molecule contains a poly(ethylene glycol) ether chain providing a flexible, hydrophilic spacer, capped by a propargyl group and a terminal bromide. It features an alkyne carbon-carbon triple bond, ether linkages, and a C–Br bond suitable for substitution chemistry, with overall polarity consistent with PEG-mediated solubility.

Reactivity: The bromide can undergo nucleophilic substitution with amines, thiols, or other nucleophiles under standard organic conditions, allowing attachment to PROTAC warheads or handles. The terminal alkyne enables bioorthogonal coupling approaches such as copper-catalyzed azide–alkyne cycloaddition or related alkyne conjugation methods. Reactions are typically performed in polar aprotic or mixed solvents, with base and inert atmosphere when appropriate to maintain functional group compatibility.