Propargyl-PEG2-COOtBu

Propargyl-PEG2-COOtBu is a polyethylene glycol-based PROTAC linker featuring a terminal alkyne for orthogonal conjugation and a protected carboxylate handle for controlled functional group unveiling. Its flexible PEG segment supports productive ternary-complex formation by improving solubility and reducing steric bias, while the propargyl functionality enables modular attachment to ligands under widely used click-compatible chemistries. The following points describe its structure and practical reactivity considerations for constructing targeted protein degraders.

Structure: The linker contains a PEG-derived polyether chain providing conformational flexibility and hydrophilicity, coupled to a propargyl (terminal alkyne) moiety and a tert-butyl-protected carboxylate. It includes ether linkages and carbon–carbon/ carbon–oxygen bonds, with functional groups designed for sequential, orthogonal derivatization.

Reactivity: For PROTAC assembly, the terminal alkyne is suited to copper-catalyzed azide–alkyne cycloaddition or related alkyne-compatible conjugations, typically using Cu(I) generated in situ, with appropriate ligands to control copper speciation. The tert-butyl ester can be deprotected under acid conditions to reveal a carboxylate for amide or ester coupling to targeting ligands. Solvent choice should support both deprotection and subsequent coupling without degrading sensitive moieties.