N-(m-PEG4)-N'-(m-PEG4)-O-(m-PEG4)-O'-(propargyl-PEG4)-Cy5

This PEG-based, Cy5-conjugated PROTAC linker is designed to provide a hydrophilic, conformationally flexible tether that supports efficient ternary-complex formation in targeted protein degradation workflows. Its multivalent PEG architecture can improve solubility and reduce nonspecific interactions, while the incorporated propargyl handle enables orthogonal conjugation to ligands or targeting modules. The following sections describe the linker’s structure and practical reactivity considerations in detail.

Structure: The linker contains multiple polyethylene glycol segments that are connected through ether linkages, yielding a highly flexible, water-compatible scaffold. A terminal propargyl-derived alkynyl functionality provides a reactive handle, while the Cy5 moiety contributes a fluorescent reporter for monitoring conjugation and biological workflows.

Reactivity: The propargyl functionality is suitable for copper-catalyzed azide–alkyne cycloaddition or related click-type conjugation strategies to assemble PROTACs with azide-bearing targeting ligands. Typical preparations use polar organic/aqueous solvent mixtures with appropriate copper catalysts and stabilizing ligands to control reaction rate and minimize side reactions. Copper-free SPAAC is not applicable to this unstrained propargyl group; CuAAC is the appropriate azide–alkyne route for this handle.