N-(azide-PEG3)-N'-(Amine-C3-Amide-PEG4)-Cy5

This N-(azide-PEG3)-N'-(Amine-C3-Amide-PEG4)-Cy5 linker is designed to integrate a fluorescent Cy5 handle with orthogonal reactive groups for modular PROTAC construction. Its PEG-based architecture improves aqueous compatibility and linker flexibility, supporting efficient conjugation and subsequent targeted protein degradation workflows. The azide functionality enables bioorthogonal “click” coupling, while the amine-bearing segment facilitates controlled amide formation.

Structure: The molecule contains a Cy5 chromophore connected through PEG spacers, with an azide moiety and a terminal amine that is incorporated into a C3 amide-containing PEG segment. Ether-rich PEG chains provide flexibility, while amide and ether linkages confer chemical stability under typical coupling conditions.

Reactivity: The azide group is suited for copper-catalyzed azide–alkyne cycloaddition or strain-promoted azide–alkyne ligation, enabling attachment of complementary PROTAC fragments under mild, orthogonal conditions. The terminal amine supports amide-bond formation with activated carboxylic acids or activated esters, typically using standard coupling reagents and polar organic/aqueous solvent systems. Reaction design should prioritize compatibility of the Cy5 dye and orthogonality between functional groups.