N-(Propargyl-PEG4)-biocytin

N-(Propargyl-PEG4)-biocytin is a PEG-based PROTAC linker building block that combines a biotin-derived recognition handle with a terminal alkyne for orthogonal conjugation. Its flexible ethylene glycol segments promote productive spatial presentation of attached ligands, while the propargyl group enables reliable “click” coupling to complementary azide partners. These features make it suitable for constructing modular, multicomponent targeted protein degradation systems, with the linker described in detail below.

Structure: The molecule contains a biotin-derived amide linkage coupled to a propargyl substituent and a poly(ethylene glycol) chain. It features an alkynyl functional group for bioorthogonal reactions, multiple ether linkages within the PEG segment, and stable amide and carbon–nitrogen bonds. The PEG backbone confers water compatibility and conformational flexibility.

Reactivity: The terminal alkyne is designed for copper-catalyzed azide–alkyne cycloaddition, enabling efficient conjugation to azide-functionalized PROTAC components under commonly used click chemistry conditions. Successful coupling typically relies on maintaining anhydrous-to-moderately hydrated conditions compatible with copper catalysis, using standard ligands to stabilize the active copper species and selecting solvents that dissolve both partners. The reaction proceeds via formation of a copper acetylide intermediate followed by cycloaddition to form a stable triazole linkage.