Propargyl-PEG4-CH2-acid

Propargyl-PEG4-CH2-acid is a PEG-based linker designed for modular assembly of PROTACs, enabling efficient conjugation between a ligand and an E3-recruiting or target-binding element. Its flexible poly(ethylene glycol) segment supports favorable spatial presentation, while the terminal propargyl handle enables chemoselective coupling strategies. The carboxylic acid functionality provides a practical anchor for amide or ester formation, facilitating robust synthetic workflows. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a flexible PEG chain with ether linkages, terminating in a propargyl group and a carboxylic acid. The propargyl moiety provides an alkyne suitable for click-type transformations, while the acid enables formation of stable amide/ester derivatives. Overall, it is polar and conformationally adaptable.

Reactivity: The terminal alkyne supports copper-catalyzed azide–alkyne cycloaddition for rapid, high-yield conjugation to azide-functional partners, typically using Cu(I) sources and polar solvents under inert or controlled atmospheres. The carboxylic acid can be activated using standard coupling reagents to form amide bonds with amine-bearing ligands, or converted to activated ester intermediates. These reactions are commonly performed under mild conditions to preserve sensitive functional groups.