Propargyl-PEG5-NHS ester

Propargyl-PEG5-NHS ester is a PEG-based bifunctional linker designed for assembling PROTACs through orthogonal conjugation chemistry. The NHS ester enables efficient acylation of primary amines, while the propargyl group provides a terminal alkyne handle for subsequent click-type ligations. This combination supports modular synthesis, improved solubility, and controlled spatial separation between targeting and E3-binding elements, facilitating systematic PROTAC optimization. The following points describe its structure and practical reactivity for PROTAC construction in detail below.

Structure: The linker contains a polyethylene glycol chain terminated by an NHS ester and a propargyl (terminal alkyne) moiety. It features an activated carboxylate for amide formation and a carbon–carbon triple bond suitable for bioorthogonal coupling. The PEG segment imparts hydrophilicity and conformational flexibility.

Reactivity: The NHS ester reacts with primary amines to form stable amide bonds under mild, aqueous-compatible conditions, typically using a base to promote nucleophilic acyl substitution while avoiding prolonged exposure to strong nucleophiles that can hydrolyze the activated ester. The terminal alkyne can be engaged in copper-catalyzed or strain-promoted azide–alkyne cycloaddition strategies, enabling stepwise PROTAC assembly. Common solvents include buffered aqueous media with compatible organic co-solvents, and reaction progress is monitored by standard analytical methods.