Sulfosuccinimidyl-(4-azidosalicylamido)hexanoate

This Sulfosuccinimidyl-(4-azidosalicylamido)hexanoate linker is designed for constructing PROTACs by coupling a reactive NHS ester to an azide-bearing salicylamide handle. Its bifunctional architecture supports modular synthesis, enabling efficient attachment of targeting ligands and subsequent conjugation steps under standard bioconjugation conditions. The sulfo-NHS functionality improves water compatibility and promotes controlled acylation, while the azide enables orthogonal click-type functionalization. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a sulfonated N-hydroxysuccinimide ester for amide bond formation, a hexanoate spacer providing conformational flexibility, and a salicylamide motif bearing an azide substituent. It features an activated ester, amide linkages, and an azide group suitable for bioorthogonal conjugation.

Reactivity: The NHS-activated ester reacts with primary amines to form stable amide bonds via nucleophilic acyl substitution. For PROTAC assembly, use mild aqueous or mixed aqueous buffers that preserve azide integrity and maintain NHS reactivity, typically at conditions commonly used for NHS ester bioconjugations. The azide handle can be engaged in copper-free or copper-mediated azide–alkyne cycloaddition depending on the downstream chemistry, with appropriate catalysts and solvent systems selected to minimize side reactions.