Sulfo-SAPB

Figure 5.25 The reaction of sulfo-SAPB with an amine group is done first to form an amide bond derivative through its NHS ester end. Subsequent exposure to UV light causes the phenyl azide group to ring-expand to a highly reactive dehydroazepine, which can couple to nucleophiles, such as amines.

Sulfosuccinimidyl 4-(p-azidophenyl)butyrate (sulfo-SAPB) is a photoreactive heterobifunctional reagent containing an amine-reactive sulfo-NHS ester at one end (Pierce). 

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