NHS-ASA

Figure 5.17 NHS-ASA reacts with amine-containing compounds to form stable amide linkages. Photoactivation with UV light results in ring expansion to a dehydroazepine intermediate, which can react with amines to form covalent bonds.

Finally, the small amine-reactive and photoreactive crosslinker, NHS-ASA (Chapter 5, Section 3.1), can be iodinated to provide a non-cleavable radioactive conjugate. 

Figure 171 NHS-ASA reacts with amine-containing compounds to form stable amide linkages. Photolyz-...

The absorption maximum of simple arylazides such as HSAB is about 265 to 275 nm, and the molar extinction coefficient is at 2 x 10 M" cm". The substitution of the aromatic ring with iodine (a nitro or a hydroxyl group) moves the absorption maximiun toward higher wavelengths (the absorption maximum of NHS-ASA is about 305 nm). 

B Label the cross-linker radioactively (radioactive cross-linkers are available in retail, e.g., H-HSAB or I-Denny-Jaffe reagent from NEN, or other, such as NHS-ASA or SASD, are easy to iodinate). Treat the radioactive cross-linker with an excess of nonradioactive ligand. Separate the radioactive PAL from unchanged ligand. 

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