Photolabeling of human serum albumin by 4-azido-2-([14C]-methylamino) trifluorobenzonitrile. A high-efficiency, long wavelength photolabel

Fluoro Aryl Azides: Synthesis, Reactions and Applications

Background:

The complex photochemistry of aryl azides has fascinated scientists for several decades. Spectroscopists have investigated the intermediates formed by different analytical techniques. Theoretical chemists have explained the intrinsic interplay of intermediates under different experimental conditions.

Objective & Method:

A complete understanding of the photochemistry of a given fluoro aryl azide is a basic requisite for its use in chemistry. In this review, we will discuss the synthesis of several fluoro substituted aryl azides and the reactions and intermediates generated upon photolysis and thermolysis of these azides and some examples of their applications in photoaffinity labeling and organic synthesis.

Conclusion:

In spite of the extensive research on the photochemistry of fluoro aryl azides, there are some areas that remain to be investigated. The application of this reaction in the synthesis of novel heterocyclic compounds has not been fully studied. Since fluorophenyl azides are known to undergo C-H and N-H insertion reactions, they could be used to prepare new fluorinated molecules or in the biochemical process known as photoaffinity labeling.

Chemistry of bifunctional photoprobes. 6. Synthesis and characterization of high specific activity metalated photochemical probes: development of novel rhenium photoconjugates of human serum albumin and fab fragments

Functionalization of perfluoro aryl azides by bifunctional chelating agents (BFCAs) capable of forming high specific activity complexes with (99m)Tc (for gamma-imaging) and (188)Re (for radiotherapy) is described. The synthesis of multidonor BFCAs containing N(2)S(2), N(4), and N(3)S donor groups containing imidazole, pyridine, and pyrazine functionalities that may be important for tuning the pharmacokinetic parameters is also described. Functionalization of perfluoro aryl azides at various sites on BFCAs yields novel bifunctional photolabile chelating agents (BFPCAs) that are useful for covalent attachment to biomolecules. A representative Re-BFPCA 8a in a model solvent, diethylamine, proceeded to give a high yield of intermolecular NH insertion product without the decomplexation of the metal ion from 8a. All products originated from the photolysis of 8a in diethylamine are characterized by analytical techniques, and a plausible mechanism of formation of different photolytic products is suggested. The high yield of intermolecular NH insertion of Re-BFPCA 8a is extended to labeling of human serum albumin (HSA) and Fab fragments under aqueous conditions. The photolabeling technology developed here offers a new way to attach diagnostically and therapeutically useful radiotracers (e.g., (99m)Tc, (188)Re) to Fab fragments for potential noninvasive imaging and therapy of cancer.

Preservation of immunoreactivity in the photolabeling of the B72.3 human antibody

A versatile photochemical method of labeling human antibodies is described. Labeling is achieved by photolyzing 4-azido-2,3,5,6-tetrafluoro-14C-methylbenzoate and the B72.3 human antibody in a buffer at physiological pH. The photochemically produced nitrene presumably inserts into bonds in the hydrophobic part of the antibody resulting in > 75% attachment of the photoprobe. An immunoassay of B72.3 with mucin (B72.3 antigen) reveals > 97% retention of immunoreactivity and suggests that photochemical labeling is a viable alternative for the conjugation of biomolecules.