Multifunctional cross-linking reagents. I. Synthesis and properties of novel photoactivable, thiol-directed fluorescent reagents.

Bifunctional photo-activable fluorescent thiol reagents of a new type were synthesized. A maleimide group was bonded to an azidocoumarin group via a methylene chain as a spacer. Reagents of this type react first with a cysteine residue of a protein through the maleimide group, and then form another bond with an amino acid side chain of the protein upon irradiation with light, through a nitrene group formed from the azide. Although the reagent is non-fluorescent, the products are highly fluorescent. The fluorescence characteristics of model compounds of these reagents are also described.