PHOTOCHEMICAL-REACTIONS OF AZIDOCOUMARINS

Photochemical reactions of 6-azidocoumarin and 7-azido-4-methylcoumari n in the presence of secondary amines have been investigated for their potential applications in photoaffinity labeling. It was found that t he singlet nitrene generated from 6-azidocoumarin isomerized to a dehy droazepine intermediate that reacted with an amine to yield two isomer ic adducts. Photolysis of 7-azido-4-methylcoumarin, in contrast, gave a tripler nitrene that abstracted hydrogen atoms from secondary amine molecules to form 7-amino-4-methylcoumarin as the major product. The d ifference in the intersystem crossing rate between the two compounds o riginates from the azido position relative to the carbonyl group. Beca use of its ability to form a covalent linkage with a nucleophile, 6-az idocoumarin is deemed to have a greater potential as a photoaffinity l abel than 7-azido-4-methylcoumarin.