PHOTOCHEMISTRY OF PHOSPHATE-ESTERS - ALPHA-KETO PHOSPHATES AS A PHOTOPROTECTING GROUP FOR CAGED PHOSPHATE

Irradiation of two families of alpha-keto phosphates yielded rearrangement products and deprotected phosphates as the major products. For both sets of reactants, the triplet excited state of the ketone reacted with quantum efficiencies that ranged from 0.10 to 0.38. Desyl phosphates yielded 2-phenylbenzo[b]furan independent of the nature of the solvent whereas phosphate esters of alpha-hydroxy-p-methoxyacetophenone rearranged to esters of p-methoxyphenylacetic acid. In all cases, the phosphate group with the remaining ligands intact was released in nearly quantitative yield. The desyl group was further developed as a cage ligand for cAMP. Upon photolysis, the desyl caged ester of cAMP (13) quantitatively released the nucleotide with a quantum efficiency of 0.33 +/- 0.01 and a unimolecular rate constant of 7.1 X 10(8) s-1. Additional synthetic, product, and mechanistic studies are reported for the two series of alpha-keto phosphates.