Photoreleasable protecting groups based on electron transfer chemistry. Donor sensitized release of phenacyl groups from alcohols, phosphates and diacids

The electron transfer mediated photochemical release of alcohols, phosphate s and diacids is examined. The alcohols can be protected as mixed phenacyl carbonate esters. Irradiation of mixtures containing electron donating sens itizers and phenacyl alkyl carbonate eater initiates a series of bond sciss ion reactions that result in clean release of the corresponding alcohols. T his was demonstrated for a variety of primary, secondary and tertiary hydro xyl groups, including the 5'-hydroxy group of thymidine. Sensitizers that w ere effective in promoting photolytic release include 9,10-dimethylanthrace ne and 9-methylcarbazole. GC/MS and NMR analysis of the by-products formed in these release reactions implicates the intermediacy of radical ion inter mediates in these reactions. It is further demonstrated that the electron t ransfer sensitized release method can be extended to phosphate esters and d i-functional acids. (C) 1999 Elsevier Science Ltd. All rights reserved.