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, phosphates and diacids is examined. The alcohols can be protected as mixed phenacyl carbonate esters. Irradiation of mixtures containing electron donating sensitizers and phenacyl alkyl carbonate ester initiates a series of bond scission reactions that result in clean release of the corresponding alcohols. This was demonstrated for a variety of primary, secondary and tertiary hydroxyl groups, including the 5'-hydroxy group of thymidine. Sensitizers that were effective in promoting photolytic release include 9,10-dimethylanthracene and 9-methylcarbazole. GC/MS and NMR analysis of the by-products formed in these release reactions implicates the intermediacy of radical ion intermediates in these reactions. It is further demonstrated that the electron transfer sensitized release method can be extended to phosphate esters and di-functional acids. (C) 1999 Elsevier Science Ltd. All rights reserved.