Selective formation and conformational analysis of carbohydrate-derived radicals

Abstract

Carbohydrate free radicals are generated in non-aqueous solution by abstraction of bromine, iodine or selenophenyl with photolytically generated stannyl radicals from appropriately substituted pyranose derivatives and their e.s.r. spectra are recorded in the temperature range from –30 to 70 °C. From the hyperfine splitting parameters the preferred conformations of these sugar radicals are derived. The findings are compared with results from investigations in aqueous solution and an attempt is made to identify the factors which determine the conformations. From the α-¹³C coupling constant of the tetra-acetylglucosyl radical it is concluded that pyranosyl radicals are of the π-type. A novel 1,2-migration of an acetoxy group in tetra-acetylgalactosyl radical is reported. The mechanism of interaction of nitrosugars and related compounds with tin radicals is discussed.