Radical reactions of carbohydrates. Part 2. An electron spin resonance study of the oxidation of D-glucose and related compounds with the hydroxyl radical

Abstract

E.s.r. spectra are described for a variety of radicals obtained from the reactions of α-D-glucose, β-D-glucose, and some related substrates with the hydroxyl radical (generated from the Ti^III–H₂O₂ reaction in a flow system). Evidence is presented that attack of ˙OH is largely unselective; for both glucose anomers, all six radicals which can be formed via C–H abstraction are identified. A study has also been made of the relative ease with which these αβ-dioxygen-substituted radicals undergo acid-catalysed fragmentation; this appears to be governed not only by the nature of the leaving group (OH^–, OR^–) but also by the geometry of the radical (in particular, an axial β-OH group is much more readily lost than an equatorial group). Potential routes for carbohydrate degradation via glycosidic cleavage of first-formed radicals have been identified.