Isotopic labelling of quercetin 3-glucoside

The potentially important dietary antioxidant, quercetin 3-O-beta-D-glucoside, has been C-13-labelled at C-2 of the flavonoid unit by synthesis in 15% yield over five steps from [C-13] carbon dioxide. The route is appropriate for radiochemical synthesis. Formation of the protected 3-glucosylated flavonol appears to result from [1,7]-sigmatropic rearrangement with migration of a benzyl group followed by cyclisation. A free 5-OH results even when a phosphazene superbase is used. (c) 2006 Elsevier Ltd. All rights reserved.