Untersuchungen zum Mechanismus der Umwandlung von 4.2′.4′.6'-Tetrahydroxychalkon in Taxifolin in Chamaecyparis obtusa.

Abstract

For the formation of dihydroflavonols (3-hydroxyflavanones) from flavanones (chalcones) several pathways can be formulated: 1. Direct oxydation of a flavanone at C-3. 2. Formation via chalconeepoxide. 3. The pathway flavanone → flavone → flavonol → dihydroflavonol. 4. Addition of water to the 2.3-double bond of a flavone. For the purpose of eliminating either pathways 1 and 2 or pathways 3 and 4 as possibilities, an experiment was carried out in which a chalcone labelled in the β-position both with 14C and tritium was synthesized and administered to a plant producing a dihydroflavonol. In the case of pathways 1 and 2 the tritium should be retained in the dihydroflavonol whereas it would be lost in the case of pathways 3 and 4. which involve a flavone as an intermediate. 4.2′,4′.6′-Tetrahydroxychalcone-2′-glucoside-[β - 14C-β-T] (I) with a 14C/T ratio of 1 : 2.1 was fed to leaves of Chamaecyparis obtusa. The isolated Taxifolin-3-xyloside (II) had a 14C/T ratio of 1 : 2,3. When II was oxidized to quercetin-3-xyloside this ratio increased to 1 : 0,13 proving that the bulk of the tritium in II was located at the exspected position. These results exclude the pathways 3 and 4 and make it probable that 3-hydroxyflavanones arise by a stereospecific oxydation of flavanones at the 3-position.