Zur Biogenese der Flavonoide X: Über den Zeitpunkt der Hydroxylierung im Ring B

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Abstract
The question of whether the oxygenation pattern of the B-ring of flavonoids is determined at the cinnamic acid stage or at the stage of a C15-intermediate remains to be solved. 3.4.2′.4′.6′Penta-hydroxychalcone-2′-glucoside-[β-14C] (I) was synthesized and the incorporation of I and of 4.2′.4′.6′ Tetra-hydroxychalcone-2′ glucoside-[β14C] (II) into quercetin and cyanidin in buckwheat seedlings was compared in parallel experiments. The percentage incorporation of II into quercetin was about 35 per cent higher than that of I, whereas the incorporation rates and dilution values of both chalcones into cyanidin were about equal. These findings are discussed in the light of earlier results. It is concluded that in the case of asters, buckwheat and red cabbage the 3′-hydroxyl group in ring B is in all probability not introduced until after the formation of a chalcone intermediate. These results are compared with those obtained by other workers with different plants.