Anthocyanidins modifications

Modifications of the Heterocycle (Fig, 770). In the next step the open chain structure is closed to form ring A. We obtain the kind of substance which we recognize, namely, a chalcone. Isotope experiments, especially those of Grisebach, have removed all doubt that such chalcones are the parent substances of all flavan derivatives. The chalcones are converted to flavones and all of the subsequent reaction sequences up to the anthocyanidins consist only of appropriate modifications of the central ring system. We should realize that the elucidation of the biosynthesis of the anthocyanins implies at the same time an understanding of the biosynthesis of all flavan derivatives. This is because the individual flavan derivatives are either precursors of the anthocyanins or they can be derived from such precursors. 

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