Die Struktur des Neobetanidins. 5. (vorläufige) Mitteilung. Über die Konstitution des Randenfarbstoffes Betanin

Betanin, the violet‐red pigment of the beet, and its aglucone, betanidin, were converted by mild methods to several derivatives of a new structure, called neobetanidin. On the basis of elementary analyses, transformations, color changes with acid, mass‐spectrographic evidence and especially nmr‐spectra it was possible to assign structures II to X to these derivatives of neobetanidin. As examples of the nmr‐spectra in which all signals could be identified those of II and VIII are discussed in detail and compared with model compounds. It is evident that neobetanidin incorporates a dihydroindol‐and a pyridin‐ring, an enamin bond, three carboxyl functions, two phenolic hydroxyl groups and a weakly basic nitrogenous polymethine system of the cyanin type.