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    Author(s): Jan P. Steynberg; E. Vincent Brandt; Daneel Ferreira; Carin A. Helfer; Wayne L. Mattice; Dominika Gornik; Richard W. Hemingway
    Date: 1995
    Source: Magnetic Resonance in Chemistry 33:611-620
    Publication Series: Miscellaneous Publication
    PDF: View PDF  (2.2 MB)

    Description

    The profisetinidins are the most important polyflavanoids of commerce, making up the major constituents of wattle and quebracho tannins. Even within the dimeric profisetinidins, substantial complexity exists because of stereo-, regio-, rotational and conformational isomers. Definition of the stereochemistry of the upper and lower flavan units, the location of the interflavanoid bond, the conformation of the heterocyclic rings in the upper and lower flavan units and the conformations of major and minor rotational isomers in a series of methyl ether acetate derivatives of dimeric profisetinidin diastereomersis possible by application of COSY and NOE experiments. All compounds studied were present in two rotameric forms with the more compact conformation favored. The heterocyclic ring in the upper chain extender unit was predominantly in an E-conformation (i.e. half-chair in 2R,3S isomers and a 'reverse' half-chair in the 2S,3R isomers). The heterocyclic ring conformation of the terminal catechin unit, although mostly in an E-conformation, was often represented by significant proportions of A-conformers.

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    Citation

    Steynberg, Jan P.; Brandt, E. Vincent; Ferreira, Daneel; Helfer, Carin A.; Mattice, Wayne L.; Gornik, Dominika; Hemingway, Richard W. 1995. Conformational analysis of oligomeric flavanoids. Magnetic Resonance in Chemistry 33:611-620

    Keywords

    NMR, 1H NMR, condensed tannins, profisetinidins, stereochemistry, conformation, rotational isomers

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