Six flavone C-glycosides were isolated from young leaves of barley. One of the C-glucosides has a new type of nucleus, a 2‘,4‘,5,5‘,7-penta-OH-substituted flavone bearing a 6-C-β-d-glucoside, which has apparently never been isolated before. One mono- and two di-C-glycosyl flavones were isolated for the first time from barley and identified as isoscoparin 7-O-β-d-glucoside, carlinoside, and shaftoside, respectively. Other flavones were 7-O-β-d-glucosides of isoorientin and isovitexin. The known problematic NMR structure elucidation of C-glycosyl flavonoids has been solved by using both a temperature close to the freezing point of the solvent (22.5 °C in DMSO-d6) and a high temperature (70, 90 °C) for comparison during NMR measurements. Structural determination of all the compounds was achieved by employing 1D and 2D NMR techniques.
NOE, barley; Hordeum vulgare; C-glycosyl flavone; phenolic hydroxyl group; NMR
NCBI PubMed ID: 10820082Publication DOI: 10.1021/jf9910640Journal NLM ID: 0374755Publisher: American Chemical Society
Correspondence: rikke.norbaek@agrsci.dk
Institutions: Danish Institute of Agricultural Sciences, Department of Fruit, Vegetable and Food Science, Aarslev, Denmark, Chemical Instrument Center, Nagoya University, Nagoya, Japan
Methods: 13C NMR, 1H NMR, TLC, ESI-MS, HPLC, extraction, derivatization, evaporation, HR-EI-MS
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