The NMR-structures of six polyphenols, resveratrol (1), (-)-epicatechin (2), pelargonidin chloride (3), cyanidin chloride (4), cyanin chloride (5), and keracyanin chloride (6), were fully assigned. For the glycosylated polyphenols 5 and 6, the three-dimensional solution structure and long-range 1 H- 13C-coupling constants across the glycosidic bond were measured. Satisfactory fit to standard Karplus-equations was achieved for glycosides directly attached to the aromatic core in cyanin chloride. Molecular dynamics simulation data in vacuum at the AM1-level of theory were shown to approximate the NMR-solution data reasonably well. Selective HCl-catalyzed H/D-exchange was observed for aromatic protons H6 and H8 in flavonoid structures containing a 5,7-metadisubstituted chromelynium core with free OH-groups. The exchange took place readily in compounds 3, 4, and 6, whereas 1, 2, and 5 did not exchange.
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Franz, A. H.,
Structure assignment and H/D-exchange behavior of several glycosylated polyphenols.
ARKIVOC, 2014(5), 1–29.