Structure assignment and H/D-exchange behavior of several glycosylated polyphenols

Abstract

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-13 C-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.

NMR solution structures and MD-simulation of procyanidin B1, B2, and C1

“…These constitute precision of measurement and not necessarily accuracy. Unlike observed by us earlier for the chromenylium core of anthocyanins, 33 no deuterium exchange was observed for H6 and H8 in the chroman system even after several months.…”

Enzymatic pre-treatment of grape seeds for an oil with higher antioxidant activity

“…Other specific peaks are covered by the concentrated commercial enzyme signal (see Figure 4a) and the signal of the citric acid (2.5-2.8 ppm) from the buffer. Small peaks at 6.6-7.5 ppm evidenced the presence of aromatic compounds which were most likely traces of polyphenols (PPs) (Franz et al, 2014). There was no peak at 5.29 ppm in the residue spectrum (Figure 4b), signal characteristic for -CH=CH-of fatty acid (Chambre et al, 2019) as one may see in Figure 5, proving that no oil was lost during pre-treatment.…”