Reactivity of Anthocyanins and Pyranoanthocyanins. Studies on Aromatic Hydrogen–Deuterium Exchange Reactions in Methanol

Abstract

Reactivity studies involving anthocyanin structures and their equilibrium forms will lead to better understanding of the properties of these antioxidants. Hydrogen-deuterium (H --> D) exchange reactions at various sites of the 3-glucosides of delphinidin (1), petunidin (2), malvidin (3), and the corresponding 3-glucosides of carboxypyranodelphinidin (4), carboxypyranopetunidin (5), carboxypyranomalvidin (6), and the flavonol quercetin 3-O-(6-alpha-rhamnopyranosyl-beta-glucopyranoside)(7) have been examined at room temperature in pure CD 3OD and in CD 3OD acidified with CF 3CO 2D. The H --> D exchange rate constants of H-6 and H-8 of 2 determined from (1)H NMR integration data were found to be independent upon pigment concentration (up to 4 x 10 (-2) M) and trifluoroactic acid concentration (0-15%, v/v), respectively. This suggest that these reactions follow first-order kinetics and unexpectedly to be independent of the acid concentration. H-6 and H-8 of the flavylium cation A-rings of 1- 3, and in the corresponding hydrogens of the hemiketal forms, exchanged with half-lives of approximately 100 h ( 1) and approximately 50 h ( 2 and 3), respectively. The pyranoanthocyanins (4-6) experienced no H --> D exchange for the analogous hydrogens, but H --> D exchange of H-beta (H-4)(t 1/2 approximately 25 h) for these compounds was observed. Only H-8 underwent significant H --> D exchange in 7. It is concluded that a stabilization of the sigma-complexes, assumed to be the intermediates in the reactions, takes place for the common anthocyanins (1-3) contrary to the pyranoanthocyanins (4-6).

Probing the interaction of a quercetin bioconjugate with Bcl‐2 in living human cancer cells with in‐cell NMR spectroscopy

“…This suggestion was further supported by the absence of the STD signals of the Ha protons at 3.3 and 3.7 ppm. Finally, the decreased STD signal of proton H–8 of 3′ quercetin‐alanine is attributed to the hydrogen‐deuterium (H → D) exchange effect that has been previously reported .…”

Isomeric Effect on H/D Exchange of Resveratrol Studied by NMR Spectroscopy

“…The data fitting of the relative integrations of these proton resonances follows first-order kinetics as reported. 30 The exchange rate constants (k) deduced in Figure 2 show an obvious order of H-2,6＞ H-4 for each isomer. Besides, the exchange rates of trans-isomer are much larger than those of cis-isomer, which means the former undergoes faster H/D exchange.…”

“…Since the exchange reactivity is mainly determined by the first step, the carbon atom which is more negatively charged would be more susceptible for attack by the deuterium atom. 30,35 In addition, it was found that the negatively charged oxygen-substitute group on aromatic ring is expected to stabilize the σ-complex intermediate, 35 and consequently results in the increase of exchange reactivity. This In previous studies on H/D exchange of polyphenol, the site in the middle of two meta hydroxyl group seems to have priority of exchange.…”

“…24,25 Polyphenolic compounds, such as flavonoids, isoflavonoids, anthocyanidins, proantho-cyanidins and lignans, can undergo H/D exchange on ortho and para positions of phenolic hydroxyl group in acid or base solutions. [26][27][28][29][30] As far as we know, H/D exchange of resveratrol, one of important polyphenolic compounds and its derivatives, is less studied. 31 In this article, H/D exchange of trans-and cis-resveratrol and their 2-O-β-D-glucoside derivatives (Scheme 1) was studied using 1 H NMR spectroscopy.…”

Subtle Chemical Shifts Explain the NMR Fingerprints of Oligomeric Proanthocyanidins with High Dentin Biomodification Potency

“…13–15,31 Under acidic conditions (e.g., CF 3 COOD), H/D exchange reactions of phenolic hydrogens occur rapidly, over seconds to minutes, via keto–enol tautomerization or electrophilic-substitution reaction. 31–33 On the other hand, under neutral conditions, H/D exchange takes from several hours to days (S12, Supporting Information), 14,34 and recent evidence shows that amines (e.g., [hydroxy-]lysine in collagen) can facilitate deuteration under very mild conditions. 35 In the present study, the H/D exchange process of 1 dissolved in CD 3 OD could be followed over time in the 1D NMR spectra.…”