Condensed tannins: competing nucleophilic centres in biomimetic condensation reactions

Botha, Jacobus J.; Viviers, Phillip M.; Ferreira, Daneel; Roux, David G.

doi:10.1016/0031-9422(82)80127-1

Cited by 12 publications

(8 citation statements)

References 9 publications

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“…8). 9,10 The rates of exchange of these two protons of EGCg in the absence and presence ofˇ-CD were measured by monitoring the sum of the integration values of these two proton signals in 1 H NMR spectra. As shown in Fig.…”

Section: Also the Egcg Intramolecular Roes Between H3 And H2mentioning

confidence: 99%

Structure and intramolecular flexibility of β‐cyclodextrin complex with (−)‐epigallocatechin gallate in aqueous solvent

Ishizu

Hirata

Yamamoto

et al. 2006

Magnetic Reson in Chemistry

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The probable structure of the inclusion complex of beta-cyclodextrin (beta-CD) and (-)-epigallocatechin gallate (EGCg) in D2O was investigated using several NMR techniques. EGCg formed a 1:1 complex with beta-CD, in which the A ring and a portion of the C ring of EGCg were included at the head of the phenolic hydroxyl group attached to C7 of EGCg in the beta-CD cavity from the wide secondary hydroxyl group side. In the 1:1 complex with beta-CD, EGCg maintained the conformation in which the B and B' rings of EGCg took pseudoequatorial and pseudoaxial positions with respect to the C ring, respectively. The structure of the inclusion complexes of beta-CD and EGCg obtained from NMR experiments supported those determined from AM1 semiempirical SCF MO calculations well.

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Section: Also the Egcg Intramolecular Roes Between H3 And H2mentioning

confidence: 99%

Structure and intramolecular flexibility of β‐cyclodextrin complex with (−)‐epigallocatechin gallate in aqueous solvent

Ishizu

Hirata

Yamamoto

et al. 2006

Magnetic Reson in Chemistry

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“…The H 6 and H 8 protons in the A ring of catechins are easily exchanged with deuterium in D 2 O. [12,13] The rates of exchange of these two protons of ECg in the absence and presence of β-CD were measured by monitoring www.interscience.wiley.com/journal/mrc the sum of the integration values of these two proton signals in 1 H NMR spectra. As shown in Fig.…”

Section: Inclusion Complex Of Ecg With β-Cdmentioning

confidence: 99%

Diastereomeric difference of inclusion modes between (−)‐epicatechin gallate, (−)‐epigallocatechin gallate and (+)‐gallocatechin gallate, with β‐cyclodextrin in aqueous solvent

Ishizu

Kajitani

Tsutsumi

et al. 2008

Magnetic Reson in Chemistry

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Inclusion complexes of (-)-epicatechin gallate (ECg) as well as (+)-gallocatechin gallate (GCg) and beta-cyclodextrin (beta-CD) in an aqueous solution were investigated using several NMR techniques and a computational method. ECg and EGCg formed a 1:1 complex with beta-CD, in which the A ring and a portion of the C ring were included from the wide secondary hydroxyl group side of the beta-CD cavity, and the B and B' rings were left outside the cavity. GCg formed a 1:2 complex with beta-CD, in which the A and B rings of GCg were included by two molecules of beta-CD. The difference between the two modes of inclusion of the 1:1 complex of ECg, EGCg.beta-CD and the 1:2 complex of GCg.beta-CD might have resulted from the size of the space between the B and B' rings in aqueous solution. As a result of nuclear Overhauser effect (NOE) experiments, GCg was considered to have a large enough space between the B and B' rings to include the B ring in the beta-CD cavity; on the other hand, ECg and EGCg have no such large space.

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“…The term tannin, in wine, describes a range of polyphenolic compounds that includes flavan-3ol monomers and proanthocyanidins. Figure 1 shows a generalised proanthocyanidin polymer, comprised of a flavan-3-ol terminal subunit and extension subunits derived from flavan-3,4-diols connected by the interflavan bond (Geissman and Dittmar 1965, Botha et al 1982, Delcour et al 1983, Haslam 1998). These compounds have been reported in the seedcoats and skins of the grape berry (Fougère-Rifot et al 1993, Amrani-Joutei et al 1994, Thorngate and Singleton 1994 and their structures and composition in grapes and wines has been studied extensively.…”

Section: Introductionmentioning

confidence: 99%

Analysis of tannins in seeds and skins of Shiraz grapes throughout berry development

Downey

Harvey

Robinson

2003

Aust J Grape Wine Res

335

425

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The flavan‐3‐ol and proanthocyanidin composition of both seeds and skin of Vitis vinifera L. cv. Shiraz grapes was determined by reversed‐phase HPLC after acetone extraction and acid‐catalysis in the presence of excess phloroglucinol. Samples were taken at weekly intervals from fruit‐set until commercial harvest. The main period of proanthocyanidin accumulation in grape seeds occurred immediately after fruit‐set with maximum levels observed around veraison. Over two seasons there was variation in both the timing and content of proanthocyanidins in seeds. In skin, proanthocyanidin accumulation occurred from fruit set until 1–2 weeks after veraison. Proanthocyanidin subunit composition was different in seeds and skin and changed during berry development but the mean degree of polymerisation of the tannin polymers in skins was higher than in the seeds at all stages of berry development. Proanthocyanidin levels in both seeds and skin decreased between veraison and harvest. Additional proanthocyanidin subunits were released when the residues remaining after acetone extraction were subjected to direct acid‐catalysis in the presence of phloroglucinol. In the seeds, these accounted for much of the post‐veraison decrease, but not in grape skin. At harvest, 75% of extractable berry proanthocyanidin was in the seeds. Accumulation of proanthocyanidins in the seeds appears to be independent of that in the skins, but in both tissues synthesis occurs early in berry development and maximum levels are reached around veraison.

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Condensed tannins: competing nucleophilic centres in biomimetic condensation reactions

Cited by 12 publications

References 9 publications

Structure and intramolecular flexibility of β‐cyclodextrin complex with (−)‐epigallocatechin gallate in aqueous solvent

Structure and intramolecular flexibility of β‐cyclodextrin complex with (−)‐epigallocatechin gallate in aqueous solvent

Diastereomeric difference of inclusion modes between (−)‐epicatechin gallate, (−)‐epigallocatechin gallate and (+)‐gallocatechin gallate, with β‐cyclodextrin in aqueous solvent

Analysis of tannins in seeds and skins of Shiraz grapes throughout berry development

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