Identification of triterpene saponins in Quercus robur L. and Q. petraea Liebl. Heartwood by LC-ESI/MS and NMR.

A detailed structural study of the major acidic triterpene saponins from European oak heartwood, Quercus robur L. and Q. petraea Liebl., revealed the presence of 2 alpha,3 beta,19 alpha-trihydroxyolean-12-ene-24,28-dioic acid (1), 2 alpha,3 beta,19 alpha-23-tetrahydroxyolean-12-ene-24,28-dioic acid (2), and their corresponding glycosides, 28-beta-D-glucopyranosyl-2 alpha,3 beta,19 alpha-trihydroxyolean-12-ene-24,28-dioic acid (3), and 28-beta-D-glucopyranosyl-2 alpha,3 beta,19 alpha,23-tetrahydroxyolean-12-ene-24,28-dioic acid (4). Compounds were isolated and purified by successive flash chromatography and semi-preparative HPLC, and structurally determined by NMR and LC-ESI/MS in the negative ion mode. Compounds 2 and 4 have been identified for the first time in Quercus species and are new compounds.

Rapid fractionation of grape seed proanthocyanidins.

A rapid method that permits separation of grape seed proanthocyanidins according to their polymerization degrees has been developed. This method was based on liquid/liquid extraction and relative solubility of these compounds in different solvents (water, ethyle acetate, methanol, and chloroform). The different fractions obtained were then analyzed by various HPLC techniques (normal phase, reversed phase after thiolysis, and gel permeation) to determine their mean degree of polymerization (DP) and molecular weight profiles. Results show that this method can be used on a preparative scale to separate these polymers according to their sizes.

Incidence of Molecular Structure in Oxidation of Grape Seed Procyanidins.

The kinetics of decomposition of the following flavan-3-ol derivatives isolated from grape seeds under oxidative conditions by airing and using metal ion catalysis (iron and copper) are determined: (+)-catechin and (-)-epicatechin; seven natural procyanidin dimers, B1 [(-)-epicatechin-(4-->8)-(+)-catechin], B2 [(-)-epicatechin-(4-->8)-(-)-epicatechin], B3 [(+)-catechin-(4-->8)-(+)-catechin], B4 [(+)-catechin-(4-->8)-(-)-epicatechin], B6 [(+)-catechin-(4-->6)-(+)-catechin], B7 [(-)-epicatechin-(4-->6)-(+)-catechin], and B8 [(-)-epicatechin-(4-->6)-(-)-epicatechin]; trimers, C1 [(-)-epicatechin-(4-->8)-(-)-epicatechin-(4-->8)-(-)-epicatechin], (+)-catechin-(4-->8)-(+)-catechin-(4-->8)-(-)-epicatechin, and (+)-catechin-(4-->8)-(-)-epicatechin-(4-->6)-(+)-catechin, monogallate esters of B2 and B4 and digallate of B2, which were isolated from grape seeds. Kinetic decomposition comparisons were monitored by HPLC. The following order was found for oxidative decomposition for procyanidin dimers: B3 approximately B4 > B7 approximately B6 > B1 approximately B2 > B8. In the conditions of this study, the gallate ester of (-)-epicatechin is more unstable than (-)-epicatechin; inversely, kinetic decompositions of dimeric procyanidins B2 and B4 are much more important than those of their gallate esters. Molecular mechanics (MM2) and (1)H NMR studies of dimeric 3-O-gallate structures show a pi-pi stacking arrangement between the aromatic gallate and catechol rings, absent in analogous dimeric procyanidins, which reduces the total surface accessible to oxidizing agents.

[Evolution of phenolic compounds during wine aging]. / Evolution des composés phénoliques au cours du vieillissement du vin.

The phenolic compounds of red wine are separated and isolated by a method involving two precipitations (by EtOH and by MeOH-CHCl2), adsorption of the precipitates and supernatants on to p.v.p., and selective desorption of different fractions by mydroalcoholic and acidic solvents. The method permits the definition of wine composition by groups of phenolic compounds which are identified and quantified, and whose molecular mass is determined. Tanins exist in wine in different forms: combinations with salts (T-S) and with polysaccharides (T-P), highly condensed tanins (TtC), condensed tanins (TC), tanin-anthocyanin complexes (T-A), less condensed tanins (T), procyanidin dimer (P). The combinations of tanins with polysaccharides comprise a new class of compounds whose importance is relatively limited in young wine but increases with time during wine maturation (20 to 30 p. cent of the tanins can exist in this form after 20 years of conservation). The percentage of each class varies in the case of young wine, with the cepage, the level of grape maturaity and the conditions of vinification. During the maturation process, the percentage corresponding to the procyanidin dimer group (P), rapidly attains zero after several years. The tanins of old wines are primarily composed of condensed tanins (TC + TtC) and combinations with polysaccharides and with salts. The anthocyanins exist in wine in 3 forms: free anthocyanins, combined anthocyanins and polymerised anthocyanins which belong to the condensed tanins. The free anthocyanins rapidly dissapear during the first few years of wine maturation. The combined and polymerised anthocyanins generally remain present in regard-less of wine age. These groups play an important role in the determination of wine colour.