Christine Le Guernevé

Structure of a new dimeric acetaldehyde malvidin 3-glucoside condensation product

A new pigment was detected in wine-like model solution containing malvidin 3-O-glucoside and acetaldehyde. This compound was isolated, and its structure was investigated by UV, MS and NMR spectroscopies. The analytical data allowed identification of it to 8,8 methyl methine-linked malvidin 3-O-glucoside dimer. The occurrence of this pigment was demonstrated in red wine. A polymeric fraction was also isolated from the model solution and analysed by LC/MS. Detection of methyl methine-linked malvidin 3-O-glucoside oligomers proved that acetaldehyde mediated self-condensation of anthocyanins is possible, and that the C6 position of anthocyanins seems reactive as the C8 although to a lesser extent.

Structure of a new xanthylium salt derivative

A new polyphenolic compound with a xanthylium skeleton has been synthesised from (+)-catechin and glyoxylic acid. Its structural elucidation was achieved by UV, MS and NMR spectroscopies. Its formation involved glyoxylic acid-mediated dimerisation of (+)-catechin1 giving thus compound2, followed by cyclisation to a xanthene derivative3 which by oxidation afforded the xanthylium compound4. The detection and structural determination of the xanthene compound confirmed the postulated mechanism.

Straightforward Synthesis of Deuterated Precursors To Demonstrate the Biogenesis of Aromatic Thiols In Wine

Straightforward synthesis of labeled S-3-(hexan-1-ol)-glutathione and S-4-(4-methylpentan-2-one)-glutathione has been developed through a conjugate addition optimization study. Sauvignon blanc fermentation experiments with the [(2)H(10)] S-4-(4-methylpentan-2-one)-glutathione used as a tracer released the corresponding deuterated thiol, thus proving the direct relationship with the 4-mercapto-4-methylpentan-2-one under enological conditions. The conversion yield of such transformation was estimated to be close to 0.3%, opening an avenue for additional study on varietal thiol biogenesis.

New phenolic compounds obtained by evolution of (+)-catechin and glyoxylic acid in hydroalcoholic medium

Abstract The reaction between (+)-catechin 1 and glyoxylic acid in model solution system was investigated by LC/DAD and LC/ESI-MS analysis and the formation of new phenolic compounds 2 , 3 , 4 exhibiting absorption maxima near 300 nm were observed. The structures of these compounds were elucidated by ESI-MS and 1D and 2D NMR spectroscopy.

Methods for Determining the Degree of Polymerization of Condensed Tannins: A New 1H-NMR Procedure Applied to Cider Apple Procyanidins

The degree of polymerization (DP) that corresponds to the number of flavan-3-ol units is one of the most important features that characterize condensed tannins (proanthocyanidins) because of its direct link to the various properties of this kind of phenolic compound. In their definition of vegetable tanning substances, Bate-Smith and Swain1 referred to the molecular weight that must range from 500 to 3,000. By considering their extraction, their biological activities, their sensory effects, condensed tannins often behave according to their molecular weight, although this single feature is quite insufficient to show evidence of all their properties. On the whole, the molecular weight of condensed tannins is related to their ability to associate with proteins and polysaccharides; this “tanning capacity” varies in an increasing order with the DP.2–6 This property is also related to other applications. For instance, the work of Lea and Arnold7 pointed out the influence of the DP of procyanidins in relation to bitterness and astringency of cider. Proanthocyanidins are also partly involved in haze formation in beers: the capacity of beer tannins to precipitate proteins increases with the DPn.4,5,8 Many studies dealing with the biological activities of proanthocyanidins also show that antioxidant,9 antifungal,10 anti-enzymic,11 antisecretory,12 or antitumor13 activities may correlate with the DP.

A comprehensive investigation of guaiacyl-pyranoanthocyanin synthesis by one-/two-dimensional NMR and UPLC–DAD–ESI–MSn

In red and rosé wines, the grape anthocyanins are progressively converted to more stable pigments, including phenylpyranoanthocyanins. One-/two-dimensional NMR and UPLC-DAD-ESI-MS(n) measurements were used to monitor the synthesis of guaiacylpyranomalvidin 3-O-glucoside from malvidin 3-O-glucoside and vinylguaiacol in model solutions and identify the products formed during the reaction. The highest conversion rates (30%, determined by (1)H qNMR) were obtained with a small excess of vinylguaiacol in methanol/water (70/30) at pH 3 and 35°C. Two reaction pathways competed with the formation of guaiacylpyranomalvidin 3-O-glucoside. The first one only concerns malvidin 3-O-glucoside and consists in C-ring cleavage with formation of malvone and smaller molecular weight breakdown products. This pathway is favored at higher pH and incubation temperature. At lower pH values or in the presence of large vinylguaiacol excess, faster consumption of malvidin 3-O-glucoside resulted from the formation of more complex pyranoanthocyanins substituted by vinylguaiacol oligomers.

p-Hydroxyphenyl-pyranoanthocyanins: An Experimental and Theoretical Investigation of Their Acid-Base Properties and Molecular Interactions.

The physicochemical properties of the wine pigments catechyl-pyranomalvidin-3-O-glucoside (PA1) and guaiacyl-pyranomalvidin-3-O-glucoside (PA2) are extensively revisited using ultraviolet (UV)-visible spectroscopy, dynamic light scattering (DLS) and quantum chemistry density functional theory (DFT) calculations. In mildly acidic aqueous solution, each cationic pigment undergoes regioselective deprotonation to form a single neutral quinonoid base and water addition appears negligible. Above pH = 4, both PA1 and PA2 become prone to aggregation, which is manifested by the slow build-up of broad absorption bands at longer wavelengths (λ ≥ 600 nm), followed in the case of PA2 by precipitation. Some phenolic copigments are able to inhibit aggregation of pyranoanthocyanins (PAs), although at large copigment/PA molar ratios. Thus, chlorogenic acid can dissociate PA1 aggregates while catechin is inactive. With PA2, both chlorogenic acid and catechin are able to prevent precipitation but not self-association. Calculations confirmed that the noncovalent dimerization of PAs is stronger with the neutral base than with the cation and also stronger than π–π stacking of PAs to chlorogenic acid (copigmentation). For each type of complex, the most stable conformation could be obtained. Finally, PA1 can also bind hard metal ions such as Al3+ and Fe3+ and the corresponding chelates are less prone to self-association.

Synthesis, Identification, and Structure Elucidation of Adducts Formed by Reactions of Hydroxycinnamic Acids with Glutathione or Cysteinylglycine

Grape polyphenols, especially hydroxycinnamic acids such as caftaric and caffeic acid, are prone to enzymatic oxidation reactions during the winemaking process, forming o-quinones and leading to color darkening. Glutathione is capable of trapping these o-quinones and thus limiting juice browning. In this study, the addition of glutathione or cysteinylglycine onto caftaric or caffeic acid o-quinones formed by polyphenoloxidase-catalyzed reactions was investigated by UPLC-DAD-ESIMS and NMR data analyses. Complete identification of adducts has been achieved via NMR data. The results confirmed that the favored reaction is the substitution of the sulfanyl group of cysteine at C-2 of the aromatic ring. Several minor isomers, namely, the cis-isomer of the 2-S adduct and trans-isomers of the 5-S and 6-S adducts, and the 2,5-di-S-glutathionyl adducts were also identified and quantified by qNMR. With the exception of 2-(S-glutathionyl)- and 2,5-di(S-glutathionyl)-trans-caftaric acid, these products had never been formally identified. In particular, the 5-S and 6-S derivatives are reported here for the first time. The first formal identification of 2-S cis-derivatives is also provided. Moreover, NMR and UPLC-DAD-ESIMS analysis showed that signature UV and MS spectra can serve as markers of the conformation and substitution position in the aromatic ring for each of the isomers.

The host plant Pinus pinaster exerts specific effects on phosphate efflux and polyphosphate metabolism of the ectomycorrhizal fungus Hebeloma cylindrosporum: a radiotracer, cytological staining and 31P NMR spectroscopy study

Ectomycorrhizal (ECM) association can improve plant phosphorus (P) nutrition. Polyphosphates (polyP) synthesized in distant fungal cells after P uptake may contribute to P supply from the fungus to the host plant if they are hydrolyzed to phosphate in ECM roots then transferred to the host plant when required. In this study, we addressed this hypothesis for the ECM fungus Hebeloma cylindrosporum grown in vitro and incubated without plant or with host (Pinus pinaster) and non-host (Zea mays) plants, using an experimental system simulating the symbiotic interface. We used 32 P labelling to quantify P accumulation and P efflux and in vivo and in vitro nuclear magnetic resonance (NMR) spectroscopy and cytological staining to follow the fate of fungal polyP. Phosphate supply triggered a massive P accumulation as newly synthesized long-chain polyP in H. cylindrosporum if previously grown under P-deficient conditions. P efflux from H. cylindrosporum towards the roots was stimulated by both host and non-host plants. However, the host plant enhanced 32 P release compared with the non-host plant and specifically increased the proportion of short-chain polyP in the interacting mycelia. These results support the existence of specific host plant effects on fungal P metabolism able to provide P in the apoplast of ectomycorrhizal roots.

Mapping of the detergent-exposed surface of membrane proteins and peptides by 1H solution NMR in detergent: Application to the gramicidin A ion channel.

The present work evaluates the use of intermolecular polypeptide–detergent 1H through-space connectivities to determine the bilayer exposed-surface and the bilayer topography of membrane polypeptides solubilized in non- deuterated detergents. For this purpose, the membrane peptide gramicidin A, solubilized in non-deuterated sodium dodecylsulfate as its dimeric β6,3 helix channel conformation was used. For this peptide, a high-resolution 3D structure, as well as reasonable assumptions concerning its membrane arrangement, exist. Band-selective 2D NOESY, ROESY and 3D NOESY-NOESY experiments were used to detect detergent–polypeptide through-space correlations in the presence of an excess of the non-deuterated detergent. The observed intermolecular NOEs appear to be strongly temperature- dependent. Based on the known 3D structure of the gramicidin channel, the detergent–polypeptide through-space correlations appear to be selective for 1H located on the hydrophobic surface of gramicidin A with very few contributions from interior 1H or water-exposed 1H. It is suggested that this method can be of general use to evaluate the bilayer-exposed surface and topography of membrane peptides and small proteins.