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In a continuing search for neuroprotective stilbenoids, two uncommon diastereomeric stilbenoid glucosides, africanoside A (1) and B (2) as well as fifteen known stilbenes, E-resveratrol, E-gnetifolin E, E-piceid, E-resveratroloside, E-gnetifolin K, E-gnetol, E-isorhapontigenin, E-isorhapontin, E-isorhapontigenin-4′-O-glucopyranoside, E-gnetin C, E-bisisorhapontigenin B, E-gnemonoside A, E-gnemonoside C, E-gnemonoside D, and E-gnetin E, were isolated from rhizomes of Gnetum africanum, using a combination of centrifugal partition chromatography and preparative HPLC. The structure of these two stilbenoids was investigated by NMR, vibrational circular dichroism (VCD), and electronic circular dichroism (ECD) experiments. The absolute configurations of 1, and 2 were established by VCD as (7aS,8aS) and (7aR,8aR), respectively. Compound 1 significantly chelated Fe(II) at 100, 250 and 500 μM. The ability of stilbenoids to chelate ferrous ions which are implicated in physiopathological hallmark of Alzheimer’s disease provides useful data for potential treatment.

Centrifugal partition chromatography (CPC) and all countercurrent separation apparatus provide chemists with efficient ways to work with complex matrixes, especially in the domain of natural products. However, despite the great advances provided by these techniques, more efficient ways of analyzing the output flow would bring further enhancement. This study describe a hyphenated approach made by coupling NMR with CPC through a hybrid-indirect coupling made possible by using a solid phase extraction (SPE) apparatus intended for high-pressure liquid chromatography (HPLC)-NMR hyphenation. Some hardware changes were needed to adapt the incompatible flow-rates and a reverse-engineering approach that led to the specific software required to control the apparatus. 1D 1HNMR and 1H–1H correlation spectroscopy (COSY) spectra were acquired in reasonable time without the need for any solvent-suppression method thanks to the SPE nitrogen drying step. The reduced usage of expensive deuterated solvents from several hundreds of milliliters to the milliliter order is the major improvement of this approach compared to the previously published ones.

Stilbenoids have received increasing attention over the last two decades since the discovery of resveratrol in wine. With an ever-growing rhythm, a multitude of biological activities of naturally occurring stilbenes are being reported. In this work, we investigated minor stilbenoid compounds from Vitis vinifera stalks. The compounds were purified by means of centrifugal partition chromatography (CPC), a countercurrent-separation technique. Electrospray ionization–ion trap mass spectrometry (ESI–IT-MS) after optimization proved to be extremely efficient for the detection of these new molecules, providing both structural information for structure elucidation and a means to achieve identification even with minute amounts. Here a new stereoisomer of E-miyabenol C, E-cis-cis-miyabenol C (2), along with the already reported E-trans-cis-miyabenol C (1) and E-cis-trans-miyabenol C (3), was purified from a complex Vitis vinifera cane extract, using adapted solvent systems K and L from the ‘Arizona’ solvent system range, without the need for any solid support. Moreover, compounds 1–3 showed an inhibitory activity on α-synuclein filament formation.

Dimeric stilbene glucosides 1–3 [two diastereomers of (−)-gnemonoside A (1a and 1b), (−)-gnemonoside C (2), and (−)-gnemonoside D (3)] as well as a mixture of the two enantiomers of gnetin C (4) were isolated from the rhizomes of Gnetum africanum. The two enantiomers of gnetin C, (+)-4 and (−)-4, were obtained from the aglycones of 1a and 1b, respectively. The configurations of these stilbenoids were investigated by NMR and vibrational circular dichroism (VCD) experiments. The absolute configurations of (−)-1a, (−)-2, (−)-3, and (−)-4 were established as 7aS,8aS by VCD spectroscopy in combination with density functional theory calculations. The antiamyloidogenic activity of the isolated stilbenes was also evaluated versus beta-amyloid fibrils. The four glucosides of gnetin C (1a, 1b, 2, and 3) were found to be the most active compounds, with inhibition percentages of 56, 56, 58, and 54 at 10 μM, respectively.

Grapevine canes are rich in resveratrol and its complex derivatives. These compounds have many biological activities and are needed mainly for health purposes. Canes, which are often wasted, can be used to produce these high-value compounds at low cost. We studied sixteen Vitis vinifera L. cultivars among the most widely cultivated ones worldwide. Polyphenols were extracted from their canes and identified by liquid chromatography–nuclear magnetic resonance spectroscopy. We accurately determined the content of E-ε-viniferin, E-resveratrol, E-piceatannol, and vitisin B and, for the first time, that of hopeaphenol and miyabenol C. The canes did not contain these major stilbene compounds in similar proportions, and their abundance and order of abundance varied according to the cultivar. For instance, Pinot noir has very high levels of E-resveratrol and E-ε-viniferin; Gewurztraminer has very high levels of vitisin B, and Carignan and Riesling have very high levels of hopeaphenol. These findings suggest that the right cultivar should be used to obtain the highest yield of a polyphenol of interest.

Microglia-driven inflammatory processes are thought to play an important role in ageing and several neurological disorders. Since consumption of a diet rich in polyphenols has been associated with anti-inflammatory and neuroprotective effects, we studied the effects of twenty-five stilbenoids isolated from Milicia excelsa, Morus alba, Gnetum africanum, and Vitis vinifera. These compounds were tested at 5 and 10 µM on BV-2 microglial cells stimulated with bacterial lipopolysaccharide. Ten stilbenoids reduced lipopolysaccharide-induced nitric oxide production at 5 and/or 10 µM. Two tetramers, E-vitisin A and E-vitisin B, were the most effective molecules. Moreover, they attenuated the expression of the inducible NO synthase protein and gene.

Flavours extracted from oak wood during barrel ageing contribute to the organoleptic character of wines and spirits. The aim of this work was to identify the glycosidic precursors of the key volatile compounds responsible for oak wood aroma. Oak extract is a very complex matrix and, furthermore, precursors are present in very small quantities. Preparative centrifugal partition chromatography (CPC) is a promising solution for purifying the oak extract. The solvent system was selected on the basis of the partition coefficient of glycosidase enzyme activity (Kca). Thanks to the efficacy of CPC separation, three glucoside gallates were subsequently isolated by HPLC chromatography. Vanillin-(6′-O-galloyl)-O-β-d-glucopyranoside, 3,4,5-trimethoxyphenyl-(6′-O-galloyl)-O-β-d-glucopyranoside, and (6R,9R)-3-oxo-α-ionol-9-O-(6′-O-galloyl)-β-glucopyranoside (macarangioside E) were isolated and identified. This was the first time that vanillin-(6′-O-galloyl)-O-β-d-glucopyranoside was identified and the first time that macarangioside E was isolated from oak wood. Heating macarangioside E resulted in the formation of megastigmatrienone, which has an aroma reminiscent of tobacco.

Wine is a major dietary source of numerous potentially health promoting stilbenoids that have been the subject of many qualitative and quantitative studies. However, our initial HPLC–MS analyses of crude wine samples demonstrated the presence of compounds with molecular weights matching characteristic stilbenoid dimers, trimers, and tetramers that were unaccounted for in the literature. Due to the likelihood that these are known compounds, a chemical dereplication method is highly desirable. We developed such a method using LC-DAD–MS monitored fractionation steps, using adsorption and centrifugal partition chromatography (CPC), to obtain fractions rich in stilbenoids for analysis in stopped-flow LC–NMR. 1H NMR spectra and MS data were cross-referenced with our laboratory database and the literature for identification. This method yielded highly useful structural information, allowing the characterization of previously unidentified stilbenoids in wine, ampelopsin C, isohopeaphenol, quadrangularin A, and E-ω-viniferin. These results demonstrate the usefulness of stop-flow LC–NMR in conjunction with LC–MS guided fractionation for the dereplication of compounds of interest in general, and specifically for expanding the current knowledge of wine chemistry.

We present stilbenoid profiles of canes from 16 grapevines. Fifteen stilbenoids were obtained through isolation and structure identification using MS, NMR, and [α]D or as commercial standards. An HPLC–UV method for the simultaneous quantification of nine of these stilbenoids was developed and applied to canes of Vitis amurensis, Vitis arizonica, Vitis berlandieri, Vitis betulifolia, Vitis cinerea, Vitis × champini, Vitis × doaniana, Vitis labrusca, Vitis candicans (syn. Vitis mustangensis), Vitis riparia, Vitis rupestris, Vitis vinifera, Muscadinia rotundifolia, and a V. vinifera × M. rotundifolia hybrid. In these species, E-ampelopsin E, E-amurensin B, E-piceid, E-piceatannol, E-resveratrol, E-resveratroloside, E-ε-viniferin, E-ω-viniferin, and E-vitisin B were quantified, when found in sufficient amounts. Total concentrations ranged from ∼2.2 to 19.5 g/kg of dry weight. Additional stilbenoids, E-3,5,4′-trihydroxystilbene 2-C-glucoside, Z-ampelopsin E, Z-trans-miyabenol C, E-trans-miyabenol C, scirpusin A, and Z-vitisin B, were identified but not quantified. Our results indicate that canes, particularly those of non-vinifera species, have substantial quantities of valuable, health-promoting stilbenoids.

The interaction between Vitis vinifera and trunk disease fungi requires better understanding. We studied the role of phenolics as possible plant defense compounds in this context. The impact of 24 grapevine phenolic compounds was determined on 6 major wood decay fungi by an in vitro agar plate assay. Hydroxystilbenoids, especially oligomers such as miyabenol C, isohopeaphenol, and vitisin A and B, greatly reduced the growth of the fungi, except that of Phaeoacremonium aleophilum. A detailed investigation in 10 Botryosphaeriaceae strains revealed that all of the studied members of this family display a common susceptibility to phenolics that is more or less significant. Then we undertook a quantitative analysis of stilbenoid content in grapevine plantlets inoculated with Botryosphaeriaceae to investigate whether in planta these fungi have to counteract the most active phenolics. On the basis of our results, the possible role of phenolics in grapevine defense against trunk disease agents is discussed.

Countercurrent chromatography techniques are increasingly used in the fractionation and purification steps of natural products due to their excellent versatility and efficiency. However, one of the major bottlenecks in liquid-liquid chromatography is the solvent system selection. In this work, a NMR-based analysis of complex solvent mixtures was developed for biphasic system selection and modification. This allowed us to develop more versatile separation conditions, such as gradients. Additionally, we hyphenated our countercurrent chromatography device with NMR and mass spectrometry. Our hybrid technique afforded a time-saving approach with a significant reduction in compound handling, an asset in working with minor and/or sensitive compounds. Current results and further developments will be presented and discussed.

The phytochemical study of the root extract of the stilbenoid-rich Vitis riparia × Vitis berlandieri grapevine was carried out by centrifugal partition chromatography (CPC). For this reason, we developed a new elution mode we named back-step, which allowed us to obtain cleaner fractions and a more efficient separation process when used in conjunction with a classical elution approach. Three hydroxystilbenes: (E)-resveratrol, (E)-ɛ-viniferin and (E)-vitisin C, with greater than 90% purity were thus obtained through such process, with minimal sample handling and purification steps. Online coupling of CPC to ESI mass spectrometry was used for optimization of the separation parameters and to facilitate the characterization of the stilbenoids. This study details the first phytochemical investigation of stilbenoids from the hybrid species together with a new elution mode able to widen the range of ARIZONA biphasic systems.