Shan He

Stilbene oligomers from Parthenocissus laetevirens: isolation, biomimetic synthesis, absolute configuration, and implication of antioxidative defense system in the plant.

Five new stilbene oligomers, laetevirenol A-E (4-8), were isolated from Parthenocissus laetevirens, together with three known stilbene oligomers (2, 3, and 9). The structures of the new compounds were elucidated by spectroscopic analysis, including 1D and 2D NMR experiments. Afterward the absolute configurations were determined. Biomimetic transformations revealed a possible biogenetic route, where stilbene trimers were enzymatically synthesized for the first time. In addition, their antioxidant activities were evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The results showed that stilbene oligomers with an unusual phenanthrene moiety exhibited much stronger antioxidant activities. Thus, the photocatalyzed cyclization of stilbenes was supposed to be an antioxidant activity promoting transformation, which was hypothesized to play a role in the antioxidative defense system of the plant.

Red Wine Polyphenols for Cancer Prevention

Conventional cancer therapies, the second leading cause of death worldwide, result in serious side effects and, at best, merely extend the patients lifespan by a few years. Searching for effective prevention is of high priority in both basic and clinical sciences. In recent decades natural products have been considered to be an important source of cancer chemopreventive agents. Red wine polyphenols, which consisted of various powerful antioxidants such as flavonoids and stilbenes, have been implicated in cancer prevention and that promote human health without recognizable side effects. Since resveratrol, a major component of red wine polyphenols, has been studied and reviewed extensively for its chemopreventive activity to interfere with the multi-stage carcinogenesis, this review focuses on recent progress in studies on cancer chemopreventive activities of red wine polyphenol extracts and fractions as well as other red wine polyphenols, like procyanidin B5 analogues and myricetin.

Pallidol, a resveratrol dimer from red wine, is a selective singlet oxygen quencher

Pallidol is a naturally occurring resveratrol dimer from red wine with antioxidant and antifungal activities. In this report, with the use of the EPR spin-trapping technique, the scavenging and quenching effects of pallidol on reactive oxygen species (ROS) were investigated. The results demonstrated that pallidol showed strong quenching effects on singlet oxygen at very low concentrations, but it was ineffective to scavenge hydroxyl radicals or superoxide anions. Further kinetic study revealed that the reaction of pallidol with singlet oxygen had an extremely high rate constant (k(a)=1.71x10(10)). Therefore, pallidol is a potent and selective singlet oxygen quencher in aqueous systems. It may be used in singlet oxygen-mediated diseases as a pharmacological agent, which may contribute to the health beneficial effects of red wine.

Preparative isolation and purification of antioxidative stilbene oligomers from Vitis chunganeniss using high‐speed counter‐current chromatography in stepwise elution mode

Preparative high-speed counter-current chromatography (HSCCC) was successfully applied to the isolation and purification of three stilbene oligomers from Vitis chunganeniss using stepwise elution with a pair of two-phase solvent systems composed of n-hexane-ethyl acetate-methanol-water at (2:5:2:5, v/v) and (1:2:1:2, v/v). The preparative HSCCC separation was performed on 800 mg of crude sample yielding hopeaphenol (21.1 mg), amurensin G (37.2 mg) and vitisin A (95.6 mg) in a one-step separation, with purities over 95% as determined by HPLC. The structures of these three compounds were identified by MS, (1)H NMR and (13)C NMR. In addition, their antioxidant activities were screened by DPPH assay, where vitisin A showed strong antioxidant activity. Further EPR experiments with spin-trapping technique demonstrated that vitisin A is a potent and selective singlet oxygen quencher, which may be used in singlet oxygen-mediated diseases as a pharmacological agent.

New tyrosinase inhibitory sesquiterpenes from Chloranthus henryi.

Chemical investigation of the leaves and stems of Chloranthus henryi resulted in the isolation and characterization of two new eudesmane‐type sesquiterpenes, 1 and 2, and two new germacrane‐type sesquiterpenes, 3 and 4, together with two known compounds. The inhibitory activities against tyrosinase of all isolates were also evaluated.

Resveratrol and Its Oligomers from Wine Grapes Are Selective 1O2 Quenchers: Mechanistic Implication by High-Performance Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry and Theoretical Calculation

Resveratrol and its oligomers, abundantly present in wine grapes, are believed to be effective phytoalexins for the phenomenon French paradox partially by virtue of their powerful antiradical properties. EPR spin-trapping technique was utilized, demonstrating all polyphenols were selective (1)O2 quenchers but not effective (•)OH and O2(•¯) scavengers. On the basis of the HPLC-ESI-MS(2) analysis for the simulated reactions of polyphenols with (1)O2, the molecular weights of the resulting photochemical products were 14 or 28 Da higher than those of their substrates. No fragment C2H2O (42 Da), which was rather distinctive of the resorcinol rings in these cases, had been observed, whereas their MS/MS spectra displayed characteristic neutral fragments including carbon monoxide (CO, 28 Da) and 2-hydroxy[1,4]benzoquinone (C6H4O3, 124 Da). Finally, PM3 semiempirical calculations and HR-FTICR-MS experiments were performed, supporting the assertion that their quenching mechanism involved physical and chemical pathways. Chemical quenching underwent an endoperoxide intermediate form to generate quinones.

Characterization of polyphenol compounds from the roots and stems of Parthenocissus laetevirens by high-performance liquid chromatography/tandem mass spectrometry.

A facile method based on high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC/(-)ESI-MSn) has been established for the analyses of polyphenol compounds in the root and stems of Parthenocissus laetevirens. Two characteristic fragments [C3O2 (68 Da) and C2H2O (42 Da)] were utilized for the structural identification of polyphenols. Based on the reference standards, the fragment C3O2 was presented when the compound possessed a 2,3-dihydro-1H-indene-4, 6-diol moiety. Meanwhile, the C2H2O fragment (42 Da) yielded from the resorcinol ring was confirmed by resveratrol and three synthesized compounds identified as (E)-5-styrylbenzene-1,3-diol, (E)-4-styrylphenol and (E)-4-(3,4,5-trimethoxystyryl)phenol. FTICR-MSn was performed to further confirm the structures of the fragments. Overall, 15 polyphenol compounds were characterized. Three polyphenol compounds were initially and tentatively characterized from P. laetevirens for the first time, and one was proposed as a novel compound. Furthermore, a pair of stereoisomers was readily distinguished by breakdown curves, and the trans-, cis-isomers could be identified by HPLC/DAD-UV spectra.

Chunganenol: An Unusual Antioxidative Resveratrol Hexamer from Vitis chunganensis

Chunganenol (1), an unusual resveratrol hexamer, has been isolated from Vitis chunganensis. Its unprecedented structure has been assigned through detailed analyses of 2D NMR data and consideration of oligostilbene biosynthetic pathway, representing the first highly condensed stilbene oligomer from Vitaceous plants. It also featured a novel interunit lingkage where two stilbene units are connected by a methylene bridge. Moreover, 1 exhibited potent and selective quenching effects on singlet oxygen, and might play a role in the antioxidative defense system of the plant.

Selective 1O2 quenchers, oligostilbenes, from Vitis wilsonae: Structural identification and biogenetic relationship

Two previously unknown resveratrol trimers named wilsonols A-B, as well as a resveratrol tetramer named wilsonol C, were isolated from Vitis wilsonae Veitch, together with 12 known oligostilbenes. Their chemical structures have been elucidated by detailed analyses of 1D and 2D NMR spectroscopic data, as well as chemical evidence obtained via either catalysis with HRP (horseradish peroxidase) and H(2)O(2) (hydrogen peroxide), acid, or UV irradiation. During the chemical processes, a biomimetic resveratrol tetramer named diviniferin B that has not been found in nature was obtained. These oligostilbenes showed potent scavenging abilities towards DPPH radicals and selective quenching effects on (1)O(2) radicals. Furthermore, the biogenetic transformations between the 16 oligostilbenes have been elaborated chemically to provide a comprehensive mechanism of the antioxidative defense system in this plant species.

An integrative approach for the isolation, screening and analysis of antitumor agents by liquid chromatography combined with mass spectrometry.

A rapid approach has been developed for screening trace level compounds with antitumor activities based on their interactions with microtubules. This interaction can be quantified with liquid chromatography (LC) by measuring the difference of bioactive compounds concentration before and after the formation of compound-microtubule complexes in the fast dialyzers. To test the effectiveness of this approach, several antitumor drugs such as colchicine, taxol, daunorubicin, and a non-antitumor reagent ketoprofen were used. Results indicate that the antitumor constituents can be identified without any disturbance, and the inactive components can be excluded. This screening method was then successfully applied to some potential antitumor compound mixtures, and the active compounds could be separated and screened rapidly. The binding activities measured were consistent with their cytotoxicity assays. This integrative approach is rapid and convenient for screening, isolating, and analyzing potential antitumor active compounds from a mixture.