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3. Antioxidant Mechanisms of Polyphenolic Caffeic Acid Oligomers, Constituents of Salvia officinalis

Author

WOLF BORS, MICHEL CHRISTA, KURT STETTMAIER, LU YINRONG, and FOO L. YEAP

Subjects
Caffeic acid oligomer, catechol semiquinone, electron paramagnetic resonance, hydroxyl radical, kinetic modeling, pulse radiolysis, Salvia officinalis, Biology (General), QH301-705.5
Abstract

Caffeic acid, rosmarinic acid and oligomers of caffeic acid with multiple catechol groups are all constituents of Salvia officinalis. Their antioxidant potential was investigated with regard to their radical scavenging activity and the stability and structure of the intermediate radicals. Pulse-radiolytic studies revealed very high rate constants with hydroxyl radicals. Evidence from kinetic modeling calculations suggested an unusual complex behavior due to the presence of both O4- and O3-semiquinones and formation and decay of a hydroxyl radical adduct at the vinyl side chain. The radical structures observed by EPR spectroscopy after autoxidation in slightly alkaline solutions were only partially identified due to their instability and generally represented dissociated O4-semiquinones. Hybrid density-functional calculations of the potential radical structures showed distinct differences between the resonance stabilization of the O4- and O3-semiquinones of caffeic and dihydrocaffeic acids, reflected also in the considerably faster decay of the O3-semiquinone observed by pulse radiolysis. No evidence was found for dimerization reactions via Cb radicals typical for lignin biosynthesis

Published
2004

7. Novel nor-sesquiterpenoids in New Zealand honeys: the relative and absolute stereochemistry of the kamahines, an extension of the Mosher method to hemiacetals

Author

Broom, Susan J., Wilkins, Alistair L., Lu, Yinrong, and Ede, Richard M.

Subjects
Terpenes -- Research, Honey -- Research, Molecules -- Models, Biological sciences, Chemistry
Abstract

A comparative study of the NMR data of kamahine A and B acetates with those of kamahine E acetate helps determine the relative stereochemistries of the diasteroisomeric kamahines A and B, novel non-sesquiterpenoids in New Zealand honeys. NMR and molecular modeling of diastereoisomeric hemiacetal methoxymandelate esters help establish the absolute configurations of the kamahines. Mosher-Trost model efficiently predicts the absolute by considering the positive torsion angle between methine hydrogen and carbonyl of hemiacetate mandelate esters.

Published
1994

16. Antioxidant mechanisms of polyphenolic caffeic acid oligomers, constituents of Salvia officinalis

Author

Kurt Stettmaier, Wolf Bors, Foo L. Yeap, Lu Yinrong, and Michel Christa

Subjects
catechol semiquinone, Antioxidant, Radical, medicine.medical_treatment, Medicinal chemistry, General Biochemistry, Genetics and Molecular Biology, Antioxidants, chemistry.chemical_compound, food, Caffeic Acids, medicine, Caffeic acid, Salvia officinalis, lcsh:QH301-705.5, Autoxidation, Caffeic acid oligomer, hydroxyl radical, Hydroxyl Radical, Rosmarinic acid, pulse radiolysis, Electron Spin Resonance Spectroscopy, General Medicine, kinetic modeling, food.food, electron paramagnetic resonance, chemistry, Biochemistry, lcsh:Biology (General), Radiolysis, Hydroxyl radical, caffeic acid oligomer, General Agricultural and Biological Sciences, Pulse Radiolysis
Abstract

Caffeic acid, rosmarinic acid and oligomers of caffeic acid with multiple catechol groups are all constituents of Salvia officinalis. Their antioxidant potential was investigated with regard to their radical scavenging activity and the stability and structure of the intermediate radicals. Pulse-radiolytic studies revealed very high rate constants with hydroxyl radicals. Evidence from kinetic modeling calculations suggested an unusual complex behavior due to the presence of both O4- and O3-semiquinones and formation and decay of a hydroxyl radical adduct at the vinyl side chain. The radical structures observed by EPR spectroscopy after autoxidation in slightly alkaline solutions were only partially identified due to their instability and generally represented dissociated O4-semiquinones. Hybrid density-functional calculations of the potential radical structures showed distinct differences between the resonance stabilization of the O4- and O3-semiquinones of caffeic and dihydrocaffeic acids, reflected also in the considerably faster decay of the O3-semiquinone observed by pulse radiolysis. No evidence was found for dimerization reactions via Cbeta radicals typical for lignin biosynthesis.

Published
2004

47. Evaluation of Sage Phenolics for Their Antileishmanial Activity and Modulatory Effects on Interleukin-6, Interferon and Tumour Necrosis Factor-a-Release in RAW 264.7 Cells

Author

Radtke, Oliver A., Foo, Lai Yeap, Lu, Yinrong, Kiderlen, Albrecht F., and Kolodziej, Herbert

Abstract

A series of sage phenolics was tested for activity against a panel of Leishmania parasites and for immunomodulatory effects on macrophage functions including release of tumour necrosis factor (TNF), interleukin-6 (IL-6), and interferon (IFN)-like activities. For this, functional bioassays were employed including an in vitro model for leishmaniasis in which macrophage- like RAW 264.7 cells were infected with Leishmania parasites, an extracellular Leishmania growth-inhibition assay, a fibroblast-lysis assay for TNF-activity, a cell proliferation assay using IL-6 sensitive murine B9 hybridoma cells, and a virus protection assay for IFN-like activity. Whereas none of the test samples exhibited marked activities against extracellular Leishmania promastigotes (IC50> 700 to > 2800 n?; > 500 µg/ml), caffeic acid, salvianolic acids K and L as well as the methyl ester of salvianolic acid I showed pronounced antileishmanial activities against intracellular amastigote stages within RAW cells (IC503-23 n? vs. 10-11 n? for the reference Pentostam®). Noteworthy, the phenolic samples showed no cytotoxicity against the host cells (IC50 > 600 to > 2200 n?; > 400 µg/ml). Tested sage phenolics activated Leishmania-infected RAW 264.7 for release of TNF ranging 22-117 U/ml and IL-6 ranging 3-42 U/ml. In contrast, their TNF- or IL-6-inducing potential in experiments with non-infected host cells was negligible. Furthermore, caffeic acid and salvianolic acid K induced a modest release of IFN-like activity (5-9 and 2-4 U/ml, respectively) as reflected by inhibition of the cytopathic effect of encephalomyocarditis virus on L929 cells. The results support the emerging picture that plant polyphenols may be credited for the profound healthbeneficial properties of various herbal medicines and agricultural products.

Published
2003
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48. Biphenyl-linked biflavanoids from grape pomace

Author

Foo, L. Yeap, Lu, Yinrong, and Wong, Herbert

Abstract

Two novel biphenyl linked biflavanoids commonly associated with polyphenol oxidase-coupled products were isolated from Chardonnay grape pomace. Their chemical structures were established by long-range H,C couplings as epicatechin [6′ → 8]-epicatechin and epicatechin [6′ → 8] catechin. The disproportionate representation of the epicatechin unit as compared with catechin among the isolated biflavanoids could not be accounted for by their relative concentration in the pomace and suggested that the 2,3- trans configuration provided more steric constraints than the 2,3- cis one during grape polyphenol enzymatic oxidation of the B-ring leading to the quinone intermediate.

Published
1998
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