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Special Issue "Special Issue Dedicated to Late Professor Takuo Okuda, “Tannins and Related Polyphenols Revisited: Chemistry, Biochemistry and Biological Activities”"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Natural Products Chemistry".

Deadline for manuscript submissions: 30 June 2018

Special Issue Editors

Guest Editor
Prof. Dr. Hideyuki Ito

Faculty of Health and Welfare Science, Okayama Prefectural University, Kuboki, Soja, Okayama 719- 1197, Japan
Website | E-Mail
Interests: tannins; flavonoids; isolation and structure elucidation; biological activity; bioavailability; metabolites
Guest Editor
Prof. Dr. Tsutomu Hatano

Faculty of Pharmaceutical Sciences, Okayama University, Tsushima-naka, Okayama 700-8530, Japan
E-Mail
Interests: tannins; flavonoids; isolation and structure elucidation; biological activity; antibiotic
Guest Editor
Emeritus Prof. Dr. Takashi Yoshida

Faculty of Pharmaceutical Sciences, Okayama University, Tsushima-naka, Okayama, 700-8530, Japan
E-Mail
Interests: tannins; flavonoids; terpenoids; isolation and structure elucidation; biological activity; chemoprevention

Special Issue Information

Dear Colleagues,

Molecules is pleased to announce a memorial Special Issue, dedicated to Emeritus Professor Dr. Takuo Okuda at Okayama University, Japan, on the occasion of his passing away in December 2016, for his outstanding contribution in the research field of vegetable tannins and related polyphenols.

Prof. Okuda (born in 1927) was Professor of Medicinal Plants Chemistry at the Okayama University, in Japan, from 1970 to 1993. He was one of the pioneers of the chemistry of hydrolyzable tannins and related polyphenols in traditional medicinal plants in Japan, China, and South-East Asian countries. His prolific scientific activity is documented by more than 300 papers concerning the isolation and characterization of tannins and related polyphenolics in many plant species, including their diverse pharmacological functions beneficial to human health care, particularly to antioxidants, chemoprevention of life-related diseases such as cancers, diabetes, arteriosclerosis, and heart diseases. Prof. Okuda established fruitful collaborations with many pharmacologists, biochemists, and microbiologists. Prof. Okuda received the Tannin Award in the 4th Tannin Conference in 2004 (Philadelphia, USA), Groupe Polyphenol Medal in 2014 (Nagoya), for his achievements in the field of polyphenolic natural products.

This memorial Special Issue welcomes submission of previously unpublished manuscripts (original researches or reviews) on the investigation of tannins and biologically active polyphenolic compounds isolated from plants. We plan to receive submissions from April 2017 to the end of June 2018. Manuscripts will be published on an ongoing basis after being processed.

Prof. Dr. Hideyuki Ito
Prof. Dr. Tsutomu Hatano
Emeritus Prof. Dr. Takashi Yoshida
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • New polyphenolic natural products
  • New tannins and flavonoids
  • Improved methodology of analysis
  • Biological activity
  • Bioavailability and metabolites
  • Structure elucidation
  • Organic synthesis
  • Mechanism of action

Published Papers (9 papers)

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Research

Jump to: Review

Open AccessArticle (−)-Epigallocatechin 3-Gallate Synthetic Analogues Inhibit Fatty Acid Synthase and Show Anticancer Activity in Triple Negative Breast Cancer
Molecules 2018, 23(5), 1160; https://doi.org/10.3390/molecules23051160
Received: 4 April 2018 / Revised: 2 May 2018 / Accepted: 10 May 2018 / Published: 11 May 2018
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Abstract
(−)-Epigallocatechin 3-gallate (EGCG) is a natural polyphenol from green tea with reported anticancer activity and capacity to inhibit the lipogenic enzyme fatty acid synthase (FASN), which is overexpressed in several human carcinomas. To improve the pharmacological profile of EGCG, we previously developed a
[...] Read more.
(−)-Epigallocatechin 3-gallate (EGCG) is a natural polyphenol from green tea with reported anticancer activity and capacity to inhibit the lipogenic enzyme fatty acid synthase (FASN), which is overexpressed in several human carcinomas. To improve the pharmacological profile of EGCG, we previously developed a family of EGCG derivatives and the lead compounds G28, G37 and G56 were characterized in HER2-positive breast cancer cells overexpressing FASN. Here, diesters G28, G37 and G56 and two G28 derivatives, monoesters M1 and M2, were synthesized and assessed in vitro for their cytotoxic, FASN inhibition and apoptotic activities in MDA-MB-231 triple-negative breast cancer (TNBC) cells. All compounds displayed moderate to high cytotoxicity and significantly blocked FASN activity, monoesters M1 and M2 being more potent inhibitors than diesters. Interestingly, G28, M1, and M2 also diminished FASN protein expression levels, but only monoesters M1 and M2 induced apoptosis. Our results indicate that FASN inhibition by such polyphenolic compounds could be a new strategy in TNBC treatment, and highlight the potential anticancer activities of monoesters. Thus, G28, G37, G56, and most importantly M1 and M2, are anticancer candidates (alone or in combination) to be further characterized in vitro and in vivo. Full article
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Open AccessArticle Preliminary Quality Evaluation and Characterization of Phenolic Constituents in Cynanchi Wilfordii Radix
Molecules 2018, 23(3), 656; https://doi.org/10.3390/molecules23030656
Received: 5 February 2018 / Revised: 5 March 2018 / Accepted: 12 March 2018 / Published: 14 March 2018
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Abstract
A new phenolic compound, 2-O-β-laminaribiosyl-4-hydroxyacetophenone (1), was isolated from Cynanchi Wilfordii Radix (CWR, the root of Cynanchum wilfordii Hemsley), along with 10 known aromatic compounds, including cynandione A (2), bungeisides-C (7) and –D (8
[...] Read more.
A new phenolic compound, 2-O-β-laminaribiosyl-4-hydroxyacetophenone (1), was isolated from Cynanchi Wilfordii Radix (CWR, the root of Cynanchum wilfordii Hemsley), along with 10 known aromatic compounds, including cynandione A (2), bungeisides-C (7) and –D (8), p-hydroxyacetophenone (9), 2′,5′-dihydroxyacetophenone (10), and 2′,4′-dihydroxyacetophenone (11). The structure of the new compound (1) was elucidated using spectroscopic methods and chemical methods. The structure of cynandione A (2), including a linkage mode of the biphenyl parts that remained uncertain, was unambiguously confirmed using the 2D 13C–13C incredible natural abundance double quantum transfer experiment (INADEQUATE) spectrum. Additionally, health issues related to the use of Cynanchi Auriculati Radix (CAR, the root of Cynanchum auriculatum Royle ex Wight) instead of CWR have emerged. Therefore, constituents present in methanolic extracts of commercially available CWRs and CARs were examined using UV-sensitive high-performance liquid chromatography (HPLC), resulting in common detection of three major peaks ascribed to cynandione A (2), p-hydroxyacetophenone (9), and 2′,4′-dihydroxyacetophenone (11). Thus, to distinguish between these ingredients, a thin-layer chromatography (TLC) method, combined with only UV irradiation detection, focusing on wilfosides C1N (12) and K1N (13) as marker compounds characteristic of CAR, was performed. Furthermore, we propose this method as a simple and convenient strategy for the preliminary distinction of CWR and CAR to ensure the quality and safety of their crude drugs. Full article
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Open AccessArticle Characterization of Condensed Tannins from Purple Prairie Clover (Dalea purpurea Vent.) Conserved as either Freeze-Dried Forage, Sun-Cured Hay or Silage
Molecules 2018, 23(3), 586; https://doi.org/10.3390/molecules23030586
Received: 1 February 2018 / Revised: 27 February 2018 / Accepted: 2 March 2018 / Published: 6 March 2018
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Abstract
Conservation methods have been shown to affect forage nutrient composition and value, but little information is available about the effect of forage conservation on plant condensed tannins (CT). The objective of this study was to assess the effects of conservation method on the
[...] Read more.
Conservation methods have been shown to affect forage nutrient composition and value, but little information is available about the effect of forage conservation on plant condensed tannins (CT). The objective of this study was to assess the effects of conservation method on the concentration, chemical composition and biological activity of CT. Whole-plant purple prairie clover (PPC, Dalea purpurea Vent.) was harvested at full flower and conserved as freeze-dried forage (FD), hay (HAY) or silage (SIL). Concentration of CT in conserved PPC was determined by the butanol-HCl-acetone method. Structural composition, protein-precipitation capacity and anti-bacterial activity of CT isolated from conserved forage were determined by in situ thiolytic degradation followed by HPLC-MS analysis, a protein precipitation assay using bovine serum albumin and ribulose 1,5-disphosphate carboxylase as model proteins and by an Escherichia coli (E. coli) growth test, respectively. Conservation method had no effect on concentration of total CT, but ensiling decreased (p < 0.001) extractable CT and increased (p < 0.001) protein- and fiber-bound CT. In contrast, hay-making only increased (p < 0.01) protein-bound CT. Regardless of conservation method, epigallocatechin (EGC), catechin (C) and epicatechin (EC) were the major flavan-3-ol units, and gallocatechin (GC) was absent from both terminal and extension units of PPC CT. The SIL CT had the lowest (p < 0.001) EGC, but the highest (p < 0.01) EC in the extension units. Similarly, SIL CT exhibited a lower (p < 0.001) mean degree of polymerization (mDP), but higher (p < 0.001) procyanidins (PC) than FD or HAY CT. The protein-precipitating capacity of CT in conserved PPC ranked (p < 0.001) as FD > HAY > SIL. E. coli growth n M9 medium was inhibited by 25–100 µg/mL of CT isolated from FD, HAY and SIL (p < 0.05), but preservation method had no effect on the ability of CT to inhibit bacterial growth. The results demonstrated that ensiling decreased the extractability and protein-precipitating capacity of CT by increasing the proportions of PC. Purple prairie clover conserved as hay retained more biologically active CT than if it was conserved as silage. Full article
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Open AccessArticle Different Inhibitory Potencies of Oseltamivir Carboxylate, Zanamivir, and Several Tannins on Bacterial and Viral Neuraminidases as Assessed in a Cell-Free Fluorescence-Based Enzyme Inhibition Assay
Molecules 2017, 22(11), 1989; https://doi.org/10.3390/molecules22111989
Received: 23 October 2017 / Revised: 14 November 2017 / Accepted: 15 November 2017 / Published: 17 November 2017
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Abstract
Neuraminidase is a key enzyme in the life cycle of influenza viruses and is present in some bacterial pathogens. We here assess the inhibitory potency of plant tannins versus clinically used inhibitors on both a viral and a bacterial model neuraminidase by applying
[...] Read more.
Neuraminidase is a key enzyme in the life cycle of influenza viruses and is present in some bacterial pathogens. We here assess the inhibitory potency of plant tannins versus clinically used inhibitors on both a viral and a bacterial model neuraminidase by applying the 2′-(4-methylumbelliferyl)-α-d-N-acetylneuraminic acid (MUNANA)-based activity assay. A range of flavan-3-ols, ellagitannins and chemically defined proanthocyanidin fractions was evaluated in comparison to oseltamivir carboxylate and zanamivir for their inhibitory activities against viral influenza A (H1N1) and bacterial Vibrio cholerae neuraminidase (VCNA). Compared to the positive controls, all tested polyphenols displayed a weak inhibition of the viral enzyme but similar or even higher potency on the bacterial neuraminidase. Structure–activity relationship analyses revealed the presence of galloyl groups and the hydroxylation pattern of the flavan skeleton to be crucial for inhibitory activity. The combination of zanamivir and EPs® 7630 (root extract of Pelargonium sidoides) showed synergistic inhibitory effects on the bacterial neuraminidase. Co-crystal structures of VCNA with oseltamivir carboxylate and zanamivir provided insight into bacterial versus viral enzyme-inhibitor interactions. The current data clearly indicate that inhibitor potency strongly depends on the biological origin of the enzyme and that results are not readily transferable. The therapeutic relevance of our findings is briefly discussed. Full article
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Open AccessArticle Characterization of Proanthocyanidin Oligomers of Ephedra sinica
Molecules 2017, 22(8), 1308; https://doi.org/10.3390/molecules22081308
Received: 14 July 2017 / Revised: 27 July 2017 / Accepted: 3 August 2017 / Published: 6 August 2017
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Abstract
Ephedra sinica, an important plant in Chinese traditional medicine, contains a complex mixture of proanthocyanidin oligomers as major constituents; however, only the minor components have been chemically characterized. In this study, oligomers with relatively large molecular weights, which form the main body
[...] Read more.
Ephedra sinica, an important plant in Chinese traditional medicine, contains a complex mixture of proanthocyanidin oligomers as major constituents; however, only the minor components have been chemically characterized. In this study, oligomers with relatively large molecular weights, which form the main body of the proanthocyanidin fractions, were separated by adsorption and size-exclusion chromatography. Acid-catalyzed degradation in the presence of mercaptoethanol or phloroglucinol led to the isolation of 18 fragments, the structures of which were elucidated from their experimental and TDDFT-calculated ECD spectra. The results indicated that (−)-epigallocatechin was the main extension unit, while catechin, the A-type epigallocatechin–gallocatechin dimer, and the A-type epigallocatechin homodimer, were identified as the terminal units. Among the degradation products, thioethers of gallocatechin with 3,4-cis configurations, a B-type prodelphinidin dimer, a prodelphinidin trimer with both A- and B-type linkages, and a prodelphinidin dimer with an α-substituted A-type linkage were new compounds. In addition, a phloroglucinol adduct of an A-type prodelphinidin dimer, a doubly-linked phloroglucinol adduct of epigallocatechin, and a unique product with a flavan-3-ol skeleton generated by the rearrangement of the aromatic rings were also isolated. Full article
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Open AccessArticle Chemical Composition, Antibacterial and Antifungal Activities of Crude Dittrichia viscosa (L.) Greuter Leaf Extracts
Molecules 2017, 22(7), 942; https://doi.org/10.3390/molecules22070942
Received: 12 May 2017 / Revised: 31 May 2017 / Accepted: 3 June 2017 / Published: 30 June 2017
Cited by 2 | PDF Full-text (407 KB) | HTML Full-text | XML Full-text
Abstract
The small amount of data regarding the antifungal activity of Dittrichia viscosa (L.) Greuter against dermatophytes, Malassezia spp. and Aspergillus spp., associated with the few comparative studies on the antimicrobial activity of methanolic, ethanolic, and butanolic extracts underpins the study herein presented. The
[...] Read more.
The small amount of data regarding the antifungal activity of Dittrichia viscosa (L.) Greuter against dermatophytes, Malassezia spp. and Aspergillus spp., associated with the few comparative studies on the antimicrobial activity of methanolic, ethanolic, and butanolic extracts underpins the study herein presented. The total condensed tannin (TCT), phenol (TPC), flavonoid (TFC), and caffeoylquinic acid (CQC) content of methanol, butanol, and ethanol (80% and 100%) extracts of D. viscosa were assessed and their bactericidal and fungicidal activities were evaluated. The antibacterial, anti-Candida and anti-Malassezia activities were evaluated by using the disk diffusion method, whereas the anti-Microsporum canis and anti-Aspergillus fumigatus activities were assessed by studying the toxicity effect of the extracts on vegetative growth, sporulation and germination. The methanolic extract contained the highest TPC and CQC content. It contains several phytochemicals mainly caffeoylquinic acid derivatives as determined by liquid chromatography with photodiode array and electrospray ionisation mass spectrometric detection (LC/PDA/ESI-MS) analysis. All extracts showed an excellent inhibitory effect against bacteria and Candida spp., whereas methanolic extract exhibited the highest antifungal activities against Malassezia spp., M. canis and A. fumigatus strains. The results clearly showed that all extracts, in particular the methanolic extract, might be excellent antimicrobial drugs for treating infections that are life threatening (i.e., Malassezia) or infections that require mandatory treatments (i.e., M. canis or A. fumigatus). Full article
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Review

Jump to: Research

Open AccessReview Vegetable Tannins Used in the Manufacture of Historic Leathers
Molecules 2018, 23(5), 1081; https://doi.org/10.3390/molecules23051081
Received: 28 March 2018 / Revised: 28 April 2018 / Accepted: 1 May 2018 / Published: 3 May 2018
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Abstract
In this review, a brief description of how animal skins were transformed in leathers in Europe using different vegetable tannins will be presented. Special attention will be dedicated to the description of the type of tannins and the characteristics of the most important
[...] Read more.
In this review, a brief description of how animal skins were transformed in leathers in Europe using different vegetable tannins will be presented. Special attention will be dedicated to the description of the type of tannins and the characteristics of the most important type of historic leathers thus obtained. The text will also focus on the description of the techniques used in the identification of these tannins in historic objects: colorimetric tests and spectroscopic analysis. Full article
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Open AccessReview Tannins from Acacia mearnsii De Wild. Bark: Tannin Determination and Biological Activities
Molecules 2018, 23(4), 837; https://doi.org/10.3390/molecules23040837
Received: 7 March 2018 / Revised: 20 March 2018 / Accepted: 3 April 2018 / Published: 5 April 2018
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Abstract
The bark of Acacia mearnsii De Wild. (black wattle) contains significant amounts of water-soluble components acalled “wattle tannin”. Following the discovery of its strong antioxidant activity, a wattle tannin dietary supplement has been developed and as part of developing new dietary supplements, a
[...] Read more.
The bark of Acacia mearnsii De Wild. (black wattle) contains significant amounts of water-soluble components acalled “wattle tannin”. Following the discovery of its strong antioxidant activity, a wattle tannin dietary supplement has been developed and as part of developing new dietary supplements, a literature search was conducted using the SciFinder data base for “Acacia species and their biological activities”. An analysis of the references found indicated that the name of Acacia nilotica had been changed to Vachellia nilotica, even though the name of the genus Acacia originated from its original name. This review briefly describes why and how the name of A. nilotica changed. Tannin has been analyzed using the Stiasny method when the tannin is used to make adhesives and the hide-powder method is used when the tannin is to be used for leather tanning. A simple UV method is also able to be used to estimate the values for both adhesives and leather tanning applications. The tannin content in bark can also be estimated using NIR and NMR. Tannin content estimations using pyrolysis/GC, electrospray mass spectrometry and quantitative 31P-NMR analyses have also been described. Tannins consists mostly of polyflavanoids and all the compounds isolated have been updated. Antioxidant activities of the tannin relating to anti-tumor properties, the viability of human neuroblastoma SH-SY5Y cells and also anti-hypertensive effects have been studied. The antioxidant activity of proanthocyanidins was found to be higher than that of flavan-3-ol monomers. A total of fourteen papers and two patents reported the antimicrobial activities of wattle tannin. Bacteria were more susceptible to the tannins than the fungal strains tested. Several bacteria were inhibited by the extract from A. mearnsii bark. The growth inhibition mechanisms of E. coli were investigated. An interaction between extracts from A. mearnsii bark and antibiotics has also been studied. The extracts from A. mearnsii bark inhibit the growth of cyanobacteria. Wattle tannin has the ability to inactivate α-amylase, lipase and glucosidase. In vivo experiments on anti-obesity and anti-diabetes were also reported. Several patents relating to these enzymes for anti-diabetes and anti-obesity are in the literature. In addition, studies on Acacia bark extract regarding its antitermite activities, inhibition of itching in atopic dermatitis and anti-inflammatory effects have also been reported. The growth of bacteria was inhibited by the extract from A. mearnsii bark, and typical intestinal bacteria such as E. coli, K. pneumoniae, P. vulgaris and S. marcescenes was also inhibited in vitro by extracts. Based on these results, the Acacia bark extract may inhibit not only the growth of these typical intestinal bacteria but also the growth of other types of intestinal bacteria such as Clostridium and Bacteroides, a so-called “bad bacteria”. If the tannin extract from A. mearnsii bark inhibits growth of these “bad bacteria” in vivo evaluation, the extracts might be usable as a new dietary supplement, which could control the human intestinal microbiome to keep the body healthy. Full article
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Open AccessReview Chemical and Biological Significance of Oenothein B and Related Ellagitannin Oligomers with Macrocyclic Structure
Molecules 2018, 23(3), 552; https://doi.org/10.3390/molecules23030552
Received: 5 February 2018 / Revised: 26 February 2018 / Accepted: 26 February 2018 / Published: 2 March 2018
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Abstract
In 1990, Okuda et al. reported the first isolation and characterization of oenothein B, a unique ellagitannin dimer with a macrocyclic structure, from the Oenothera erythrosepala leaves. Since then, a variety of macrocyclic analogs, including trimeric–heptameric oligomers have been isolated from various medicinal
[...] Read more.
In 1990, Okuda et al. reported the first isolation and characterization of oenothein B, a unique ellagitannin dimer with a macrocyclic structure, from the Oenothera erythrosepala leaves. Since then, a variety of macrocyclic analogs, including trimeric–heptameric oligomers have been isolated from various medicinal plants belonging to Onagraceae, Lythraceae, and Myrtaceae. Among notable in vitro and in vivo biological activities reported for oenothein B are antioxidant, anti-inflammatory, enzyme inhibitory, antitumor, antimicrobial, and immunomodulatory activities. Oenothein B and related oligomers, and/or plant extracts containing them have thus attracted increasing interest as promising targets for the development of chemopreventive agents of life-related diseases associated with oxygen stress in human health. In order to better understand the significance of this type of ellagitannin in medicinal plants, this review summarizes (1) the structural characteristics of oenothein B and related dimers; (2) the oxidative metabolites of oenothein B up to heptameric oligomers; (3) the distribution of oenotheins and other macrocyclic analogs in the plant kingdom; and (4) the pharmacological activities hitherto documented for oenothein B, including those recently found by our laboratory. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Type: Article
Title: Composition and Structural Features of Condensed Tannins from Legumes Exhibiting Methane Abatement Activity during in vitro Rumen Digestion
Authors: Harley D. Naumann 1, Rebecka Sepela 2, Aria Rezaire 2, Laurie A. Reinhardt 3, Jamison T. Robe 3, Wayne Zeller 3, Ann E. Hagerman 2
Affiliations: 1 Division of Plant Sciences, University of Missouri, Columbia, MO, United States.
2 Department of Chemistry and Biochemistry, Miami University, Oxford, OH, United States.
3 U.S. Dairy Forage Research Center, USDA-ARS, Madison, WI, United States.
Abstract: Previous studies showed that a series of purified condensed tannins (CTs) from warm-season perennial legumes exhibited high variability in their modulation of methane production during in vitro rumen digestion. The molecular weight difference of these CTs did not provide correlation with either the in vitro methane production or the ability to precipitate bovine serum albumin. In an effort to delineate other structure-activity relationships from these methane abatement experiments, the structures of purified CTs from legumes representing Papilionoideae (Desmodium paniculatum, Lespedeza stuevei, and Lespedeza cuneata and Mimosoideae (Mimosa strigillosa, Leucaena retusa, Neptunia lutea, Desmanthus illinoensis, and Acacia angustissima var hirta) were assessed through a combination of methanolysis, quantitative thiolysis, ESI-MS, MALDI-TOF MS and high resolution 1H-13C HSQC NMR spectroscopy. The structural composition of these CTs were as follows: D. paniculatum proanthocyanidin to proanthodelphinidin (PC/PD) ratio 55/45, cis/trans ratio 87/13, mDP ~20; L. stuevei, PC/PD ratio, 42/58, cis/trans ratio 31/69 (NMR), 64/36 (thiolysis), mean degree of polymerization mDP (~10) and a trace of galloylated subunits; L. cuneata, PC/PD ratio 5/95, cis/trans ratio 75/25 (NMR), 93/7 (thiolysis), mDP ~14 and a trace of galloylated subunits; M. strigillosa PC/PD ratio 15/85, cis/trans ratio 89/11, mDP ~10 and 43% of the flavan-3-ol subunits galloylated; L. retusa PC/PD ratio 99/1, cis/trans ratio 98/2, mDP ~6 and ~25% of the flavan-3-ol subunits galloylated; N. lutea PC/PD ratio 12/88, cis/trans ratio 94/6, mDP ~12 and 32% of the flavan-3-ol subunits galloylated; and D. illinoensis PC/PD ratio 4/96, cis/trans ratio 99/1, mDP ~6 and 75% of the flavan-3-ol subunits galloylated. The CT isolated from A. angustissima presented an unusual challenge as it was resistant to standard thiolytic degradation conditions and exhibited an atypical set of cross-peak signals in the 2D NMR. Efforts to elucidate the structure of this CT will be discussed.

Type: Review
Title: Structural revisions in natural ellagitannins
Author: Hidetoshi Yamada
Abstract: In this manuscript, we summarized structural revision of 28 natural ellagitannins. Major focuses in the account are the outline of the initial structural determination, the processes to find the errors in the structure, and methods for revision of the structure. Ellagitannins adopted here are alnusiin, alnusnins A and B, castalagin, cercidinins A and B, chebulinic acid, chebulagic acid, corilagin, geraniin, isoterchebin, nobotanins B, C, E, G, H, I, J, and K, punicalin, punicalagin, punigluconin, roxbin B, sanguiins H-2, H-3, and H-6, terchebin, and vescalagin.

Type of paper: Article
Title: Characterization of condensed tannins from freeze-dried, silage or hay purple prairie clover (Dalea purpurea Vent.): structure composition, protein precipitation and anti-Escherichia coli properties
Authors: K. Peng1, 2, Q. Q. Huang3, Z. Xu2, T. A. McAllister2, S. Acharya2, S. Wang1, C. Drake4, I. Mueller-Harvey4, Y. Wang2
Affiliations:

1 College of Engineering, China Agricultural University, Beijing, 100083, China
2 Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre, Lethbridge, Albert, T1J 4B1, Canada
3 College of Animal Science and Technology, Yangzhou University, Yangzhou, 225009, China.
4Chemistry and Biochemistry Laboratory, Food Production and Quality Division, School of Agriculture, Policy and Development, University of Reading, P.O. Box 236, 1 Earley Gate, Reading RG6 6AT, UK
Abstract: Conservation methods have been shown to affect forage nutrient composition and value, but little information is available about the effect of forage conservation on plant condensed tannins (CT). The objective of this study was to assess the effects of conservation method on the concentration, chemical composition and biological activity of CT. Whole plant purple prairie clover (PPC, Dalea purpurea Vent.) was harvested at the full-flower stage and conserved as freeze-dried forage (FD), silage (SIL) or hay (HAY). Concentration of CT in conserved PPC was determined by the butanol-HCl-acetone method. Structural composition, protein-precipitation capacity and anti-bacterial activity of CT isolated from conserved forage were determined by in situ thiolytic degradation followed by LC-MS analysis, a protein precipitation assay using bovine serum albumin (BSA) and ribulose 1,5-disphosphate carboxylase (Rubisco) as model proteins and an Escherichia coli growth test, respectively. Conservation method had no effect on concentration of total CT, but ensiling decreased (P < 0.001) extractable CT and increased (P < 0.001) fiber-bound and protein-bound CT. In contrast, hay only increased (P < 0.01) protein-bound CT. Regardless of conservation method, epigallocatechin (EGC), catechin (C) and epicatechin (EC) were the major flavan-3-ol subunits, and gallocatechin (GC) was absent from both terminal and extension units of PPC CT. The SIL CT had the lowest (P < 0.001) EGC but the highest (P <0.01) EC in the extension units. Similarly, SIL CT exhibited a lower (P < 0.001) mean degree of polymerization (mPD), but a higher (P < 0.001) procyanidin/prodelphinidin ratio (PC/PD) than FD or HAY CT. The protein-precipitating capacity of CT in conserved PPC ranked (P < 0.001) as FD > HAY > SIL. Growth of E. coli in M9 medium was inhibited by 25-100 µg/ml of CT isolated from FD, SIL and HAY (P < 0.05), but preservation method had no effect on the ability of CT to inhibit bacterial growth. The results demonstrated that ensiling decreased the extractability and protein-precipitating capacity of CT by increasing the PC/PD ratio. Purple prairie clover conserved as hay retained more biologically active CT than if it was conserved as silage.
Keywords: Purple prairie clover, forage conservation, condensed tannins, protein-precipitation capacity, antimicrobial activity

Type of paper: Review
Authors: L. Falcão and MEM Araújo
CQB and Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Portugal
Title: Vegetable tannins used in the manufacture of historic leathers
Abstract: In this review a brief description of how in Europe animal skins were transformed in leathers using different kinds of vegetable tannins will be described. Special attention will be dedicated to the description of the kind of tannin and the characteristics of the most important type of historic leathers thus obtained. The text will also focus on de description of the techniques used in the identification of these tannins in historic objects: colorimetric tests and spectroscopic analysis.

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