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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".

Deadline for manuscript submissions: 31 March 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 March 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 (3 papers)

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Research

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; doi:10.3390/molecules22111989
Received: 23 October 2017 / Revised: 14 November 2017 / Accepted: 15 November 2017 / Published: 17 November 2017
PDF Full-text (3345 KB) | HTML Full-text | XML Full-text | Supplementary Files
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
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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
Figures

Open AccessArticle Characterization of Proanthocyanidin Oligomers of Ephedra sinica
Molecules 2017, 22(8), 1308; doi:10.3390/molecules22081308
Received: 14 July 2017 / Revised: 27 July 2017 / Accepted: 3 August 2017 / Published: 6 August 2017
PDF Full-text (8684 KB) | HTML Full-text | XML Full-text | Supplementary Files
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
Figures

Figure 1

Open AccessArticle Chemical Composition, Antibacterial and Antifungal Activities of Crude Dittrichia viscosa (L.) Greuter Leaf Extracts
Molecules 2017, 22(7), 942; doi:10.3390/molecules22070942
Received: 12 May 2017 / Revised: 31 May 2017 / Accepted: 3 June 2017 / Published: 30 June 2017
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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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 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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