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Natural Flavonoids: Structure Elucidation, Distribution and Applications

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

Deadline for manuscript submissions: closed (30 June 2018) | Viewed by 56476

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Dr. Tsukasa Iwashina

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Department of Botany, National Museum of Nature and Science, Amakubo 4-1-1, Tsukuba, Ibaraki 305-0005, Japan
Interests: flavonoids; natural products; anthocyanins; flower colors; flavonoid function
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Dear Colleauges,

Flavonoid is the general name of compounds that have a fifteen-carbon skeleton, which consists of two phenyl rings (A- and B-rings) connected by a three-carbone bridge (C-ring). In general, vascular plants and bryophytes alone possess the biosynthetic ability of the flavonoids, except for a few green alga, fungi, and marine coral. Flavonoids are divided into several classes, e.g., anthocyanins, flavones, flavonols, chalcones, aurones, flavanones, dihydroflavonols, isoflavonoids, flavan and proanthocyanidins, biflavonoids etc. Moreover, numerous sorts of flavonoids occur in plants with additional hydroxyl, methoxyl, methyl and/or glycosyl substitution patterns. Additionally, aromatic and aliphatic acids, sulfate, methylenedioxyl or prenyl groups also attach to flavonoid nucleus and their glycosides. Thus, ca. 9000 kinds of flavonoids have been reported as naturally-occurring compounds. The isolation and identification, structures and distribution of the flavonoids in plants have been reviewed by many authors. Flavonoids, as medicinal resources, were also reviewed. Especially, the pigments, anthocyanins, were recently observed as having effects including antioxidant, antitumor, astringents, etc. However, the secondary metabolites involved in flavonoids were considered to be waste products of plant metabolism in the early days of the 20th century. One of the most important functions of flavonoids may be to serve as an ultraviolet filter in land plants. It has been shown by surveys of some plants that flavonoids act as a UV shield. The occurrence of anthocyanins as pollinator attractants is well-known as a function of flavonoids in plants. Additionally, it is known that flavones and flavonols, which can hardly be seen by the human eye, also act as pollinator attractants in addition to visible anthocyanins. Recently, other functions, e.g., oviposition stimulants, feeding attractants, feeding deterrents, allelopathy and phytoalexins of naturally-occurring flavonoids, have been reported by many authors. However, although almost vascular plants have synthesize abilities of the flavonoids, the presence of flavonoids may be known in ca. 25% of all plants on the Earth, and, moreover, the function of flavonoids in plants are hardly reported.

In this Special Issue, we will publish papers on new flavonoids, new flavonoid resources, flavonoid functions in plants, including as a UV shield, phytoalexins, allelopathy, oviposition stimulants, feeding attractants, feeding deterrent, and contribution of flavonoids, including anthocyanins to flower colors, and so on.

Prof. Dr. Tsukasa Iwashina
Guest Editor

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Keywords

flavonoid distribution in plants
new flavonoid resources
new compounds
chemical ecology
chemical adaptation
medicinal resources
phytoalexins
allelopathy
plant pigments
flower colors

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Published Papers (8 papers)

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Research

9 pages, 1083 KiB

Open AccessArticle

Utilization of Flavonoid Compounds from Bark and Wood. III. Application in Health Foods

by Sosuke Ogawa, Yosuke Matsuo, Takashi Tanaka and Yoshikazu Yazaki

Molecules 2018, 23(8), 1860; https://doi.org/10.3390/molecules23081860 - 26 Jul 2018

Cited by 80 | Viewed by 4692

Abstract

Dietary supplements ACAPOLIA^® and ACAPOLIA PLUS have been sold in Japan under the classification “Foods in General” for a number of years. In April 2015, the classification of “Foods with Function Claims” was introduced in Japan to make more products available to the public that were clearly labeled with functional claims based on scientific evidence. In order to obtain recognition of ACAPOLIA PLUS under this new classification, the following information needed to be established. The safety of the bark extract of Acacia mearnsii was shown from the history of the long-term safe consumption of the extract as a health supplement, together with several additional clinical safety tests. Robinetinidol-(4α,8)-catechin was detected by high performance liquid chromatography (HPLC) in the supplement and was suitable for use as the basis of the quantitative analysis. In clinical tests, the amount of change in the plasma glucose concentration in the initial 60 min after rice consumption by a test group who had been given the Acadia extract was significantly lower than the glucose concentration in the group that was given a placebo. The blood glucose incremental areas under the curve (IAUC) in the first 60 min after rice consumption were also significantly lower in the Acacia group. The functional mechanisms were explained in terms of the inhibition of the absorption of glucose in the small intestine and the reduction in the activity of the digestive enzymes caused by proanthocyanidins derived from A. mearnsii bark. As a result, ACAPOLIA PLUS was accepted as a “Food with Function Claims” in August 2016. ACAPOLIA PLUS is now sold under this new classification. The growth of a typical intestinal bacterium is inhibited by an extract containing flavonoid compounds from A. mearnsii bark; thus, one of the future directions of study must be a comprehensive investigation of the effect that flavonoid compounds, proanthocyanidins, have on intestinal bacteria. Full article

(This article belongs to the Special Issue Natural Flavonoids: Structure Elucidation, Distribution and Applications)

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8 pages, 2037 KiB

Open AccessArticle

Change of Petals′ Color and Chemical Components in Oenothera Flowers during Senescence

by Yada Teppabut, Kin-ichi Oyama, Tadao Kondo and Kumi Yoshida

Molecules 2018, 23(7), 1698; https://doi.org/10.3390/molecules23071698 - 12 Jul 2018

Cited by 17 | Viewed by 6975

Abstract

Oenothera flower petals change color during senescence. When in full bloom, the flowers of O. tetraptera are white and those of O. laciniata and O. stricta are yellow. However, the colors change to pink and orange, respectively, when the petals fade. We analyzed the flavonoid components in these petals as a function of senescence using HPLC-DAD and LC-MS. In all three species, cyanidin 3-glucoside (Cy3G) was found in faded petals. The content of Cy3G increased in senescence. In full bloom (0 h), no Cy3G was detected in any of the petals. However, after 12 h, the content of Cy3G in O. tetraptera was 0.97 µmol/g fresh weight (FW) and the content of Cy3G in O. laciniata was 1.82 µmol/g FW. Together with anthocyanins, major flavonoid components in petals were identified. Quercitrin was detected in the petals of O. tetraptera and isosalipurposide was found in the petals of O. laciniata and O. stricta. The content of quercitrin did not change during senescence, but the content of isosalipurposide in O. laciniata increased from 3.4 µmol/g FW at 0 h to 4.8 µmol/g FW at 12 h. The color change in all three Oenothera flowers was confirmed to be due to the de novo biosynthesis of Cy3G. Full article

(This article belongs to the Special Issue Natural Flavonoids: Structure Elucidation, Distribution and Applications)

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19 pages, 1244 KiB

Open AccessArticle

Green Tea Quality Evaluation Based on Its Catechins and Metals Composition in Combination with Chemometric Analysis

by Wojciech Koch, Wirginia Kukula-Koch, Łukasz Komsta, Zbigniew Marzec, Wojciech Szwerc and Kazimierz Głowniak

Molecules 2018, 23(7), 1689; https://doi.org/10.3390/molecules23071689 - 11 Jul 2018

Cited by 93 | Viewed by 9609

Abstract

Green tea infusions are one of the most popular beverages consumed across the world, especially is Asian countries. Green tea quality is primarily based on catechin content, however, the concentration of elements could also significantly influence its biological properties and thus quality and safety. The main purpose of the present study was the evaluation of catechin, antioxidant activity and metal content (K, Na, Ca, Mg, Fe, Mn, Cu, Zn, Cr, Pb, Cd and Ni) in different green tea types cultivated in Japan, Sri Lanka, South Korea, India, China and Japan. The chemical analysis of samples was performed using LC-ESI-Q-TOF-MS for organic constituents and atomic absorption spectrometry (flame and electrothermal) method for inorganic ones. The obtained results were subjected to chemometric elaboration. EGC (213 mg/100 mL of the tea infusion in South Korean Jeoncha) and EGCG (124 mg/100 mL in Japanese Sencha) were the dominant catechins in all green tea samples. Chinese and Indian green tea samples contained the highest concentration of toxic heavy metals, however these values were far below appropriate limitations for green teas. PCA revealed significant similarities between Japanese samples and Korean Jeoncha. In general the latter one was evaluated to have the best quality based on the investigated parameters. Full article

(This article belongs to the Special Issue Natural Flavonoids: Structure Elucidation, Distribution and Applications)

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11 pages, 3290 KiB

Open AccessArticle

Correlation between the Potency of Flavonoids on Mushroom Tyrosinase Inhibitory Activity and Melanin Synthesis in Melanocytes

by Worrawat Promden, Wittawat Viriyabancha, Orawan Monthakantirat, Kaoru Umehara, Hiroshi Noguchi and Wanchai De-Eknamkul

Molecules 2018, 23(6), 1403; https://doi.org/10.3390/molecules23061403 - 9 Jun 2018

Cited by 47 | Viewed by 8273

Abstract

Twenty-seven flavonoids isolated from Dalbergia parviflora with vast structural diversity were screened for inhibitory activity against mushroom and murine tyrosinases using l-DOPA as the substrate. Among the flavonoids tested, only four—khrinone (5), cajanin (9), (3RS)-3′-hydroxy-8-methoxy vestitol (21), and (6aR,11aR)-3,8-dihydroxy-9-methoxy pterocarpan (27)—reacted with mushroom tyrosinase, with IC₅₀ values of 54.0, 67.9, 67.8, and 16.7 μM, respectively, and only compound 27 showed inhibitory activity against murine tyrosinase. With cell-based assays, only compounds 9 and 27 effectively inhibited melanogenesis in B16-F10 melanoma cells (by 34% and 59%, respectively), at a concentration of 15 μM, without being significantly toxic to the cells. However, the crude extract of D. parviflora and some of the flavonoid constituents appeared to increase melanin production in B16-F10 cells, suggesting that there are flavonoids with both inhibitory and stimulatory melanogenesis in the crude extract. Studies on the correlation between the enzyme-based and cell-based assays showed that only the flavonoids with IC₅₀ values below 50 μM against mushroom tyrosinase could inhibit the mammalian tyrosinase, and thus, reduce melanogenesis in B16-F10. Flavonoids with the IC₅₀ values greater than 50 μM, on the other hand, could not inhibit the mammalian tyrosinase, and had either no effect or enhancement of melanogenesis. In conclusion, the tyrosinase enzyme from mushroom is not as selective as the one from mammalian source for the enzyme-based melanogenesis inhibitory screening, and the mammalian cell-based assay appears to be a more reliable model for screening than the enzyme-based one. Full article

(This article belongs to the Special Issue Natural Flavonoids: Structure Elucidation, Distribution and Applications)

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16 pages, 17172 KiB

Open AccessArticle

Efficient Approach for the Extraction and Identification of Red Pigment from Zanthoxylum bungeanum Maxim and Its Antioxidant Activity

by Xi Chen, Zhiqiang Wei, Lei Zhu, Xing Yuan, Daneng Wei, Wei Peng and Chunjie Wu

Molecules 2018, 23(5), 1109; https://doi.org/10.3390/molecules23051109 - 8 May 2018

Cited by 38 | Viewed by 5629

Abstract

Red pigment (RP) was extracted from the peels of Zanthoxylum bungeanum Maxim (PZB) by ultrasonic-assisted extraction (UAE) in this work. Box–Behnken design–response surface methodology (BBD-RSM) was employed to research the efficiency of the RP extraction. Based on the optimization of RSM, results showed that the optimal extraction conditions were as follows: liquid–solid ratio of 31 mL/g, extraction time of 41 min, and extraction temperature of 27 °C, and under these conditions, the actual absorbance value was 0.615 ± 0.13%, highly agreeing with the predicted value by the model. Furthermore, ultra-performance liquid chromatography–mass spectrometry (UPLC-MS) was used to separate and analyze RP. The compounds of RP were mainly flavonoids, and there were five compounds detected for the first time in PZB. In addition, RP showed significant antioxidant activities in vitro, which could be developed for anti-aging candidate drugs and functional foods. In conclusion, ultrasound-assisted extraction with BBD-RSM and chromatographic separation technology with UPLC-MS are efficient strategies for the isolation and identification of RP from PZB. Full article

(This article belongs to the Special Issue Natural Flavonoids: Structure Elucidation, Distribution and Applications)

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10 pages, 1657 KiB

Open AccessFeature PaperArticle

Synthesis of New Glycosylated Flavonoids with Inhibitory Activity on Cell Growth

by Ana R. Neves, Marta Correia-da-Silva, Patrícia M. A. Silva, Diana Ribeiro, Emília Sousa, Hassan Bousbaa and Madalena Pinto

Molecules 2018, 23(5), 1093; https://doi.org/10.3390/molecules23051093 - 5 May 2018

Cited by 9 | Viewed by 6730

Abstract

Natural flavonoids and xanthone glycosides display several biological activities, with the glycoside moiety playing an important role in the mechanism of action of these metabolites. Herein, to give further insights into the inhibitory activity on cell growth of these classes of compounds, the synthesis of four flavonoids (5, 6, 9, and 10) and one xanthone (7) containing one or more acetoglycoside moieties was carried out. Acetyl groups were introduced using acetic anhydride and microwave irradiation. The introduction of one or two acetoglycoside moieties in the framework of 3,7-dihydroxyflavone (4) was performed using two synthetic methods: the Michael reaction and the Koenigs-Knorr reaction. The in vitro cell growth inhibitory activity of compounds 5, 6, 7, 9, and 10 was investigated in six human tumor cell lines: A375-C5 (malignant melanoma IL-1 insensitive), MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer), U251 (glioblastoma astrocytoma), U373 (glioblastoma astrocytoma), and U87MG (glioblastoma astrocytoma). The new flavonoid 3-hydroxy-7-(2,3,4,6-tetra-O-acetyl-β-glucopyranosyl) flavone (10) was the most potent compound in all tumor cell lines tested, with GI₅₀ values < 8 μM and a notable degree of selectivity for cancer cells. Full article

(This article belongs to the Special Issue Natural Flavonoids: Structure Elucidation, Distribution and Applications)

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22 pages, 5738 KiB

Open AccessArticle

Development of Phaleria macrocarpa (Scheff.) Boerl Fruits Using Response Surface Methodology Focused on Phenolics, Flavonoids and Antioxidant Properties

by Khurul Ain Mohamed Mahzir, Siti Salwa Abd Gani, Uswatun Hasanah Zaidan and Mohd Izuan Effendi Halmi

Molecules 2018, 23(4), 724; https://doi.org/10.3390/molecules23040724 - 22 Mar 2018

Cited by 15 | Viewed by 7430

Abstract

In this study, the optimal conditions for the extraction of antioxidants from the Buah Mahkota Dewa fruit (Phaleria macrocarpa) was determined by using Response Surface Methodology (RSM). The optimisation was applied using a Central Composite Design (CCD) to investigate the effect of three independent variables, namely extraction temperature (°C), extraction time (minutes) and extraction solvent to-feed ratio (% v/v) on four responses: free radical scavenging activity (DPPH), ferric ion reducing power assay (FRAP), total phenolic content (TPC) and total flavonoid content (TFC). The optimal conditions for the antioxidants extraction were found to be 64 °C extraction temperature, 66 min extraction time and 75% v/v solvent to-feed ratio giving the highest percentage yields of DPPH, FRAP, TPC and TFC of 86.85%, 7.47%, 292.86 mg/g and 3.22 mg/g, respectively. Moreover, the data were subjected to Response Surface Methodology (RSM) and the results showed that the polynomial equations for all models were significant, did not show lack of fit, and presented adjusted determination coefficients (R²) above 99%, proving that the yield of phenolic, flavonoid and antioxidants activities obtained experimentally were close to the predicted values and the suitability of the model employed in RSM to optimise the extraction conditions. Hence, in this study, the fruit from P. macrocarpa could be considered to have strong antioxidant ability and can be used in various cosmeceutical or medicinal applications. Full article

(This article belongs to the Special Issue Natural Flavonoids: Structure Elucidation, Distribution and Applications)

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12 pages, 6979 KiB

Open AccessArticle

Protective Mechanism of the Antioxidant Baicalein toward Hydroxyl Radical-Treated Bone Marrow-Derived Mesenchymal Stem Cells

by Yage Tian, Xican Li, Hong Xie, Xiaozhen Wang, Yulu Xie, Chuanbing Chen and Dongfeng Chen

Molecules 2018, 23(1), 223; https://doi.org/10.3390/molecules23010223 - 20 Jan 2018

Cited by 36 | Viewed by 5993

Abstract

Our study explores the antioxidant and cytoprotective effects of baicalein and further discusses the possible mechanisms. A methyl thiazolyl tetrazolium (MTT) assay revealed that baicalein could considerably enhance the viability of hydroxyl radical-treated bone marrow-mesenchymal stem cells (bmMSCs) at 37–370 µM. The highest viability rate was 120.4%. In subsequent studies, baicalein was observed to effectively scavenge hydroxyl radical and PTIO• radicals, reducing Fe³⁺ and Cu²⁺ ions. In the Fe²⁺-chelating UV-vis spectra, mixing of baicalein with Fe²⁺ yielded two evident redshifts (275 → 279 nm and 324 → 352 nm) and a broad absorption peak (λ_max ≈ 650 nm, ε = 1.6 × 10³ L mol⁻¹·cm⁻¹). Finally, we compared the Fe²⁺-chelating UV-vis spectra of baicalein and its analogues, including 5-hydroxyflavone, 6-hydroxyflavone, 7-hydroxyflavone, catechol, pyrogallol, and chrysin. This analysis revealed that the 4-keto group of the C-ring played a role. The 5,6,7-trihydroxy-group (pyrogallol group) in the A-ring served as an auxochrome, enhancing the absorbance of the UV-vis spectra and deepening the color of the Fe²⁺-complex. We concluded that baicalein, as an effective hydroxyl radical-scavenger, can protect bmMSCs from hydroxyl radical-mediated oxidative stress. Its hydroxyl radical-scavenging effects are likely exerted via two pathways: direct scavenging of hydroxyl radicals, possibly through electron transfer, and indirect inhibition of hydroxyl radical generation via Fe²⁺ chelation through the 4-keto-5,6,7-trihydroxy groups. Full article

(This article belongs to the Special Issue Natural Flavonoids: Structure Elucidation, Distribution and Applications)

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