黄烷-3-醇

黃烷醇 (全名: 黃烷-3-醇類) 的化學結構

黃烷醇(flavanol)全名黃烷-3-醇類(flavan-3-ol),是一種植物黄酮类化合物,為2-苯基-3,4-二氫-2H-色烯-3-醇骨架黃烷的衍生物;此類化合物屬於一種植物自然產生的抗氧化劑,特別是可可类植物。适量黃烷醇对有益健康,过量摄入则会有肝毒性。它們在植物防禦中發揮作用,並且存在於大多數植物中[1]

與許多抗氧化劑比較起來,黃烷醇可幫助身體對付自由基的存在,也會增加血中一氧化氮,增加血液流量、降血壓;這些類型的抗氧化劑也防止血液凝塊。也有一些證據表明,類黃酮化合物可以幫助降低血液中的低密度脂蛋白或壞膽固醇水平。

黃烷-3-醇類包括:兒茶素、表兒茶素沒食子酸酯、沒食子兒茶素(棓儿茶素,(-)-gallocatechin)、表沒食子兒茶素沒食子酸酯原花青素茶黃素茶紅素

注意:黃烷醇(flavanols)不可與含酮基的黃酮類化合物——黃酮醇flavonols)混淆。

化學結構

單分子(單體)兒茶素,或異構體表兒茶素,可將四個羥基加至黃烷-3-醇,是串接聚合物(原花青素)和高階聚合物(花青素)的構件[2]

黃烷醇具有兩個手性碳,這意味著出現4個非对映异构。 它們有別於槲皮素蘆丁等黃色含酮類黃酮,它們被稱為黃酮醇。早期使用的術語生物類黃酮被不准確地應用到包括黃烷醇,黃烷醇的特點是不存在兒茶素的單體、二聚體和三聚體(低聚物)是無色的。 更高階的聚合物,花青素,表現出加深的紅色並變成單寧[2]

兒茶素表兒茶素差向異構體,其中 (–)-表兒茶素和 (+)-兒茶素是自然界中最常見的光學同分異構體。 兒茶素最初是從植物提取物兒茶中分離出來的,因此得名。 加熱兒茶素超過其分解點會釋放鄰苯二酚(也稱為兒茶酚),這解釋了這些化合物名稱的共同來源。

與表兒茶素和兒茶素相比,表沒食子兒茶素和沒食子兒茶素分別含有一個額外的酚羥基,類似於鄰苯三酚鄰苯二酚的差異。

兒茶素沒食子酸酯是兒茶素的沒食子酸; 一個例子是表沒食子兒茶素沒食子酸酯(EGCG),它通常是茶葉中最豐富的兒茶素。 原花青素茶紅素是低聚黃烷-3-醇。

與許多其他類黃酮不同,黃烷-3-醇不以通常的糖苷形式存在於植物中[3]

結構: (表) 兒茶素、(表) 兒茶素沒食子酸酯、(表) 沒食子兒茶素、和 (表) 沒食子兒茶素沒食子酸酯。
黃烷(flavan)化合物骨架編號 (+)-兒茶素 Guibourtinidol英语Guibourtinidol

表兒茶素生物合成

Figure 1
Figure 1

Figure 1:Schematic overview of the flavan-3-ol (-)-epicatechin biosynthesis in plants: Enzymes are indicated in blue, abbreviated as follows: E1, phenylalanine ammonia lyase (PAL), E2, tyrosine ammonia lyase (TAL), E3, cinnamate 4-hydroxylase, E4, 4-coumaroyl: CoA-ligase, E5, chalcone synthase (naringenin-chalcone synthase), E6, chalcone isomerase, E7, Flavonoid 3'-hydroxylase, E8, flavonone 3-hydroxylase, E9, dihydroflavanol 4-reductase, E10, anthocyanidin synthase (leucoanthocyanidin dioxygenase), E11, anthocyanidin reductase. HSCoA, Coenzyme A. L-Tyr, L-tyrosine, L-Phe, L-phenylalanine.

参考文献

  1. ^ Ullah C, Unsicker SB, Fellenberg C, Constabel CP, Schmidt A, Gershenzon J, Hammerbacher A. Flavan-3-ols Are an Effective Chemical Defense against Rust Infection. Plant Physiology. December 2017, 175 (4): 1560–1578. PMC 5717727可免费查阅. PMID 29070515. doi:10.1104/pp.17.00842. 
  2. ^ 2.0 2.1 Schwitters B, Masquelier J. OPC in Practice 3rd. 1995. OCLC 45289285. 
  3. ^ Del Rio D, Rodriguez-Mateos A, Spencer JP, Tognolini M, Borges G, Crozier A. Dietary (poly)phenolics in human health: structures, bioavailability, and evidence of protective effects against chronic diseases. Antioxidants & Redox Signaling. May 2013, 18 (14): 1818–1892. PMC 3619154可免费查阅. PMID 22794138. doi:10.1089/ars.2012.4581. 

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