In the research on ellagitannin metabolism, two unique dehydroellagitannins, carpinins E (1) and F (2), bearing dehydrohexahydroxydiphenoyl (DHHDP) and hydrated biscyclohexenetrione dicarboxyl ester (HBCHT) groups, were isolated from young leaves of Carpinus japonica. Upon heating in H₂O or treatment with pH 6 buffer at room temperature, 1 and 2 afforded the reduction product 3, isocarpinin A, with an (R)-hexahydroxydiphenoyl (HHDP) group, suggesting the occurrence of redox disproportionation of the (S)-DHHDP group. This was supported by the increase in production of 3 in the pH 6 buffer solution by coexistence of epigallocatechin-3-O-gallate (15), accompanied by oxidation of 15. In contrast, treatment of 1 and 2 with ascorbic acid yielded 4, carpinin A, with an (S)-HHDP group. Upon heating with ascorbic acid, the HBCHT group was also reduced to an (S)-HHDP group, and 2 was converted to 2,3;4,6-bis(S)-HHDP glucose. In leaves of C. japonica, the tannins 1 and 2 are dominant in young spring leaves, but compounds 3 and 4 become the major components of tannins in mature leaves. These results suggest that, in ellagitannin biosynthesis, oxidative coupling of the two galloyl groups first generates a DHHDP group, and subsequent reduction of DHHDP esters produces HHDP esters.

中文翻译：

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海棠高氧化鞣花单宁及其氧化还原歧化

在鞣花单宁的代谢的研究，两个独特dehydroellagitannins，carpinins E（1）和F（2），轴承dehydrohexahydroxydiphenoyl（DHHDP）和水合biscyclohexenetrione二羧基酯（HBCHT）基团，是从嫩叶分离鹅耳枥粳稻。在 H ₂ O 中加热或在室温下用 pH 6 缓冲液处理后，1和2提供还原产物3，异果皮素 A，带有 ( R )-六羟基二苯甲酰基 (HHDP) 基团，表明 ( S )-DHHDP 组。这得益于产量增加3在 pH 6 的缓冲溶液中，表没食子儿茶素-3 - O-没食子酸酯 ( 15 )共存，伴随着15的氧化。相比之下，用抗坏血酸处理1和2产生了4，carpinin A，具有 ( S )-HHDP 组。在与抗坏血酸一起加热时，HBCHT 基团也被还原为 ( S )-HHDP 基团，并且2转化为 2,3;4,6-bis( S )-HHDP 葡萄糖。在C. japonica的叶子中，单宁1和2在年轻的春叶中占优势，但化合物3和4成为成熟叶片中单宁的主要成分。这些结果表明，在鞣花单宁生物合成中，两个没食子酰基的氧化偶联首先产生 DHHDP 基团，随后 DHHDP 酯的还原产生 HHDP 酯。