Fagopyrins are phenantroperylenequinones present in the flowers of Fagopyrum esculentum (buckwheat) endowed with photodynamic activity. It has been reported that fagopyrin extracts actually contain a complex mixture of closely related compounds, differing only on the nature of the perylenequinone substituents. We report our systematic and detailed study on the chemical composition of fagopyrin extracts by a combination of preparative and analytical techniques. The combined use of 1H-NMR and CD spectroscopy was found to be particularly suited to fully characterize all stereochemical aspects of the extracted fagopyrins. For the first time nine isomers have been structurally characterized and their stereochemistry fully elucidated. The presence of two different heterocyclic ring substituents, two stereogenic centers and the inherent axial chirality of the aromatic system provides a complex stereochemical relationships among isomers, thus giving account of the high level of molecular multiplicity found in the extract.

中文翻译：

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荞麦花中的苦荞苷：通过组合 NMR/CD 光谱和理论计算进行结构和立体化学表征。

荞麦苷是存在于荞麦花中的菲苝醌，具有光动力活性。据报道，苦荞苷提取物实际上含有密切相关的化合物的复杂混合物，仅在苝醌取代基的性质上有所不同。我们报告了通过结合制备和分析技术对苦荞苷提取物的化学成分进行的系统和详细的研究。 1H-NMR 和 CD 光谱的结合使用特别适合全面表征提取的荞麦苷的所有立体化学方面。首次对九种异构体进行了结构表征，并充分阐明了它们的立体化学。两个不同的杂环取代基、两个立体中心和芳香系统固有的轴向手性的存在提供了异构体之间复杂的立体化学关系，从而说明了提取物中发现的高水平的分子多样性。