Covalent anthocyanin–flavone dimer from leaves of Oxalis triangularis

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• 作者：Torgils Fossen ; Saleh Rayyan ; Maya H. Holmberg ; Manfred Nimtz ; Ø ; yvind M. Andersen
• 关键词：Oxalis triangularis ; Leaves ; Anthocyanin– ; flavone C-glycoside dimer ; Malvidin 3-rutinoside-5-glucoside (malonate) apigenin 6-C-sophoroside ; Colour ; Equilibrium forms ; HSQC-TOCSY ; ¹³C NMR
• 刊名：Phytochemistry
• 出版年：2007
• 期刊代码：85_00319422
• 类别：ch
• 出版时间：March 2007
• 卷：68
• 期：5
• 页码：652-662
• 文件大小：418 K

摘要

The anthocyanin–flavone C-glycoside, (malvidin 3-O-(6^II-O-α-rhamnopyranosyl^AIV-β-glucopyranoside^AII)-5-O-β-glucopyranoside^AIII) (apigenin 6-C-(2^II-O-β-glucopyranosyl^FIII-β-glucopyranoside^FII)) malonate^AV (A^IV-4 → A^V-1, F^III-6 → A^V-3) (1), has been isolated from leaves of Oxalis triangularis A. St.-Hil. In the 1D ¹H NMR spectrum of 1 dissolved in CD₃OD–CF₃CO₂D (95:5), MTFA, recorded 45 min after sample preparation, this covalently linked dimer occurred mainly as flavylium cation (38%) and two equilibrium forms assigned to be quinonoidal bases (54%), whereas only minor amounts of the hemiacetal forms were present. After five days storage at 300 K, the hemiacetals (39%) and flavylium cation (38%) constituted the main forms of 1. More simple anthocyanins are normally considered to be on the flavylium cation form in acidified deuterated methanol. The cross-peaks observed in NOESY NMR spectra of 1 indicated the presence of vertical ’π–π’ stacking between the B-ring of the flavone unit and the A-ring of each of the two forms assigned to be quinonoidal bases. It was not possible to discriminate between inter- or intramolecular association mechanisms. The equilibria between the various forms of 1 were studied by two-dimensional NOESY and ROESY NMR spectroscopy. 2D HSQC-TOCSY NMR spectroscopy was among the methods used for characterization of the various forms.