Covalent anthocyanin–flavonol complexes from the violet-blue flowers of Allium ‘Blue Perfume’

• Published in: Phytochemistry (Oxford) 2012-08, Vol.80, p.99-108
• Main Authors: Saito, Norio, Nakamura, Maiko, Shinoda, Koichi, Murata, Naho, Kanazawa, Toshinari, Kato, Kazuhisa, Toki, Kenjiro, Kasai, Hiroko, Honda, Toshio, Tatsuzawa, Fumi
• Format: Article
• Language: English
• Subjects: absorption; acetic acid; acylation; Alliaceae; Allium - chemistry; Allium schoenoprasum; Allium ‘Blue Perfume’; Anthocyanin and flavonols disubstitute malonate; Anthocyanins - chemistry; Anthocyanins - isolation & purification; Anthocyanins - metabolism; Buffers; color; cotton; coumaric acids; delphinidin; Delphinidin 3-glucoside kaempferol 3-glycoside-7-glucosiduronic acids and malonic acid; Flavonols - chemistry; Flavonols - isolation & purification; Flavonols - metabolism; Flower color; flowers; Flowers - chemistry; Glucosides - chemistry; Glucosides - metabolism; Hydrogen-Ion Concentration; Intramolecular copigmentation; kaempferol; myrtillin; Pigmentation
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2012.04.011

Three covalent anthocyanin-flavonol complexes (pigments 1–3) and one acylated kaempferol glycoside (pigment 4) were isolated from the violet-blue flowers of Allium ‘Blue Perfume’. [Display omitted] ► Covalent anthocyanin–flavonol complexes were isolated from the violet-blue flowers of Allium. ► Covalent anthocyanin–flavonol complexes were based on delphinidin 3-glucoside. ► The violet-blue flower color of Allium was exhibited by strong intramolecular copigmentation. Three covalent anthocyanin–flavonol complexes (pigments 1–3) were extracted from the violet-blue flower of Allium ‘Blue Perfume’ with 5% acetic acid-MeOH solution, in which pigment 1 was the dominant pigment. These three pigments are based on delphinidin 3-glucoside as their deacylanthocyanin and were acylated with malonyl kaempferol 3-sophoroside-7-glucosiduronic acid or malonyl-kaempferol 3-p-coumaroyl-tetraglycoside-7-glucosiduronic acid in addition to acylation with acetic acid. By spectroscopic and chemical methods, the structures of these three pigments 1–3 were determined to be: pigment 1, (6I-O-(delphinidin 3-O-(3I-O-(acetyl)-β-glucopyranosideI)))(2VI-O-(kaempferol 3-O-(2II-O-(3III-O-(β-glucopyranosylV)-β-glucopyranosylIII)-4II-O-(trans-p-coumaroyl)-6II-O-(β-glucopyranosylIV)-β-glucopyranosideII)-7-O-(β-glucosiduronic acidVI))) malonate; pigment 2, (6I-O-(delphinidin 3-O-(3I-O-(acetyl)-β-glucopyranosideI)))(2VI-O-(kaempferol 3-O-(2II-O-β-glucopyranosylIII)-β-glucopyranosideII)-7-O-(β-glucosiduronic acidVI))); and pigment 3, (6I-O-(delphinidin 3-O-(3I-O-(acetyl)-β-glucopyranosideI)))(2VI-O-(kaempferol 3-O-(2II-O-(3III-O-(β-glucopyranosylV)-β-glucopyranosylIII)-4II-O-(cis-p-coumaroyl)-6II-O-(β-glucopyranosylIV)-β-glucopyranosideII)-7-O-(β-glucosiduronic acidVI))) malonate. The structure of pigment 2 was analogous to that of a covalent anthocyanin–flavonol complex isolated from Allium schoenoprasum where delphinidin was observed in place of cyanidin. The three covalent anthocyanin–flavonol complexes (pigment 1–3) had a stable violet-blue color with three characteristic absorption maxima at 540, 547 and 618nm in pH 5–6 buffer solution. From circular dichroism measurement of pigment 1 in the pH 6.0 buffer solution, cotton effects were observed at 533 (+), 604 (−) and 638 (−) nm. Based on these results, these covalent anthocyanin–flavonol complexes were presumed to maintain a stable intramolecular association between delphinidin and kaempferol units closely related to that observed between an