Kenjiro Toki

New aspects of anthocyanin complexation. Intramolecular copigmentation as a means for colour loss

Two series of structurally related anthocyanins, extracted from the blue flowers of Evolvulus pilosus cv. Blue Daze and from the blue-purple flowers of Eichhornia crassipes, exhibit remarkable colour stabilities in aqueous solution at mildly acidic pH values. All the pigments possess the same chromophore (delphinidin), but a different pattern of glycosylation and acylation. Moreover, one of the pigments has an apigenin 7-glucoside molecule (a flavone) attached to the glycosidic chain by two ester bonds with malonic acid, instead of an aromatic acid and is the only known anthocyanin with such a structure. All the molecules studied, except one which has only a 3-gentiobioside (a disaccharide) as substituent, denote an effect of reduction in the hydration constant when compared with the parent delphinidin 3-glucoside or 3,5-diglucoside molecules, which supports the existence of intramolecular hydrophobic interactions between the chromophoric skeleton and the acyl or flavonoid groups. The role played by the sugar units on the hydrophobicity/hydrophilicity of the pigments is also discussed.

New features of intramolecular copigmentation by acylated anthocyanins

Abstract Three series of structurally related anthocyanins, extracted from the red–purpleflowers of Dendrobium Pramot, xLaeliocattleya cv. Mini Purple, Bletilla striata and Phalaenopsis all belonging to the Orchidaceae family and another series extracted from the pinkflowers of Senecio cruentus (Compositae) allowed the confirmation of the existence of strongintramolecular copigmentation effects. These interactions confer stability to the coloured formsof the molecules, in a wide range of slightly acidic to neutral aqueous media. Moreover, theexistence of structural relationships among the four series stressed the different influencesexerted by the diverse substituent groups. The existence of a malonylglucoside attached toposition 3 of all but three of the molecules put forward a new role for the malonyl residue, in thisparticular position.

Acylated anthocyanins of Clitoria ternatea flowers and their acyl moieties.

Abstract Two acyl moieties, prepared by alkaline deacylation or H2O2 oxidation of ternatin mixture from Clitoria ternatea flowers, were determined as E-4-O-β- d -glucopyranosyl-p-coumaric acid and 6-O-malonyl- d -glucopyranose respectively through FABMS and NMR. Furthermore, six ternatins A1, A2, B1, B2, D1 and D2 in C. ternatea flowers were isolated by reversed phase HPLC and their structures were partly characterized as highly acylated delphinidin derivatives.

Influence of trans-cis isomerisation of coumaric acid substituents on colour variance and stabilisation in anthocyanins

The recently isolated pigments from Petunia integrifolia and Triteleia bridgesii present a distinct feature that sheds new light on the understanding of intramolecular copigmentation of anthocyanins. These are among the infrequent anthocyanins that naturally present a coumaric acid substituent in both cis and trans forms. As a consequence, the two isomers demonstrate substantial variations of their thermodynamic and kinetic constants and also colour properties. A possible explanation for these characteristics is presented, making use of molecular modelling and taking into account the three-dimensional structures of the pigments.

Cyanidin 3-malonylglucuronylglucoside in Bellis and cyanidin 3-malonylglucoside in Dendranthema

Abstract -The major anthocyanin of three red cultivars of Dendranthema morifolium has been identified as cyanidin 3- O -(6- O -malonyl-β- d -glucopyranoside) by FABMS and NMR spectroscopy. The major anthocyanin of red flowers of Bellis perennis has been identified as cyanidin 3- O -(6- O -matonyl-4- O -(β- d -glucuronyl)-β- d -glucopyranoside). Both malonylanthocyanins were more stable in neutral solution than cyanidin 3-glucoside, but less stable than cyanidin 3-glucuronylglucoside.

Tetra-acylated cyanidin 3-sophoroside-5-glucosides from the flowers of Iberis umbellata L. (Cruciferae)

The structures of 11 acylated cyanidin 3-sophoroside-5-glucosides (pigments 1-11), isolated from the flowers of Iberis umbellata cultivars (Cruciferae), were elucidated by chemical and spectroscopic methods. Pigments 1-11 were acylated with malonic acid, p-coumaric acid, ferulic acid, sinapic acid and/or glucosylhydroxycinnamic acids. Pigments 1-11 were classified into four groups by the substitution patterns of the linear acylated residues at the 3-position of the cyanidin. In the first group, pigments 1-3 were determined to be cyanidin 3-O-[2-O-(2-O-(acyl)-beta-glucopyranosyl)-6-O-(trans-p-coumaroyl)-beta-glucopyranoside]-5-O-[6-O-(malonyl)-beta-glucopyranoside], in which the acyl moiety varied with none for pigment 1, ferulic acid for pigment 2 and sinapic acid for pigment 3. In the second one, pigments 4-6 were cyanidin 3-O-[2-O-(2-O-(acyl)-beta-glucopyranosyl)-6-O-(4-O-(beta-glucopyranosyl)-trans-p-coumaroyl)-beta-glucopyranoside]-5-O-[6-O-(malonyl)-beta-glucopyranoside], in which the acyl moiety varied with none for pigment 4, ferulic acid for pigment 5 and sinapic acid for pigment 6. In the third one, pigments 7-9 were cyanidin 3-O-[2-O-(2-O-(acyl)-beta-glucopyranosyl)-6-O-(4-O-(6-O-(trans-feruloyl)-beta-glucopyranosyl)-trans-p-coumaroyl)-beta-glucopyranoside]-5-O-[6-O-(malonyl)-beta-glucopyranoside], in which the acyl moiety varied with none for pigment 7, ferulic acid for pigment 8, and sinapic acid for pigment 9. In the last one, pigments 10 and 11 were cyanidin 3-O-[2-O-(2-O-(acyl)-beta-glucopyranosyl)-6-O-(4-O-(6-O-(4-O-(beta-glucopyranosyl)-trans-feruloyl)-beta-glucopyranosyl)-trans-p-coumaroyl)-beta-glucopyranoside]-5-O-[6-O-(malonyl)-beta-glucopyranoside], in which acyl moieties were none for pigment 10 and ferulic acid for pigment 11. The distribution of these pigments was examined in the flowers of four cultivars of I. umbellata by HPLC analysis. Pigment 1 acylated with one molecule of p-coumaric acid was dominantly observed in purple-violet cultivars. On the other hand, pigments (9 and 11) acylated with three molecules of hydroxycinnamic acids were observed in lilac (purple-violet) cultivars as major anthocyanins. The bluing effect and stability on these anthocyanin colors were discussed in relation to the molecular number of hydroxycinnamic acids in these anthocyanin molecules.

Anthocyanin–aluminium and –gallium complexes in aqueous solution

Complexation of aluminium and gallium ions with synthetic anthocyanin models and natural anthocyanins extracted from the blue flowers of Evolvulus pilosus cv ‘Blue Daze’ and the violet flowers of Matthiola incana has been thoroughly investigated in aqueous solution. From UV–VIS spectroscopic data collected at pH 2–5, the presence of complexes, involving not only the coloured forms but also the colourless forms of the pigments is demonstrated. A theoretical treatment is developed for the calculation of the corresponding stability constants. The pigments studied throughout this work can be divided into two series, one sharing a cyanidin chromophore and the other a delphinidin one. Within both series, individual pigments are distinguished according to the degree and type of glycosylation and/or acylation. Intramolecular effects such as copigmentation of anthocyanin–aluminium complexes and the effect of the presence of a malonyl group on the formation of those complexes are discussed. These results are important to plant pigmentation and, for instance, a narrow pH domain in which colour amplification due to complexation is at a maximum has been found.

Acylated kaempferol glycosides from the flowers of delphinium formosum

Abstract One new flavonol glycoside, kaempferol 3-(4″,6″-diacetylglucoside)-7-rhamnoside and three other known kaempferol glycosides: kaempferol 3-glucoside-7-rhamnoside, kaempferol 3-(6″-acetylglucoside)-7-rhamnoside, and kaempferol 7-rhamnoside, were isolated and characterised from flowers of Delphinium formosum. The structures were elucidated by spectral and chemical methods.

Acylated anthocyanins and flavonols from purple flowers of Dendrobium cv. ‘Pompadour’

Abstract Two rare anthocyanins, cyanidin 3-(6-malonylglucoside)-7,3′-di(6-sinapylglucoside) and the demalonyl derivative, were characterised as the purple floral pigments of Dendrobium cv. ‘Pompadour’. Nine known flavonol glycosides were also identified, including the 3-rutinoside-7-glucosides of kaempferol and quercetin. One new glycoside was detected: the ferulyl ester of quercetin 7-rutinoside-7-glucoside. These flavonoid patterns are typical for plants in the family Orchidaceae.

An acylated delphinidin glycoside in the blue flowers of Evolvulus pilosus

Abstract A new acylated anthocyanin was isolated from the blue flowers of Evolvulus pilosus cv ‘Blue Daze’ as a major anthocyanin. The structure of this pigment was determined to be delphinidin 3- O -(6- O -( trans -4- O -(6- O -( trans -3- O -(β-d-glucopyranosyl)-caffeyl)-β-d-glucopyranosyl)-caffeyl)-β-d-glucopyranoside)-5- O -((6- O -malonyl)-β-d-glucopyranoside) by chemical and spectral methods.