Cyanidin, structure

Six anthocyanidins are commonly found in plants and plant-derived foods and beverages pelargonidin, cyanidin, delphinidin, peonidin, petunidin, and malvidin. Their structures differ in the number and position of hydroxyl and methoxyl groups on the flavan nucleus. The most commonly occurring anthocyanidin is cyanidin, and all these anthocyanidins are found in plants as glycosides with or without acylation, leading to around 400 different stractures. 

Research into the copigmentation of anthocyanins started as early as 1913 when Willstatter and Everest determined the chemical structure of cyanidin 3-glucoside isolated from blue cornflowers and red roses, and attributed the color changes to different pH levels in cell saps. This theory, however, was questioned and in 1916, Willstatter and Zollinger,revising the previous work, proposed a new theory according to which the colors of the anthocyanins varied significantly by the effects... 

Quantitation of anthocyanins has become simple and fast since many anthocy-anin standards became commercially available as external standards in the past decade. When the standards are not available, individual anthocyanins or total monomeric anthocyanins can be determined by the use of a generic external standard such as commercial cyanidin-3-glucoside or other compound structurally similar to the analytes of interest. Individual and total peak areas are measured at 520 nm or their and quantified using external standards by which values are typically slightly different from those via the pH differential method. ... 

Another problem is that the anthocyanin mixtures may be very complicated and not all absorptivity coefficients may be known. Even when they are known, it is necessary to first evaluate whether the objective is the estimation of total anthocyanin content or the determination of individual pigments, and then to decide which absorption coefficient(s) to use. The absorptivity is dependent on both the chemical structure of the pigment and also on the solvent used, and preferably the coefficient used should be one obtained in the same solvent system as the one used in the experiment. If the identity of the pigment is unknown, it has been suggested that it could be expressed as cyanidin-3-glucoside since that is the most abundant anthocyanin in nature. 

FIGURE 13.1 Typical structures for main pigment classes zeaxanthin (carotenoid), chlorophyll a (chlorophyll), quercetin (flavonoid), cyanidin (anthocyanidin), betanin (betalain), and alizarin (anthraquinone). 

Bartolome, B., Hernandez, T., Bengoechea, M. L., Quesada, C., Gomez-Cor-doves, C., and Estrella, I., Determination of some structural features of pro-cyanidins and related compounds by photodiode-array detection, /. Chromatogr. A, 723, 19, 1996. 

Mazza, G. and Brouillard, R., Color stability and structural transformations of cyanidin 3,5-diglucoside and four deoxyanthocyanins in aqueous solutions. J. Agric. Food Chem. 35, 1987. Roehri-Stoeckel, C. et al.. Synthetic dyes simple and original ways to 4-substituted flavylium salts and their corresponding vitisin derivatives. Can. J. Chem. 79, 1173, 2001. 

FIGURE 10.2 The number of anthocyanins based on the various anthocyanidins. The upper dark part of each bar represents the anthocyanins reported later than 1992. Pg, pelargonidin Cy, cyanidin Pn, peonidin, Dp, delphinidin Pt, petunidin Mv, malvidin RMS, rare methylated structures 60H, 6-hydroxy- Des, desoxy- Pyr, pyrano- Sp, sphagnorubins. See Table 10.1 for structures. 

Four cyanidin 4 -glucosides have recently been isolated from pigmented scales of red onion. These structures were established by extensive use of 2D NMR spectroscopy and electrospray LC MS. The previous report on 4 -glucosyl linkages in two anthocyanins from... 

The reports on anthocyanins from Anemone coronaria Pulsatilla cernua and Ranunculus asiaticus reveal structures that are very different from the anthocyanins described above. Many of these latter pigments are based on lathyroside or sambubioside residues located at the 3-hydroxyl of delphinidin, pelargonidin, or cyanidin (Table 10.2). Among these, four unusual anthocyanins containing the acyl moiety tartaryl have been isolated from Anemone coronaria Six of the anthocyanins in this plant have a glucur-onoside in the 3 -position. 

Tamura, FI. et al.. Structures of a succinyl anthocyanin and a malonyl flavone, two constituents of the complex blue pigment of cornflower Centaurea cyanus. Tetrahedron Lett., 24, 5749, 1983. Sulyok, G. and Laszlo-Bencsik, A., Cyanidin 3-(6-succinyl glucoside)-5-glucoside from flowers of seven Centaurea species. Phytochemistry, 24, 1121, 1985. 

There are five anthocyanidins in the grape delphinidin 1, petunidin 2, malvidin 3, cyanidin 4, and peonidin 5. These aglycones exist in different heterosidic forms or as anthocyanins 3-monoglucosides, 3,5-diglucosides, and acylated heterosides, whose structures, in the case of malvidin, are represented by formulas 6, 7, and 8. In the acylated anthocyanins, one molecule of cinnamic acid, more generally p-coumaric acid, is esterified with the —OH group in the sixth position of a glucose molecule (12). 

All anihocyanidins have tile 2 phcnylhen/opyrylium or flavylitim cation structure, a resonance hybrid of oxonium forms and carbcnium forms. There are three fundamental groups of anihocyanidins to which all the other anihocyanidins could be referred. In the following structure R = R = H designates pelargonidin R = OH. R = H is cyanidin and R = R = OH is dclphinidin. 

Figure F1.4.1 The structure of the major anthocyanin, cyanidin 3-0-(2"-0-p-glucopyranosyl-6"-O-a-rhamnopyranosyl-p-glucopyranoside), isolated from tart cherries, Prunus cerasus. Structure number 15 corresponds to 1H and 13C NMR data in Tables F1.4.4 and F.1.4.5.

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