Anthocyanidins structures

Polcin and Rapson [12] have shown that hydrosulfite predominantly attacks simple quinoid, a,p-unsaturated aldehyde and anthocyanidine structures found in groundwood pulps prepared from western hemlock (Tsuga heterophylla) and eastern spruce (Picea glauca). A few years later, de Vries et al. [13,14] have demonstrated that hydrosulfite can reduce many types of aldehydes and ketones in solution according to the mechanism shown in Figure 13.1. Ketones were found to react sluggishly in water, esters are hydrolyzed, while carboxylic acids and amines are not reduced. 

Fig. 7.3 Benzopyran derivatives (a) flavan structure - basic structure of anthocyanidins (aglycosides of anthocyanins) (b) anthocyanidin structure (c) structure of an anthocyanin showing conjugation with sugars.

On Figure 8, the most commonly occurring anthocyanidin structures are shown together with the basic chemical properties. On Figure 9 the most commonly occurring mono-saccharides bound to the anthocyanidin skeleton at position 3 and/or 5 are presented together with their basic chemical properties. 

Among the plant phenols, the flavonoids and the anthocyanidins, belonging to the 1,3-diphenylpropans, have been studied in most detail, mainly because of their potential health benefits. With more than 4,000 different flavonoids known, systematic studies of the effects of variation in molecular structure on physico-chemical properties of importance for antioxidative effects have also been possible (Jovanovic et al, 1994 Seeram and Nair, 2002). Flavonoids were originally found not to behave as efficiently as the classic phenolic antioxidants like a-tocopherol and synthetic phenolic antioxidants in donating... 

Anthocyanins and anthocyanidins, compounds present with high structural diversity in fruits and wines, showed a pattern as antioxidants different from that of the tea catechins with respect to the effect of substituents. In a liposomal model system induced peroxidation was inhibited increasingly by anthocyanins/ anthocyanidins with an increasing number of hydroxyl groups in the B-ring (Fig. 16.6), while the opposite was seen for the catechins (Seeram and Nair, 2002). For anthocyanidins, the presence of a 3-hydroxy group is important... 

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. 

FIGURE 4.3.1 Structures of anthocyanidins and pyroanthocyanidins occurring in foods. 

Timberlake, C.F. and Bridle, P., Flavylium salts anthocyanidins and anthocyanins. Structural transformations in acid solutions, J. Sci. Food Agric., 18, 473, 1967. 

The numbers and types of fragments depend on the anthocyanin structure pattern. The aglycone (anthocyanidin) ordinarily is very stable and cannot be broken easily. In most cases, cleavage of the glycosidic groups will occur to generate small amounts of anthocyanidins in addition to the intact anthocyanin molecular ions. 

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

FIGURE 13.4 Typical structures for main classes of flavonoids naringin chalcone, 4,6,4 -trihydroxyaurone, apigenin (flavone), and pelargonidin (anthocyanidin). 

Figure 3.7. Structural relationships among flavonols, anthocyanidin, and anthocyanin.

Flavonoids are a complex group of polyphenolic compounds with a basic C6-C3-C6 structure that can be divided in different groups flavonols, flavones, flavanols (or flavan-3-ols), flavanones, anthocyanidins, and isoflavones. More than 6,000 flavonoids are known the most widespread are flavonols, such as quercetin flavones, such as lu-teolin and flavanols (flavan-3-ols), such as catechin. Anthocyanidins are also bioactive flavonoids they are water-soluble vegetable pigments found especially in berries and other red-blue fruits and vegetables. 

Chemically, anthocyanins are glycosides of anthocyanidins and are based on a 2-phenylbenzopyrilium structure. The properties of the anthocyanins depend on the anthocyanidins from which they originate. 

Fig. 8.4 Top. Structures of the major anthocyanidins in foods. Middle. Structure of betanine. Bottom. Pigments in turmeric.

Fig. 2.112. The structures of the flavan-3-ol(4a — 8)pelargonidin 3-0-/f-glucopyranosides (1-4) isolated from strawberry extract. The letter A denotes the aglycone ring systems belonging to the anthocyanidin substructure, whereas the letter F denotes the aglycone ring system belonging to the flavanol substructure. Reprinted with permission from T. Fossen et al. [252].

Wilmouth RC, TumbuU JJ, Welford RW, Clifton U, Prescott AG, Schofield CJ (2002) Structure and mechanism of anthocyanidin synthase from Arabidopsis thaliana. Structure 10(1) 93-103... 

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