Anthocyanin reference compounds

Another kind of reaction has been demonstrated for the cationic forms of anthocyanins, resulting in the formation of a second pyran ring. The mechanism involves both the electron deficient C-4 and the 5-hydroxyl group of the anthocyanin with compounds possessing a polarizable double bond (d). The new pigments thus formed are referred to as pyranoanthocyanins. 

Ishikura, N. (1976). Seasonal changes in contents of phenolic compounds and sugar in Rhus, Euonymus and Acer leaves with special reference to anthocyanin formation in autumn. Botanical Magazine, Tokyo 89 251-257. 

This limited overview on the analysis of four classes of the following secondary potato metabolites is, except for anthocyanins, largely limited to our own studies of glycoalkaloids, calystegine alkaloids, and phenolic compounds. Because interest in these potato constituents arises from potential health benefits and occasional toxicity, we also include in this overview a brief discussion of these aspects that relate to composition and a description of experimental methods. The interested reader should consult the cited references for an entry into the extensive worldwide literature on the diverse analytical and biological aspects for these metabolites. 

Flavanol oligomers and polymers are also called condensed tannins or proan-thocyanidins. The term tannin refers to their capacity to interact or react with proteins and precipitate them out. When heated under acidic conditions, these molecules release red anthocyanidin pigments, hence the term proanthocyanidins. The term leucoanthocyanidin, also referring to this particular property, is sometimes encountered in the literature. However, this should be restricted to another group of compounds, flavan 3,4-diols, which are intermediates in the biosynthetic pathway leading to flavanols and anthocyanins (Stafford and Lester 1984 Nakajima et al. 2001 Abrahams et al. 2003) but have never been isolated from grapes, presumably due to their instability. 

The word flavonoid comes from Latin flavus, which means yellow, and included at the beginning only a yellow-colored group of compounds with a flavone nucleus (Jovanovic et al 1998). Today, the term is used in a broader context and includes colorless (flavan-3-ol) to less colored (flavanone) compounds, as well as the red and blue anthocyanins, all commonly occurring in plants. For a period, flavonoids were referred to as vitamin P because of their ability to decrease capillary fragility and permeability in humans. The term vitamin C2 has also been used, as it was known... 

Anthocyanins are water soluble pigments responsible for the red to purple colour in plants. The common basic structure of all these compounds is the cation flavylium, which was proposed for the first time by Wilstaer in 1913 and later confirmed by Robinson in 1922. A special kind of flavonoids related to anthocyanins are the proanthocyanidins, also referred to as leucoanthocyanidins, in the case of monomeric proanthocyanidins, and condensed proanthocyanidins for the polymers of flavan-3-ols [32],... 

Pharmacokinetics. Recently, it has been shown that human urine of 87 volunteers after ingestion of a purple-fleshed sweet potato beverage contained peonidin 3-caffeoylsophoroside-5-glucoside. Absorption of this compound into the bloodstream of rats and presence as an intact acylated form in their plasma has been demonstrated previously (Oki et al. 2006 and references therein). Urinary excretion of anthocyanins is usually low due to metabolization. 

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