Anthocyanidin pigments

Flavylium salts with 4-methyl substitution (e.g., 2 in Scheme 10.2) might be further gently reacted with aromatic aldehydes affording anthocyanidin pigments of the pyranoanthocyanidin type. ... 

Aromatization of the central oxygen heterocycle by oxidation leads to the flavones, which are yellow or orange depending on their substituents. Dehydration leads to the red or blue anthocyanidins, pigments of flowers and fruit. This important group of molecules also includes plant growth hormones and defence compounds. 

Condensed tannins, on the other hand, occur in the bark of all conifers and hardwoods examined to date, and they are frequently present in the wood. They are primarily responsible for the tan to brown color of wood after it is exposed to air. In their purest form, condensed tannins are colorless, but they become colored very readily once isolated because of their propensity to oxidize to quinones. The primary characteristic of the water-soluble condensed tannins (4) is dehydration/oxidation to intensely colored anthocyanidin pigments (5) when refluxed in butanol and hydrochloric acid (Figure 2). For this reason, there has been a tendency to refer to these compounds as proanthocyanidins in the last few years. Prior to that, they were referred to as leucoanthocyanidins (i.e., the colorless chemical form of anthocyanidins). All references earlier than the late 1950 s, when the structure of these substances was just beginning to be understood, used the term condensed tannin. 

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. 

Other flavonoids that are able to enhance the luminal release of PG in vivo are the glucoside of hypolaetin [117], the anthocyanidin pigment IdB 1027 [213], and the flavonic extract of Bidens aurea [214] therefore their antiulcer effect could be related to an enhancement of PGE2 levels in gastric mucosa and also to a generalized stimulation of the defensive mucosal mechanisms. 

The presence of proanthocyanidins in plant tissue may be readily detected by hydrolysis with hot alcoholic acid (108) to produce the anthocyanidin pigment (e.g. cyanidin) that may be positively identified by paper chromatography or cellulose TLC in Forestal solvent (H0Ac H20 HCl, 30 10 3 v/v/v), or by a colorimetric method using vanillin and concentrated hydrochloric acid (17). The latter is very sensitive. 

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