2.4.6 Anthocyanidin Glycosides
In addition to chlorophyll, anthocyanins represent the most important class of natural plant pigments visible to the naked eye. Anthrocyanidine (aglyconoes) are structurally closely related to each other. It has been established that there exist six prominent anthrocyanidines whose chemical structres are entirely based on the structure of pelargonidin. These six aglyconoes differ from pelargonidin by having one or two additional hydroxyl or methoxyl moieties strategically positioned at C-3’ and
C-5’ in the latter, as shown in Table 4.2.
It is, however, pertinent to mention here that the sugar components are invariably attached to C-3’ position, and more rarely to C-5’ position. It is worth mentioning here that in the flavone glycosides the attachement is normally at C-7 position. These sugar moieties may be:
Monosaccharides : e.g.: arabinose, galactose, glucose and rhamnose
Disaccharides : e.g.: rhamnoglucosides (present in Antirhinum sp.)
Trisaccharides : e.g.: 5-glucosides-3-rutinoside (present in some Solanaceae species such as: Atropa and Solanum.)
Leucoanthocyanidins (or Proanthocyanidins) Procanthocyanidins represent a group of highly water soluble naturally occuring plant pigments that are closely related to anthocyanidins. However, they may be easily differentiated from other flavonoids by virtue of the fact that the procanthocyndins are easily converted into their corresponding anthocyanidins on being boiled either with alcoholic
or aqueous hydrochloric acid.
In general, they are considered equivalent to flavan 3, 4-diols chemically, which may be present either in their monomeric/ polymeric forms or as their corresponding derivatives. Examples:
(-)-Melacacidin obtained from Acacia melanoxylan and other related species.
The isomelacidin has the 2,3-cis and 3,4 –trans. configuration
