PHENOLIC SUBSTANCES 



199 



ANTHOCYANINS 



The basic aromatic unit is referred to as a phenylbenzo- 

 pyrilium salt with the configuration shown below. This class includes 

 most of the red and blue plant pigments. 



6' 5' 



All naturally occurring anthocyanins have the 4', 3, 5, and 7 

 positions occupied by an hydroxyl or some substituted group. They 

 usually occur as glycosides with the sugars attached at positions 3 or 

 3 and 5. Sugars commonly reported are glucose, galactose, rhamnose, 

 and arabinose. Disaccharides (for example, rhamnoglucose) may 

 occur as well as 3,5-dimonosides and even trisaccharides. 



In acylated anthocyanins the organic acid is frequently p- 

 hydroxybenzoic, protocatechuic, p-hydroxycinnamic or other 

 phenolic acid. The attachment of the acyl group is apparently at 

 a free hydroxyl in the ring or an hydroxyl group of the sugar. 



The aglycone of the anthocyanin, which may be obtained by 

 acid hydrolysis, is referred to as an anthocyanidin. Although dozens 

 of anthocyanins have been described, only a few anthocyanidins are 

 known, and some of these are rather rare. These compounds differ in 

 the substitution pattern involving positions 3', 4', 5', 3, 5, and 7. 



Representative anthocyanidins. 



,0H 



/^ 



B VOH 



OH 



OH 



pelargonidin 



cyanidin 



pCHa 



OH 



OH 



delphinidin 



OCH3 

 malvidin 



Hirsutidin is a 7-methoxy analog of malvidin. Capensinidin, a 5- 

 methoxy analog of malvidin, has been obtained from Plumbago 

 capensis (Harborne, 1962). 



QCH3 



peonidin 



Rosinidin, a 7-methoxy analog of peonidin, has been reported to occur 

 in Primula rosea (Harborne, 1958). 



