FLAVONOIDS AND RELATED COMPOUNDS 



183 



TABLE 2. HYDROXYLATION PATTERNS OF SOME FLAVONOIDS 



Compounds 



ANTHOCYANINS 



The anthocyanins are the common red to blue pigments of flower petals, making up 

 as much as 30% of the dry weight in some flowers. They also occur in other parts of 

 higher plants and throughout the plant kingdom except in the fungi. Unlike the other classes 

 of flavonoids, they seem always to occur as glycosides except for traces of the aglycones, 

 anthocyanidins. Hydrolysis may occur during autolysis of plant tissues or during isolation 

 of the pigments so that anthocyanidins are found as artifacts. At the normal pH of vacuoles 

 where they occur the anthocyanins exist as cations. They were originally thought to be 

 oxonium compounds with the positive charge residing on the heterocyclic oxygen. It is 

 probably more accurate to consider the molecule as a whole as possessing a non-localized 

 charge. As the solution becomes more basic a purple color -base first appears and then 

 a blue colored salt form: 



OH OH- 





 OH (PURPLE) 



\0H- 



A PHENOLATE ANION 

 (BLUE) 



