Chapter 9 



FLAVONOIDS AND 

 RELATED COMPOUNDS 



The flavonoid group may be described as a series of Cg - C3 - Cg compounds. That 

 is, their carbon skeleton consists of two Cg groups (substituted benzene rings) connected 

 by a three -carbon aliphatic chain. 



Q^c-c-chQ 



flavonoid skeleton 



The different classes within the group are distinguished by additional oxygen-heterocyclic 

 rings and by hydroxyl groups distributed in different patterns. Flavonoids frequently 

 occur as glycosides. The largest group of flavonoids is characterized by containing a 

 pyran ring linking the three -carbon chain with one of the benzene rings. The numbering 

 system for these flavonoid derivatives is given below: 



2' 3' 



Among the typical flavonoids having the above skeleton the various types are dis- 

 tinguished by the oxidation state of the C3 chain. Going from most reduced to most ox- 

 idized, the structures and their names are as follows (only the key portion of the molecule 

 is shown): 



V^ \.u_ 



CH 



CH' 



I 



CHOH 



catechins 



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