FLAVONOIDS AND RELATED COMPOUNDS 



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three types of catechin are known differing in the number of hydroxyl groups in ring B. 

 They have two asymmetric carbons (starred) and therefore 4 possible isomers: 



hQ^oh 



,H H H 



catechin 



gallocatechin 



afzelechin 



The sterochemistry of these compounds has been elucidated (13). The (+) and (-) catechins 

 have the number 2 and 3 hydrogens trans, whereas they are cis in the epicatechins. Epi- 

 merization involves inversion of the 2-aryl group rather than the 3-hydroxy group. 



The leucoanthocyanidins have only recently had their structures elucidated. Although 

 they are basically flavan-3, 4-diols, certain variations have been found. Some examples 

 of established structures and their sources follow: 



melacacidin 

 (Australian blackwood) 



H OH 



peltogynol 



(Peltogyne porphyrocardia) 



(from Cleistanthus collinus) 



