FLAVONOIDS AND RELATED COMPOUNDS 



leucoanthocyanidin 



(monomers) 



179 



anthocyanidin 



condensed 

 tannins 



phlobaphenes 



catechin 



The ill-defined catechutannic acid is a dehydration product of either catechin or a catechin 

 polymer, probably as follows: 



It has recently been found that not all compounds which give anthocyanidins with acid 

 have the flavan-3, 4-diol structure, and a new class of natural products called "proantho- 

 cyanidins" has been suggested (22, 23). Some of these are found to be dimers and some 

 polymers. One of the dimers found in Gleditschia triacanthos on heating with acid forms 

 cyanidin, epicatechin, and other products. It has the structure: 



PCiP"°" 



OH H H 



The red colors obtained on heating many plant parts with acid have been ascribed to 

 the presence of leucoanthocyanidins. However, the phlobaphenes may be red; and humic 

 acid, present in some leaves, also gives a red color on heating with acid (24) so that a 

 better criterion than mere color should be applied (e. g. absorption spectra). 



