188 



FLAVONOIDS AND RELATED COMPOUNDS 



CHALCONES AND DfflYDROCHALCONES 



The numbering convention for these compounds differs from that of the flavonoids 

 having a pyran ring: 



Only a few natural representatives are known, so that far-reaching generalizations about 

 their structure are premature. However, hydroxylation patterns generally agree with 

 those of the other flavonoids; a hydroxyl group is always present in position-2, correspond- 

 ing to the hetero oxygen atom of the flavanones etc. The conversion of chalcones to fla- 

 vanones in fact occurs readily in acid solution and the reverse reaction in base. This 

 interconversion is shown for the chalcone butein and the flavanone butin: 



Hl_^HOy;^>v^O 



OH' 



butein 



butin 



The reaction is easily observable since the chalcones are much more highly colored than 

 the flavanones, especially in basic solution where they are orange-red. Because of this 

 reaction acidic hydrolysis of chalcone glycosides yields a flavanone aglycone as an arti- 

 fact rather than the chalcone. This is shown for carthamin, a glycosidic pigment of the 

 saf flower. 



0-&LUCOSE 



OH H* 



♦ G-LUCOSE 



carthamin 



carthamidin 



