CAROTENOIDS 



with either perphthalic or perbenzoic acid in chloroform solution. 

 In the presence of traces of hydrogen chloride a chloroform solution of 

 a 5 : 6-epoxide isomerizes producing a furanoid type of compound. 

 (5 : 8-epoxide) and at the same time regenerating a small amount of 

 the parent compound. ^ ^ 



Violaxanthin and flavoxanthin have now been shown to be com- 

 pounds of this type » 4. 3 6 . violaxanthin is the di-epoxide of zeaxanthin 

 (*3 : 3'-dihydroxy-(3-carotene, ^-carotene 3 : 3'-diol) and flavoxanthin 

 is the furanoid isomer of lutein (xanthophyll). ' • 



M^ Me Mc 



Me Me Me 



Zeaxanthin 



Me Me Me 



Me Me Me 



Violaxanthin (5:6, 5':6' -diepoxyzeaxanthin) 



Flavoxanthin (5:8-epoxyluteln) 



Zeaxanthin which Kuhn and Brockmann * ' had previously failed to 

 observe in leaves was noted by Strain in traces (about 2 per cent, of 

 the total xanthophylls). 



Whereas ^-carotene predominates over a-carotene in leaves, it is 

 the dihydroxy- a-carotene (lutein (xanthophyll) ) which predominates 

 over the dihydroxy- ^-carotene (zeaxanthin). There is yet no proof 

 that xanthophylls are produced via the corresponding hydrocarbons 

 (see p. 84) so no significance can, at the moment, be attached to this 



* The same doubt exists concerning the position of the OH groups in 

 zeaxanthin as in the j3-ionone ring of lutein {see p. 13). 



16 



