.500 VI. CAROTENOIDS AND RELATED COMPOUNDS 



A comparison of the properties of antlieraxanthiii and mutatoxanthin is 

 given in Table 5. Although mutatoxanthin might be expected to be an 

 intermediate in the metabolism of zeaxanthin epoxide in plants, it has not 

 as yet been identified among such pigments. 



(e) Zeaxanthin Di-epoxide, Violaxanthin, C40H66O4. Zeaxanthin di- 

 epoxide can also l)e prepared by the oxidation of zeaxanthin with per- 

 phthalic acid. This compound has oxygens combined with both /3-ionone 

 rings in positions 5,6 and 5', 6', respectively. Karrer and Jucker^^^ found 

 this compound to be identical with violaxanthin, which had been isolated 

 frequently from many natural sources. The structure and properties of 

 zeaxanthin di-epoxide are therefore discussed in the section on violaxanthin 

 (see Section (fi) below). 



(6) Violaxanthin 



Violaxanthin was first obtained from the petals of the yellow wild pansy 

 (Viola tricolor) ."^^^ Obviously, it derives its name from this origin. 



a. Structure. Violaxanthin has been known to have the empirical 

 formula C\oH5604, but it differs from taraxanthin, which has the same em- 

 pirical formula, in giving a deep-blue color reaction with hydrochloric acid. 

 Other oxygen-containing polyenes such as lutein, fucoxanthin, capsanthin, 

 capsorubin, and azafrin give completely negative results with hydrochloric 

 acid, while flavoxanthin responds with only a transitory reaction. The 

 recent demonstration by Karrer and Jucker'^^ that violaxanthin is actually 

 zeaxanthin di-epoxide fits in with the earlier isolated facts about the nature 

 of the molecule. 



HjC CH3 H,C CHj 



C CHj CH3 CH, CHj c 



/\ hhIhhhIhhhhIhhhIhh /\ 

 hzc c-c:c-c:c-c:c-c:c-c:c-c:c-c:c-c:c-c:c-^c ch? 



H\l |> I 1/H 



C C^ C C 



HO^ \ / \ / \ / ^OH 



"^ C CH3 HjC C 



Hi Hz 



Violaxanthin (zeaxanthin di-epoxide) 



Violaxanthin has only 9 double bonds. ^^^ It is believed that two oxy- 

 gens must be in the same position as in lutein (3 and 3'), which explains 

 the formation of esters with fatty acid. Kuhn and Winterstein,^^'* on the 

 basis of the Zerewitinoff reaction, believe that all four oxygens are asso- 

 ciated with hydroxyl groups, although Karrer and Morf*^'^ could detect 

 only three active hydrogens. When violaxanthin is treated with lead 



336 p. Karrer and U. Solmssen, Helv. Chim. Acta, 19, 1024-1025 (1936). 



337 p. Karrer and R. Morf, Helv. Chim. Acta, I4, 1044-1046 (1931). 



