5 ANTHERAXANTHIN 191 



Violaxanthin is formed together with antheraxanthin, though in somewhat 

 poorer yield. It is a natural pigment of wide occurrence and has been repeatedly 

 investigated within recent years. It will be described in detail on p. 193. 



d) Auroxanthin: 



CH, CH, CH3 CH, 



\/ 



C 

 CH CH3 CH3 CH3 H3C CH=C CHg 



CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH C CHOH 

 Auroxanthin 



The furanoid dioxide of zeaxanthin, auroxanthin, is a carotenoid occurring 

 in blossoms. It can be obtained by the isomerisation of violaxanthin^" in the 

 presence of acids, a reaction which proves its constitution. A detailed description 

 of auroxanthin will be found on p. 196. 



5. ANTHERAXANTHIN C40H56O3 



In the course of investigations on the carotenoids of the anthers of Liliiim 

 tigrinum, Karrer and Oswald''^ discovered a previously unknown phyto- 

 xanthin which they termed antheraxanthin. Antheraxanthin occurs together 

 with capsanthin and is found below the latter in the chromatogram. It shows 

 an entirely hypophasic character in the partition test and its absorption 

 spectrum differs very little from that of zeaxanthin. Karrer and Oswald deter- 

 mined the molecular formula of the pigment, but were unable to establish the 

 nature of the third oxygen atom. 



The constitution of antheraxanthin was elucidated later'^, when the pig- 

 ment was identified with zeaxanthin mono-epoxide obtained by the oxidation 

 of zeaxanthin with monoperphthalic acid. The two compounds could not be 

 separated by chromatography on zinc carbonate and gave no mixed melting 

 point depression. This partial synthesis established the constitution of anthera- 

 xanthin (cf. p. 189). The formula is in agreement with the fact that the pigment 

 absorbs 11 mols of hydrogen on catalytic hydrogenation'^. 



\V \V 



CHq Cxlq CHq H O \J 



/\ I I I I /\ 



CHj C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CH^ 



HaC-C CHOH 



HOCH C \ / 



\^ / \^ Antheraxanthin CHj 



CH2 CH3 

 References p. 214— 2iy. 



