4 ZEAXANTHIN 183 



CH, CH, CH3 CH. 



\V \V 



C CH, CH3 CH3 CH3 C 



/\ i I I \ /\ 



CH2 C=CHCH=C-CH=CHCH=C-CH=CHCH=CH-C=CHCH=CH-C=CHCH=C CHj 



HjC-C CO 

 Rhodoxanthin ^ / 



CH 



CHo CHo 



\V 



CH3 CH3 CH3 CH3 C 



C- CH=CH- C=CHCH=CH- C=CHCH=CHCH=C- CH=CHCH=C- CH=CH- C CHg 



HaC-C CO 

 Dihvdrorhodoxanthin 



CHj 

 CHo CHg 



\/ 



CHo CHo CHo CHo C 



/\ I I I I /\ 



CH, C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CH, 



1 II II I 



HOCH C-CH3 HjC-C CHOH 



\ y^ Zeaxanthin \^ y^ 



CHj CH2 



This transformation of rhodoxanthin into zeaxanthin represents the first 

 partial synthesis of a C40 carotenoid and also confirms the constitution of both 

 pigments. 



Karrer and Jucker^'' also carried out another partial synthesis of zea- 

 xanthin by treating xanthophyll with sodium ethoxide. This resulted in the dis- 

 placement of the isolated double bond into conjugation and the zeaxanthin thus 

 obtained was identical in spectral properties and melting point with the natural 

 pigment. These experiments show that polyenes containing an isolated double 

 bond readily undergo prototropic rearrangement to the fully conjugated 

 isomer. 



Chemical Constitution^ •^'^ 



CH3 CH3 CXI3 CH3 



C CHo CHo CM« CHo C 



/\ r I I I ■ /\ 



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



i II II I 



HOCH C-CHa HjC-C CHOH 



\ / Zeaxanthin \ / 



CH2 CH^ 



The elucidation of the constitution of zeaxanthin is mainly due to Karrer 

 and co-workers, and is similar to the corresponding investigations on xantho- 

 phyll (cf. p. 201). The empirical formula and the number of hydroxyl groups 

 References p. 214-217. 



