i8o CAROTENOIDS CONTAINING HYDROXYL GROUPS XI 



of the small amount of material available it has not yet been obtained in a 

 crystalline state. 



Solvent: Absorption maxima: 



Carbon disulphide 456 424 m^ 



Cis-trans Isomers 



A number of cis-trans isomers of cryptoxanthin have been prepared by 

 Zechmeister and Lemmon^'. According to these authors, natural crypto- 

 xanthin has an a.\\-trans configuration (cf. p. 38). By standing or boiling a 

 solution of the pigment, by fusion of the crystals, by treatment with iodine 

 or illumination with sunlight, various isomers are formed which are believed 

 to contain a number of cw-double bonds. 



The sequence of isomers in the table below is that in which they are observed 

 in the chromatogram. 



A hsorption ntaxima 

 (in petroleum ether) 



Neo-Cryptoxanthin U 478.5 448 m^ 



(Cryptoxanthin) M83.5 452.5 m^) 



Neo-Cryptoxanthin A 477 446 m/j. 



Neo-Cryptoxanthin B 479.5 449.5 m/i 



Apart from natural cryptoxanthin, none of these compounds has been 

 obtained in a crystalline state. The absorption curves of the pigments can 

 be found in the original communication. 



4. ZEAXANTHIN C4oH5g02 



History 



1929 Karrer, Salomon and Wehrli^^ isolate a new phytoxanthin, for which 



they propose the name zeaxanthin, from maize. 

 1931-32 Karrer and co-workers elucidate the constitution of zeaxanthin^^. 



Occurrence 



Zeaxanthin is widely distributed in plants in the free state as well as 

 esterified (physalien). Some plants contain zeaxanthin as the main pigment, 

 so that its isolation in appreciable amounts is relatively easy to achieve. 



References p. 214—217. 



