FLA VOXANTHIN 

 Chemical Constitution 



209 



The first attempts to elucidate the constitution of flavoxanthin were made 

 by KuHN and Brockmann^^. These authors determined the empirical formula 

 and the number of double bonds and reported the presence of three hydroxyl 

 groups. According to more recent investigations^"* °, however, flavoxanthin 

 contains only 2 hydroxyl groups, the third oxygen atom being present in the 

 form of an ether grouping. The nature of this oxygen atom was only established 

 by the investigation of Karrer and Jucker^^" in the course of which flavo- 

 xanthin was partially synthesized. Flavoxanthin was obtained together with 

 the isomeric chrysanthemaxanthin by the action of very dilute hydrochloric 

 acid (in the form of aged chloroform) on xanthophyll epoxide. According to 

 the discussion on p. 62 this transformation proceeds as follow. 



CHo CHo 



\/ 



C CH, 



/\ I 



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



I 1)0 



HOCH C Epoxide residue 



^ of xanthophyll- 



CH2 CH3 epoxide 



\V 



c 



/\ 



CH2 C=CH CH3 

 HOCH C CH-C=CHCH=CH- 



CH2I Furanoid residue of 

 CH, flavoxanthin 



Thus flavoxanthin and the isomeric chrysanthemaxanthin have the 

 following constitution : 



CHo CHo 



\V 



CHq CHo 



/\ \V 



CHs C=CH CH3 CH, CH, CH, C 



I I I I I I I /\ 



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



I I 



H,C-C CHOH 



CH 



Flavoxanthin 



All the properties of the pigment are in complete agreement with this 

 formulation. The partially synthetic product proved to be identical in all 

 respects with natural flavoxanthin^^''-^^^. 



Properties and Physical Constants 



Crystalline form: Flavoxanthin crystallises from methanol on rapid cooling 

 in narrow, clustered prisms, which are golden yellow in colour and possess a 

 beautiful surface lustre. M.p. 184° (corr., evacuated capillary). 

 References p. 214— 2IJ, 

 Carotenoids 14 



