554 VI. CAROTENOIDS AND RELATED COMPOUNDS 



represent a group in which kitein is a specific type. Karrer and Notthafft ^^^ 

 retained the historic term for the chief component of leaf xanthophylls, and 

 have coined the expression phytoxanthin for the polyene alcohols of the C40 

 series. At the present time, the tendency is to employ the term lutein for 

 the polyene alcohol from green leaves and from egg-yolk, since these are 

 apparently identical. There seems to be little doubt that the egg-yolk 

 lutein is derived from the xanthophyll in the diet. 



a. Structure. The empirical formula for lutein is C40H56O2. Since it 

 is known to contain two functional alcohol groups, this may better be 

 written as C4oH54(OH)2. The similarity in structure between the carotenes 

 and lutein has long been suspected on the basis of the correspondence of 

 their general properties. Zeaxanthin and lutein will add 11 molecules of 

 hydrogen, just as is the case with j8- or a-carotene; this indicates that the 

 polyene alcohols must contain two ring systems. 



The nature of the oxygen union was proved by Karrer, Helfenstein, and 

 Wehrli,^''^ who showed that lutein has two active hydrogen atoms, accord- 

 ing to the Zerewitinoff reaction, and that these must be present as com- 

 ponents of hydroxyl groups. Further evidence that the oxygen atoms exist 

 in alcohol groups is also afforded by the demonstration that lutein may occur 

 naturally as a fatty acid ester. '^""^^i The final evidence that the alcohol- 

 like reactions are not the result of enolization but depend upon a true alco- 

 hol structure is obtained through oxidation of the perhydroxanthophyll to a 

 diketone. According to Karrer et al.^^^ this demonstrates that the hy- 

 droxyls are present as secondary alcohol groups. 



The nature of the ring system and the position of the hydroxyl group 

 have been established by oxidative degradation. Lutein and zeaxanthin 

 both yield dimethyl malonic acid, HOOC-C(CH3)2-COOH, and a,a- 

 dimethylsuccinic acid, HOOC-C(CH3)2-CH2-COOH, while no a,a- 

 dimethylglutaric acid, HOOC-C(CH3)2-CH2-CH2-COOH, or geronic acid, 

 CH3 • CO • CH2 • CH2 • CH2 • C(CH3)2 • COOH, is produced. These data indi- 

 cate that the ionone ring must be substituted, which prevents the forma- 

 tion of the last-named products. ^"'^^^'^^^ Since this is the case, the hydroxyl 

 must be in the para position to the carbon where the side chain is at- 

 tached. For this reason, the hydroxyl groups are assigned to positions 3 

 and 3'. 



2'6 P. Karrer, A. Helfenstein, and H. Wehrli, Heb. Chim. Acta, 13, 87-89 (1930). 

 ^" R. Kuhn and A. Winterstein, Naturwissenschafien, 18, 754 (1930). 

 -^* R. Kuhn, A. Winterstein, and W. Kaufmann, Nalunvissenschaflen, 18, 418 (1930). 

 2" R. Kuhn, A. Whiterstein, and W. Kaufmann, Ber., 63, 1489-1497 (1930). 



280 L. Zechmeister and L. v. Cholnoky, Z. physwl. Chem., 189, 159-161 (1930). 



281 L. Zechmeister and L. v. Cholnoky, Ann., 481, 42-56 (1930). 



282 P. Karrer, A. Zul)rvs, and R. Morf, Helv. Chim. Ada, 16, 977-979 (1933). 



283 P. Karrer, H. WehrH, and A. Helfenstein, Helv. Chim. Acta, IS, 268-273 (1930). 

 281 R. Nilsson and P. Karrer, Helv. Chim. Ada, I4, 843-845 (1931). 



