CAROTENOIDS WITH LESS THAN FORTY CARBON ATOMS 593 



of the sex organs of the mollusc, St. Jacques mussel or scallop {Pecten maxi- 

 mus). The same pigment apparently occurs in the sea-weed-inhabiting 

 ascidian, BotnjUus schlosseri.''^^^ The pigment has been named pectenoxan- 

 thin. It has 1 1 conjugated double bonds and 2 active hydrogens, probably 

 in hydroxyl groups. This carotenoid is inactive as a precursor for vitamin 

 A, which indicates that there are no unsubstituted /3-ionone rings. It can 

 be separated in long yellow-brown prisms from dilute pyridine; these melt 

 at 182°C. The pigment dissolves better in 90% methanol than in petro- 

 leum ether. Benzene, carbon disulfide, and pyridine are excellent solvents. 

 Karrer and Solmssen''^^ found a pigment with similar absorption peaks in 

 the red scallop (Pecten jacobaeus) which they considered might possibly be 

 identical with pectenoxanthin. 



d. Cynthiaxanthin. In connection with studies of the pigments of vari- 

 ous types of Ascidiae, Lederer^''^ reported that, in addition to astacene, 

 another unknoAMi carotenoid pigment is present in the red solitaiy fixed 

 ascidian, Cynthia (Halocynihia) papillosa. He named the pigment cynthia- 

 xanthin. Karrer and Solmssen^^^ were unable to confirm the presence of 

 the pigment in material of the same kind ; it may have been masked by the 

 bands for astacene. 



5. Structure and Occurrence of Carotenoids Having Less Than 



Forty Carbon Atoms 



It has long been known that several polyene acids having a smaller num- 

 ber of carbon atoms than the C40 series exist in nature. Kuhn and Winter- 

 stein''* have advanced the hypothesis that certain compounds in this cate- 

 gory, such as bixin, crocetin, and azafrin, originate through the oxidative 

 sphtting of the carotenoids. There is some support for such a theory, since 

 bixin dialdehyde and two molecules of methylheptenone originate on oxida- 

 tion of lycopene with chromic acid. Bixin dialdehyde can be readily 

 changed to bixin. ^^^ Moreover, it is believed that a glucoside of crocetin 

 originates by the breakdown of a bicyclic C40 carotenoid which has been 

 paired with sugar. In this reaction, two molecules of picrocrocin are 

 formed. The relationship of the C40 polyenes to the simpler members of 

 this class is schematically represented in Figure 2. 



(1) Bixin and Related Compounds 



Bixin has long been known as a dye present in the seed hulls of the tropical 

 anatto tree {Bixa orellana L.). Up to the present time this constitutes the 

 main commercial source of the dye anatto (also called orlean or orellin). 

 This coloring matter was characterized as early as 1825 by Bossingault,^^" 

 while Etti*'*^ succeeded in crystallizing it in 1878. Later (1917) Heiduschka 



**oj. B. Bossingault, Ann. chim. [2], 28, 440-443 (1825). 

 <" C. Etti, Ber., 11, 864-870 (1878). 



