HYDROCAKBON CAKOTLiNOIDS OF THE C4u SERIES 513 



The present designation carotenoids (carotinoids) was originally pro- 

 posed by Tswett^^ to include those chromolipoids which are chemically 

 and generically related to carotin. A further subdivision of the carote- 

 noids, suggested by Tswett, was into carotenes (the hydrocarbons) and 

 xanthophylls (oxyhydrocarbons) . The latter designation has now been 

 replaced by carotenols for the oxycarotenoids containing an alcohol group, 

 while no satisfactory designation to cover all of the oxygen-containing 

 carotenoids is at present in general use. 



It is now recognized that many classes of plant and animal pigments 

 occur which do not belong to the carotenoid group. Some of these may 

 have a yellow or orange color similar to that of the carotenoids. Examples 

 of such compounds are the flavones, xanthones, anthoxanthones, and 

 anthocyanins, in the plant kingdom, and the bile pigments in the animal 

 products. These are in all cases distinguished from carotenoids by their 

 solubility in water rather than in organic solvents. 



2. Structure and Occurrence of Hydrocarbon Carotenoids of the C40 



Series 



Prior to 1931, it was believed that carotene was a single entity. Some 

 confusion existed, however, since carotenes which were isolated from dif- 

 ferent plant sources had variable melting points, although superficially they 

 appeared to be the same compounds. Thus, Collison, Hume, Smedley- 

 MacLean, and Smith'*'' reported that the melting points of carotene prepara- 

 tions from cabbage, spinach, and carrots were 178°C., 163-164°C., and 

 164-170°C., respectively. Moore^^ noted that carotene from palm oil 

 melted at 162°C. while that from carrots melted at 174°C. 



Another discrepancy among various carotene preparations was noted in 

 their optical activity. Although Kuhn and Lederer^^-*^ reported that the 

 carotene preparations from winter spinach, grass, and stinging nettle 

 (Urtica dioica) were uniformly inactive as far as optical rotation is con- 

 cerned, they found that many carotene samples were dextro-rotatory after 

 having been subjected to several crystallizations. It was found that the 

 carotenes from palm oil,^^ carrots, Sorhus aucuparia (European mountain 

 ash), and Aesculus hippocastanum (horse chestnut) all belong to the latter 

 category. These workers also demonstrated that the opticall}^ active caro- 

 tene preparations could be separated by chromatographic adsorption as 

 well as by fractional precipitation with iodine into two isomers. The first 



** D. L. Collison, E. M. Hume, I. Smetlley-MacLean, and H. H. Smith, Biochem. J., 

 23, 634-6-17 (1929). 



« T. Moore, Biochem. ./., 2S, 1267-1272 (1929). 



"" R. Kuhn and E. Lederer, Xaturwissenschaften, 19, 306 (1931). 



" R. Kuhn and E. Lederer, Ber., 64, 1. 349-1357 (1931). 



^8 R. Kuhn and E. Lederer, Z. physiol. Chew., 200, 246-2.54 (1931). 



" R. Kuhn and II. Brockmann, Z. physiol. Chem., 200, 255-258 (1931). 



