CAROTENOIDS 



This definition includes such naturally occurring compounds as 

 vitamin A and azafrin only in so far as they are considered breakdown 

 products (apocarotenoids) of carotenoids containing 40 carbon atoms. 

 Although compounds such as bixin containing less than 40 carbon 

 atoms (8 isoprene residues) are included in Karrer's definition, only 

 those containing 8 isoprene residues are discussed in detail in this book ; 

 others are mentioned only in so far as they are concerned with the bio- 

 chemistry of tlie C40 carotenoids. 



NUMBERING AND NOMENCLATURE 



The conventions used in this book for describing carotenoids are, 

 with one exception and some additions, those recommended by the 

 " Union internationale de Chimie "" in a report by the ** Commission 

 de nomenclature de chimie organique et Commission de nomenclature 

 de chimie biologique." A previous report by the American " Com- 

 mittee on Biochemical Nomenclature of the National Research 

 Council "' differs slightly from the International Commission's report. 



The carbon atoms of a carotenoid molecule are numbered according 

 to the scheme proposed some years ago by Karrer, in which the 

 carotenoid is divided into two parts, viz. 



CHj CH3 



\/ 



CI 



^ / \6 7 8 9 10 II 12 13 14 15 15' 14' 13' 12' 11' 10' 9' 8' 7' 6\X \ 



2CH, c-c = c-c=*c-c=c-c=c-c-c-c=c-c==c-c=c-c=c-r CH22' 



I II H H CH3 H H H CH3 H H H H CH3 H H H CH3 H H II | 



3CH2 C-CH3 CH3-C CH, 3' 



/"2 CH, 



P-carotene 



If the carotenoid under discussion is asymmetrical, the half con- 

 taining the p-ionone residue is designated by plain numerals ; e.g. 



CHj CH3 CHj CHj 



'/. ^C 



.^^^ \$ 7 8 9 10 II 12 13 14 15 15' 14' 13' 12' II' lO' 9' 8' 7' 6'/ \ 



2 CHj C— C==C-C = C-C = C-C = C-C=C-C = C-C=C— C = C-C=C-C CHj 2 



I 1 H H CH, H H H CHj H |i| H H CHj H H H CHj H H I | 



3 CHj C-CHj CHj-C. CH23' 



CHa CHj 



4 4' 



ec-carotene 

 2 



