CAROTENOIDS 



The Commission has not discussed carotenoids which, by virtue of 

 their ability to undergo keto-enol tautomerism, exhibit acidic properties, 

 e.g., astaxanthin {see p. 169). In this book these will be tenned add 

 carotenoids, and should not be confused with the carotenoid acids 

 (carboxycarotenoids) just discussed. 



In many countries the usual group name for the oxygen-containing 

 carotenoids is xanthophylls. This name is not accepted by the Inter- 

 national Commission because of Karrer's plea that a worker who first 

 isolates a compound in a pure state has the privilege of naming that 

 compound. The main oxygenated pigment of green leaves was first 

 isolated pure by Karrer^ and named xanthophyll. Later Kuhn and 

 his collaborators^ obtained the same pigment, called it lutein, and 

 suggested xanthophyll as a group name for the hydroxy carotenoids. 



One must respect Karrer's plea, but the influence of established 

 custom, be it mistaken or not, cannot be completely ignored. It is 

 hoped that the rule followed in this book will not be confusing ; lutein 

 {xanthophyll) will be used to designate Karrer's individual pigment 

 wherever any possible ambiguity exists, otherwise lutein alone will be 

 used. Xanthophylls will be retained as a group term ; in this sense it 

 will be generally used only in the plural. 



Labile cis-trans isomers of the carotenoids are prefixed by " neo- " 

 and suffixed by an identifying capital letter {see p. 9) ; e.g., neo-(i- 

 carotene B, neo-^-carotene U. An aldehydic, ketonic, or carboxylic 

 fragment obtained by degradation of a carotenoid takes the suffix, 

 *' al," " one," or " oic " only when the prefix " apo " is used. This 

 prefix is followed by the numeral indicating the carbon atom of the 

 aldehyde, ketone, or acid group, e.g., 



CH, CH3 



'\/ 



/ \6 7 9 10 II 12 13 14 15 is' 14' iV 12' ll' lO' 9' 8>^ 



2 CH^ c-c=c-c=c-c=--c— c=c— C=C-C=C-C-=C— C--C— C'^ 



I II H fH CH3 H H H CH3 H H H H c'hj H H H CH3 H 



3 CH, C-CH, 



4 CHj 



3-apo-8'-carotenal 



It should be noted that this enumeration is different from that first 

 proposed by Karrer,^^ by whom most of the work on apocarotenes has 

 been reported. In the original scheme, the number following the 

 prefix " apo " indicated the number of double bonds removed from 

 the original carotenoid molecule ; thus the above example would on 

 the old system be termed p-apo-2-carotenal. 



