CAROTENOIDS WITH LESS TliAN FORTY CARFiON ATOMS 597 



Labile or stable norbixin 



norbixin are known, one of which corresponds to labile bixin (cis) and the 

 other of which is related to stable bixin (trans). Labile norbixin can be 

 prepared by the saponification of natural bixin by hydrolysis in the cold 

 over a 24-hour period with 10% methanolic potash. Stable norbixin 

 originates through saponification of labile bixin with hot aqueous-alcoholic 

 potash or by hydrolysis of stable bixin in the cold.-^ A direct conversion of 

 one form of norbixin to the other form has not been achieved. Norbixins 

 have not been found naturally. 



Fig. 3. Suggested stereochemical structures of stable bixin (all- 

 Irans) (structure I) and of natural bixin (labile or cis) (structure II). 

 The carboxyl groups are represented by black circles. ^^ 



c. Bixin Dimethyl Esters. Other commonly recognized products re- 

 lated to the bixins are the labile and stable dimethyl esters of bixin. 

 These represent the cis and trans isomers, respectively. Both have the 

 empirical formula of C26H32O4, and the stiiicture H3CO • OC • C22H26 • CO • 

 OC'Hs. Neither of these compounds has been found naturally. 



{2) Crocetin 



Crocetin is another example of a naturally occurring carotenoid having 

 less than 40 carbon atoms. It resembles bixin in many respects, although 

 it contains only the middle 20 carbons of the C40 carotenoid molecule (8 to 

 8' inclusive), while bixin is made up of the central 24 carbon atoms (6 to 6' 

 inclusive). Crocetin also appears to be more \videly distributed in nature 

 than is bixin. One of the most important natural products containing this 

 carotenoid is the medicinal compound saffron. 



