26o 



CAROTENOID CARBOXYLIC ACIDS 

 TABLE 50 



NOMENCLATURE OF BIXIN DERIVATIVES^^ 



XIII 



Karrer and Solmssen have attempted to solve the question as to which 

 double bond of the bixin molecule possesses the czs-confignration^^. They 

 subjected the bixins to permanganate degradation* and compared the products 

 obtained from labile bixin and stable bixin. Each isomer yielded a different 

 apo-l-norbixinal methyl ester I and, very probably, a different apo-2-norbixinal 

 methyl ester II**, distinguished by their melting points and absorption spectra. 

 Both bixins also give rise to an identical apo-3-norbixinal methyl ester III. 

 These results show that the isomerism of the two bixins probably depends on 

 the different configuration of the third double bond in the chain, counting from 

 the unesterified carboxyl group. In view of the incompletely established diffe- 

 rence of the apo-2-norbixinal methyl esters, it is possible that cis-trans isomerism 

 of the second double bond may also be involved. 



CH, 



CH, 



CH, 



CH, 



HsCOOC- CH=CH- C=CHCH=CH- C=CHCH=CHCH=C- CH=CHCH=C- CHO 



I 



CH, 



CH, 



CH, 



HsCOOC- CH=CH- C=CHCH=CH- C=CHCH=CHCH=C- CH=CH- CHO 



II 



^* Cf. p. 47. 



The identity of the two compounds could not be established with certainty because 

 the apo-2-norbixinal methyl esters were only obtained crystalhne in the form of their 

 oximes. 



References p. 2go—2g4. 



