560 VI. CAROTENOIDS AND RELATED COMPOUNDS 



HjC CHj HjC CHj 



C CHj CHj CHj CHi ^(.^ 



/\ hh|hhhIhhhhIhhhIhhh/\ 

 HzC G-c:C'C:C'C:G'C:c-c:C-C:G'C:C'C:c-C:C-C CHz 



H^l l> I l/H 



,c c^ c c 



HO^ \ / \ / ^ / ^OH 



C CHj HjC G 



Hz H 



Lutein epoxide 



The presence of an oxygen atom on the double bond of the /3-ionone ring 

 is indicated by several facts. In the first place, there is a shift in the ab- 

 sorption maximum of the epoxide of only 7 mn from that of xanthophyll. If 

 oxidation had occurred on one of the double bonds of the aliphatic side 

 chain, an interference in the conjugation would have resulted, and a con- 

 siderably greater alteration m absorption maximum in the ultraviolet 

 might have been expected. Second, a dioxy-a-carotene, prepared earlier 

 by Kari-er et al.,^^^ in which oxidation occurred on the 5,6 position of the 

 jS-ionone ring, had an absorption band at a wave length identical with that 

 of lutein epoxide. The latter finding would seem to place the additional 

 oxygen on the j8- rather than on the a-ionone ring. 



Lutein epoxide was found to separate in reddish yellow crystals (m.p., 

 192°C.) which are difficultly soluble in alcohol, but which dissolve easily in 

 benzene. It possesses two active hydrogens as determined by the Zere- 

 witinoff reaction ; it absorbs 1 1 molecules of hydrogen on catalytic hydro- 

 genation in glacial acetic acid. The maximum absorption in carbon di- 

 sulfide was found ^^^ to be at 501.5 and 472 niju. 



One of the most interesting properties of this epoxide is exhibited when it 

 is treated with dilute acids. When hydrochloric acid is added to a methanol 

 solution of lutein epoxide to make a 1% solution, an immediate shift of ab- 

 sorption maxima to shorter wave lengtlis occurs (479 and 450 mju) . How- 

 ever, the new products cannot be ciystallized from methanol. On the 

 other hand, a similar shift of absorption maxima was also observed when 

 the lutein epoxide was dissolved in chloroform; this change in position of 

 the maxima was much greater than the usual difference of 7 to 8 m/x ob- 

 served in chloroform. Karrer and Jucker^^^ were able to crystallize two 

 new compounds responsible for the lower absorption values from the chloro- 

 form solution; these had empirical formulas of C4oH660,3. They were iden- 

 tified as flavoxanthin and chrysanthemaxanthin ; the latter appear to be 

 optical isomers with different configurations on carbon atom 3 of the ^- 

 ionone ring. Their formation in chloroform is to be attributed to the small 

 amount of hydrochloric acid present in this solvent, which brings about 

 what is practically a catalytic conversion of lutein epoxide to these new 

 compounds. The reaction is believed to be similar to that occurring in 

 methanol when hydrochloric acid is added. 



