582 VI. CAKOTExVOIDS AND RELATED COMPOUNDS 



HjC CH3 H jC CH3 



p CHs CH3 CH3 CH3 CH 



/\ hhIhhhIhhhhIhhhIhhh \ 



H2C c-c:c-c:c-c:c-c:c-c:c-c;c-c:C'C:c-c:c-c CH 



I II II 11 



H2C C C CH 



\ / \ / \ / 



C CH3 HjC C 



He II 







Myxoxaiithin (?) 



The empirical formula is C40H54O. The free pigment absorbs 12 mole- 

 cules of hydrogen, whereas the myxoxanthin oxime will take up 13 moles, 

 indicating that the pigment has 12 double bonds and a carbonyl group. 

 When reduced with aluminum isopropoxide in isopropanol, it is changed to 

 a secondary alcohol, myxoxanthol. Myxoxanthin must have an unsubsti- 

 tuted /3-ionone ring, since it possesses activity as a provitamin A. 



Myxoxanthin crystallizes in deep violet colored prisms, from a pyridine- 

 methanol mixture, which melt at 168-1 69°C. Myxoxanthin dissolves well 

 in a mixture of chlorofonn-diethyl ether or chloroform-petroleum ether, but 

 only poorly in chloroform alone. It is epiphasic. Myxoxanthin oxime, 

 C40H65ON, forms cinnabar-red platelets which melt at 195-196°C. 



{16) Myxoxanthophyll 



In addition to myxoxanthin, lutein, and jS-carotene, Heilbron and 

 Lythgoe^^" found a new hypophasic pigment in the purple plankton alga 

 {Oscillatoria ruhescens) which they named myxoxanthophyll. It was 

 found ^^"'^^^ to have an empirical formula of C40H56O7. The carotenoid ab- 

 sorbs 10 molecules of hydrogen rapidly and one mole slowly, which would 

 indicate the presence of 10 double bonds and of a carbonyl group. The re- 

 maining 6 oxygens occur in hydroxyl groups. Myxoxanthophyll forms a 

 tetraacetate, indicating that 4 of the hydroxyls are secondary alcohol 

 groups; proof that the remaining 2 oxygens are components of tertiary 

 alcohol groups is obtained by the Zerewitinoff reaction, which indicates that 

 2 free hydroxyl groups still remain on the tetraacetate. The tentati\'e 

 formula sho^\^Q here is believed to indicate the probable structure.'*^ 



HjC CHj HjC CH5 



^/ CH3 CH3 CH, CH, ^CH ^ 



H\/\/hh|hhhIhhhhIhhhIhh ,/ 



c c-c : c • c : c • c : c • c : c • c : c • c : c • c : c • c: c • c : c • ch c ^ 



"S-'i I II IT 



" C C-OH C C 



"" C CH, HjC C OH 



H 



Myxoxanthophyll (?) 



