5 ASTACENE AND ASTAXANTHIN 229 



Myxoxanthophyll tetraacetate C^^^^iOi-i^: 



The ester is prepared by treating myxoxanthophyll with acetic anhydride 

 in pyridine. It crystallises from methanol in lustrous violet leaflets, m.p. 131- 

 132°. Myxoxanthophyll tetraacetate is entirely hypophasic on partition between 

 methanol and petroleum ether. 



Solvent Absorption maxima 



Carbon disulphide 544 508 479 mfx 



Karrer and Rutschmann^* also prepared myxoxanthophyll benzoate, 

 but the compound was not obtained pure because of shortage of material. 



5. ASTACENE C40H48O4 AND ASTAXANTHIN C40H52O4 



Introduction 



The pigments of Crustacea have long aroused the interest of chemists and 

 zoologists^^. It is only in recent years, however, that it has been possible to 

 obtain some indication of the nature of these pigments (cf. p. 234), and that the 

 investigations regarding the chemical constitution of these compounds has 

 reached a certain degree of finality. The first pigment of this type was isolated 

 in 1933 in the form of astacene from lobster shelP^. Astacene was later recognised 

 as a j3-carotene tetraketone by Karrer and co-workers^^. Some years later, 

 KuHN and Sorensen^^ found that the pigment from lobster eggs known as 

 "ovoester" was not an ester of astacene but an entirely new pigment^^. It was 

 termed astaxanthin, and it was shown that it is readily converted into astacene 

 in alkaline solution under the influence of atmospheric oxygen. It therefore 

 appeared possible that astacene is an artefact formed by the alkaline saponifi- 

 cation of astaxanthin esters and that astaxanthin is the natural pigment^^. 

 This supposition has been proved in a number of cases while in others the 

 necessary experiments have not yet been carried out. It has been found that 

 astaxanthin occurs fairly freciuently in the animal organism^^ and also in 

 plants^'"*. 



The close relationship of the two carotenoids and the facile conversion of 

 astaxanthin into astacene under the influence of atmospheric oxygen in alkaline 

 solution are established without doubt. The two pigments will therefore be 

 dealt with together in this chapter. 



History 



1933 Kuhn and Lederer^^ isolate crystalline astacene from lobster shell. In the 

 animal, the pigment is partly combined mth protein and partly esterified. 

 References p. 253—255. 



