5 ASTACENE AND ASTAXANTHIN 235 



by zinc dust and acetic acid in pyridine solution to give a light yellow deriv- 

 ative*". 



Microhydrogenation of astacene showed the presence of 13 double bonds, 

 two of which are formed by enolisation. Free astacene is only slightly enoHsed 

 as shown by the slow etherification with diazomethane and by Zerewitinoff 

 determinations. The weakly acidic nature of the pigment disappears on hydro- 

 genation, as would be expected. 



Karrer, Loewe and Hubner*^ investigated the epiphasic astacene ester from 

 lobster and described it as astacene dipalmitate. 



CH3 CH3 CH3 CH3 



C CH, CH3 CH3 CH3 C 



/\ I I I I /\ 



CH C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CH 



II II II II 



CH3(CH2)i4C00C C-CH3 HjC-C C00C-(CH2)i4-CH3 



\ / Astacene dipalmitate \ / 



CO CO 



It is probable that the compound is actually the dipalmitic acid ester of 

 astaxanthin. 



Chetnical Constitution of Astaxanthin C40H52O4: 



CH, CH, CH3 CH3 



C CH3 CH3 CH3 CH3 C 



/X I I I I /\ 



CH2 C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CHj 



HOCH C-CH3 HjC-C CHOH 



\ / Astaxanthin \ y^ 



CO CO 



The isolation of a crystalline "ovoester" from the eggs of lobster was 

 described by Kuhn and Lederer^^. It was later shown by Kuhn and Soren- 

 SEN that the "ovoester" is not an ester but a free phytoxanthin. It was named 

 astaxanthin and has the molecular formula €40115204*2. By analogy with the 

 formula of astacene established by Karrer and co-workers, Kuhn and Soren- 

 SEN*2 assigned the structure of a 3:3'-dihydroxy-4:4'-diketo-|S-carotene to 

 astaxanthin*. This formulation is based on the fact that, in the absence of air, 

 astaxanthin forms a deep blue salt in potassium hydroxide solution, while 

 under aerobic conditions the pigment absorbs exactly 2 mols of oxygen in 

 alkaline solution and is converted into astacene. The conversion of astaxanthin 

 into astacene represents the autoxidation of a di-a-ketol. In agreement with the 



The alternative structure, 4:4'-dihydroxy-3:3'-diketo-/3-carotene, is excluded by the 

 spectral properties of astaxanthin (cf. p. 237). 



References p. 253-235. 



