234 CAROTENOIDS CONTAINING CARBONYL GROUPS XII 



extracted on the filter with strongly cooled acetone. The deep red extract is covered 

 with a fifth of its volume of petroleum ether, and diluted carefully with one volume 

 of distilled water, when most of the pigment separates in beautifully glistening 

 plates. After filtering, the petroleum ether solution is extracted with 90 % methanol, 

 the methanol solution is covered with freshly distilled benzene, and a further 

 quantity of astaxanthin is precipitated by careful addition of water. The two 

 fractions are crystallised together from a mixture of pyridine and water^^. 750 mg 

 of pure pigment are thus obtained. Two other methods of preparation of the two 

 pigments are described by Karrer and co-workers^^. 



Chemical Constitution of Astacene C40H48O4: 



CH, CH3 CH, CH, 



C CH3 CH, CH, CH, C 



/\ I I I I /\ 



CH2 C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CH, 



I i II I 



OC C-CHj HgC-C CO 



\^ / Astacene (Ketoform) \ / 



CO CO 



CH3 CH3 CH, CH,* 



\V \V 



C CH, CH, CH, CH, C 



/\ \ I I \ /\ 



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



HOC C-CHg ■ HjC-C COH 



\ / Astacene (Enolform) \^ / 



CO CO 



The formula for astacene (3 13' 14 14' tetraketo-j3-carotene) was proposed by 

 Karrer^^. Elementary analysis of the compound itself and of the dioxime gave 

 the molecular formula C4QH48O4 which differs from that of j3-carotene only by 

 the presence of 8 fewer hydrogen atoms and 4 additional oxygen atoms. From 

 the molecular formula and the nature of the oxygen atoms, Karrer and co- 

 workers concluded that the constitution of the pigment must be that of a 

 tetraketo-j3-carotene. Astacene forms a dioxime which contains 4 active 

 hydrogen atoms. Two of these are derived from the oxime residues, while the 

 other two must be due to the enolisation of the other two carbonyl groups. The 

 four keto groups therefore differ in nature, two being capable of forming an 

 oxime, and the other two undergoing enolisation. Astacene gives a bis-phenazine 

 derivative with o-phenylene diamine, which shows that each pair of carbonyl 

 groups must be adjacent. By the oxidation of astacene with permanganate, 

 Karrer and co-workers obtained dimethylmalonic acid. On oxidation of the 

 bis-phenazine derivative, a:a-dimethylsuccinic acid was also isolated, thus 

 establishing the presence of the 4 carbonyl groups in the 3:3':4:4'-positions. 

 This is in accord with the finding of Willstaedt that astacene can be reduced 

 References p. 253—253. 



