17 



ECHINENONE 325 



in vacuum. The residual acetone solution is then diluted with water and the pigments 

 are first extracted with petroleum ether and then with benzene. From the petroleum 

 ether solution mainly polyene hydrocarbons are obtained, while the benzene extract 

 contains mainly phytoxanthins and is worked up for pentaxanthin (p. 327). The 

 petroleum ether solution is shaken with 90% methanol and the phytoxanthins 

 thus extracted are worked up together with those obtained from the benzene 

 solution. 



For the isolation of echinenone, the petroleum ether extract is washed with 

 water and then saponified with methanohc potassium hydroxide. After working 

 up in the usual way and freezing out accompanying steroids, the pigments are 

 adsorbed on a column of calcium carbonate from petroleum ether solution. The 

 echinenone fraction is separated and chromatographed on alumina. a-Carotene 

 and /3-carotene are adsorbed on the lower part of the column. The echinenone fraction 

 found in the upper part of the column is still not homogeneous, so that the pigment 

 must be chromatographed repeatedly on alumina and on calcium carbonate. It is 

 finally crystallised from a mixture of benzene and methanol. From 400 sea urchins 

 about 4 mg of echinenone can be obtained in this manner. 



A certain amount of information is available regarding the chemical con- 

 stitution of this pigment, but the structure* has not yet been fully clarified. 

 The elementary analysis of echinenone gives the molecular formula C40H58O 

 ( ± H2) . It produces strong vitamin A activity in rats and therefore probably 

 contains an unsubstituted ^-ionone ring. The single-banded (?) absorption 

 spectrum** suggests the presence of a carbonyl group and the epiphasic 

 behaviour of the pigment excludes the presence of a hydroxyl group. In its 

 general properties echinenone is reminiscent of /3-semicarotenone (p. 139). 

 Lederer suggested the possibility that echinenone may be identical with 

 myxoxanthin (p. 225). Some of the properties of the two compounds are in 

 fact in good agreement, but Heilbron considers it unlikely that the two 

 pigments are identical. (Private communication to Lederer). 



Echinenone crystallises from petroleum ether or from a mixture of benzene 

 and methanol in violet needles with a metallic lustre, m.p. 178-179°. (On a 

 single occasion Lederer obtained crystals melting at 193°, but the m.p. 

 178-179° is more probably correct). The absorption maxima of the pigment in 

 carbon disulphide solution are located at 520, 488 and 450 mfi**. 



On partition between methanol and petroleum ether, echinenone exhibits 

 purely epiphasic behaviour. By treatment with iodine the pigment can be 

 precipitated from petroleum ether solution as the iodide from which it can be 



A possible structure for echinenone is proposed by E. Lederer and T. Moore, 

 Nature, London, 737 (1936) 996. 



** E. Lederer observed a single band at 488 m/n on examination in a visual spectro- 

 meter. Photoelectric determinations by R. Kuhn showed the presence of two additional 

 weak bands at 520 and 450 m^. E. Lederer considers it possible that these weak bands 

 belong not to echinenone itself but to an accompanying carotenoid. This question requires 

 further investigation. 



References p. 341-34.3. 



