296 CAROTENOIDS OF UNCERTAIN STRUCTURE XIV 



benzene and chromatographed on calcium hydroxide. The chromatogram is first 

 developed with a mixture of benzene and petroleum ether and then with petroleum 

 ether alone. The salmon-red zone of rhodoviolascin is eluted with a mixture of 

 methanol and benzene, the solvent is removed by distillation and the remaining 

 pigment is combined with the crystalline rhodoviolascin (see above). The following 

 pigments were obtained from the other chromatogram zones : rhodovibrin, rhodopin, 

 rhodopurpurin, /3-carotene( ?) and flavorhodin. 



For further purification, the crude rhodoviolascin is chromatographed several 

 times on calcium hydroxide and finally recrystallised from benzene. In order to 

 obtain 0.9 g of pigment, Karrer and Koenig worked up 19,320 1 of ripe bacteria 

 nutrient solution in the course of two years. 



Chemical Constitution 

 CHo CHo CHq CHa 



CH CHo CHq CHi CHo CH 



/ I I I I V 



CHa CH-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-CH Cfi^ 



I II II I 



HaCO-C C-CHs HjC-C C-OCHs 



X/ Rhodoviolascin(?) (I) \/' 



CH CH 



Karrer and Solmssen^^ proposed a tentative structural formula for 

 rhodoviolascin which was subsequently modified by Karrer and Koenig^^ 

 (Formula I). However, even the modified structure cannot yet be regarded as 

 established with certainty. 



The molecular formula of rhodoviolascin is C42Hgo02. Methoxy 1 determinations 

 show the presence of two methoxyl groups. On catalytic hydrogenation, 13 

 moles of hydrogen are taken up. The long- wavelength location of the absorption 

 maxima (573.5, 534, 496 m// in carbon disulphide) shows that all the double 

 bonds must be in conjugation. The pigment does not react with hydroxylamine 

 and yields no dihydro-derivative on treatment with pyridine, acetic acid and 

 zinc. In contrast to carotenoid diketones, it exhibits the same absorption 

 spectrum in petrol and methanol. 



Karrer and Koenig subjected rhodoviolascin to stepwise degradation 

 with permanganate^^ and obtained at least 6 different oxidation products. 

 From these, bixindialdehyde could be isolated and identified, thus establishing 

 the structure of the central part of the molecule from carbon atom 6 to carbon 

 atom 27. Besides bixindialdehyde, another dialdehyde was obtained in very 

 small yield which was found above bixindialdehyde on the chromatogram and 

 had absorption maxima located at 40 m/* towards longer wavelengths. It must 

 therefore contain 2 conjugated double bonds more than bixindialdehyde. 

 Methoxyl determination gave a negative result and the compound is probably 

 2 : 6 : 10 : 15 : ig : 23-hexamethyltetracosaundecaene-i : 24-dial (II) : 

 References p. 341-343. 



