330 CAROTENOIDS OF UNCERTAIN STRUCTURE XIV 



torulin and rhodoviolascin (p. 295) and suggested that the former may be formed 

 from rhodoviolascin by cyclisation of one half of the molecule, which would 

 explain the shorter wavelength location of the absorption maxima. This 

 suggestion, however, lacks experimental foundation. 



24. TORULARHODIN C37H48O2 



History and Occurrence 



In 1933, Lederer''^ investigated the carotenoids of Torula rubra. Besides 

 ^-carotene, he found the previously unknown pigment torulin, as well as two 

 other polyene pigments, one of which appeared to be a hydrocarbon while the 

 other exhibited acidic properties. 



Fink and Zenger^" later carried out similar investigations and also observed 

 the two last-mentioned pigments. The investigation of Torula rubra pigments 

 was continued by Karrer and Rutschmann^^. These authors were able to 

 elucidate the main features of the constitution of the acidic pigment which they 

 termed torularhodin. 



Up to the present time torularhodin has only been observed in the red 

 yea.st-Torula rubra. 



Preparation^^' ^^ 



After pre-extraction with ethanol in an atmosphere of carbon dioxide, the yeast 

 cells are ground with quartz sand in a large porcelain mortar and then extracted 

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

 are extracted with a small quantity of petroleum ether. For the separation of the 

 pigments this solution is adsorbed on alumina and the chromatogram is developed 

 with a mixture of ether and methanol. Torularhodin forms an upper light-red zone 

 in the chromatogram and is eluted with a mixture of ether and acetic acid (10:1). 

 This solution is washed free from acid, the ether is evaporated and the oily residue 

 is dissolved in a little methanol. The methanol solution is allowed to stand for 2-3 

 weeks at room temperature in an evacuated tube. During this period, torularhodin 

 crystallises out, together with a considerable quantity of aliphatic acids, which are 

 removed by washing with petroleum ether. The torularhodin remains undissolved 

 and is obtained in a fairly pure condition after boiling with petroleum ether and 

 methanol. The yield from 1 kg of yeast amounted to about 3-5 mg. For analysis, 

 the pigment is reprecipitated several times from a mixture of benzene and methanol, 

 but nevertheless still contains varying amounts of ash. 



Chemical Constitution''^ 



Torularhodin probably has the molecular formula C37H48O2 and contains 

 12 conjugated double bonds. It is a monocarboxylic acid, as shown by its 

 behaviour towards alkalis and the preparation of a well-crystalhsed mono- 

 methyl ester. The latter exhibits vitamin A activity which is considerably 



References p. 34.1-343. 



