3 MYXOXANTHIN 225 



This compound was prepared by Kuhn and BrockmannI' by the reduction 

 of a solution of rhodoxanthin in pyridine and glacial acetic acid with zinc. 

 Dihydrorhodoxanthin crystallises from a mixture of benzene and methanol in 

 golden yellow leaflets, m.p. 219° (corr., evacuated capillary). Its solubility is 

 similar to that of rhodoxanthin. The chromophoric system of dihydrorhodo- 

 xanthin is the same as that of j3-carotene and zeaxanthin, as shown by the 

 similarity of the absorption maxima. 



Solvent Absorption maxima 



Dihydrorhodoxanthin Zeaxanthin 



Carbon disulphide ... 514 479 448 m/< 517 482 459 m^ 



Chloroform 492 460 431 m^t 495 462 429 m// 



Petrol 483 452 425 m/< 483.5 451.5 423 m^ 



Ethanol 480 450 422 mn 483 451 423 m/x 



Hexane(cf. Fig. 13. p. 353) 480 449 422 m/^ 



Dihydrorhodoxanthin is optically inactive. In solution (e.g. in piperidine or 

 pyridine containing a small proportion of alcoholic potassium hydroxide) it is 

 rapidly dehydrogenated by atmospheric oxygen to rhodoxanthin. On catalytic 

 hydrogenation in decalin, the pigment absorbs 13 mols of hydrogen. By the 

 reduction of dihydrorhodoxanthin Karrer and Solmssen (cf. p. 60, 183) ob- 

 tained zeaxanthin. 



Dihydrorhodoxanthin dioxime C40H54O2N2: 



This derivative is obtained by a procedure analogous to that described for 

 the preparation of rhodoxanthin dioxime (p. 224). The dioxime crystallises 

 from ethanol in reddish-yellow needles, m.p. 226-227° (corr., in vacuum). 



Solvent Absorption maxima 



Carbon disulphide .... 514 479 448 m^ 



Petrol 483 451.5 424 m/z 



Hexane 480 449 422 m^ 



3. MYXOXANTHIN C40H54O 



History ayid Occurrence 



Heilbron, Lythgoe and Phipers^^ found a previously unknown epiphasic 

 carotenoid, which they termed myxoxanthin in the algae Rivularia nitida. This 

 pigment was later observed in Oscillatoria ruhescens^^ and in Calothrix scopu- 



Preparation 



From Oscillatoria rubescens^'^ : The algae are dehydrated with methanol and then 

 extracted first with methanol and then with ether. The combined extracts are 



References p. 253-253. • 



Carotenoids 15 



