CAROTENOLS AND OXYCAROTENOLS OF THE C40 SERIES 581 



"citraurin," but Karrer et alJ^^'^''^ have suggested that it be referred to as 

 "jS-citraurin" to differentiate it from a somewhat similar product which is 

 called a-citraurin. /3-Citraurin has been found only in the orange peel. 



/3-('itraurin has an empirical formula of CS0H40O2. It is an aldehyde. 

 Karrer and Solmssen'^^ suggested that jS-citraurin is 3-oxy-/3-apo-2-carot- 

 enal, and this hypothesis was later proved to be correct. ^''^■^^ This com- 

 pound is formed when zeaxanthin is hydrolyzed with strong alkali or when 

 lutein is oxidized with permanganate.^''^ In the latter case, a-citraurin also 

 results. Konig^'* likewise obtained /3-citraurin from capsanthin by per- 

 manganate oxidation. 



HjC CH3 



r- CHj CH3 CH3 CH3 



/\ hhIhhhIhhhhIhhhI ^0 

 H2C C'C:c-C:C'C:C'C:c-C:C'C:C'C:C-C:C- C— H 



Hs I II 



C C 



C CH. 



j3-Citraurin 



jS-Citraurin separates from a benzene-ligroin mixture as thin orange-to- 

 yellow plates which appear almost colorless when viewed under the micro- 

 scope. It melts at 147°C. It is readily soluble in acetone, ethanol, ben- 

 zene, and carbon disulfide. /3-Citraurin forms an oxime, C30H41O2N, when 

 treated with hydroxylamine. This melts at 188°C. It can also be 

 characterized as the semicarbazone (C31H43O2N3). /3-Citraurin semicarba- 

 zone crystallizes from benzene as reddish brown platelets which melt at 

 approximately 190°C. 



(15) Myxoxanthin 



Heilbron, Lythgoe, and Phipers^''^ separated an unknown pigment from 

 the fresh-water, blue-green alga (Rivularia nitida), which was found to be 

 an epiphasic carotenoid. It was given the name "myxoxanthin." The 

 same pigment was later identified in the purple fresh-water plankton alga 

 [Oacillatoria ruhescens)^^^; it is likewise probably the pigment found in the 

 marine blue alga {Calothrix scopulorum) .^^^ Although the structure of 

 myxoxanthin is not certain, the following formula is strongly suggested by 

 the work of Heilbron and Lythgoe ^^"^ and of Karrer and Rutschmann.^*^ 



"^ P. Karrer, A. Ruogger, and U. Solmssen, Helv. Chim. Acta, 21, 448-451 (1938). 

 3" L. Zechmeister and L. v. Cholnoky, Ann., 530, 291-300 (1937). 

 ^^* H. Konig, Dissertation, University of Zurich, 1940. Cited by P. Karrer and E. 

 .Tucker, Carotinoide, Birkhauser, Basle, 1948, p. 221. 



"9 I. M. Heilbron, B. I.ythgoe, and R. F. Phipers, Nature, 136, 989 (193.5). 

 ="» I. M. Heilbron and B. Lythgoe, J. Chem. Soc., 1936, 1376-1380. 



381 J. Tischer, Z. physiol. Chem., 251, 109-128 (1938). 



382 P. Kurrcr and .J. Rutschmann, Helv. Chim. Acta. 27, 1691-1095 (1944). 



