552 IX. CAROTENOIDS AND VITAMINS A 



60 mg., respectively.''^'* For a further discussion of the synthesis and prop- 

 erties of the above-mentioned synthetic compounds, the reader is referred 

 to The Lipids, Vol. I, pages 704 to 709. 



(d) Vitamin A Hydrocarbon. This compound was prepared by Karrer 

 and Benz;^^^ it was called "axerophthene." The compound was reported 

 by Euler and Karrer^^" to be biologically active to the extent of 10% of the 

 biopotency of vitamin A, but its lower homologues are entirely devoid of 

 vitamin A potency. It was concluded that, in order that a substance 

 possess vitamin A activity, the entire C20-chain must be arranged in a 

 specific manner; the substituents on the terminal carbon of the aliphatic 

 chain are of httle significance. Meunier et al.^^^'^^^ objected to the term 

 "axerophthene," and suggested ''dihydroaxerophthene" as preferable. 



(c) Anhydrovitamin A {Aij and Rehydrovitamin A. Anhydrovitamin A 

 is chieflj^ a laboratory product which is formed when vitamin A remains in 

 contact with small concentrations of hydrogen chloride in ethanoP^'^'*^^ or 

 is produced by re fluxing an alcoholic solution of the natural vitamin A es- 

 ^gj.g 834,835 Anhydrovitamin A is believed to originate from vitamin A by 

 the loss of a molecule of water; this results in a compound having six rather 

 than five conjugate double bonds and a CH=CH2 end group. In 1943, 

 Meunier et al.^^^ proposed that anhydrovitamin A possessed a retro struc- 

 ture, i.e., an o;-ionone ring connected by a double bond with the side chain 

 {cf. also Shantz^" and Robeson*^^). Karrer and Kebrle^^^ and Oroshnik 

 et al.^'^'^ furnished conclusive proof that the re^roionylidene structure exists. 

 The biopotency of anhydrovitamin A was reported to be 17,500 I.U./g., by 

 Shantz et al.^^^ This may not be significant, since it might arise from re- 

 hydrovitamin A formed in vivo from the anhydro compounds. However, 

 Shantz*^'' is convinced that anhydrovitamin A per se has biologic activity. 



829 P. Karrer and J. Benz, Helv. Chim.. Acta, 31, 1048-1054 (1948). 



830 H. V. Euler and P. Karrer, Helv. Chim. Ada, 32, 461-463 (1949). 



831 P. Meunier, Compt. rend., 227, 206-207 (1948). 



832 A. Guerillot-Vinet, P. Meunier, J. Jouanneteau, and M. Gourevitch, Compt. rend., 

 226, 128-130 (1948). 



833 J. R. Edisbury, A. E. Gillam, I. M. Heilbron, and R. A. Morton, Biochem. J., 26, 

 1164-1173 (1932). 



834 N. D. Embree, /. Biol. Chem., 128, 187-198 (1939). 



835 E. Le B. Gray and J. D. Cawley, /. Nutrition, 23, 301-307 (1942). 



836 p. Meunier, R. Dulou, and A. Vinet, Bull. soc. chim. biol, 25, 371-378 (1943). 



837 E. M. Shantz, /. Biol. Chem., 182, 515-524 (1950). 



838 C. D. Robeson, U. S. Patent, No. 2,583,594 (Jan. 29, 1952). 



839 P. Karrer and J. Kebrle, Helv. Chim. Acta, 35, 2570-2573 (1952). 



8« W. O. Oroshnik, G. Karmas, and A. D. Mebane, J. Am. Chem. Soc, 74, 295-304 

 (1952). 



8" E. M. Shantz, J. D. Cawley, and H. D. Embree, J. Am. Chem. Soc, 65, 901-906 

 (1943). 



