550 IX, CAROTENOIDS AND VITAMINS A 



when administered orally, intraperitoneally, or subcutaneously into rats. 

 This reduction can be mediated in the gut wall and in other tissues. Gou- 

 nelle and collaborators,^" and Katsampes et al.^^- demonstrated that vita- 

 min Ai aldehyde (retinenei) is readily absorbed and converted to vitamin 

 Ai alcohol by man. Cama and associates'^" noted that retinene2 (vitamin 

 A2 aldehyde) is also readily converted to the corresponding alcohol, namely 

 vitamin A2, in the rat. Although the liver was first thought to be the site 

 for the conversion of vitamin A aldehyde to vitamin A alcohol, ^^^ it was 

 later noted that there is no substantial evidence to support such a theory. ^^^ 



There is considerable proof of the reverse transformation, namely that 

 of vitamin A to vitamin A aldehyde. Thus, the aldehyde is readily pre- 

 pared from vitamin A alcohol by shaking concentrates of the latter in 

 petroleum ether with potassium permanganate, acidified with sulfuric 

 acid.^^^ Hawkins and Hunter^^^ obtained the aldehyde from vitamin A 

 alcohol by oxidation with aluminum zsopropoxide in the presence of acet- 

 aldehyde. Ball et al.^-^ obtained better yields when oxidation was pro- 

 duced by a specially prepared manganese dioxide kept for six to ten days in 

 the dark; yields of aldehyde as high as 80% of the theoretical were re- 

 ported. Vitamin Ai aldehyde is obtained by the oxidation of /3-caro- 

 tene.^*'""^^''^^ The biopotency of the ordinary vitamin A] aldehyde (all- 

 trans) was reported by Arens and van Dorp^^^ to be essentially that of 

 natural crystalline vitamin A, although more recent determinations^^^'''^' 

 give the value as 2,800,000 1.U./g. Retinene2 can readily be prepared from 

 vitamin A2 by oxidation with manganese dioxide. ^^^'^"^ According to 

 Milas, only about one-half the amount of manganese dioxide (0.3 g.) is re- 

 quired to oxidize 10 mg. of vitamin A2 as is needed for a like amount of 

 vitamin At. Although Meunier-^^ reported that an oxidation product of 

 lycopene was vitamin A-active and appeared to have properties similar to 

 those of retinene2. Painter and Glover'^" were unable to demonstrate any 

 vitamin A biopotency in apo-15-lycopenal, as determined by growth re- 

 sponse in vitamin A-deficient rats, whereas 2 txg. of vitamin A/day re- 

 sulted in prompt recovery. 



Vitamin A aldehyde, like vitamin A, exists in four stereoisomeric forms.^^'' 



811 H. Gounelle, C. Marnay, R. Cheroux, and Y. Raoul, Compt. rend. soc. bioL, I46, 

 523-525 (1952). 



812 C. p. Katsampes, A. B. McCoord, R. N. Hamburger, and S. W. Clausen, Pedi- 

 atrics, 12, 191-197 (1953). 



813 S. Ball, J. Glover, T. W. Goodwin, and R. A. Morton, Biochem. J., J,l, xxiv (1947). 



814 R. A. Morton and T. W. Goodwin, Nature, 153, 405-406 (1944). 



815 E. G. E. Hawkins and R. F. Hunter, /. Chem. Soc, 1944, 411. 



816 J. F. Arens and D. A. van Dorp, Rec. trav. chim., 68, 604-608 (1949). 



81' P. Meunier and J. Jouanneteau, Bull. soc. chim. biol, 30, 260-264 (1948). 



