532 VI. CAROTENOIDS AND RELATED COMPOUNDS 



alcohol by reduction of the aldehyde by aluminum isopropoxide in isopro- 

 panol. It is a crystalline solid which gives a blue color with antimony 

 trichloride. The /3-apo-2-carotenol forms yellow platelets which melt at 



C CHj CHj CH3 CHj 



/\ hhIhhhIhhhhIhhhI 

 HjC C-c:C-c:C-C:C'C:C'C:C'C:C-C:C'C:C- CHjOH 



H?C C 



\ / \ 



C CH3 



/3-Apo-2-carotenol 



145°C. A secondary alcohol with similar spectroscopic properties was sub- 

 sequently prepared by Karrer et al.^*^^ by treatment of |8-apo-2-carotenal 

 with ethyl magnesium bromide. Both of these products have been found 

 to be effective as sources of vitamin A in the animal body, as demonstrated 

 by rat growth tests. ^*^ 



H3C CH3 



c ch3 ch3 ch3 ch3 



/\ hhIhhhIhhhhIhhhIh 

 HzC C-c:c-c:c-c:C'C:c-c:C-C:C-C:C-C:C-C' CHXH, 



I II OH 



HjC c 



\ / \ 



C CH3 



H? 



Secondary alcohol 



(p) ^-ApoA-carotenal, C25H34O. The /3-apo-4-aldehyde is obtained on 

 permanganate oxidation of /3-carotene, in addition to the corresponding 

 apo-2-compound. Although the apo-4-aldehyde has not been obtained in 

 crystalline form, a well-defined oxime (m.p., 165°C.) and a semicarbazone 

 (red powder melting at 217°C.) are known. i8-Apo-4-carotenal is biologically 

 active. 



HjC CH3 



\ / 

 c 



CH, CH3 CH3 



/\ HHlHHHiHHHHIH 



HjC c • C : C • C : C • C : C • C : C • C : c • c : C • C=0 



I II 



HjC C 



\ / \ 

 C CH3 



/3-Apo- 4-carotenal 



(q) ^-Apo-i-carotenol, C25H36O. The alcohol corresponding to the apo-4- 

 aldehyde can be prepared by the reduction of the latter compound with 



i«8 p. Karrer, A. Ruegger, and A. Geiger, Helv. Ckim. Acta, 21, 1171-1174 (1938). 

 i«9 H. V. Euler, G. Gtinther, M. Malmberg, and P. Karrer, Helv. Chim. Acta, 21, 1619- 

 1621 (1938). 



