70S VII. VITAMINS A 



\ / 



q CHj CH3 



/*'\ hhIhhhIhh 



"'?'' ' C . C : C • C : C • C : C . C : C • CH- CH^OCaHs 



HzCo' 2'C 



\3V \ 



C CH3 



Hz 



Homovitamin A ethyl ether 

 (including Milas's numbering system) 



5-Dehydrohomovitamin A ethyl ether (C21H29OC2H5) is a closely related 

 compound which is readily changed to the corresponding homovitamin A 

 by reduction with palladium in the presence of calcium carbonate. Chemi- 

 cally, the 5-dehydrovitamin A ether is known as [l-(2',6',6'-trimethylcy- 

 clohexen-l'-yl)-3,7-dimethyldeca-l,3,7-trien-5-ynyl]-10-ethyl ether. The 

 structural formula is given here. 



HjC CHj 



\ / 



C 



CH3 CHj 



/ \ H H I H I H 



HzC C'C:C-C:C-CiC'C:C' CHa'CHjOCzHj 



I II 



HzC C 



\ / \ 

 C CHj 



Hz 



o-Dehydrovitamin A ethyl ether 



The homologues of the vitamin A ethers show properties almost indis- 

 tinguishable from those of the true vitamin A ethers themselves. Thus, 

 the 5-dehydrohomovitamin A ethyl ether has a single absorption band with 

 a maximum (X,nax.) = 321 m^) in the ultraviolet only slightly lower than 

 that of the vitamin A ether; in the Carr-Price reaction, the purplish blue 

 color produced has two maxima practically identical with those of true vita- 

 min A ether, i.e., 580 and 622 m/x. Homovitamin A ethyl ether prepared 

 by different methods gave somewhat different absorption maxima; in one 

 case, the single maximum absorption was at 321 m/x, while in the other case 

 the main absorption maximum was at 328 mn, with a slight inflection at 

 367 m/i. Other properties are listed in Table 10. 



Both of the homologues possess slight biological activity. Harris'" re- 

 ported that 5-dehydrohomovitamin A ethyl ether cured xerophthalmia and 

 caused an average weight gain, in rats, of 32 g. over a 28-day period, when 

 administered in doses of 96 mg. daily. In the case of the homovitamin A 

 ethyl ester, it was found that 60 mg. were active, but Milas^^ noted that the 

 compound was highly unstable. The absorption spectra of the vitamin A 

 homologues are given in Figure 4. 



'" R. S. Harris, cited by N. A. Mila.s, Vitamins and Hormones, 5, b (1947). 



