OCCUKKENCE AND STKUCTUUE OF RELATED COMPOUNDS 701 



4. Occurrence and Structure of Compounds Related to Vitamins A 



(1) Vitamin A Aldehyde 



The importance of vitamin A aldehyde as an intermediate in vitamin A 

 metaboHsm has recently been emphasized by the demonstration that 

 retinenei is vitamin Ai aldehyde, while retinene^ is vitamin A2 aldehyde.*'^' 

 82,156-158 Morton,'^^ in 1944, first suggested that retinenei must be the 

 vitamin A aldehyde ; later he confirmed this finding. ^^^ This was the most 

 plausible explanation for the displacement of the absorption maximum from 

 326 mju to 369 m^u in retinenei Avhen compared with vitamin Ai. Such a 

 marked alteration in the absorption spectrum can best be explained by an 

 increase in the number of conjugated bonds from 5 to 6; if the terminal 

 — CH2OH group of vitamin A is replaced by a — CHO group, this would 

 provide the sixth conjugated bond. 



The close relationship between vitamin A aldehyde and vitamin A is em- 

 phasized by Glover, Goodwin, and Morton, ^^° whose work showed that 

 retinenei, when administered orally, subcutaneously, or intraperitoneally, is 

 rapidly converted to vitamin Ai. The conversion of the aldehyde to 

 the vitamin A alcohol is a reduction which occurs in the gut or in the sub- 

 cutaneous tissues. Although Ball et al.^^^ had suggested earlier that the 

 liver could effect the conversion of vitamin A aldehyde to vitamin A alco- 

 hol, it was later stated by some of the same authors ^^'^ that no direct evi- 

 dence exists to substantiate such a change in the liver. It is believed that 

 retinenei may be an intermediate product in the transformation of /3-caro- 

 tene to vitamin Aj in vivo. 



CHj CH: 



HjC CHj 



\ / 



c , I 



/\ hhIhhhIh /^O 



HzC c • C :C' c: C" c: C- c: C' C-H 



I II 



HzC C 



\ / \ 



C CHj 



Hz 



Vitamin Ai aldehyde 



Vitamin A aldehyde has been prepared by a number of workers. Al- 

 though it was expected that direct oxidation of vitamin A alcohol would re- 

 sult in an attack not only on the terminal alcohol group but also on the 

 double bonds, Morton and Goodwin^'' apparently were able to prepare some 

 of the aldehyde by shaking vitamin A concentrates dissolved in light 



'58 M. K. Salah and R. A. Morton, Eepts. Biochem. Soc, Dec. 4, 1948, pp. 6-7. 



'^' G. Wald, ./. Gen. Physiol, 20, 45-56 (1936-1937). 



"^^ R. A. Morton, M. K. Salali, and A. L. Stubbs, Biuchem. J., 1,0, lix-lx (1946). 



"^9 R. A. Morton, M. K. Salah, and A. L. Stubbs, Biochem. J., 4I, xxiv (1947). 



'«> J. Glover, T. W. Goodwin, and K. A. Morton, Biochem. J., 43, 109-114 (1948). 



1" S. Ball, J. Glover, T. W. Goodwin, and R. A. Morton, Biochem. J., 4I, xxiv (1947). 



