STmTOTUUER OF VITAMINS D 



783 



(/) Vitamin D2 



As early as 1932, Windaiis and co-workers ^^^ demonstrated that vitamin 

 D2 has an empirical formula of C28H44O, which is identical with that of 

 ergosterol, from which it is derived. As a result of the investigations of a 

 large number of workers, the structure of vitamin D2 has been thoroughly- 

 elucidated. The formula which is universally accepted is given here. 



CH3 



HzC" ''C 





'CH 



HzC^ G- >C C HCC 



HO J I II ^^ |\h3 



H2 H 



Vitamin Dj 



The oxygen present in the molecule must be in an hydroxyl group, since 

 vitamin D2 is usually present in nature in the form of an ester. The posi- 

 tion of this secondary alcohol group must logically be on position 3 ; this is 

 the location where it is invariably found in a large variety of sterols, some of 

 which are provitamins D. 



Important information on the structure of vitamin D2 (XVIII) can be 

 gleaned from the number and position of the double bonds. When this 

 vitamin is catalytically hydrogenated, 4 molecules of hydrogen are ab- 

 sorbed (XIX — octahydrovitamin D2), which can be interpreted only as in- 

 dicative of the presence of 4 unsaturated linkages. ^^* 



However, only 3 double bonds can be demonstrated by titration with 

 perbenzoic acid. This discrepancy between the two different methods 

 for the demonstration of the double bonds can be brought into harmony by 

 employing a different preliminary procedure for the perbenzoic acid tests. 

 If vitamin D2 (XVIII) is first reduced with sodium ethylate, one molecule 

 of hydrogen is absorbed and a dihj^drovitamin D2 (XX) is produced. Two 



^* R. Kuhn and E. F. IMoller, Angew. Chem., 47, 145-149 (1934). 



