STRUCTURES OF VITAMINS D 



787 



An interpretation of the above results allows one to deduce the positions 

 of the third and fourth double bonds in vitamin D2. In the first place, it is 

 indicated that when maleic anhydride combines with vitamin D2, a hy- 

 dronaphthalene derivative is formed. A reaction of this nature is possible 

 only when the two new bonds are in conjugation with the third double 

 bond known to be at the 7,8 position. This would place the two new bonds 

 in vitamin D2 at the 5,6 and 10,18 positions. The addition of maleic an- 

 hydride has apparently been on Ce and Cis. 



Further proof that the side-chain methyl group, designated as number 

 18 in ergosterol, has become a methylene group in vitamin Do has been 

 furnished by oxidation experiments. Thus, an acid permanganate converts 

 this methylene group into formic acid; in the presence of ozone it yields 

 formaldehyde. 2" 



These results are sufficient to establish the structure of vitamin D as given 

 earlier. Moreover, other types of approach have yielded confirmatory 

 evidence that the postulated structure for vitamin D2 is correct. Thus, 

 permanganate oxidation yields, in addition to formic acid, an unsaturated 

 ketone which can be changed to the same saturated ketone (XXVII) ob- 

 tained by direct oxidation of the 22-dihydro derivative, when selective hy- 

 drogenation is employed. If vitamin D2 (XVIII) is carefully oxidized with 

 chromic acid, a rupture of the 5,0 bond obtains, and one is able to isolate 

 the doubly unsaturated aldehyde (XXXII). ^-^^ This compound corres- 

 ponds to the products which one would expect to obtain from the postu- 

 lated vitamin D^J'^ 



a. Pyrocalciferol and Isopyrocalciferol. When vitamin D2 is heated at 

 160-190°C. in the absence of air, it is converted to two new products — 

 pyrocalciferol and isopyrocalciferol. These are of aid in establishing the 

 structure, not only of vitamin Do but also of some of the intermediate ir- 

 radiation products. These pyro-compounds separate as crystalline addi- 

 tion products; after acetylation they can be isolated by fractional crystal- 

 lization. 



On the basis of molecular weight determinations and of elementary 

 analyses, one must conclude that they, also, are isomers of vitamin D2 and 



269 I. M. Heilhron, R. N, Jones, K. M. Samant, and F, S. Si)ring, ./. Chem. Soc, 1936, 

 905-907. 



