784 



VTir. PROVITAMINS D AND VITAMINS D 



different isomers of dihydrovitamin D2 are simultaneously formed. In the 

 case of dihydrovitamin D2 1, 3 additional double bonds are demonstrable by 

 oxidation, ^'^^ and a crystalline trioxide (XXI) is formed.^'''' 



Oxidation of Dihydrovitamin D2 with Perbenzoic Acid 



Since vitamin D2 has thus been shown to have 4 double bonds instead of 

 the 3 present in ergosterol, while at the same time both the provitamin D2 

 and the vitamin D2 have an identical number of carbon and hydrogen 

 atoms, the conclusion is inescapable that vitamin D2 can have only 3 rings 

 in place of the 4-ring system present in the sterols. This supposition is 

 further borne out by the results obtained when vitamin D2 is subjected to 

 dehydrogenation with selenium. Whereas all sterols yield the same char- 

 acteristic hydrocarbon, namely, 7-methylcyclopentenophenanthrene, on 

 such treatment, vitamin D2 and tachysterol2 fail to produce the above 

 typical hydrocarbon.^** 



The position of the double bonds is the next consideration of importance 

 in establishing the structure of vitamin D2. One of these occurs in the side 

 chain between carbons 22 and 23, just as it does in ergosterol, since on ozo- 

 nolysis of vitamin D2 methylisopropylacetaldehyde, (CH3)2-CH-CH- 

 (CH3)-CH0, is formed. 122 



The fact that the remaining 3 double bonds are probably in conjugation 

 with each other can be deduced from the absorption spectrum and the 

 magnitude of the extinction coefficient. Absolute proof of the conjuga- 

 tion of two of its double bonds is afforded bj^ the fact that vitamin D2 ace- 

 tate (XXII) forms an addition product with maleic anhydride (XXIII). 2" 



The maleic anhydride addition product of vitamin D2 acetate (XXIV) 

 has been the starting material for carrying out the several reactions neces- 

 sary for the complete elucidation of the remaining facts concerning the 

 structure of vitamin D2. When the latter compound is subjected to 

 saponification, a dicarboxylic acid is formed; on treatment with diazo- 

 me thane this product forms the corresponding dimethyl ester (XXV), 

 which exists in two isomeric forms. 



268 A. Windaus and C. Roosen-Runge, Z. vhijsiol. Chern., 260, 181-184 (1939). 

 266 S. V. Reichel and M. Deppe, Z. physiol. Chem., 239, 143-146 (1936). 

 2*' A. Windaus and W. Thiele, Ann., 521, 160-175 (1935). 



