786 



VIII. PKOVITAMINS D AND VITAMINS D 



The ketone group must be located on what was the C ring of the ergo- 

 sterol molecule. Presumably it would occur at the position where the C 

 ring was attached to the rest of the molecule. In ergosterol, this connec- 

 tion is through carbons 8 and 9. However, since only one carbon in the 

 saturated ketone has been oxidized, it would appear that, in vitamin D2, 

 ring B no longer exists and only one point of combination with the rest of the 

 molecule occurs. This hypothesis is supported by earlier evidence that 

 only 3 rings are possible in vitamin D2, as contrasted with the 4 cyclic groups 

 in ergosterol. 



The fact that the point of union of ring C with the rest of the molecule is 

 changed to a ketone group, indicates that the ketone has replaced a double 

 bond. Such a double bond could not occur between carbons 9 and 10, 

 since Cio is quaternary. It then follows that the ketone can only be at Cg, 

 and the double bond in vitamin D2 must have a linkage between carbons 7 

 and 8. The cleavage of ring B of ergosterol must have occurred between 

 C9 and Cio before vitamin D2 synthesis can take place. 



The final proof of the structure of ring A, and the nature of the connec- 

 tion between ring A and the portion of the molecule isolated as the satu- 

 rated ketone, can be deduced by reduction of the original dimethyl ester 

 and its acid. When this is carried out on the free dicarbox^dic acid (XX- 

 VIII) by platinum dehydrogenation, naphthalene (XXIX) and naph- 

 thoic acid (XXX) are the products. On the other hand, when a selenium 

 dehydrogenation is performed on the diester (XXV), 2,3-dimethylnaphthal- 

 ene (XXXI) is obtained. Earlier work in which a dehydrogenation of di- 

 carboxylic acid esters was carried out proved that the methyl groups origi- 

 nate from the carboxyl groups. ^^^ 



\ 



Reduction Reactions of the Dicarboxylic Acid (XXVIII) and of the Dimethyl Ester 

 (XXV) of the Maleic Acid Anhydride Addition Product of Vitamin D2 Acetate 



258 W. Thielc and G. Trautmann, Ber., 6S, 2245-2247 (1935). 



