790 



VIII. PROVITAMINS D AND VITAMINS D 



0, 



a. Pyrovitamin D3 and Isopyrovitamin D3. When vitamin D3 is sub- 

 jected to a temperature of 200°C., it is converted to pyro- and isopyrovita- 

 min Ds^^^ by a reaction analogous to that which occurs with vitamin D2. 

 The analogy can be carried further since, on dehydrogenation with mer- 

 curic acetate, pyrovitamin D3 forms 9,ll-dehydrolumisterol3, while iso- 

 pyrovitamin D3 forms 7,8,9, 11-dehydrocholesterol. Ergosterol bears the 

 same relationship to isopyrocalciferol as 7-dehydrocholesterol does to iso- 

 pyrovitamin D3; moreover, pyrocalciferol is closely related to lumisterol2, 

 just as pyrovitamin D3 is quite similar to lumisterols. 



(3) Vitamin Da 



Vitamin D4 is the vitamin formed when the provitamin, 22-dihydro- 

 ergosterol, is activated. On the basis of the structures of vitamins D2 and 

 D3, Windaus and Trautmann^^^ have assigned the structure shown here to 

 vitamin D4 (XXXVD. 



H2C C C CHg 



H2 CH, I I I I 



.C. II CH2 CH JZHz .CH2 



C II 0^2 CH CH, ( 

 HjC C V X HC^ 

 HGsl I II ^^ '^ 



H, H 



H,C 



/ 



CH3 



CH, 



Vitamin D* 



(4) Vitamin Ds, 



Vitamin D5 (XXXVII), which is the activated 7-dehydrositosterol, 

 would be expected to have a structure analogous to that of vitamins D2, 

 D3, and D4, except for the variation in the side chain. Although proof has 

 not been deduced that such is the case, one cannot fail to arrive at that 

 conclusion in view of the evidence available. The formula for vitamin D5 

 would, therefore, be that given here. 



2" A. Wiudaus, M. Deppe, and C. Rooson-Ruiige, Ann., 537, 1-10 (1938). 



