STRUCTURES OF VITAMINS D 



789 



Luinisterol2 



Pyrocalciferol 



The p3a'o-compoiinds are broken down on irradiation with ultraviolet 

 light, but apparently an entirely different set of reactions obtains from that 

 which occurs when ergosterol is subjected to similar treatment. ^^* Further- 

 more, the pyro- and isopyrocalciferol have no antirachitic efficacy, and no 

 biologically active products can be demonstrated after their irradiation. 

 The ineffectiveness of the irradiation products is further corroborated by 

 the observation that no absorption bands occur in the critical spectral re- 

 gion between 248 and 320 m^. Finally, the reactions caused by irradia- 

 tion of the pyro- and isopyro-compounds are reversible, and presumably in- 

 volve only a rearrangement of the double bonds on ring B. 



(2) Vitamin Di 



Since vitamin D3 is derived from 7-dehydrocholesterol, by a series of re- 

 actions similar to those which occur when vitamin D2 is synthesized from 

 ergosterol, one can tentatively assign the accompanying formula to vita- 

 min D3 (XXXIII). 



H2C c— 



CH, 



HzCHz 



C I C^. CH 

 H,C Y C X 



H0\ I I II 



I 



CH, 



HX 



/ 



CH, 



"^^wnr 



When vitamin Do is oxidized with ozone, formaldehyde, a saturated ke- 

 tone (XXXIV), and an unsaturated aldehyde (XXXV) are the products 

 formed. ^"^''"^ These compounds are characterized by the semicarbazones 

 and by the 2,4-dinitrophenylhydrazone derivatives. Thus, it would ap- 

 pear that such compounds could originate only by cleavage of the 10,18, 

 5,6, or 7,8 double bonds. Since these are the same positions at which the 

 unsaturated linkages occur in the case of vitamin D2, it would appear to be 

 definite that the structure is identical with the latter except for the side 

 chain on C17. 



