626 X. VITAMINS D 



been reported by Rosenheim and Webster''^ to be aeti\"ated to the same 

 degree as was ergosterol itself. Ergosteryl pahnitate^'' and vitamm D2 

 palmitate''^ were found to be less readily activated than is free ergosterol, 

 while the allophanate, cinnamate, diphenylacetate, oxalate, a-naphthyl- 

 urethane, and phenyhu^ethane derivatives are all completely inactiveJ^ 

 This variation in effectiveness as provitamins D is not due to the fact that 

 the sterol portion of the molecule cannot be activated by ultraviolet light, 

 but rather to the circumstance that the esters cannot be utilized by the 

 animal. When the inactive esters are saponified, the product exerts a bio- 

 logic potency equal to that of activated free ergosterol." Bailey''^ reported 

 that the acti^'ities of \ntamins D in different fish oils were increased when 

 the vitamin D esters present were saponified; the percentage increase 

 varied from to 100%, according to the oil tested. 



Considerable variations in activity obtain when substitutions other than 

 those involving esterification are made on the C3. Thus, when the hy- 

 droxyl group is replaced by a chlorine or bromine atom, the new compound 

 produced still possesses the capacity to undergo activation when exposed 

 to ultraviolet light. However, these halides, which are known to be re- 

 sistant to saponification, were found by Bernstein et al?^ to be devoid of ac- 

 ti\dty when fed to rats or chickens. Similarly, when the hydroxyl group 

 of 7-dehydrocholesterol was replaced with a thiol group, the compound 

 produced on irradiation, although it had a spectral picture similar to that of 

 activated 7-dehydrocholesterol, was not antirachitic, according to the 

 chick bone ash test." ''^ It is not kno^\^l whether or not activated 7-de- 

 hydro-3-homocholesterol, as prepared by Strating and Backer,^^ is physio- 

 logically active; in this case, the hydroxyl of 7-dehydrocholesterol is re- 

 placed by a HOCH2 — group. 



The variation in structure due to the asymmetry of the C3 position ap- 

 parently does not affect the biopotency of the provitamins. Thus, both 

 epiergosterol and 7-dehydroepicholesterol are readily activated. ^•**' Ac- 

 cording to the Windaus group,^^ the irradiated 7-dehydroepicholesterol is 

 about one-tenth as active as the corresponding product prepared from 7- 

 dehydrocholesterol. On the other hand, when the asymmetry, is on the C9 



'6 B. E. Bailey, /. Fisheries Research Board Can., 6, 103-108 (1943). 

 '«S. Bernstein, J. J. Oleson, H. B. Ritter, and K. J. Sax, ./. Am. Chnn. Sor., 71, 

 2576-2577 (1949). 



" J. Strating and H. J. Backer, Rec. trav. chim., 69, 909-920 (1950). 

 ^« S. Bernstein and H. J. Sax, J. Org. Chem., 16, 685-693 (1951 ). 

 '8 J. Strating and H. J. Backer, Rec. trav chim., 70, 389-402 (1951 ). 

 so A. Windaus and K. Buchholz, Ber., 72, 597-599 (1939). 

 81 A. Windaus and J. Naggatz, Ann., 542, 204-218 (1939). 



