VITAMINS 



213 



and a methylene group (CH2=) is formed from the methyl group attached 

 to rings A and B. Similar changes are wrought in the structure of 

 7-dehydrocholesterol and quite likely in all other sterols during their 

 activation. Vitamin ^2, or calciferol as the irradiation product of 

 ergosterol is known, is a white crystalline substance that differs from 



(2i)^cH 



(IS) I (20) 



(22)%^ 



CH2 I 



CHa^^jj 



CH2 



1(2) 

 1(3) 



HO-CH 



<^(i) 



(19) 

 CH3 



1(11) 



(13) 



CH 



(9) 



(10) (S) 



B 



(14) 



117)^ 

 (16) 



D 



(23TCH 



! 



(24)CH— CHj 



I (25) 



CH2 (26)CH — CH3 



(27) 



CH- 



— CH ^^^^^^' 



(5)^ 

 (4)x/'"V) 



CH2 CH 



C 



^^^CH 



(21) 

 H3C, 



Ergosterol, C28H43OH 



^CH(20) 



(18) 



CH2 ^^'cn 



^12)\/,^17)\ 



(16) 



,CH 



(22)-^5^«^^ 



(ll^CH 



1 (25) 



(24) CH— CH3 



CH2 (13)^ 

 (19) |(11) C 



.CH2 ?f ^ CH2 (^^ICH- 

 CH2 <^(io) (s)C 



D 



CH2 (26)CH— CH3 

 I (27) 



^CH2 (28)CH3 



1(2) 



1(3) (5) 



CH2 



'<(6)>H 

 ^CH 



Calciferol, C28H43OH 



the parent sterol in several properties such as melting point, optical rota- 

 tion, solubility, and precipitability. 



It seems quite probable that the three double bonds between carbons 

 10 and 19, 5 and 6, and 7 and 8, respectively, (designated by * in the 

 above formula) are necessary for vitamin activity, since this grouping 

 is present in each of the D vitamins whose chemical structures have 

 been accurately determined. In spite of the rather large number of 

 D vitamins that have been produced in the laboratory, only two of 

 natural occurrence (D2 and D3) have been isolated thus far. Vitamin 

 D3, which is obtained from fish-liver oils, is identical with the vitamin 

 formed by the action of ultraviolet light upon 7-dehydrocholesterol. 

 Vitamins D2 and D3 have approximately the same potency toward mam- 

 mals, including man, but D3 is about 30 times as effective as D2 is for 

 fowls. The D vitamins are so resistant to high temperatures that prac- 

 tically no loss of activity is suffered when a food is cooked. 



