780 VIII. PROVITAMINS D AND VITAMINS D 



products are more readily formed at 160-190°C. Vitamin D2 is generally 

 considered to have a biopotency of 40,000,000 I.U. per gram. Although it 

 possesses maximum activity as an antirachitic agent for the rat, it is almost 

 completely ineffective for the chicken. 



(2) Vitamin Dz 



Vitamin D3, or activated 7-dehydrocholesterol, has a molecular weight of 

 384. It melts more than 30° lower than vitamin D2, at 82-83°C. The 

 specific rotation ([q;]d) in acetone is +83.3°.^°^ 



The absorption maximum in hexane is identical with that of vitamin 

 D2, namely, at 265 m^t. However, it has slightly higher extinction co- 

 efficients. The molecular extinction (e) is reported as 19,200,^°^ while the 

 E (1%, 1 cm.) value is 500. The complete absorption curve is given in 

 Figure 7. 



Vitamin D3, likewise, forms crystalline esters with the nitrobenzoic 

 acids. The 3,5-dinitrobenzoate develops two poljmiorphic forms which 

 melt at 129° and 140°C. and have [a]|? = +98° in chloroform. The p- 

 nitrobenzoate ester melts at 127°C. and shows an optical rotation ([aJo) 

 of +114° in chloroform. Vitamin D3 has a biopotency of 40,000,000 I.U. 

 per gram. It is equally effective for rats and for chickens.^* 



{3) Vitamin D4 



Vitamin D4, or activated 22-dihydroergosterol, melts at 107-108 °C.^^* 

 The specific rotation in acetone was found to be +89.3°. Vitamin D4 

 also forms a 3,5-dinitrobenzoate ester which melts at 135-136°C. and has a 

 [q!]d value of +94.5° in acetone. It has been shown to have a biopotency 

 in rats of from 20,000,000 to 30,000,000 I.U. per gram; in the case of the 

 chicken, it was found to have an activity of approximately 20% of that in 

 the rat.^^ McDonald^^^ indicates that it has a greater effectiveness than 

 has irradiated ergosterol in the chicken, but less than that of cod liver oil. 

 However, it compares favorably with some samples of tuna oil in this re- 

 spect. 



(4) Other Vitamins D 



Little can be said about the properties of the other members of the vita- 

 min D group. Some data on biopotencies have, however, been re- 

 ported. Vitamin D5 (activated 7-dehydrositosterol) has an activity of 

 500,000 I.U. per gram in rats, while its effectiveness in the chick is 1 : > 13.^^° 



2« A. Windaus and G. Trautmann, Z. physiol. Chem., 247, 185-188 (1937). 

 2« F. G. McDonald, J. Biol. Chem., II4, Ixv (1936). 

 26» W. Grab, Z. physiol. Chem., 243, 63-89 (1936). 



