192 



VITAMIN D GROUP 



Lumisterol, the initial phototransformation product of ergosterol, was 

 isolated by Windaus et al."^^^ and Askew et al."^^^ in 1932. From acetone- 

 methanol it crystallizes in fine needles. It is easily soluble in chloroform, 

 ether, and acetone, somewhat difficultly soluble in methanol. In air it 

 oxidizes "only slowly." Like ergosterol, it is isomerized by hydrogen chlo- 

 ride. It gives the color reactions of ergosterol with minor differences. It 

 does not give a precipitate with digitonin. It is physiologically inert but 

 is activated by irradiation. It forms a molecular addition compound with 

 calciferol, this complex being the old vitamin Di of the German school. 



The structure of lumisterol has been the subject of many studies, which 

 are critically reviewed by Rosenberg,^* with the conclusion that the only 



HO 



Ergosterol 



Lumisterol 



HO 



Tachysterol Calciferol 



Fig. 13. Ergosterol irradiation products of known structure. 



difference between lumisterol and ergosterol is an epimerization of the 

 methyl group at C-10. It is conventional to indicate such steric differences 

 by a dotted bond line, as shown in Fig. 13. 



c. Proiachyslerol 



In 1931, before much was known about the individual products of irra- 

 diation, Windaus and Auhagen^^^ made a remarkable study of the stability 

 of irradiated ergosterol. A solution of ergosterol in dioxane-petroleum 1:9 

 was irradiated, the unconverted ergosterol frozen out and filtered off, and 

 the filtrate stored and examined polarimetrically and spectroscopically — all 

 in a closed system practically devoid of oxygen. It was found that, over a 

 period of 50 days at room temperature, the specific rotation changed from 

 — 17° to a constant value at -f-7°, and the absorption spectrum at 280 m^* 



281 A. Windaus, K. Dithmar, and E. Fernholz, Ann. 493, 259 (1932). 



282 A. Windaus and E. Auhagen, Hoppe-Seyler's Z. pMjsiol. Chem. 196, 108 (1931). 



