II. CHEMISTRY 201 



levels several times higher than the usual dose for calciferol. They are only 

 slightly toxic. 



Suprasterol I crystallizes in fine needles from acetone, and suprasterol II 

 in dense prisms from acetone or methanol. Suprasterol I is less sensitive to 

 oxidation than ergosterol or calciferol, but slowly yellows in contact with 

 air; suprasterol II was not observed in this connection. 



From the work of Windaus et al.^^'^ and other studies reviewed and ex- 

 tended by Muller,2«^ it appears that the suprasterols have three double 

 bonds and are therefore tetracyclic, but the ring structure may not be that 

 of the sterols. In other words, the ring closure suffered by calciferol in the 

 formation of the suprasterols may not be at the point of rupture of the 

 original ring B of ergosterol and lumisterol. Certainly the double bonds are 

 no longer in conjugated position, for the suprasterols show no absorption 

 bands. 



i. 7-Dehydrocholesterol. Provitamin Dz 



C27H440-H20. Molecular weight 402.638. Two double bonds. Melting 

 point 149° to 150°.^" Principal absorption maxima at 262.5, 271, 281.5, and 

 293 m/x.2^1. 265 Molecular extinction coefficient at 281.5 m/i = 10,920 (in 

 alcohol). 251 [a]f = -124° (in chloroform). ^0 



The series of irradiation products which stem from 7-dehydrocholesterol 

 is in every respect analogous to the ergosterol series, but it has not been 

 studied in quite as much detail. Windaus et al.^^^ have proposed a nomencla- 

 ture for these products, according to which the names of the ergosterol 

 series are retained, but a subscript number 3 is added; thus lumisterols and 

 tachysterols are the 7-dehydrocholesterol products corresponding to lumi- 

 sterol and tachysterol. Similarly, for the 22-dihydroergosterol series the 

 subscript 4 is used. 



7-Dehydrocholesterol crystallizes in slender platelets from ether-meth- 

 anol.^* It is difficultly soluble in methanol, and readily soluble in ether."" 

 The crystals contain one mole of water^^ which cannot be completely re- 

 moved.** 7-Dehydrocholesterol forms a precipitate with digitonin.** It also 

 gives the color reactions of ergosterol with minor differences.*'^ Its specific 

 rotation is a little less strongly levorotatory than that of ergosterol.'''' Its 

 absorption spectrum is practically identical with that of ergosterol, ^^i' -^^ 

 and brides the four major bands, minor inflections are exhibited at 252, 

 321, and 336 m/x.-^^ 



7-Dehydrocholesterol is much more unstable than ergosterol.**' ^^i. sis Ji 

 shows yellowing in less than 2 days when exposed to air at room tempera- 

 ture, even in the dark. However, when it is crystallized together with cho- 

 lesterol, a remarkable stabilization results, depending upon the amount of 



316 H. R. Rosenberg and W. W. Woessner, U. S. Pat. 2,434,015 (1948). 



