788 



VIII. PROVITAMINS D AND VITAMINS D 



of ergosterol. It is believed, on the basis of catalytic hydrogenation^^^ as 

 well as of perbenzoic acid titration, ^^"^ that the pyro-compounds contain 

 only three double bonds. This would indicate that a ring closure occurs 

 when the pyrocompounds are formed. Furthermore, when dehydrogenated 

 with selenium, pyro- and isopyrocalciferols yield 7-methylcyclopenteno- 

 phenanthrene, which is the characteristic product yielded by compounds 

 having the intact steroid nucleus. ^^^ This latter evidence seems to prove 

 that the ring closure involves the same carbons which were concerned in the 

 case of the ring cleavage when ergosterol was changed to vitamin D2. 



Of the three double bonds in the pyrocalciferols, one obviously is in the 

 side chain between carbons 22 and 23. The remaining two double bonds 

 are in conjugation, since the pyro-compounds form addition products with 

 maleic anhydride. Further proof that they exist on the same ring is af- 

 forded by their behavior when subjected to nitric acid oxidation; in this 

 case, toluene 2,3,4,5-tetracarboxylic acid is obtained. ^^^ 



The difference between pyro- and isopyrocalciferol is probably one of 

 steric configuration. These relationships are indicated in Table 6. 



TABLE 6 

 Comparison op Properties of Pyro- and Isopyrocalciferol with Those of 



Ergosterol 



Treatment 

 employed 



Results of reaction on 



Pyrocalciferol 



Isopyrocalciferol 



Ergosterol 



Digitonin" 



Dehydrogenation with 

 eosin in visible light'' 



Dehydrogenation with 

 mercuric acetate 



No precipitation 

 Bimolecular com- 

 pound 

 A^ii-Dehydro- 

 lumisteroU" 



Precipitation 

 No reaction 



A^."-Dehydro- 

 ergosteroP 



Precipitation 



Bimolecular com- 

 pound 



A9>ii-Dehydro- 

 ergosterol'^i'^i* 



" H. R. Rosenberg, Chemistry and Physiology of the Vitamins, Interscience, New York, 

 1945. 

 '' T. Kennedy and F. S. Spring, J. Chem. Soc, 1939, 250-253. 

 " A. Windaus and K. Dimroth, Ber., 70, 376-379 (1937). 



<* I. M. Heilbron, F. S. Spring, and P. A. Stewart, J. Chem. Soc, 1936, 1221-1223. 

 ' M. Muller, Z. -physiol. Chem., 231, 75-84 (1935). 



From the data presented in Table 6, it is evident that isopyrocalciferol 

 and ergosterol differ only in spatial arrangement in position 9, while 

 lumisteroh and pyrocalciferol differ from ergosterol and isopyrocalciferol 

 solely by the position of the substituents on carbon 10. Comparative 

 formulas are given here. 



Ergosterol 

 «» P. Busse, Z. physiol. Chem., BI4, 211-222 (1933). 



Isopyrocalciferol 



