754 



VIII. PROVITAMINS D AND VITAMINS D 



only by reaction Avith a ketone group 3 carbons removed from the first one. 

 The diketone is, therefore, ergosta-3,G-dione and the ergostane-triol has 

 the constitution ergostane-3,5,6-triol. The second double bond can, there- 

 fore, be only in the 5,6 position. 



Pyridazine derivative 

 of ergosta-3,6-dione 



HO OH 



Ergostaiie- 

 3,5,6-triol 



The location of the third double bond can likewise be determined. The 

 fact that it forms a conjugate bond is indicated by the refractive index, ^^'^ 

 by its x-ray pattern, ^^^ and also by its ultraviolet absorption spectrum. 

 This third double bond cannot be present in the side chain, so that it must 

 be conjugated to the A^'^-linkage. This would place it at the 7,8 position. 

 The fact that ergosterol is readily reduced with sodium and amyl alcohol, ^^® 

 as well as that it forms an addition product with maleic anhydride,'^" is 

 further evidence of conjugation of 2 unsaturated linkages. The 7,8 posi- 

 tion is also indicated by the maleic anhydride condensation, since this is 

 only effected when the 2 double bonds are in the same ring. The formation 

 of toluene-2,3,4,5-tetracarboxylic acid on nitric acid oxidation offers further 

 proof of the location of the third double bond. The double bonds in ergo- 

 sterol are therefore located in the 5,6-, 7,8-, and 22,23-positions. 



(3) 7-Dchydrocholesierol {Provitamm D-i) 



The structure of 7-dehydrocholesterol has been established by virtue of 

 its synthesis from cholesterol by Windaus, Lettre, and Schenck.^^ The 

 basic structure of cholesterol has been established in an earlier section (see 

 Chapter IV). The location of the double bonds is also evident because the 

 conjugate system is the same as in ergosterol. 



'" K. V. Auwers and E. Wolter, Nachr. Ges. Wiss. GoUingen, Math, physik. Klasse, 

 III, 101-119 (1931). 



128 G. E. R. Schulze, Z. physik. Chem., A171, 436-444 (1934). 



129 A. Windaus and J. Brunken, Ann., 460, 225-235 (1928). 



130 A. Windaus and A. Luttringhaus, Ber., 6.',, 850-854 (1931). 



