340 IV. WAXES, HIGHER ALCOHOLS, ETC. 



matic relation of cholesterol and epicholesterol is pictured here. Accord- 

 ing to the Ruzicka scheme, cholesterol and epi-allo-cholesterol are both 

 trans, although the configurations of the hydroxyl group are opposite. 

 The comparative relationship of the terminology by these two methods is 

 shown in Table 5. 



" The Schoenheimer-Evans designation would appear to be the more 

 satisfactory, since the methyl group on Cio occupies the same position on 

 all known sterols and on bile acids, in contrast to the hydrogen atom on C5, 

 which may be in one of two positions. Using this system of nomenclature, 

 all sterols precipitable with digitonin are cis derivatives, while all epi forms 

 have a trans configuration and are not precipitated with digitonin. Accord- 

 ing to Lettre^"^ this system of terminology provides a satisfactory means of 

 indicating which saturated sterols will show molecular compound fonnation 

 because of opposite configurations at C3 and C5. One difficulty in the ter- 

 minology does exist, however, since lumisterol, formed on irradiation of 

 cholesterol, does have the methyl group on Cio on the opposite side of the 

 molecule. ^"^ 



Although the conversion of the normal to the epi series cannot be demon- 

 strated directly with cholesterol, the interrelationship can be shown in the 

 test tube when the ketones cholestanone or coprostanone are reduced. 

 When cholestanone is reduced in neutral solution,-"^ or with sodium and 

 amyl alcohol, dihydrocholesterol is formed, while in an acidic medium the 

 epidihydrocholesterol results. ^^^ Windaus and Uibrig^o^ jj^fj previously 

 obtained epidihydrocholesterol by epimerization of dihydrocholesterol 

 with sodium ethylate, but the equilibrium point was reached when only 10% 

 of the dihydrocholesterol was changed. The conditions are reversed with 

 coprostanone, the normal alcohol arising when reduction occurs in acidic 

 solution,-'" while the epi isomer arises in neutral solution. '" Windaus 

 and Uibrig^" and Windaus^'^ working by himself had previously been able 

 to demonstrate the interconversions of the epimers. 



The interrelationship of the normal and alio compounds where the varia- 

 tion depends upon the configuration on Cb is more difficult to demonstrate 

 chemically than is that of the ordinary and epi derivatives having differ- 

 ences in configuration on C3. In the case of allocholesterol, the configura- 

 tion of A/B rings cannot be altered on hydrogenation, followed by oxidation 

 to cholestanone and then by reduction to the epimeric alcohols dihydro- 

 cholesterol and epidihydrocholesterol. Both of these isomers still retain 



205 H. Lettr^, Ber., 68, 766-767 (1935). 



2»6 K. Dimroth, Ber., 69, 1123-1129 (1936). 



207 O. Diels and E. Abderhalden, Ber., 39, 884-890 (1906). 



208 G. Vavon and Z. Jakubowiez, Bull. soc. chim. [4], 53, 581-588 (1933). 

 2o» A. Windaus and C. Uil)rig, Ber., 47, 2384-2388 (1914). 



210 H. Cirasshof, Z. physiul. Cheni., 225, 197-198 (1934). 

 2" A. Windaus and C. Uibrig, Ber., J+8, 857-863 (l!)15). 

 212 A. Windaus, Ber., .'+9, 1724-1734 (1916). 



