NATURAL WAXES 



339 



Dihydrocholesterol 



Epidihydrocholesterol 



According to the Ruzicka scheme, the configuration of the hydroxyl 

 group on Cs for epicholesterol and epiergosterol is similar to its position in 

 epidihydrocholesterol, even though the reference asymmetric C(C5) no 

 longer exists as a coordination point. 



Table 5 



Comparative Configuratiox of Hydroxyl Group on C3 of Some Sterols as 



Compared with H on C'5 or with CH., Group on Cio" 



" The designations in parentheses do not exist, since C5 is not asj^mmetrie in these 

 cases. They are based upon the theory that the hydroxyl on C3 and the methyl on do 

 maintain similar relations to C5 as when C5 is asymmetric. 



* R. Schoenheimer and E. A. Evans, Jr., J. Biol. Chem., 114, 567-582 (1936). 



" L. Ruzicka, cited by H. R. Rosenberg, Chemistry and Physiology of the Vitamins, 

 Interscience, New York, 1945. 



A second method for classifying the ordinary and epi forms has been sug- 

 gested bj^ Schoenheimer and Evans-"* which corrects the above difl&culty. 

 The basis for their classification of as3nnmetry on C3 consists in referring it 

 to the methyl group on Cio. Those compounds such as cholesterol, ergos- 

 tcrol, 7-dehydrocholesterol, 7-dihydrocholesterol, and coprosterol all be- 

 long to the cis group and are the ordinary forms; the epi isomers are those 

 in which the 0H(C3) and CH3(Cio) relationships are trans. The diagram- 



Cholesterol Epicholesterol 



20* R. Schoenheimer and E. A. Evans, .Jr., /. Biol. Chem., II4, 507-582 (1930). 



