34 T. F. Gallagher 



C-24, in view of the fact that there was none at C-23 or C-22 

 this possibihty seems unreasonable. Since there is con- 

 siderably more than one atom it cannot all be at the tertiary 

 carbon C-25. Thus the methyl groups are a highly probable 

 situation and we have concluded that these must be the loci 

 of the side chain deuterium. 



The remainder of the isotope (approximately 1 • 2 atoms per 

 molecule) was found in the vicinity of the unsaturated bond 

 and secondary alcohol group as shown by the following 

 experiments. Oxidation of cholesterol to cholestenone and 

 equilibration with base in aqueous alcohol resulted in loss of 

 1-14 atomiS of deuterium per molecule (Fig. 6). This isotope 

 lost must have been on carbons 2, 3, 4 or 6, since only hydro- 

 gen from these positions would be lost in the oxidation or 

 exchanged with the medium after oxidation upon treatment 

 with base. Thus more than 97 per cent of the isotope must 

 have been on carbons 2, 3, 4, 6, 26 and 27. 



Further localization of the ring isotope was possible. 

 Another sample of cholesterol with a different isotopic content, 

 but similar distribution, was reduced with ordinary hydrogen 

 in the usual way and the saturated cholestanol isolated. 

 Oxidation to cholestanone caused a minor loss and this must 

 be ascribed to a small amount of deuterium attached to C-3. 

 More important, however, was the finding that refluxing with 

 base in aqueous alcohol did not result in any further loss of 

 isotope. This clearly proved that in the deuterated choles- 

 terol there was no isotope at either C-2 or C-4, and since there 

 was no hydrogen at C-5 the location of the deuterium in the 

 ring system of the cholesterol obtained from the exchange 

 reaction was in small measure at C-3, and in preponderant 

 amount at C-6. We thus find that the platinum-catalysed 

 exchange reaction yielded a deuterated cholesterol in which 

 practically all of the isotope was on one ring carbon and in the 

 i^opropyl group at the end of the side chain. 



The results clearly suggest that the localization of isotope 

 will be different with different steroids and that a random 

 distribution in an unsymmetrical molecule is unlikely. The 



