TERPENOIDS AND STEROIDS 



135 



squalene 



No triterpenoids so far have been found to have monocyclic or dicyclic structures. Tri- 

 cyclic ones are rare. Several tetracyclic triterpenoids are known. They are of interest 

 chiefly because of their resemblance and probable biogenetic relationship to the steroids. 

 For a long time some of them were thought to be sterols, and this misconception is re- 

 flected in their names. The best known of these compounds is lanosterol which occurs 

 in wool fat, yeast, and some higher plants (e.g. Euphorbia electa) . Like squalene, it 

 appears to be an intermediate in steroid biosynthesis. Other tetracyclic triterpenoids 

 are the alcohol euphol from Euphorbia spp. and the so-called elemi acids of Canarium 

 commune. The tetracyclic triterpenoids are reviewed by Jones and Halsall (13). 



lanosterol 



HOOC^ 



elemadienolic acid 



