TERPENOIDS AND STEROIDS 



159 



CHq 



I 

 / 



CHo 



CH2CH=CHCH=CH2 



C=CH 



pyrethrin I 



The compounds responsible for the physiological action of marihuana (Cannabis 

 sativa) contain one ring having a p-menthane type structure and a second ring which does 

 not appear to be related to the terpenoids. For example, cannabidiol is: 



CH^CH^CH^CH aCHa 



ISOLATION 



It is clear from the great variety of structures found among the terpenoids and 

 steroids that no general method of isolation can be applicable to all of them. However, a 

 large number are decidedly non-polar compounds and may therefore be separated from 

 polar plant constituents by extraction with such solvents as benzene or ether. Such an 

 extract would also contain other types of lipids, esters, waxes, etc. Most of these may 

 be removed by saponification in alcoholic alkali followed by extraction with ether. Acids 

 and low molecular weight alcohols remain in the alkaline phase while most terpenoids and 

 steroids will go into the ether extract along with high molecular weight alcohols, non- 

 terpenoid hydrocarbons, etc. 



A few exceptions to this general procedure must be noted. Glycosidic compounds 

 such as the saponins and cardiac glycosides are insoluble in non-polar solvents. They 

 are most conveniently extracted from plants with 70-95% hot ethanol and extraneous lipids 

 removed from this solution by extraction into benzene. The order of extraction may also 

 be reversed - i. e. lipids extracted first with ether or benzene and then glycosides ex- 

 tracted with hot alcohol. Some of the glycosides will precipitate when a hot alcoholic solu- 

 tion of them is cooled, and this may aid in separations (54). Acidic terpenoids, when 

 present as the free acid, are soluble in non-polar solvents but on saponification will pass 

 into the alkaline phase. Terpenoid and steroid alkaloids, of course, behave like other 

 alkaloids in being more soluble in non-polar solvents under alkaline conditions than they 

 are under acidic conditions. Rubber is insoluble in acetone but soluble in benzene, so a 

 preliminary acetone extraction is used to remove contaminants if rubber is to be isolated. 

 A general procedure for extracting and separating triterpenoids has been described by 

 Pourrat and Hammouda (55). 



