An efficient chemical method for separation of corsolic acid from its isomeric maslinic acid

Based on the difference in steric bulk around C12-C13 double bond, the two isomeric dihydroxy pentacyclic triterpenic acids viz: corsolic acid and maslinic acid have been quantitatively separated via their methyl esters by reacting with the bulky m-chloroperbenzoic acid. Corsolic acid methyl ester was obtained in pure form, whereas maslinic acid methyl ester was separated as 12-oxo derivative formed via its epoxide. Alkaline hydrolysis of corsolic acid methyl ester afforded the desired acid. This method was also found to work well with the isomeric amyrin mixture (alpha- and beta-), but not highly selective. The high selectivity of this method with corsolic maslinic acid system can be rationalized in terms of 2alpha-hydroxy functionality, which provides additional crowding around the double bond and completely prevented corsolic acid from its reaction with perbenzoic acid.