Novel pentacyclic triterpenoids with allyl and propargyl substituents

Lupane- and ursane-type pentacyclic triterpenoids (betulin, betulinic and ursolic acids) are abundant in Nature, being present in plants, and are of interest for medical research for their diverse biological activities. However, the low solubility of natural triterpenoids in water and in physiological fluids restricts their medical applications. In the last decade, numerous semisynthetic betulinic and ursolic acid derivatives have been prepared by modification of the functional groups at ¿-3, ¿-28, or ¿-30. Transformations of ring ¿ of triterpenoids at ¿-2 are promising but considerably less studied. Chemoselective methods for the synthesis of ¿-2 propargyl-substituted lupane- and ursane-type triterpenoids were developed based on ¿-alkylation with propargyl bromide of potassium enoxytriethylborates or potassium enolates generated from betulonic or ursolic acid. The resulting compounds are reactive building blocks for the synthesis of new potentially biologically active terpenoids. ¿-2 Propargyl-substituted pentacyclic triterpenoids were successfully transformed to conjugates with 1,2,3-triazole-containing ¿-D-glucopyranosides via «click chemistry»