Novel oleanolic vinyl boronates: synthesis and antitumor activity.

A series of novel oleanane-type pentacyclic triterpenoids bearing a boronate ester moiety at C3 have been synthesized by palladium-catalyzed cross-coupling of bis(pinacolato)diboron with vinyl triflates, in the presence of base, and these compounds were fully characterized by 1D and 2D NMR techniques. Evaluation of their antiproliferative effects on a panel of hematological-based and solid tumor cell lines identified three active oleanolic vinyl boronates that inhibited the growth of leukemia (Jurkat, K562), Burkitt's lymphoma (Jijoye), cervix (Hela), colon (SW480), and ovary (SKOV-3) cancer cells without concomitant inhibition of non-tumoral human fibroblasts. Their mechanisms of action were investigated on the leukemia Jurkat cell line. The results show that the incorporation of boron in the oleanolic acid core combined with the presence of amide bonds afforded compounds with desirable biological effects such as apoptosis induction and inhibition of proteasomal activity on tumor cells, which makes them potential templates for further development in the anticancer drug setting.