Anticancer activity of oleanolic acid and its derivatives modified at A-ring and C-28 position.

Oleanolic acid (OA) is a five-ring triterpenoid compound, which is widely present in plants. Due to a wide range of pharmacological activities, oleanolic acid has attracted more and more attention. However, oleanolic acid is insoluble in water and has low bioavailability, which limits its clinical application.