Fig. 2 Modification on C-3/C-28
4.1.2 Modifications on ring A
UA and Oleanolic acid (OA) are isomers, the difference between which is only at the position of Me29(Fig. 3 ). Derivatives of OA such as 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) exhibit significant anti-inflammatory and anti-tumor activity due to the modification of the ring A 49,50. Considering that both UA and OA are characterized by similar triterpene templates, similar chemical modifications have been applied to UA in recent years.