Synthesis And Anti-tumor Activity Study Of Oleanolic Acid Derivatives And Their Photoaffinity Probes

Oleanolic acid?OA?is a natural pentacyclic triterpene compound,which can be converted into 3-oxo-oleanlic acid?3-O-OA?by oxidant or microbial catalytic oxidation.3-O-OA is superior to OA in in vitro proliferation inhibitory activity and bioavailability,and is also an intermediate of many oleanolic acid derivatives.For the purpose of searching more druggable and active OA derivatives,the structure of 3-O-OA was modified in this study.Firstly,3-O-OA was prepared by Jones reagent oxidation of OA.The C-2 of 3-O-OA was then modified by Mannich reaction,Michael addition reaction and Claisen-Schmidt condensation reaction.Among synthesized 14 compounds of three different types,8compounds have not been previously reported.All new compounds were characterized by ¹H NMR,¹³C NMR and MS.In addition,the synthesis process for these compounds was partly optimized to simplify the reaction process and improve the yield of the reaction.In order to investigate the effect of C-28?on the activity of 3-O-OA,the 28?-C carboxylic acid of3-O-OA and its derivatives 4b and 4e were respectively esterified or amidated.Further more,we explored the synthesis of the probes based on 3-O-OA,4b,and 4e,three biotinylated probes 6a,6d,and 6c were synthesized,which provides the basis for the further exploration of target proteins of these OA derivatives.All the synthesized compounds were evaluated on Human cytomegalovirus?MCF-7?,human hepatocellular carcinoma?Hep G2?and human hepatocytes?L-O₂?.The activity of oleanolic acid derivatives and probes were compared with the lead compound 3-O-OA and CDDO-Me which was a OA derivative in Phase III clinic.Among them,2a,3b,4b,and 4j exhibited potent antiproliferative activities against different cancer cells lines with IC₅₀ less than 15?mol/L.Compared with 3-O-OA,anti-proliferative activity of synthesized derivatives of 3-O-OA has been significantly improved.The preliminary structure-activity relationship analysis suggested that Mannich derivatives and Michael addition derivatives of 3-O-OA can increase the in vitro proliferation inhibitory activity of cells.The activities of Claisen-Schmidt condensation derivatives 4a,4b,and 4j have also been greatly increased.This result shows that the introduction of a basic nitrogen-containing substituent at the C-2 position or a more active Michael receptor can increase its activity.28?-carboxyl group may be a active site that affects the effect of 3-O-OA.When a methyl group is introduced,their activities decrease significantly,which might contribute to their decreased water solubility.When a Michael receptor is introduced to C-28?,like maleamic ethylenediamine,the activity is increased to some extent.When the bulky functional group of the probe is introduced into the 28?position,the compound loses its activity,which may be attributed to the increase in the molecular weight and\or the decrease in water solubility.