Synthesis And Biological Evaluation Of Oleanolic Acid Derivatives As Novel Inhibitors Of Protein Tyrosine Phosphatase1B

Protein tyrosine phosphatase1B (PTP1B) is implicated as a negative regulator of insulin signaling and a potential drug target for the treatment of type2diabetes and obesity.In the previous work, in order to developing novel small molecule PTP1B inhibitors, our research group synthesized series of maslinic acid derivatives and studied their structure-activity relationship on PTP1B. Some of the derivatives exhibited a dramatic increase in inhibitory potency and selectivity. In this paper, we synthesized series of oleanolic acid (OA) derivatives by modification of oleanolic acid’s A ring and C ring, respectively.We also studied on their structure-activity relationship to get some more effective small molecule PTP1B inhibitors which have higher PTP1B inhibitory activity and selectivity on other PTPs.(1) In this paper, oxidation at C-3position of OA by IBX afforded3-carbonyl oleanolic acid, which reacted with ethyl formate, diethyl carbonate, diethyl oxalate and isoamyl nitrite, respectively, in the presence of a base to introduce kinds of acyl group in the ortho position of carbonyl at C-3position. By condensation of these intermediates with hydrazine hydrate or hydroxylamine hydrochloride, series of new five-member heterocycles (substituted pyrazole, isoxazole, pyrrazolone, et.al) were introduced in the C-2and C-3position of OA. There are three to six steps from OA to the target compounds in30%-60%overall yield. Eleven compounds have been designed and synthesized. All of these compounds gave more potent biological effects than that of the lead compound, oleanolic acid, and pyrazole-fused, isoxazole-fused derivatives are better than other heterocycle-fused compounds. Moreover, introducing some substituents in heterocyclics can increase the inhibitory activity. For example, compound A-8(IC50=0.91μM) and compound A-9(IC50=0.98μM) are the best two PTP1B inhibitors, and the inhibitory activities were increased nearly3times when compared with the parent compound OA (ICso=2.96μM) (2) Oxidation of the protected OA at C-3position and C-28position with mCPBA afforded12-carbonyl oleanolic acid derivatives, which were afterwards reduced by NaBH4to produce12-hydroxyl substituted oleanolic acid derivatives. The configuration of C-12in compound B-6and B-7were confirmed by X-single crystal diffraction.By substitution of hydroxyl and other reactions, eleven compounds were prepared. Their inhibitory effects on PTP1B were evaluated, and the tests showed these derivatives has dramatically decreased inhibitory activity. Maybe the molecular’s spatial structure was changed by modification of the C-ring which made the molecule couldn’t play roles more effectivly on PTP1B. However, some of the derivatives (B-1, B-10andB-11) possess nearly3-fold selectivity for PTP1B over TCPTP compared with OA. So maybe modify the C-ring can promote the selectivity.(3) In order to further improve the PTP1B inhibitory activity and selectivity on the homogeneous enzyme (TCPTP), five compounds were synthesized by introducing five heterocycles at C-2and C-3position of compound B-1. Unfortunately, both the the activity and the selctivity decreased drmatically.