Synthesis And Structure-activity Relationships Of New Taxane Derivatives As Multidrug Resistance Reversal Agents

Part 1Multidrug resistance (MDR) in tumor cells is thought to be one of important causes of the failure in cancer chemotherapy. MDR tumors show cross-resistance to multiple anticancer drugs with different chemical structures and mechanisms of action, which eventually results in the shortage of effective chemotherapy for patients. Great interests and efforts have been focused on the development of effective multidrug resistance reversal agents. So far, multidrug resistance agent, mainly P-gp inhibitor have been developed third generation.Sinenxan A (SIA), isolated from the callus cultures of Taxus spp., with the same 6/8/6 membered ring skeleton as taxol and taxinine, can be obtained in a high yield of 2?5% (w/w). In addition, SIA exhibited moderate activity of reversing multidrug resistance. Therefore, it will be of considerable significance to prepare various derivatives. Through our previous research, we used SIA as the starting material for reorganizing the structure and synthesis of a series of new compounds to study their valuable potential. Intriguingly, two powerful MDR reversal compounds Sy1220 and NPB-14 were obtained. On the basis of these results, in this thesis, in an effort to discover more potent derivatives, a systematic study of this type of taxane has been carried out through chemo-enzymatic transformation routes using sinenxans as starting material referring to the lead compounds, Sy1220 and NPB-14. Two different types of taxoid analogues (sinenxans and taxinine) were designed and synthesized.According to the principle of structure-activity relationships, we designed five routes and employed eight taxanes as starting materials, including 9?-hydroxyl-SIA, 10?-deacetyl-SIA,5?-deacetyl-SIA,14?-deacetyl-SIA,2?,14?-diacetoxy-5?-hydroxy-10?-methoxy-taxa-4(20),11-diene,2?,5?-diacetoxy-14?-hydroxy-10?-methoxy-taxa-4(20),11-diene,2?-acetoxy-5?-hydroxy-10?-methoxy-13-oxo-taxa-4(20),11-diene and 10?-deacetyl-SIC. Focused on the C-9?and C-5?derivatization, totally 95 target compounds were synthesized. Structures of these compounds were confirmed by NMR and (HR-)ESI-MS. The in vitro reversal effects were evaluated on the proliferation inhibition activity of resistant tumor cell lines (A549/Taxol, MCF-7/DOX and MX-1/Taxol) when co-administered with paclitaxel. Among them,31 compounds exhibited resistant reversal activities, especially,23 compounds exhibited more powerful activity than the positive control verapamil did. Based on the analyses of the structures and activities of the derivatives, the structure-activity relationships were preliminary concluded:1) 9?-OH-SIA derivatives generally displayed potent reversal activities; 2) most 5?-OH derivatives showed weak MDR reversal activities; 3) 10?-OMe derivatives generally displayed reversal activities; 4) the reversal activities of 14?-OH derivatives were moderate; 5) 10?-deacetyl-SIC derivatives decreased this type of activity, almost exhibit no reversing activities.These results would provide helpful information for the further structural optimization and drug candidate search.Part 2To obtain the substrates(Sinenxans A, B, C and yunanxane) used in Part 1,5 kg Ts-19 cell cultures of Taxus chinensis was isolated by Et2O and EtOH in sequence. Through silica gel chromatography combined with semi-preparative HPLC chromatography. Five minor taxanes (1-5) have been isolated together with four major taxanes (sinenxans A, B, C and yunanxane,6-9). Among them,1-4 were new compounds. On the basis of the analyses of the chemical and spectroscopic (IR, MS, ID NMR, and 2D NMR) data, the new compounds were identified as 5?-hydroxy-2?,10?-diacetoxy-14?-(3-hydroxy-2-methyl-butyryl)oxytaxa-4(20),11-diene (1),2?,5?,10?-triacetoxy-14?-(2-hydroxy-propionyl)oxytaxa-4(20),11-diene (2), 2?,5?,10?-triacetoxy-14?-(2-hydroxy-3-methyl-butyryl)oxytaxa-4(20),11-diene (3), and 2?-benzoxy-4?,9?,10?,13?-tetraacetoxytax-11-ene (4), respectively. The compounds 1-5 were pharmacologically evaluated for their cytotoxicities against five human cancer cell lines (HCT-8, Bel-7402, BGC-823, A549 and A2780) and reversing activity towards multi-drug resistance (MDR) A549/taxol tumor cell line, and the results showed that all of the tested compounds exhibited no cytotoxicities, but exhibited moderate activity of reversing multidrug resistance, while compound 4 possessed two times of reversing activity as verapamil at 10?M.