ELUCIDATION OF THE PANCRATISTATIN CYTOTOXIC PHARMACOPHORE

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。本项目的最终目标是为治疗癌症提供新的治疗药物。从扁豆鳞茎中提取的生物碱(+)-扁豆素显示出有希望的抗肿瘤和抗病毒活性，目前正在由美国国家癌症研究所进行临床前评估。然而，由于从隔离中获得的材料数量有限，这些研究已被搁置。生物碱的有限可用性也阻碍了阐明其作用机制和结构活性研究的努力，这对于鉴定更有效和/或毒性更低的类似物至关重要。因此，发现一种既能制备天然产物本身，又能制备其类似物的高效灵活的化学途径，将极大地促进这种先导化合物的进一步开发，因此它一直是科学界长期追求的目标。方法本研究重点是实际合成具有可变截短部分的以胰虫素为基础的系列化合物。一旦合成，化合物被评估体外和体内的抗癌活性。基于所获得的SAR信息，构建了胰虎汀药效团，并将其用于开发一系列类似物，这些类似物具有(a)改善的活性/毒性谱，(b)改善的水溶性，(c)简化的结构，可用于即将进行的临床试验的大规模生产。在INBRE项目的前一年，我们开发了一种高度非对映选择性的芳基铜酸盐加成物-烷氧基-?,？-enoates，探索了它的范围，发现它的潜在适用性并不局限于这个项目，而是在合成有机化学中具有普遍的效用。本年度，我们从理论角度进一步研究了该方法，并开发了一种新的基于还原消除的模型来预测这些过程的立体化学结果。该模型有望在合成有机酸盐化学中得到普遍应用。我们将这种方法应用于构建一个胰脏抑素环B类似物文库，并对这些化合物的抗癌活性进行了评价。本研究的结论是要求环B的完整性，以保持天然化合物的效力。由于没有发现开环B与胰青藤汀类似物有活性，我们在这方面的进一步努力将集中在环C类似物的合成上。这将通过完全合成和半合成的方法来完成。后者将基于水仙素的分离，水仙素是水仙素的同系物，并将其转化为水仙素相关结构。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Background and Rationale This project is aimed at the ultimate goal of providing new therapeutic agents for the treatment of cancer. The alkaloid (+)-pancratistatin, extracted from Pancratium littorale bulbs, displays promising antineoplastic and antiviral activity and is currently undergoing preclinical evaluation by the US National Cancer Institute. However, the studies have been put on hold due to the limited quantity of material available from isolation. The alkaloid¿s limited availability has also plagued efforts towards the elucidation of its mechanism of action as well as structure ¿ activity studies, which could be crucial for the identification of more potent and/or less toxic analogues. Therefore, the discovery of an efficient and flexible chemical route enabling preparation of not only the natural product itself, but also a diverse library of its analogues will tremendously facilitate further development of this lead compound, hence it has been a long-sought objective of the scientific community. Methods This work focuses on a practical synthesis of pancratistatin-based series of compounds with variable truncated portions of the molecule. Once synthesized, the compounds are evaluated for in vitro and in vivo anticancer activity. Based on the obtained SAR information the pancratistatin pharmacophore is constructed and used for the development of a series of analogs with (a) improved activity/toxicity profiles, (b) improved water solubility, and (c) simplified structures, amenable to a large-scale production for the forthcoming clinical trials. Results In the previous year of the INBRE project we developed a highly diastereoselective arylcuprate addition to ?-alkoxy-?,?-enoates, explored its scope and found that its potential applicability is not limited to this project, but rather has a general utility in synthetic organic chemistry. In the current year we further studied this method from a theoretical perspective and developed a novel reductive elimination-based model to predict the stereochemical outcome of such processes. This model is expected to be of general use in synthetic organocuprate chemistry. We applied this method to the construction of a library of pancratistatin ring B analogues and evaluated these compounds for anticancer activity. The conclusion of this study is the requirement for the integrity of ring B to retain the potency of the natural compound. Further Study Since no activity was found with pancratistatin analogues with the open ring B, our further efforts in this area will focus on the synthesis of the ring C analogues. This will be accomplished both through totally synthetic and semisynthetic approaches. The latter will be based on isolation of narciclasine, a congener of pancratistatin, and its conversion to pancratistatin-related structures.