Carbocyclic Nucleoside Isosteres as Potential Antitumor

常规核苷的糖部分固有的灵活性通过用刚性碳环（即双环[3.1.0]己烷）取代糖部分而被抑制，该环模仿了常规核苷在假旋回环中的北(N)或南(S)构象。我们的主要目标是系统地探索一系列具有构象刚性N和S底物的核苷/核苷酸结合酶，以了解首选的结合模式。第二个目标是构建含有这些固定单元的修饰核酸，分别加强或破坏与S和N构象相关的典型B-或A- dna构象。胸腺嘧啶的构象锁定对映体，N和S甲烷碳胸腺嘧啶（N- mct和S- mct），提供了两种控制生物活性结果的关键酶有效构象识别的清晰例子。在转染HSV-TK的小鼠癌细胞（38MC）中，S-MCT是比N-MCT更好的疱疹（HSV-1）胸苷激酶（TK）底物。令人惊讶的是，另一方面，尽管细胞中存在较高水平的三磷酸S-MCT，但仅观察到N-MCT的DNA结合。我们认为这一发现首次清楚地证明了激酶和聚合酶具有不同的和相反的底物构象偏好。由于N-MCT和其他5-取代尿嘧啶碳环类似物是非常有效的抗疱疹（如5-溴）和抗水痘带状疱疹（如5-溴酰）的药物，而双环[3.1.0]己烷模板的合成相当困难，我们开始了一个项目，以开发一种简化的方法来合成这些化合物。为了解决这一挑战，我们开发了两种新的分子内环丙烷化方法，其中N和S系列的整个双环结构都是一步构建的。在此化学过程中，我们在形成双环[3.1.0]己烷体系后加入了脂肪酶催化的分解步骤，这将保证为进一步的生物学研究提供充足的纯分子化合物。相对于我们的第二个目标，我们合成了一系列短的寡脱氧核苷酸（odn），对应于自互补的EcoR1识别序列[ds(5'-CGCGAATTCGCG-3')]，其中中间的a已被锁定的腺苷取代。这些序列是当前核磁共振和晶体学研究的主题，以检测弯曲或扭结的形成。利用含有刚性S和N碱基的短odn作为DNA甲基转移酶抑制剂的研究已经完成并发表（Wang et al.）。j。化学。Soc. 2000, 122, 12422)。

The inherent flexibility of the sugar moiety of conventional nucleosides has been arrested by replacing the sugar moiety with a rigid carbocyclic ring (i.e. bicyclo[3.1.0]hexane) that mimics either the North (N) or South (S) conformations of conventional nucleosides in the pseudorotational cycle. Our main objective has been to systematically probe a series of nucleoside/nucleotide binding enzymes with sets of conformationally rigid N and S substrates to learn about the preferred mode of binding. A secondary objective has been to construct modified nucleic acids that incorporate some of these fixed units to either reinforce or disrupt the typical B- or A-DNA conformations associated with S and N conformations, respectively. The conformationally locked antipodes of thymidine, N and S methanocarba thymidines (N-MCT and S-MCT), provided a clear example of efficient conformational discrimination by two critical enzymes that control the outcome of biological activity. We have demonstrated that S-MCT is a much better substrate than N-MCT for the herpes (HSV-1) thymidine kinase (TK) in murine cancer cells (38MC) transfected with HSV-TK. Surprisingly, on the other hand, DNA incorporation was observed only for N-MCT, despite the higher levels of S-MCT triphosphate present in the cell. We believe that this finding represents the first clear demonstration that kinases and polymerases have different and opposing substrate conformational preferences. Since N-MCT and other 5-substituted uracil carbocyclic analogues are extremely potent anti-herpes (e.g. 5-bromo) and anti-varicela zoster (e.g. 5-bromovinyl) agents, and synthesis of the bicyclo[3.1.0]hexane template is rather difficult, we embarked on a project to develop a simplified approach for the synthesis of these compounds. The challenged was met by developing two novel intramolecular cyclopropanation approaches where the entire bicyclic structure is constructed in one step for both N and S series. To this chemistry, we added the inclusion of a lipase-catalyzed resolution step following the formation of the bicyclo[3.1.0]hexane system which will guarantee an ample supply of enatiomerically pure compounds required for further biological studies. Relative to our second goal, we have synthesized a series of short oligodeoxynucleotides (ODNs) corrresponding to the self-complementary EcoR1 recognition sequence [ds(5'-CGCGAATTCGCG-3')] where the middle A's have been replaced by locked adenosines. These sequences are the subject of current NMR and crystallographic studies to detect the formation of bends or kinks. The study on the use of short ODNs containing rigid S and N abasic sites as inhibitors of DNA methyltransferase was completed and published (Wang et al. J. Am. Chem. Soc. 2000, 122, 12422).