Carbocyclic Nucleoside Isosteres as Potential Antitumor

常规核苷的糖部分的固有柔性已经通过用刚性碳环取代糖部分而被抑制（即，二环[3.1.0]己烷），其模拟了伪旋转循环中常规核苷的北（N）或南（S）构象。我们的主要目标是系统地探测一系列的核苷/核苷酸结合酶的构象刚性N和S基板的集合，以了解结合的首选模式。第二个目的是构建修饰的核酸，其掺入这些固定单元中的一些以分别增强或破坏与S和N构象相关的典型B-或A-DNA构象。合成了腺苷的锁定对映体N和S甲烷卡巴腺苷（N-MCA和S-MCA）的相应的5 '-三磷酸，并将其作为HIV-RT的底物进行了测试。由于这些化合物具有3'-OH基团，因此它们允许链延长。因此，这些化合物对DNA合成链终止的任何影响都与掺入后由其锁定构象诱导的远距离畸变效应有关。使用其中我们改变相邻T残基的数目（1至4）的模板，我们研究了HIV RT到达全长DNA的能力作为掺入的N-MCA或S-MCA残基的数目的函数。结果表明，对于含有1-2个相邻T残基的模板，N-MCA的DNA合成终止主要发生在距离掺入位点7-9 nt处，而S-MCA的DNA合成终止主要发生在距离掺入位点9- 11nt处。在这两种情况下，都获得了一些全长产物。然而，随着相邻T残基数目的增加（3-4），N-MCA能够校正畸变，并且仅获得全长DNA。另一方面，在S-MCA的情况下，3-4个T残基被证明是致命的，并且没有获得全长DNA。一种新的方法用于合成北构象异构体，其中包括脂肪酶催化的决议步骤后形成的双环[3.1.0]己烷系统是非常成功的，并保证了充足的供应对映体纯的化合物。目前正在对南方类似物进行同样的研究。我们合成了一系列与自身互补的EcoR 1识别序列[ds（5 '-CGCGAATTCGCG-3'）]相对应的短寡脱氧核苷酸（ODNs），其中中间的A和中间的T被锁腺苷和锁胸苷取代。这些序列是当前NMR、CD和晶体学研究的主题。

The inherently 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) conformation 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 corresponding 5'-triphosphates of the locked antipodes of adenosine, N and S methanocarba adenosines (N-MCA and S-MCA), were synthesized and tested as substrates for HIV-RT. Since these compounds have a 3'-OH group, they allow chain elongation. Therefore, any effect on chain termination of DNA synthesis by these compounds has to be related to a distant distortion effect induced by their locked conformation, following incorporation. Using a template where we varied the number of adjacent T residues (1 through 4), we studied the ability of HIV RT to reach full length DNA as a function of the number of N-MCA or S-MCA residues incorporated. The results showed that for a template with 1-2 adjacent T residues, N-MCA termination of DNA synthesis occurred mainly 7-9 nt from the site of incorporation, while with S-MCA it occurred 9-11 nt from the site of incorporation. In both cases some full-length product was obtained. However, as the number of adjacent T residues increased (3-4), N-MCA was able to correct the distortion and only full length DNA was obtained. On the other hand, 3-4 T residues in the case of S-MCA proved fatal and no full length DNA was obtained. A novel approach for the synthesis of North conformers that involved a lipase-catalyzed resolution step following the formation of the bicyclo[3.1.0]hexane system was very successful and has guaranteed an ample supply of enatiomerically pure compounds. The same approach is being investigated for the South analogues. 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 and the middle T's have been replaced by locked adenosines and locked thymidines. These sequences are the subject of current NMR, CD and crystallographic studies.