Damha M J, Meng B, Wang D, Yannopoulos C G, Just G
Department of Chemistry, McGill University, Montreal, QC, Canada.
Nucleic Acids Res. 1995 Oct 11;23(19):3967-73. doi: 10.1093/nar/23.19.3967.
In this report we describe the synthesis of oligonucleotides containing sulfide-linked dinucleoside units, namely rT(2'OH)sdT, rT(2'OMe)sdT, dTsrU(2'OMe) and dT(2'OMe)srU(2'OMe). We also describe the interactions of such oligomers with complementary DNA and RNA targets, and provide the structural basis for their remarkable RNA binding selectivity. In all cases, the Tm values of the S/P-chimera duplexes were lower than those of the corresponding unmodified duplexes. We attribute this to steric interactions between the 5'sulfur and the atoms of the nearby base/sugar residues. The 2'-substituents (i.e., 2'OH or 2'OMe) vicinal to the alkylsulfide internucleoside linkage significantly perturb the structure and stability of the duplexes formed with DNA, and more so than with RNA. The introduction of three rT(2'OH)sdTp (or rT(2'OMe)sdTp) units into an oligodeoxynucleotide sequence was sufficient to abolish binding to complementary DNA but not RNA. The same three substitutions with dTsrU(2'OMe)p and dT(2'OMe)srU(2'OMe)p did not abolish binding to DNA but the resulting complexes had poor thermal stability. The RNA-binding 'selectivity' exhibited by these oligomers is attributed to the tendency of the 2'-substituted (branched) furanoses to adopt the C3'-endo pucker, a conformation that is inconsistent with the B-form structure of helical DNA. The preference of these sugars to exist often exclusively in the C3'-endo form is attributed to stereoelectronic effects, namely gauche and anomeric effects. Our findings support the hypothesis that nucleoside analogues puckered exclusively in the C3'-endo form may result in them being especially good binders of targeted mRNA [S.H. Kawai (1991), Ph.D. Thesis, McGill University; Kawasaki et al. (1993) J. Med. Chem. 36, 831-841].
在本报告中，我们描述了含硫醚连接二核苷单元的寡核苷酸的合成，即rT(2'OH)sdT、rT(2'OMe)sdT、dTsrU(2'OMe)和dT(2'OMe)srU(2'OMe)。我们还描述了这类寡聚物与互补DNA和RNA靶标的相互作用，并为它们显著的RNA结合选择性提供了结构基础。在所有情况下，S/P-嵌合体双链体的熔解温度（Tm）值均低于相应未修饰双链体的Tm值。我们将此归因于5'-硫原子与附近碱基/糖残基原子之间的空间相互作用。与烷基硫醚核苷间连接相邻的2'-取代基（即2'OH或2'OMe）显著扰乱了与DNA形成的双链体的结构和稳定性，对RNA的影响则更大。在寡脱氧核苷酸序列中引入三个rT(2'OH)sdTp（或rT(2'OMe)sdTp）单元足以消除与互补DNA的结合，但不影响与RNA的结合。用dTsrU(2'OMe)p和dT(2'OMe)srU(2'OMe)p进行相同的三个取代不会消除与DNA的结合，但形成的复合物热稳定性较差。这些寡聚物表现出的RNA结合“选择性”归因于2'-取代（分支）呋喃糖倾向于采用C3'-内型构象，这种构象与螺旋DNA的B型结构不一致。这些糖通常仅以C3'-内型形式存在的偏好归因于立体电子效应，即邻位交叉效应和异头效应。我们的研究结果支持这样的假设，即仅以C3'-内型构象折叠的核苷类似物可能使其成为靶向mRNA的特别好的结合剂[S.H. Kawai（1991年），麦吉尔大学博士论文；Kawasaki等人（1993年），《药物化学杂志》36，831 - 841]。
