The medicinal applications of siRNAs have been intensively examined but are still hindered by their low molecular stability under biological conditions and off-target effects, etc. The introduction of chemical modifications to the nucleoside is a promising strategy for solving these limitations. Herein, we describe the development of a new uridine analog, U*, that has a (methylthiomethoxy)methoxy group at the 2′ position. The phosphoramidite reagent corresponding to U* was easily synthesized and the RNA oligonucleotides containing U* were stably prepared using a standard protocol for oligonucleotide synthesis. The introduction of U* into the siRNA resulted in positive or negative effects on the targeted gene silencing in a position-dependent manner, and the positive effects were attributed to the improved stability under biological conditions. The thermodynamic analysis of the U*-modified RNAs revealed a slight destabilization of the dsRNA, based depending on which U was strategically utilized to restrain the off-target effects of the siRNA. This study describes a rare example of nucleoside analogs with a large substitution at the 2′-position in the context of an siRNA application and is informative for the development of other analogs to further improve the molecular properties of siRNAs for medicinal applications.

siRNA 的医学应用已得到深入研究，但仍因其在生物条件下的低分子稳定性和脱靶效应等而受到阻碍。对核苷进行化学修饰是解决这些限制的有希望的策略。在这里，我们描述了一种新的尿苷类似物 U* 的开发，它在 2' 位置具有（甲基硫代甲氧基）甲氧基。与 U* 对应的亚磷酰胺试剂很容易合成，并且使用寡核苷酸合成的标准方案稳定地制备了含有 U* 的 RNA 寡核苷酸。将 U* 引入 siRNA 以位置依赖性方式对靶向基因沉默产生积极或消极影响，这些积极影响归因于生物条件下稳定性的提高。U* 修饰的 RNA 的热力学分析揭示了 dsRNA 的轻微不稳定，这取决于战略性地利用哪个 U 来抑制 siRNA 的脱靶效应。本研究描述了一个罕见的核苷类似物在 siRNA 应用中在 2' 位发生大量取代的例子，并为开发其他类似物以进一步改善 siRNA 的分子特性用于医学应用提供了信息。