A series of new tricyclic nucleosides were synthesized and evaluated as hepatitis C virus (HCV) replication inhibitors. Initial screening in a HCV replicon system, derived from a genotype 1b isolate, identified 9-benzylamino-3-(β-D-ribofuranosyl)-3H-imidazo[4',5':5,6]pyrido[2,3-b]pyrazine (15d) as the most potent analogue. Comparative assessment of 15d activity against HCV full-length viruses or subgenomic replicons derived from genotypes 1 to 4 revealed a specificity of the compound for genotypes 1 and 3. Surprisingly, resistance mutations selected against 15d were mapped to domains II and III of the non-structural protein 5A (NS5A), but not to the RNA-dependent RNA polymerase residing in NS5B. These results argue that compound 15d might represent a lead for the development of a novel class of NS5A inhibitors.

中文翻译：

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通过 NS5A 依赖性抑制机制靶向 HCV 复制的新型核苷类似物。

一系列新的三环核苷被合成并评估为丙型肝炎病毒 (HCV) 复制抑制剂。在源自基因型 1b 分离物的 HCV 复制子系统中进行初步筛选，鉴定出 9-苄基氨基-3-(β-D-呋喃核糖基)-3H-咪唑并[4',5':5,6]吡啶并[2,3- b]吡嗪（15d）是最有效的类似物。15d 对 HCV 全长病毒或源自基因型 1 至 4 的亚基因组复制子活性的比较评估揭示了该化合物对基因型 1 和 3 的特异性。令人惊讶的是，针对 15d 选择的抗性突变被映射到非结构蛋白 5A (NS5A)，但不是 NS5B 中的 RNA 依赖性 RNA 聚合酶。这些结果表明，化合物 15d 可能代表开发一类新型 NS5A 抑制剂的先导。