Bioorthogonal chemistry has mainly been developed for proteins and carbohydrates. The chemistry of nucleic acids is different, and bioorthogonal labeling strategies that were successfully applied for proteins and carbohydrates cannot be simply transferred to DNA and RNA. Cycloadditions play a central role for bioorthogonal chemistry with nucleic acids. In vivo postsynthetic labeling of DNA and RNA requires copper-free variants of cycloaddition chemistry to achieve “bio”orthogonality that can be applied even in living cells. Currently, there are three major types of copper-free cycloadditions available for nucleic acids: (i) the ring-strain-promoted azide–alkyne cycloadditions, (ii) the “photoclick” 1,3-dipolar cycloadditions, and (iii) the Diels–Alder reactions with inverse electron demand. In principle, bioorthogonally reactive building blocks for postsynthetic modifications of nucleic acids by cycloaddition can be prepared by three different ways: (i) The organic synthesis of DNA and RNA applies phosphoramidites as building blocks for solid-phase automated chemistry. (ii) The biochemical preparation of DNA and RNA by primer extension (PEX) and PCR applies triphosphates as building blocks together with DNA/RNA polymerases, and works in aqueous buffer. (iii) DNA and RNA is labeled by the intrinsic metabolism in cells using bioorthogonally reactive nucleosides. In contrast to proteins and carbohydrates, for which metabolic labeling strategies are well developed, there are only a few examples in the literature for metabolic labeling of nucleic acids. In this review, we summarize the currently available DNA and RNA building blocks, both phosphoramidites and nucleotide triphosphates, for copper-free and bioorthogonal postsynthetic modification strategies.

中文翻译：

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通过无铜环加成反应作为生物正交反应对DNA和RNA进行后合成修饰。

生物正交化学主要用于蛋白质和碳水化合物。核酸的化学性质不同，成功应用于蛋白质和碳水化合物的生物正交标记策略不能简单地转移到DNA和RNA中。环加成在核酸的生物正交化学中起着核心作用。体内DNA和RNA的后合成标记需要环加成化学的无铜变体来实现即使在活细胞中也可以应用的“生物”正交性。当前，有三种主要类型的无铜环加成物可用于核酸：（i）环应变促进的叠氮化物-炔烃环加成；（ii）“光点击” 1,3-偶极环加成，以及（iii）逆电子需求的Diels–Alder反应。原则上，可以通过三种不同方式制备通过环加成对核酸进行后合成修饰的生物正交反应性结构单元：（i）DNA和RNA的有机合成将亚磷酰胺用作固相自动化化学的结构单元。（ii）通过引物延伸（PEX）和PCR进行DNA和RNA的生化制备，将三磷酸作为结构单元与DNA / RNA聚合酶一起使用，并在水性缓冲液中起作用。（iii）DNA和RNA通过使用生物正交反应性核苷的细胞内在新陈代谢进行标记。与蛋白质和碳水化合物相比，其代谢标记策略已得到很好的发展，文献中只有很少的核酸代谢标记实例。在这篇综述中，我们总结了目前可用的DNA和RNA构建基，包括亚磷酰胺和三磷酸核苷酸，用于无铜和生物正交的后合成修饰策略。与蛋白质和碳水化合物相比，其代谢标记策略已得到很好的发展，文献中只有很少的核酸代谢标记实例。在这篇综述中，我们总结了目前可用的DNA和RNA构建基，包括亚磷酰胺和三磷酸核苷酸，用于无铜和生物正交的后合成修饰策略。与蛋白质和碳水化合物相比，其代谢标记策略已得到很好的发展，文献中只有很少的核酸代谢标记实例。在这篇综述中，我们总结了目前可用的DNA和RNA构建基，包括亚磷酰胺和三磷酸核苷酸，用于无铜和生物正交的后合成修饰策略。