The RNA‐world hypothesis assumes that life on Earth started with small RNA molecules that catalyzed their own formation. Vital to this hypothesis is the need for prebiotic routes towards RNA. Contemporary RNA, however, is not only constructed from the four canonical nucleobases (A, C, G, and U), it also contains many chemically modified (noncanonical) bases. A still open question is whether these noncanonical bases were formed in parallel to the canonical bases (chemical origin) or later, when life demanded higher functional diversity (biological origin). Here we show that isocyanates in combination with sodium nitrite establish methylating and carbamoylating reactivity compatible with early Earth conditions. These reactions lead to the formation of methylated and amino acid modified nucleosides that are still extant. Our data provide a plausible scenario for the chemical origin of certain noncanonical bases, which suggests that they are fossils of an early Earth.

中文翻译：

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非规范RNA核苷作为早期地球的分子化石—益生元甲基化和氨基甲酸酯化生成

RNA世界假说假设地球上的生命始于催化其自身形成的小RNA分子。对该假设至关重要的是，需要针对RNA的益生元途径。然而，当代RNA不仅由四个规范的核碱基（A，C，G和U）构建，而且还包含许多化学修饰的（非规范）碱基。一个尚待解决的问题是，当生命需要更高的功能多样性（生物起源）时，这些非规范碱基是否与规范碱基（化学起源）平行或更晚地形成。在这里，我们显示异氰酸酯与亚硝酸钠的组合建立了与地球早期条件相容的甲基化和氨基甲酰化反应性。这些反应导致仍然存在的甲基化和氨基酸修饰的核苷的形成。