Firebird Biomolecular Sciences LLC, Alachua, FL 32615;
Firebird Biomolecular Sciences LLC, Alachua, FL 32615.
Proc Natl Acad Sci U S A. 2017 Oct 24;114(43):11315-11320. doi: 10.1073/pnas.1710778114. Epub 2017 Oct 9.
According to a current "RNA first" model for the origin of life, RNA emerged in some form on early Earth to become the first biopolymer to support Darwinism here. Threose nucleic acid (TNA) and other polyelectrolytes are also considered as the possible first Darwinian biopolymer(s). This model is being developed by research pursuing a "Discontinuous Synthesis Model" (DSM) for the formation of RNA and/or TNA from precursor molecules that might have been available on early Earth from prebiotic reactions, with the goal of making the model less discontinuous. In general, this is done by examining the reactivity of isolated products from proposed steps that generate those products, with increasing complexity of the reaction mixtures in the proposed mineralogical environments. Here, we report that adenine, diaminopurine, and hypoxanthine nucleoside phosphates and a noncanonical pyrimidine nucleoside (zebularine) phosphate can be formed from the direct coupling reaction of cyclic carbohydrate phosphates with the free nucleobases. The reaction is stereoselective, giving only the β-anomer of the nucleotides within detectable limits. For purines, the coupling is also regioselective, giving the -9 nucleotide for adenine as a major product. In the DSM, phosphorylated carbohydrates are presumed to have been available via reactions explored previously [Krishnamurthy R, Guntha S, Eschenmoser A (2000) 39:2281-2285], while nucleobases are presumed to have been available from hydrogen cyanide and other nitrogenous species formed in Earth's primitive atmosphere.
根据目前关于生命起源的“RNA 优先”模型，RNA 以某种形式出现在早期地球上，成为第一个支持达尔文主义的生物聚合物。 threose 核酸（TNA）和其他聚电解质也被认为是可能的第一个达尔文生物聚合物。该模型由研究人员开发，他们正在研究 RNA 和/或 TNA 从前体分子形成的“不连续合成模型”（DSM），这些前体分子可能在地球早期的前生物反应中就已经存在，目的是使该模型的不连续性降低。一般来说，这是通过检查从生成这些产物的提议步骤中分离出的产物的反应性来完成的，随着提议的矿物环境中反应混合物的复杂性的增加。在这里，我们报告称，腺嘌呤、二氨基嘌呤和次黄嘌呤核苷磷酸以及一种非规范嘧啶核苷（zebularine）磷酸可以通过环状碳水化合物磷酸与游离核苷碱基的直接偶联反应形成。该反应具有立体选择性，在可检测的限度内仅给出核苷酸的β-异构体。对于嘌呤，偶联也是区域选择性的，主要产物为腺嘌呤的-9 核苷酸。在 DSM 中，假定磷酸化碳水化合物可以通过以前探索过的反应获得[Krishnamurthy R、Guntha S、Eschenmoser A（2000）39:2281-2285]，而核碱基则假定可以从氰化氢和其他在地球原始大气中形成的含氮物质中获得。
