Synthesis of Carbohydrates in Mineral-Guided Prebiotic Cycles

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• 作者：Hyo-Joong Kim ; Alonso Ricardo ; Heshan I. Illangkoon ; Myong Jung Kim ; Matthew A. Carrigan ; Fabianne Frye ; Steven A. Benner
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：June 22, 2011
• 年：2011
• 卷：133
• 期：24
• 页码：9457-9468
• 全文大小：1275K
• 年卷期：v.133,no.24(June 22, 2011)
• ISSN：1520-5126

文摘

One present obstacle to the 鈥淩NA-first鈥?model for the origin of life is an inability to generate reasonable 鈥渉ands off鈥?scenarios for the formation of carbohydrates under conditions where they might have survived for reasonable times once formed. Such scenarios would be especially compelling if they deliver pent(ul)oses, five-carbon sugars found in terran genetics, and exclude other carbohydrates (e.g., aldotetroses) that may also be able to function in genetic systems. Here, we provide detailed chemical analyses of carbohydrate premetabolism, showing how borate, molybdate, and calcium minerals guide the formation of tetroses (C₄H₈O₄), heptoses (C₇H₁₄O₇), and pentoses (C₅H₁₀O₅), including the ribose found in RNA, in 鈥渉ands off鈥?experiments, starting with formaldehyde and glycolaldehyde. These results show that pent(ul)oses would almost certainly have formed as stable borate complexes on the surface of an early Earth beneath a humid CO₂ atmosphere suffering electrical discharge. While aldotetroses form extremely stable complexes with borate, they are not accessible by pathways plausible under the most likely early Earth scenarios. The stabilization by borate is not, however, absolute. Over longer times, material is expected to have passed from borate-bound pent(ul)oses to a branched heptulose, which is susceptible to Cannizzaro reduction to give dead end products. We show how this fate might be avoided using molybdate-catalyzed rearrangement of a branched pentose that is central to borate-moderated cycles that fix carbon from formaldehyde. Our emerging understanding of the nature of the early Earth, including the presence of hydrated rocks undergoing subduction to form felsic magmas in the early Hadean eon, may have made borate and molydate species available to prebiotic chemistry, despite the overall 鈥渞educed鈥?state of the planet.