Molybdenum(VI)-Catalyzed Rearrangement of Prebiotic Carbohydrates in Formamide, a Candidate Prebiotic Solvent.

Abstract

It has been four decades since formamide was first suggested to perform roles as a precursor and/or a solvent in prebiotic chemistry. However, little work has sought to integrate formamide into larger prebiotic schemes that might create prebiotic RNA, often proposed to have been the first Darwinian biopolymer. Here, we report that formamide can be used as a solvent to perform the Bílik reaction, which uses molybdenum(VI) oxo species as catalysts at near-neutral pH to rearrange branched carbohydrates to give linear carbohydrates; the branched carbohydrates are produced from formaldehyde (HCHO) in alkaline mixtures containing borate, whereas the linear carbohydrates are the precursors needed for ribonucleosides and ribonucleotides. Under conditions wherein the Bílik reaction does this rearrangement, carbohydrate reaction products do not require stabilization by borate. These results, therefore, connect aqueous and formamide-based processes for the prebiotic formation of RNA components. Based on data from Hadean zircons that show that the mantle of the early Earth was near the fayalite-quartz-magnetite fugacity, molybdenum in its 6+ oxidation state was likely available in the Hadean. Together, these allow us to conjecture a process that delivers ribonucleosides and ribonucleotides from hydrogen cyanide and HCHO from a Hadean atmosphere on a Hadean geosphere, without needing precisely timed transitions from one solvent system to the other.