The emergence of RNA is considered a key step in the origin of life. However, despite decades of effort, demonstrating a plausible prebiotic synthesis of RNA polymers has remained an elusive goal. For the past decade researchers within the NSF-NASA Center for Chemical Evolution (CCE) have been investigating the hypothesis that RNA was preceded by an earlier RNA-like polymer, or proto-RNA. A particular focus of CCE research is the possibility that the first informational polymers of life spontaneously formed on the prebiotic Earth from molecules that were similar to the subunits of extant RNA (i.e., phosphate, ribose, the canonical nucleobases), but were molecules with a strong propensity to form supramolecular assemblies that served as templates for proto-RNA. Problems associated with synthesizing RNA in model prebiotic reactions include formation of the glycosidic bond within nucleosides, as this bond does not spontaneously form with appreciable yields between ribose and any of the four nucleobases of RNA. Another important but less appreciated problem with prebiotic RNA synthesis is the fact that the free nucleobases of RNA, their nucleosides, and their nucleotides do not form Watson-Crick base pairs in aqueous solution, which present a conundrum for how RNA polymers would have formed in a "prebiotic soup" that would have, presumably, contained a complex mixture of similar molecules. In facing these challenges, CCE researchers have discovered several molecules that spontaneously form glycosidic bonds with ribose and other sugars that are produced along with ribose in model prebiotic reactions. Moreover, the nucleosides and mononucleotides formed by these heterocycles show a strong propensity to form supramolecular assemblies with Watson-Crick-like base pairs in water. Overall, the results of this research have revealed plausible prebiotic heterocycles, including some shown to be produced along with the nucleobases of RNA in model prebiotic reactions, that are strong candidates for the recognition units of proto-RNA.

Self-assembly meets prebiotic chemistry: Progress in the search for the chemical structure of proto-RNA

ACS Spring Meeting 2021

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