Prebiotic Syntheses of Noncanonical Nucleosides and Nucleotides

The origin of nucleotides is a major question in origins-of-life research. Given the central importance of RNA in biology and the influential RNA World hypothesis, a great deal of this research has focused on finding possible prebiotic syntheses of the four canonical nucleotides of coding RNA. However, the use of nucleotides in other roles across the tree of life might be evidence that nucleotides have been used in noncoding roles for even longer than RNA has been used as a genetic polymer. Likewise, it is possible that early life utilized nucleotides other than the extant nucleotides as the monomers of informational polymers. Therefore, finding plausible prebiotic syntheses of potentially ancestral noncanonical nucleotides may be of great importance for understanding the origins and early evolution of life. Experimental investigations into abiotic noncanonical nucleotide synthesis reveal that many noncanonical nucleotides and related glycosides are formed much more easily than the canonical nucleotides. An analysis of the mechanisms by which nucleosides and nucleotides form in the solution phase or in drying–heating reactions from pre-existing sugars and heterocycles suggests that a wide variety of noncanonical nucleotides and related glycosides would have been present on the prebiotic Earth, if any such molecules were present.