Nonenzymatic Oligomerization of 3′,5′-Cyclic CMP Induced by Proton and UV Irradiation Hints at a Nonfastidious Origin of RNA

We report that 3′,5′-cyclic CMP undergoes nonenzymatic di- and trimerization at 20 °C under dry conditions upon proton or UV irradiation. The reaction involves stacking of the cyclic monomers and subsequent polymerization through serial transphosphorylations between the stacked monomers. Proton- and UV-induced oligomerization of 3′,5′-cyclic CMP demonstrates that pyrimidines—similar to purines—might also have taken part in the spontaneous generation of RNA under plausible prebiotic conditions as well as in an extraterrestrial context. The observed polymerization of naturally occurring 3′,5′-cyclic nucleotides supports the possibility that the extant genetic nucleic acids might have originated by way of a straight Occamian path, starting from simple reactions between plausibly preactivated monomers.