Meteorite-catalyzed intermolecular trans-glycosylation produces nucleosides under proton beam irradiation.

Di-glycosylated adenines act as glycosyl donors in the intermolecular trans-glycosylation of pyrimidine nucleobases under proton beam irradiation conditions. Formamide and chondrite meteorite NWA 1465 increased the yield and the selectivity of the reaction. The glycosyl transfer process was highly regioselective in yielding canonical N 1-pyrimidine nucleosides, the natural ß-anomers prevailing in the presence of formamide and NWA 1465. These data highlight the possible role of intermolecular trans-glycosylation in the prebiotic formation of purine and pyrimidine nucleosides, avoiding the occurrence of independent synthetic pathways.

High-Energy Proton-Beam-Induced Polymerization/Oxygenation of Hydroxynaphthalenes on Meteorites and Nitrogen Transfer from Urea: Modeling Insoluble Organic Matter?

Formation and structural modification of oxygenated polycyclic aromatic hydrocarbons (oxyPAHs) by UV irradiation on minerals have recently been proposed as a possible channel of PAH transformation in astrochemical and prebiotic scenarios of possible relevance for the origin of life. Herein, it is demonstrated that high-energy proton-beam irradiation in the presence of various meteorites, including stony iron, achondrite, and chondrite types, promotes the conversion of two representative oxyPAH compounds, 1-naphthol and 1,8-dihydroxynaphthalene, to complex mixtures of oxygenated and oligomeric derivatives. The main identified products include polyhydroxy derivatives, isomeric dimers encompassing benzofuran and benzopyran scaffolds, and, notably, a range of quinones and perylene derivatives. Addition of urea, a prebiotically relevant chemical precursor, expanded the range of identified species to include, among others, quinone diimines. Proton-beam irradiation of oxyPAH modulated by nitrogen-containing compounds such as urea is proposed as a possible contributory mechanism for the formation and processing of insoluble organic matter in meteorites and in prebiotic processes.

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.

First Evidence on the Role of Heavy Ion Irradiation of Meteorites and Formamide in the Origin of Biomolecules.

Formamide (NH2CHO) has been irradiated in condensed phase at 273 K by 11B-boron beams in the presence of powdered meteorites of the chondrite and stony-iron types. Relative to the controls (no radiation or no catalysis), a variegate panel of compounds was observed, including purine and pyrimidine nucleobases (uracil, cytosine, adenine, and guanine), nucleobase analogues, heterocycles, and carboxylic acids involved in metabolic pathways. The presence of amino imidazole carbonitrile (AICN), 4,6-diamino purine (4,6-DAP) and 2,4-diamino pyrimidine (2,4-DAPy) among the observed products suggests the occurrence of an unified mechanism based on the generation of radical cyanide species (•CN). These observations contribute to outline plausible prebiotic scenarios involving 11B-boron as energy source.