Mapping the landscape of potentially primordial informational oligomers: (3'→2')-D-phosphoglyceric acid linked acyclic oligonucleotides tagged with 2,4-disubstituted 5-aminopyrimidines as recognition elements

Synthesis and base-pairing properties of pyrazine nucleic acids

The diversity of backbone modifications in the study of primitive informational polymers is partly limited by the plausible formation of their prebiotic starting components. In this paper, we synthesize pyrazine nucleic acid, an acyclic polymer, with the nucleoside derivable from a prebiotic one-pot synthesis containing alanine amide and D-ribose. Pyrazine nucleic acid (PzNA) which has a backbone structurally similar to glycerol nucleic acid (GNA), contain pyrazine derived nucleosides as informational elements that may exhibit base pairing properties similar to the pyrimidines present in RNA.^[1] We found that insertion of pyrazinone nucleotides into DNA oligonucleotide sequences is not well-tolerated, and that homogenous sequences of PzNA are unable to form duplexes with RNA or DNA. Reasons for our results may be attributed to the pyrazine-2-one moiety, which is purposed to be a thymine analog, but has a lower pK_a (pK_a ∼ 8.5) than thymine and uracil. Additionally, we discovered an "apparent" regioselective protection of pyrazine-2-one derivatives in the presence of a secondary hydroxyl group that proved crucial in the preparation of the pyrazine-2-one phosphoramidite. The regioselectivity observed is proposed to be of general interest in the context of heterocyclic chemistry. In the larger context of origins of life studies, it points to the importance of keto-enol preferences of the canonical nucleobases versus pyrazine heterocycles in functioning as recognition elements.

Prebiotic chemistry in neutral/reduced-alkaline gas-liquid interfaces

The conditions for the potential abiotic formation of organic compounds from inorganic precursors have great implications for our understanding of the origin of life on Earth and for its possible detection in other environments of the Solar System. It is known that aerosol-interfaces are effective at enhancing prebiotic chemical reactions, but the roles of salinity and pH have been poorly investigated to date. Here, we experimentally demonstrate the uniqueness of alkaline aerosols as prebiotic reactors that produce an undifferentiated accumulation of a variety of multi-carbon biomolecules resulting from high-energy processes (in our case, electrical discharges). Using simulation experiments, we demonstrate that the detection of important biomolecules in tholins increases when plausible and particular local planetary environmental conditions are simulated. A greater diversity in amino acids, carboxylic acids, N-heterocycles, and ketoacids, such as glyoxylic and pyruvic acid, was identified in tholins synthetized from reduced and neutral atmospheres in the presence of alkaline aqueous aerosols than that from the same atmospheres but using neutral or acidic aqueous aerosols.

The origin of RNA and "my grandfather's axe"

The origin of RNA is one of the most formidable problems facing prebiotic chemists. We consider RNA as a product of evolution, as opposed to the more conventional view of RNA as originally being the product of abiotic processes. We have come to accept that life's informational polymers have changed in chemical structure since their emergence, which presents a quandary similar to the paradox of "My Grandfather's Axe". Here, we discuss reasons why all contemporary components of RNA--the nucleobases, ribose, and phosphate--are not likely the original components of the first informational polymer(s) of life. We also evaluate three distinct models put forth as pathways for how the earliest informational polymers might have assembled. We see the quest to uncover the ancestors of RNA as an exciting scientific journey, one that is already providing additional chemical constraints on the origin of life and one that has the potential to produce self-assembling materials, novel catalysis, and bioactive compounds.

Chemical etiology of nucleic acid structure: the pentulofuranosyl oligonucleotide systems: the (1'→3')-β-L-ribulo, (4'→3')-α-L-xylulo, and (1'→3')-α-L-xylulo nucleic acids

Under potentially prebiotic scenarios, ribose (pentose), the component of RNA is formed in meager amounts, as opposed to ribulose and xylulose (pentuloses). Consequently, replacement of ribose in RNA, with pentulose sugars, gives rise to prospective oligonucleotide candidates that are potentially prebiotic structural variants of RNA that could be formed by the same type of chemical pathways that gave rise to RNA from ribose. The potentially natural alternative (1'→3')-ribulo oligonucleotides and (4'→3')- and (1'→3')-xylulo oligonucleotides consisting of adenine and thymine were synthesized and found to exhibit no self-pairing or cross-pairing with RNA. This signifies that even though pentulose sugars may have been abundant in a prebiotic scenario, the pentulose nucleic acids (NAs), if and when formed, would not have been competitors of RNA, or interfered with the emergence of RNA as a functional informational system. The reason for the lack of base pairing in pentulose NA highlights the contrasting and central role played by the furanosyl ring in RNA and pentulose NA, enabling and optimizing the base pairing in RNA, while impeding it in pentulose NA.

Enhanced nonenzymatic ligation of homopurine miniduplexes: support for greater base stacking in a pre-RNA world

The ancestors of RNA? There is a long-standing proposal that contemporary nucleic acids might have evolved from RNA-like polymers that utilized only purine-purine base pairs. Here we demonstrate the great advantage that increased nucleobase stacking area provides for nonenzymatic ligation.

Etiology of potentially primordial biomolecular structures: from vitamin B12 to the nucleic acids and an inquiry into the chemistry of life's origin: a retrospective

"We'll never be able to know" is a truism that leads to resignation with respect to any experimental effort to search for the chemistry of life's origin. But such resignation runs radically counter to the challenge imposed upon chemistry as a natural science. Notwithstanding the prognosis according to which the shortest path to understanding the metamorphosis of the chemical into the biological is by way of experimental modeling of "artificial chemical life", the scientific search for the route nature adopted in creating the life we know will arguably never truly end. It is, after all, part of the search for our own origin.