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Prebiotic sugar-driven synthesis of pyrazin-2-one and 2-aminopyrazine monomers and oligomers, chemical models of pre-RNA replicating molecules.

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Project Introduction

Prebiotic sugar-driven synthesis of pyrazin-2-one and 2-aminopyrazine monomers and oligomers, chemical models of pre-RNA replicating molecules.
A central question in understanding the origin of life is the nature of the chemical process(es) on the primitive Earth that generated the first catalytic-replicating polymers. This is a difficult question because it requires an energetically-favorable chemical process that can synthesize a pair of coding monomers capable of template-directed polymerization. Furthermore, the synthetic process needs to be prebiotically plausible, that is, use simple reactants and conditions that are compatible with the prebiotic environment. Past model studies of prebiotic chemically-driven template-directed polymerization have used either pre-activated monomers or chemical condensing agents to drive monomer condensation reactions. Although these studies of prebiotic polymerization have yielded oligomeric products, they are generally narrowly focused on the polymerization step and leave unanswered questions concerning how adequate concentrations of the hydrolytically labile activating agents needed for polymerization were maintained in the abiotic environment. To approach this question we propose to develop a sugar-driven 'one-pot' synthesis of a pair of potentially complementary monomers that can be polymerized without involvement of a hydrolytically labile condensing agent. Specifically, we propose to investigate the sugar-driven synthesis and polyester-yielding polymerization of lactic acid and lactaldehyde monomers that contain pyrazin-2-one and 2-aminopyrazine groups having the potential to act as a pair of RNA-like coding bases in a primitive replicating molecule. The lactic acid monomers will be synthesized in a 'one-pot' sugar-driven reaction from dihydroxyacetone, glyoxylic acid and alanine amide for the pyrazin-2-one monomer; and from dihydroxyacetone, glyoxylic acid and glycine amidine for the 2-aminopyrazine monomer. The lactaldehyde monomers will be synthesized similarly, except that the glyoxylic acid will be replaced by glyoxal. Dry-down conditions would be used to polymerize the 'nucleoside-like' lactic acid monomers; whereas, oxidative processes will be used to polymerize the 'nucleoside-like' lactaldehyde monomers. We would also study the ability of the lactaldehyde monomers to reversibly form hemiacetal-linked oligomers that could facilitate their oxidative conversion to polyester oligomers. The proposed studies will contribute to understanding the origin of polymerizaton processes required for molecular replication. The strong fluorescence of the pyrazine groups would facilitate detection and analysis by HPLC/MS, gel electrophoresis or HPLC with fluorescence and UV detection. This proposal aimed at understanding the prebiotic chemical processes that provided the carbon and energy required for the prebiotic synthesis of pyrazine monomers and polymers, considered models of pre-RNA replicating molecules, supports NASA's Exobiology Program Element in Prebiotic Chemistry that seeks to determine "what chemical systems could have served as precursors of metabolic and replicating systems on Earth and elsewhere, including alternatives to the current DNA-RNA-protein basis for life." Also, knowledge gained in this investigation of the chemistry of abiogenesis contributes to understanding the "molecular processes that set the chemical conditions within which living systems may have arisen". In this respect, it provides knowledge of the differences between the chemistries of abiotic and biotic synthetic processes, environmental requirements for the emergence of life, and the probability of life in the solar system and elsewhere. More »

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