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Abstract

Our previous kinetic and thermodynamic studies upon the reactional system HCHO/HCN/NH3 in aqueous solutions are completed. In the assumed prebiotic conditions of the primitive earth ([HCHO] and [HCN] near 1 g L-1, T = 25 degrees C, pH = 8, [NH3] very low), this system leads to 99.9% of alpha-hydroxyacetonitrile and 0.1% of alpha-aminoacetonitrile (precursor of the alpha-amino acid). The classical base-catalyzed hydration of nitriles, slow and not selective, can not modify significantly this proportion. On the contrary, we found two specific and efficient reactions of alpha-aminonitriles which shift the initial equilibrium in favor of the alpha-aminonitrile pathway. The first reaction catalyzed by formaldehyde generates alpha-aminoamides, precursors of alpha-aminoacids. The second reaction catalyzed by carbon dioxide affords hydantoins, precursors of N-carbamoyl-alpha-aminoacids. In the primitive hydrosphere, where the concentration in carbon dioxide was estimated to be higher than that of formaldehyde, the formation of hydantoins was consequently more efficient. The rates of hydrolysis of the alpha-aminoacetamide and of the hydantoin at pH 8 being very similar, the synthesis of the N-carbamoyl-alpha-amino acid seems then to be the fatal issue of the HCHO/HCN/NH3 system that nature used to perform its evolution. These N-protected alpha-amino acids offer new perspectives in prebiotic chemistry, in particular for the emergence of peptides on the prebiotic earth.

Recycling Frank: Spontaneous emergence of homochirality in noncatalytic systems

“…The preceding model is theoretical, but can be applied to concrete chemical systems of amino acid derivatives. In a prebiotic point of view, amino acids are known to be synthesized abiotically in many ways (27)(28)(29)(30). However, the formation of the first prebiotic peptides is not a trivial problem, as free amino acids are poorly reactive.…”

Polypeptides and 100 Years of Chemistry of α‐Amino Acid N‐Carboxyanhydrides

“…[323][324][325][326][327][328][329][330] These authors found that carbamoyl amino acids easily react with NO/O 2 gas mixtures to form NCAs in almost quantitative yields (Scheme 38). The carbamoyl amino acids (CAAs) result from the reaction of amino acids with cyanate ions, a prebiotic scenario that has been discussed in detail.…”

Catalysis through Induced Intramolecularity: What Can Be Learned by Mimicking Enzymes with Carbonyl Compounds that Covalently Bind Substrates?

“…The examples mentioned here demonstrate their ability to catalyze some reactions of bifunctional substrates very efficiently (a characteristic of most biochemical compounds), α-amino acid derivatives in particular. A striking indication of the involvement of these molecules in the processes from which life arose is the fact that aldehyde catalysis was demonstrated as the predominant pathway [20,96] for the hydration of α-amino nitriles in Miller's experiment showing the formation of amino acids under prebiotic conditions. [97] The hypothesis that catalysis through induced intramolecularity has played an important role in the processes resulting in the emergence of life therefore seems quite reasonable.…”