N-Carbamoyl-α-Amino Acids Rather than Free α-Amino Acids Formation in the Primitive Hydrosphere: A Novel Proposal for the Emergence of Prebiotic Peptides

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 °C, pH = 8, [NH₃] very low), this system leads to 99.9% of -hydroxyacetonitrile and 0.1% of -aminoacetonitrile (precursor of the -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 -aminonitriles which shift the initial equilibrium in favor of the -aminonitrile pathway. The first reaction catalyzed by formaldehyde generates -aminoamides, precursors of -aminoacids. The second reaction catalyzed by carbon dioxide affords hydantoins, precursors of N-carbamoyl--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 -aminoacetamide and of the hydantoin at pH 8 being very similar, the synthesis of the N-carbamoyl--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 -amino acids offer new perspectives in prebiotic chemistry, in particular for the emergence of peptides on the prebiotic earth.     

Process improvement in amino acid N-carboxyanhydride synthesis by N-carbamoyl amino acid nitrosation

Amino acid N-carboxyanhydrides (NCA), convenient monomer for polypeptide synthesis, are easily prepared in high purity as the result of N-carbamoyl amino acids (CAA) nitrosation by gaseous NOx (4:1 NO + O₂ mixture, or NOCl) in toluene. Removal of polar side products is then efficiently carried out during subsequent work-up and crystallisation so that the resulting NCA obtained in good yield is suitable for controlled, primary amine-initiated polymerisation.     

N-Carbamoyl Amino Acid Solid–Gas Nitrosation by NO/NO x : A New Route to Oligopeptides via α-Amino Acid N-Carboxyanhydride. Prebiotic Implications

α-N-Carbamoyl amino acid (CAA), whose conditions of formation in a prebiotic hydrosphere have been described previously (Taillades et al. 1998), could have been an important intermediate in prebiotic peptide synthesis through reaction with atmospheric NO _x . Nitrosation of solid CAA (glycine or valine derivative) by a 4/1 NO/O₂ gaseous mixture (1 atm) yields N-carboxyanhydride (NCA) quantitatively in less than 1 h at room temperature. The crude solid NCA undergoes quantitative oligomerization (from trimer to nonamer under the conditions we used) when treated with a (bi)carbonate aqueous buffer at pH 9. We therefore suggest that part of the prebiotic amino acid activation/polymerization process may have taken place in a dry phase (``drying-lagoon' scenario). Received: 23 June 1998 / Accepted: 7 December 1998     

Dynamic Co-evolution of Peptides and Chemical Energetics, a Gateway to the Emergence of Homochirality and the Catalytic Activity of Peptides

We propose a scenario for the dynamic co-evolution of peptides and energy on the primitive Earth. From a multi component system consisting of hydrogen cyanide, several carbonyl compounds, ammonia, alkyl amine, carbonic anhydride, borate and isocyanic acid, we show that the reversibility of this system leads to several intermediate nitriles, that irreversibly evolve to alpha-amino acids and N-carbamoyl amino acids via selective catalytic processes. On the primitive Earth these N-carbamoyl amino acids combined with energetic molecules (NOx) may have been the core of a molecular engine producing peptides permanently and assuring their recycling and evolution. We present this molecular engine, a production example, and its various selectivities. The perspectives for such a dynamic approach to the emergence of peptides are evoked in the conclusion.