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Mechanochemical prebiotic peptide bond formation in the absence of water

The presence of amino acids on the prebiotic Earth, either stemming from endogenous chemical routes or delivered by meteorites, is consensually accepted. In contrast, prebiotically plausible pathways to achieve peptides from inactivated amino acids are still unclear since most oligomerization approaches rely on thermodynamically disfavoured reactions in solution (M. Frenkel-Pinter et al., Chem. Rev. 2020, 120, 4707). Here, we show that the combination of prebiotically plausible minerals and mechanochemical activation enables the oligomerization of glycine (Gly) in the absence of water (T. Stolar et al., Angew. Chem. Int. Ed. 2021). Furthermore, we establish that cyclic glycine dimer (DKP) is a productive intermediate in the mechanochemical oligomerization of Gly and generates oligomers up to Gly10. Oligomers of Gly obtained by milling, up to Gly11, are considerably longer compared to dipeptides and tripeptides formed in hypervelocity impact experiments (H. Sugahara, K. Mimura, Geochem. J. 2014, 48, 51), making them suitable to establish 3D structure, which is the basis of the catalytic properties associated with peptides and proteins (C. M. Rufo et al., Nat. Chem. 2014, 6, 303). Finally, we show that milling L-alanine (Ala) gives oligomers up to Ala5, and milling Gly and Ala gives a complex mixture of heterooligopeptides, hence demonstrating the possibility to incorporate other amino acids in a growing peptide. Our results show that mechanochemical oligomerization is a dynamic process that provides a water-free route towards oligopeptides. This may have implications for astrobiology research and reconsideration of extra-terrestrial conditions that can give rise to peptides.

Amino Acids ; Peptides ; Mechanochemistry ; Origin of Life ; Prebiotic Chemistry

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