<p>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 unactivated
amino acids are still unclear since most oligomerization approaches rely on thermodynamically
disfavored reactions in solution. Alternative hypotheses such as the prebiotic
impact scenario postulate that the mechanical impacts from meteorites and
geochemical phenomena played an important role in delivering exogenous material
to Earth, thus providing the geochemical, mechanical, and thermal conditions to
synthesize small prebiotic organic compounds in the absence of bulk liquid
media. In this context, here we evaluate the applicability of mechanochemistry
by ball milling for peptide bond formation under a prebiotic impact scenario.
We found that the combination of mechanical forces and prebiotically plausible
and ubiquitous minerals as activators enable the oligomerization of amino acids
such as glycine in the absence of bulk water (or solvents) and at ambient
temperature. Increasing the mechanochemical reactor’s temperature is shown to
favor the degree of polymerization concomitantly with the formation of cyclic
glycine dimer [cyclo(Gly<sub>2</sub>) or DKP], a product commonly considered as
a dead-end in solution peptide bond formation. However, our study shows that DKP
can be mechanochemically activated and used as a source for glycine oligomers.
The findings of this research provide alternative mechanochemical routes
towards oligopeptides and establish new synthetic approaches for prebiotic
chemistry that are not limited by poor diffusion of the reactants, thus
complementing the current alternating wetting and drying prebiotic environment
strategy.</p>
Amino Acids and Peptides. VI. Novel Peptide Bond Formation catalyzed by Metal Ions. IV. Formation of optically Active Amino Acid Amides and Peptide Amides