Radical Formation in Sugar-Derived Acetals under Solvent-Free Conditions

The degradation of acetal derivatives of the diethylester of galactarate (GalX) was investigated by electron paramagnetic resonance (EPR) spectroscopy in the context of solvent-free, high-temperature reactions like polycondensations. It was demonstrated that less substituted cyclic acetals are prone to undergo radical degradation at higher temperatures as a result of hydrogen abstraction. The EPR observations were supported by the synthesis of GalX based polyamides via ester-amide exchange-type polycondensations in solvent-free conditions at high temperatures in the presence and in the absence of radical inhibitors. The radical degradation can be offset by the addition of a radical inhibitor. The radical is probably formed on the methylene unit between the oxygen atoms and subsequently undergoes a rearrangement.

Thioesters Provide a Robust Path to Prebiotic Peptides

The condensation of building blocks into oligomers and polymers was an early and important stage in the origins of life. High activation energies, unfavorable thermodynamics and side reactions are bottlenecks for abiotic formation of peptides. Thioesters are hypothesized to have played key roles in prebiotic chemistry on early Earth, serving as energy storing molecules, as synthetic intermediates, and as catalysts in the formation of more complex molecules, including polypeptides. However, all abiotic reactions reported thus far for peptide formation via thioester intermediates have relied on activated building blocks or condensing agents, which are of questionable prebiotic relevance. We report robust, plausible prebiotic reactions of mercaptoacids with amino acids that result in the formation of peptides and thiodepsipeptides, which contain both peptide and thioester bonds. Peptide bond formation proceeds by the condensation of mercaptoacids to form thioesters followed by thioester-amide exchange. Mercaptoacids catalyze thiodepsipeptides and peptide formation under a wide range of pH conditions and at mild temperatures. Our results offer the most robust one-pot pathway for peptide formation ever reported. These results support the hypothesis that thiodepsipeptides formed robustly on prebiotic Earth and were possible contributors to early chemical evolution.

Thioesters Provide a Robust Path to Prebiotic Peptides

The condensation of building blocks into oligomers and polymers was an early and important stage in the origins of life. High activation energies, unfavorable thermodynamics and side reactions are bottlenecks for abiotic formation of peptides. Thioesters are hypothesized to have played key roles in prebiotic chemistry on early Earth, serving as energy storing molecules, as synthetic intermediates, and as catalysts in the formation of more complex molecules, including polypeptides. However, all abiotic reactions reported thus far for peptide formation via thioester intermediates have relied on activated building blocks or condensing agents, which are of questionable prebiotic relevance. We report robust, plausible prebiotic reactions of mercaptoacids with amino acids that result in the formation of peptides and thiodepsipeptides, which contain both peptide and thioester bonds. Peptide bond formation proceeds by the condensation of mercaptoacids to form thioesters followed by thioester-amide exchange. Mercaptoacids catalyze thiodepsipeptides and peptide formation under a wide range of pH conditions and at mild temperatures. Our results offer the most robust one-pot pathway for peptide formation ever reported. These results support the hypothesis that thiodepsipeptides formed robustly on prebiotic Earth and were possible contributors to early chemical evolution.

The effect of temperature on the kinetics of enhanced amide bond formation from lactic acid and valine driven by deep eutectic solvents

Deep eutectic solvents have been found to facilitate the copolymerization of hydroxy acids and amino acids through ester-amide exchange reaction, and to drive the formation of amino acid-enriched oligomers with...

Kinetic Resolution of α-Nitrolactones by Catalytic Asymmetric Hydrolysis or Ester–Amide Exchange Reaction

C 1-Symmetric chiral ammonium salt catalysts induced a kinetic resolution of racemic α-nitrolactones through an asymmetric ester–amide exchange reaction. The corresponding amides were obtained with high enantioselectivities and high S (= k fast/k slow) values. This reaction system is a useful approach for obtaining carbocyclic quaternary α-nitroamides as chiral building blocks.

Fe(ii) and Fe(iii) dithiocarbamate complexes as single source precursors to nanoscale iron sulfides: a combined synthetic and in situ XAS approach

Fe(ii) and Fe(iii) dithiocarbamates are precursors to a range of nanoparticulate iron sulfides and in situ studies give insight into the molecular decomposition mechanism being dominated by reductive-elimination of thiuram disulfide and amide-exchange.