Abstract
The Strecker reaction of aldehydes with ammonia and hydrogen cyanide first leads to α-aminonitriles, which are then hydrolyzed to α-amino acids. However, before reacting with water, these aminonitriles can be trapped by aminothiols, such as cysteine or homocysteine, to give 5- or 6-membered ring heterocycles, which in turn are hydrolyzed to dipeptides. We propose that this two-step process enabled the formation of thiol-containing dipeptides in the primitive ocean. These small peptides are able to promote the formation of other peptide bonds and of heterocyclic molecules. Theoretical calculations support our experimental results. They predict that α-aminonitriles should be more reactive than other nitriles, and that imidazoles should be formed from transiently formed amidinonitriles. Overall, this set of reactions delineates a possible early stage of the development of organic chemistry, hence of life, on Earth dominated by nitriles and thiol-rich peptides (TRP).
Highlights
Peptide bonds are formed by the reaction of the amine group of an amino acid with an ester function
Inaasimilar similarway, way, cysteine cysteine would have been synthesized from HSCH2 CHO, itself possibly obtained from glycolaldehyde
All the and the water solvent effects were described by using the polarizable continuum model (PCM), geometries were optimized using the B3LYP functional in conjunction with the 6-31g(d,p) basis set and namely
Summary
Peptide bonds are formed by the reaction of the amine group of an amino acid with an ester function. For non-ribosomal peptides, the amide formation involves the reaction of an amine on a thioester [1] In both cases, mixed phosphoric carboxylic anhydrides are transiently formed. Reacting with ammonia and hydrogen cyanide, they would have first given α-aminonitriles, which, upon hydrolysis, would have delivered amino acids (Figure 1) [5] Even though it is exothermic, the reaction of nitriles with water is a slow process [6]; so slow that, once formed in the ocean, aminonitriles would have had ample time to react with species more nucleophilic than water
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