Covalent Linkages Used in Prebiotic Chemistry for RNA-Templated Amino Acid Transfer and Peptide Synthesis

Biological translation is a universal process taking place in the ribosome. It involves the synthesis of a protein with a particular sequence from the information encoded in a messenger RNA and the amino acids carried by transfer RNAs with the assistance of specific enzymes. However, the origin of translation in the prebiotic world and, thus, in the absence of enzymes is difficult to envisage. Past and recent studies proposed different prebiotic models, following top-down and bottom-up approaches, for the origin and evolution of a primitive ribosome. The bottom-up models made use of distinct covalent linkages to connect RNA strands with amino acids and peptides. In this review, I focus on the covalent linkages used in these prebiotic models: acyl phosphate mixed anhydrides, phosphoramidates and ureas. I describe their syntheses under prebiotically plausible reaction conditions, as well as include their main conventional preparation methods. I also comment on their properties and chemical stabilities in aqueous solution. Finally, I examine the functions of the described covalent linkages in prebiotic processes involving RNA-templated amino acid transfer and peptide synthesis.