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Numerous long-standing questions in origins-of-life research center on the history of biopolymers. For example, how and why did nature select the polypeptide backbone and proteinaceous side chains? Depsipeptides, containing both ester and amide linkages, have been proposed as ancestors of polypeptides. In this paper, we investigate cationic depsipeptides that form under mild dry-down reactions. We compare the oligomerization of various cationic amino acids, including the cationic proteinaceous amino acids (lysine, Lys; arginine, Arg; and histidine, His), along with nonproteinaceous analogs of Lys harboring fewer methylene groups in their side chains. These analogs, which have been discussed as potential prebiotic alternatives to Lys, are ornithine, 2,4-diaminobutyric acid, and 2,3-diaminopropionic acid (Orn, Dab, and Dpr). We observe that the proteinaceous amino acids condense more extensively than these nonproteinaceous amino acids. Orn and Dab readily cyclize into lactams, while Dab and Dpr condense less efficiently. Furthermore, the proteinaceous amino acids exhibit more selective oligomerization through their α-amines relative to their side-chain groups. This selectivity results in predominantly linear depsipeptides in which the amino acids are α-amine-linked, analogous to today's proteins. These results suggest a chemical basis for the selection of Lys, Arg, and His over other cationic amino acids for incorporation into proto-proteins on the early Earth. Given that electrostatics are key elements of protein-RNA and protein-DNA interactions in extant life, we hypothesize that cationic side chains incorporated into proto-peptides, as reported in this study, served in a variety of functions with ancestral nucleic acid polymers in the early stages of life.

Establishing plausible routes for the abiotic formation of nucleotides is a challenging problem because the phosphorylation of organic molecules is thermodynamically unfavorable in water, and because common phosphorous‐containing minerals such as apatite are highly insoluble. Reactions of reduced phases such as the meteoritic mineral schreibersite with ammonia containing solutions can form stable amino‐derivatives of phosphates/phosphite, and carbonate‐rich lakes have been suggested as environments where phosphate species and organic molecules could accumulate in significant abundances, thus promoting an ideal environment for abiotic phosphorylation. This work reports the catalytic properties of three CaCO3 polymorphs—calcite, aragonite, and vaterite—on diamidophosphate (DAP)‐induced phosphorylation of the uridine nucleoside during a 24‐hr dry‐down reaction. It is shown that the phosphorylation reaction is accelerated in solutions containing CaCO3 compared to those with no mineral present. For un‐buffered solutions with no mineral present, the primary products formed are uridine monophosphates (UMPs), with yields making up 22.3 ± 3.9% of the total detected species, while solutions containing calcite and aragonite formed primarily UMP dimers (yields of 15.3 ± 1.1% and 14.8 ± 1.3%, respectively). Vaterite showed a strong preference for forming cyclic UMP (cUMP) (26.3 ± 0.3% yield), and no higher order polymers were observed using any carbonate mineral. Reactions containing CaSO4·2H2O (gypsum) showed a preference for forming cUMP, though not as strong as vaterite, while those containing CaCl2 (calcium chloride) and CaWO4 (scheelite) did not yield any phosphorylated products other than UMPs. These results suggest that CaCO3 minerals could have played an important role in facilitating prebiotic phosphorylation in aqueous environments that undergo drying cycles. Plain Language Summary: The abiotic formation of biomolecules containing phosphorous (such as DNA and RNA) on the surface of early Earth faces significant challenges due to the inherent unfavorability of phosphorous‐addition reactions (called phosphorylation) and low expected abundances of available phosphorous species. Carbonate‐rich lakes and pools have been suggested as environments where significant abundances of organic molecules and dissolved phosphorous species could accumulate. This work examines the phosphorylation reaction of the molecule uridine by a prebiotically plausible amidophosphate species—diamidophosphte or DAP—in the presence of three calcium carbonate minerals: calcite, aragonite, and vaterite. The results show that adding uridine and DAP into an aqueous solution of water and minerals and allowing the mixture to dry overnight at 65°C results in for formation of several types of phosphorylated species. While phosphorylated species were detected in all of the experiments, the reactions run with minerals showed a larger abundance of cyclic and dimer species. These results suggest that CaCO3 minerals could have played an important role in facilitating prebiotic phosphorylation in aqueous environments that undergo drying cycles. Key Points: Calcium carbonate minerals produced a catalytic effect on the diamidophosphate (DAP)‐induced phosphorylation of uridineCalcite and aragonite produced predominantly dimer species, while vaterite formed mostly cyclic uridine monophosphate (UMP)The results suggest that an evaporating pool of water containing organics, salts, and reactive phosphorus could form the precursors of RNA [ABSTRACT FROM AUTHOR]

Keywords: pterins; guanosine; origins of life; RNA world; phosphorylation EN pterins guanosine origins of life RNA world phosphorylation 1 1 1 07/13/22 20220711 NES 220711 B Guanosine and pterins are depicted as the constellation Gemini b . However, like Pollux from Greek mythology, guanosine would not have been born alone - pterins would have been formed in equal (or, in this case, even in major) parts through prebiotic reactions. Pterins, guanosine, origins of life, RNA world, phosphorylation. [Extracted from the article]

Invited for the cover of this issue are the groups of César Menor-Salván, Facundo Fernández and Nicholas V. Hud at the University of Alcala and the Georgia Institute of Technology. The image depicts the authors contemplating the origin of pterins and guanosine nucleosides from a common precursor, with the art-gallery setting embodying their feeling that the common synthetic pathways of these molecules in both the prebiotic world and in biochemistry is a natural work of (chemical) art. Read the full text of the article at 10.1002/chem.202200714., (© 2022 Wiley-VCH GmbH.)