Thiophosphate photochemistry enables prebiotic access to sugars and terpenoid precursors

Mg2+-driven selection of natural phosphatidic acids in primitive membranes

Biological membranes are composed exclusively of phospholipids comprising glycerol-1-phosphate or glycerol-3-phosphate. By contrast, primitive membranes would have likely been composed of heterogeneous mixtures of phospholipids, including non-natural analogues comprising glycerol-2-phosphate, as delivered by prebiotic synthesis. Thus, it is not clear how the selection of natural phospholipids could have come about. Here we show how differences in supramolecular properties, but not molecular properties, could have driven the selection of natural phosphatidic acids in primitive membranes. First, we demonstrate that at the molecular level it is unlikely that any prebiotic synthesis or hydrolysis pathway would have enabled the selection of natural phosphatidic acids. Second, we report that at the supramolecular level, natural phospholipids display a greater tendency to self-assemble in more packed and rigid membranes than non-natural analogues of the same chain length. Finally, taking advantage of these differences, we highlight that Mg2+, but not Na+, K+, Ca2+ or Zn2+, drives the selective precipitation of non-natural phosphatidic acids from heterogeneous mixtures obtained by prebiotic synthesis, leaving membranes proportionally enriched in natural phosphatidic acids. Our findings delineate a plausible pathway by which the transition towards biological membranes could have occurred under conditions compatible with prebiotic metal-driven processes, such as non-enzymatic RNA polymerization.

Prebiotic thiol-catalyzed thioamide bond formation

Thioamide bonds are important intermediates in prebiotic chemistry. In cyanosulfidic prebiotic chemistry, they serve as crucial intermediates in the pathways that lead to the formation of many important biomolecules (e.g., amino acids). They can also serve as purine and pyrimidine precursors, the two classes of heterocycle employed in genetic molecules. Despite their importance, the formation of thioamide bonds from nitriles under prebiotic conditions has required large excesses of sulfide or compounds with unknown prebiotic sources. Here, we describe the thiol-catalyzed formation of thioamide bonds from nitriles. We show that the formation of the simplest of these compounds, thioformamide, forms readily in spark-discharge experiments from hydrogen cyanide, sulfide, and a methanethiol catalyst, suggesting potential accumulation on early Earth. Lastly, we demonstrate that thioformamide has a Gibbs energy of hydrolysis ( Δ G r ∘ ) comparable to other energy-currencies on early Earth such as pyrophosphate and thioester bonds. Overall, our findings imply that thioamides might have been abundant on early Earth and served a variety of functions during chemical evolution.

Evaluating Pigments as a Biosignature: Abiotic/Prebiotic Synthesis of Pigments and Pigment Mimics in Planetary Environments

Pigments serve a multitude of functions in biology including light harvesting for photosynthesis, radiation protection, membrane support, and defense. The ubiquity of pigments-especially within extremophiles found in high-radiation, high-salinity, and dry environments-and their detectability via mission-ready techniques have elevated these molecules as promising targets in the search for evidence of life elsewhere. Moreover, the detection of pigments has been proposed as a "smoking gun" for extraterrestrial life as it has been suggested that these molecules cannot be generated abiotically. However, while pigments may hold promise as a biosignature, current understanding of their possible prebiotic origins remains understudied and uncertain. Better understanding of the abiotic synthesis of pigments is critical for evaluating the biogenicity of any pigment detected during missions, including by the Mars Perseverance rover or from returned samples. Compounding this uncertainty is the broad definition of pigment as it includes any compound capable of absorbing visible light and by itself does not specify a particular chemical motif. While not experimentally verified, there are promising prebiotic routes for generating pigments including hemes, chlorophylls, and carotenoids. Herein, we review the biochemistry of pigments, the inherent assumptions made when searching for these molecules in the field, their abiotic synthesis in industry and prebiotic reactions, prebiotically relevant molecules that can mimic their spectral signatures, and implications/recommendations for future work.

Manganese-catalyzed Efficient Synthesis of N-heterocycles and Aminoketones Using Glycerol as a C3 Synthon

Glycerol is one of the important biomass-derived feedstocks and the high-value utilizations of glycerol have attracted much attentions in recent years. Herein, we report a manganese catalyzed dehydrogenative coupling of glycerol with amines for the synthesis of substituted 2-methylquinoxalines, 2-ethylbenzimidazoles, and α-aminoketones without any external oxidant. In these reactions, NHC-based pincer manganese complex featuring a pyridine backbone displayed high catalytic activity and selectivity, in which hydrogen and water were produced as the only by-products using glycerol as a C3 synthon.

Prebiotically plausible chemoselective pantetheine synthesis in water

Coenzyme A (CoA) is essential to all life on Earth, and its functional subunit, pantetheine, is important in many origin-of-life scenarios, but how pantetheine emerged on the early Earth remains a mystery. Earlier attempts to selectively synthesize pantetheine failed, leading to suggestions that "simpler" thiols must have preceded pantetheine at the origin of life. In this work, we report high-yielding and selective prebiotic syntheses of pantetheine in water. Chemoselective multicomponent aldol, iminolactone, and aminonitrile reactions delivered spontaneous differentiation of pantoic acid and proteinogenic amino acid syntheses, as well as the dihydroxyl, gem-dimethyl, and β-alanine-amide moieties of pantetheine in dilute water. Our results are consistent with a role for canonical pantetheine at the outset of life on Earth.

Ring Opening of Glycerol Cyclic Phosphates Leads to a Diverse Array of Potentially Prebiotic Phospholipids

Phospholipids are the primary constituents of cell membranes across all domains of life, but how and when phospholipids appeared on early Earth remains unknown. Pressingly, most prebiotic syntheses of complex phospholipids rely upon substrates not yet shown to have been available on early Earth. Here, we describe potentially prebiotic syntheses of a diverse array of complex phospholipids and their building blocks. First, we show that choline could have been produced on early Earth by stepwise N-methylation of ethanolamine. Second, taking a systems chemistry approach, we demonstrate that the intrinsically activated glycerol-2,3-cyclic phosphate undergoes ring opening with combinations of prebiotic amino alcohols to yield complex phospholipid headgroups. Importantly, this pathway selects for the formation of 2-amino alcohol-bearing phospholipid headgroups and enables the accumulation of their natural regioisomers. Finally, we show that the dry-state ring opening of cyclic lysophosphatidic acids leads to a range of self-assembling lysophospholipids. Our results provide new prebiotic routes to key intermediates on the way toward modern phospholipids and illuminate the potential origin and evolution of cell membranes.

Carbonyl Migration in Uronates Affords a Potential Prebiotic Pathway for Pentose Production

Carbohydrate biosynthesis is fundamental to modern terrestrial biochemistry, but how this collection of metabolic pathways originated remains an open question. Prebiotic sugar synthesis has focused primarily on the formose reaction and Kiliani-Fischer homologation; however, how they can transition to extant biochemical pathways has not been studied. Herein, a nonenzymatic pathway for pentose production with similar chemical transformations as those of the pentose phosphate pathway is demonstrated. Starting from a C6 aldonate, namely, gluconate, nonselective chemical oxidation yields a mixture of 2-oxo-, 4-oxo-, 5-oxo-, and 6-oxo-uronate regioisomers. Regardless at which carbinol the oxidation takes place, carbonyl migration enables β-decarboxylation to yield pentoses. In comparison, the pentose phosphate pathway selectively oxidizes 6-phosphogluconate to afford the 3-oxo-uronate derivative, which undergoes facile subsequent β-decarboxylation and carbonyl migration to afford ribose 5-phosphate. The similarities between these two pathways and the potential implications for prebiotic chemistry and protometabolism are discussed.