Fundamental Role of N-O Bond-Containing Compounds in Prebiotic Synthesis

Abstract

The emergence of biomolecules on the primordial Earth represents a pivotal scientific question for understanding the origin of life. Recent studies show that compounds containing nitrogen-oxygen bonds could serve as important feedstocks in prebiotic synthesis and intermediates in primitive metabolic pathways. Simple N-O-compounds have been identified in the interstellar medium and were likely formed from molecular nitrogen in the early Earth's atmosphere in the course of high-energy events. N-O-compounds are reactive species with rich chemistry enabling abiotic nitrogen fixation processes. Moreover, various inorganic and organic N-O-compounds are produced and used by modern organisms suggesting these species could play a crucial role at certain stages in the emergence and evolution of life. In this perspective, the potential role of N-O bond-containing compounds as fundamental building blocks and intermediates in prebiotic synthesis is summarized and discussed in a broad context (from simple nitrogen oxides to complicated organic N-O bearing molecules). In the first section, experimental and theoretical data on the detection, formation, and processing of simple N-O-compounds in space is considered. The second section focuses on the abiotic synthesis of N-O-compounds via chemical and photochemical reactions in the primordial atmosphere and ocean. The last two sections deal with the state-of-the-art laboratory-designed chemical reaction networks producing amino acids, peptides, and nucleosides from N-O compounds under prebiotically plausible conditions.

Keywords: RNA world hypothesis; abiotic amino acid synthesis; abiotic nitrogen fixation; hydroxylamine; nitric oxide; nitrite; nitrogen−oxygen compounds; prebiotic chemistry.

1

Fundamental role of N–O bond-containing compounds in nature. (a) N–O-compounds in interstellar medium. (b) Abiotic nitrogen cycle under early Earth plausible conditions. (c) N–O-compounds in natural products. (d) Reaction networks leading to biomolecules from N–O-compounds. Here and below, N–O-molecules are shown in red while potential prebiotic molecules are shown in green.

2

N–O bond-containing compounds in space. (a) Astronomically detected N–O-molecules and their fractional abundances relative to H₂. (b) Formation of N–O-molecules from N₂ or NH₃ in the ISM. (c) Interconversion of N–O-molecules in the ISM (on interstellar ices and dust grains). (d) Processing N–O-molecules in solid state and gas phase under interstellar conditions leading to simple organic prebiotic molecules.

3

N–O bond-containing compounds in the early Earth. (a) Formation and reactions of nitrogen oxides in the early Earth’s atmosphere and ocean. (b) Reactions of nitrogen oxides with atmospheric methane. ,

4

Abiotic photosynthesis of amino acids from N–O-compounds. (a) Photosynthesis of Gly and other amino acids from N₂O and CO. (b) Photosynthesis of Gly from nitrate and methanol.

5

Formation of prebiotic molecules from hydroxylamine and formaldehyde. (a) Reaction of formaldehyde with hydroxylamine hydrochloride. ,, (b) Plausible reaction network leading to amino acids. (c) Formation of peptides.

6

Moran’s reaction network producing key intermediates of the biological Krebs cycle and amino acids from pyruvate, glyoxylate, hydroxylamine and metallic iron in the aqueous phase.

7

Oligomerization of α-amino acids induced by atmospheric nitric oxide.

8

Dynamic stereoisomerization in diketopiperazine-derived alkoxyamines NO–DKP.

9

Carell’s synthesis of cytidine from cyanoacetylene, hydroxylamine and ribose. (a) Prebiotically plausible synthesis of cytidine via 3-aminoisoxazole 3-AOx. (b) Mechanism of the reductive recyclization to cytidine. (c) In-RNA reductive recyclization of N-isoxazolyl-urea to cytidine.

10

Carell’s synthesis of uridine from cyanoacetylene, hydroxylamine and ribose. (a) Prebiotically plausible synthesis of uridine via 5-aminoisoxazole 5-AOx. (b) Mechanism of the reductive recyclization to uridine. (c) In-RNA reductive recyclization of isoxazole to uridine.

11

Unified chemical scenario to pyrimidine nucleosides involving the Carell, Powner, and Sutherland intermediates. (a) Prebiotically plausible pathway for the formation of the Sutherland intermediate (SI) through the reaction with 3-aminoisoxazole (3-AOx). (b) Conversion of the Sutherland intermediate (SI) to cytidine and uridine.

12

Prebiotic synthesis of purine nucleosides via NO-Pys intermediates.

13

Prebiotic oligomerization of nucleotides activated via photochemical nitrosation-type cascade. (a) Passerini-type route for the oligomerization of the nucleosides. (b) Prebiotic photochemical synthesis of methyl isocyanide from nitrite.