Shunpei Abe

Abstract Sugars play essential roles in genetic and metabolic processes. However, it remains unclear how the sugar backbone of DNA could have formed under prebiotic conditions. In the context of the RNA world hypothesis, the abiotic formation of ribose─the backbone of RNA─has been demonstrated by hydrothermal and γ-irradiation experiments under conditions simulating meteorite parent bodies. However, the abiotic synthesis of 2-deoxyribose─the backbone of DNA─from simple carbon sources, such as HCHO and CH3OH, has been limited. Here, we show that γ-irradiation under alkaline aqueous conditions simulating the interiors of meteorite parent bodies enables the formation of sugars, including both 2-deoxyribose and ribose, from simple carbon sources. These findings imply that ribose and 2-deoxyribose could have coexisted in small bodies from which carbonaceous meteorites originated, and been delivered to the early Earth, where they could have acted as precursors for RNA and DNA. More broadly, our results highlight the importance of radiation-driven chemistry within asteroids as a key contributor to a chemically diverse stage of early molecular evolution. Moreover, early chemical evolution may have involved a broader repertoire of sugar backbones than previously assumed and multiple noncanonical nucleic acids could have contributed to the origin of life.

Abstract Various prebiotic organic compounds have been identified in meteorites. Understanding the origins of these compounds is essential to comprehending prebiotic chemistry in the early Solar System. Regarding sugar formation, the formose reaction—polymerization of formaldehyde under alkaline aqueous conditions—has been considered a plausible prebiotic process in the meteorite parent bodies. However, studies on the influence of minerals on this reaction are limited. In this study, we conducted hydrothermal experiments to examine the impact of three silicate minerals—olivine, antigorite (Mg-rich serpentine), and saponite—on the production of aldose sugars under geochemically plausible conditions in the meteorite parent bodies during aqueous alteration. The presence of these minerals enhanced aldose production, indicating promoting effects on the formose reaction. With the presence of ammonia in the initial solutions, the minerals enhanced aldose formation at 1 day of the heating experiments. However, the aldoses decreased at 3 and 7 days of the heating experiments. This is probably because ammonia promoted the formation of other compounds by consuming aldoses. These mineral–organic interactions may have played a significant role in the prebiotic chemical evolution in meteorite parent bodies, possibly contributing to the inventory of organic compounds delivered to early Earth.