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[PPS07-04] Prebiotic synthesis of 2-deoxyribose by gamma-ray-induced formose-type reaction
Keywords:Sugars, Formose-type reaction, Gamma rays, 2-deoxyribose
Introduction
It is important to consider the origin of amino acids (the building blocks of protein), sugars and nucleobases (the building blocks of RNA and DNA) in order to reveal the chemical evolution of life. Formose-type reaction [1,2] is attracted as a prebiotic sugar formation reaction. Ribose, the building blocks of RNA, has been mainly investigated because of the RNA World hypothesis and has synthesized under various conditions along with other aldoses [3,4]. However, 2-deoxyribose, the building blocks of DNA, was not been synthesized by heat-induced formose-type reaction using HCHO or CH3OH as a carbon source.
Sugars have been detected in some meteorites [2,5] along with amino acids and nucleobases. Thus, there is a possibility that these biologically essential substances formed in extraterrestrial environments were delivered to the early Earth by meteorites, comets or interplanetary dust particles. Meteorite parent bodies are considered to be one of the possible sites where formose-type reaction occurred. Since (i) it is considered that radiations such as gamma-rays or radioactive decay heat [6] could be an energy source, and (ii) aldehydes, starting material of formose-type reaction, were expected to be existed. Previous studies showed the effects of gamma-rays on the formation of sugars [3] and amino acids [7].
We have shown the usefulness of gamma-rays for sugar formation. The gamma-rays caused radical reactions and produced glycolaldehyde [8], the rate-limiting step in the formose reaction. In this study, we verified the formation of 2-deoxyribose by gamma-ray-induced formose-type reaction.
Experimental
To simulate aqueous alteration inside the meteoric parent bodies, many mixtures of HCHO, CH3OH and H2O were prepared. NH3 or Ca(OH)2 were added to some of them as a base catalyst. These samples (300 μL) were gamma-irradiated (60Co source, Institute of Science Tokyo, total dose: ~90 kGy), then, aliquots (200 μL) were analyzed using gas-chromatography mass spectrometry (GC/MS) after aldnonitrile acetate ester derivatization [3]. Hereafter, these samples are called γ-FMW (HCHO+CH3OH+H2O), γ-FMAW (HCHO+CH3OH+NH3+H2O) and γ-FMCW (HCHO+CH3OH+Ca(OH)2+H2O). These samples were mixed in the following molar ratios; the case of FMW, HCHO : CH3OH : H2O = 5 : 0.83 : 100, the case of FMAW, HCHO : CH3OH : NH3 : H2O = 5 : 0.83 : 1 : 100, the case of FMCW, Approximately 3 mg of Ca(OH)2 was added to a FMW sample (300 μL). We also prepared heated samples (h-FMW, h-FMAW, h-FMCW) as controls, and analyzed them by same procedures. Furthermore, the formation of acetaldehyde was verified for all samples by reversed-phase analysis using the 2,4-dinitrophenylhydrazine (DNPH) derivatization methods.
Results and Discussion
2-deoxyribose was formed in γ-FMAW and γ-FMCW, in addition, a possible isomer of 2-deoxyribose was confirmed. On the other hand, 2-deoxyribose was not formed in γ-FMW and all heated samples.
It has been tentatively suggested that 2-deoxyribose is formed by heating (50℃) an aqueous solution of glyceraldehyde (or formaldehyde) and acetaldehyde in the presence of CaO [9]. It has also been shown that glyceraldehyde is formed by formose-type reaction [3] promoted by a basic catalyst, and acetaldehyde is formed by gamma ray irradiation of CH3OH [7]. These substances were confirmed in gamma irradiated samples of this study. Therefore, it is possible that 2-deoxyribose was produced in this study by the reaction similar to that in the previous study [9].
From the above, it is considered that the formation of 2-deoxyribose requires a basic catalyst and gamma rays for the formation of acetaldehyde. This reaction may have occurred inside the meteorite parent bodies, and 2-deoxyribose may have been formed along with ribose, which may have been transported to the Earth and became the building blocks for life.
References
[1] Z. Iqbal et al., Curr. Org. Chem., 2012, 16, 769−788.
[2] Y. Furukawa et al., PNAS, 2019, 116, 24440-24445.
[3] S. Abe et al., ACS Earth Space Chem., 2024, 8, 1737–1744.
[4] C. Ono et al., Astrobiology, 2024, 24, 489-497.
[5] G. Cooper et al., Nature, 2001, 414, 879-883.
[6] A. Brearley, In Meteorites and the Early Solar System II, 2006, 587-624.
[7] Y. Kebukawa et al., ACS Cent. Sci., 2022, 8, 1664-1671.
[8] A. López-Islas et al., Int. J. Astrobiol., 2018, 18, 420-425.
[9] J. Oró and A. C. Cox, Fed. Proc., 1962, 21, 80.
It is important to consider the origin of amino acids (the building blocks of protein), sugars and nucleobases (the building blocks of RNA and DNA) in order to reveal the chemical evolution of life. Formose-type reaction [1,2] is attracted as a prebiotic sugar formation reaction. Ribose, the building blocks of RNA, has been mainly investigated because of the RNA World hypothesis and has synthesized under various conditions along with other aldoses [3,4]. However, 2-deoxyribose, the building blocks of DNA, was not been synthesized by heat-induced formose-type reaction using HCHO or CH3OH as a carbon source.
Sugars have been detected in some meteorites [2,5] along with amino acids and nucleobases. Thus, there is a possibility that these biologically essential substances formed in extraterrestrial environments were delivered to the early Earth by meteorites, comets or interplanetary dust particles. Meteorite parent bodies are considered to be one of the possible sites where formose-type reaction occurred. Since (i) it is considered that radiations such as gamma-rays or radioactive decay heat [6] could be an energy source, and (ii) aldehydes, starting material of formose-type reaction, were expected to be existed. Previous studies showed the effects of gamma-rays on the formation of sugars [3] and amino acids [7].
We have shown the usefulness of gamma-rays for sugar formation. The gamma-rays caused radical reactions and produced glycolaldehyde [8], the rate-limiting step in the formose reaction. In this study, we verified the formation of 2-deoxyribose by gamma-ray-induced formose-type reaction.
Experimental
To simulate aqueous alteration inside the meteoric parent bodies, many mixtures of HCHO, CH3OH and H2O were prepared. NH3 or Ca(OH)2 were added to some of them as a base catalyst. These samples (300 μL) were gamma-irradiated (60Co source, Institute of Science Tokyo, total dose: ~90 kGy), then, aliquots (200 μL) were analyzed using gas-chromatography mass spectrometry (GC/MS) after aldnonitrile acetate ester derivatization [3]. Hereafter, these samples are called γ-FMW (HCHO+CH3OH+H2O), γ-FMAW (HCHO+CH3OH+NH3+H2O) and γ-FMCW (HCHO+CH3OH+Ca(OH)2+H2O). These samples were mixed in the following molar ratios; the case of FMW, HCHO : CH3OH : H2O = 5 : 0.83 : 100, the case of FMAW, HCHO : CH3OH : NH3 : H2O = 5 : 0.83 : 1 : 100, the case of FMCW, Approximately 3 mg of Ca(OH)2 was added to a FMW sample (300 μL). We also prepared heated samples (h-FMW, h-FMAW, h-FMCW) as controls, and analyzed them by same procedures. Furthermore, the formation of acetaldehyde was verified for all samples by reversed-phase analysis using the 2,4-dinitrophenylhydrazine (DNPH) derivatization methods.
Results and Discussion
2-deoxyribose was formed in γ-FMAW and γ-FMCW, in addition, a possible isomer of 2-deoxyribose was confirmed. On the other hand, 2-deoxyribose was not formed in γ-FMW and all heated samples.
It has been tentatively suggested that 2-deoxyribose is formed by heating (50℃) an aqueous solution of glyceraldehyde (or formaldehyde) and acetaldehyde in the presence of CaO [9]. It has also been shown that glyceraldehyde is formed by formose-type reaction [3] promoted by a basic catalyst, and acetaldehyde is formed by gamma ray irradiation of CH3OH [7]. These substances were confirmed in gamma irradiated samples of this study. Therefore, it is possible that 2-deoxyribose was produced in this study by the reaction similar to that in the previous study [9].
From the above, it is considered that the formation of 2-deoxyribose requires a basic catalyst and gamma rays for the formation of acetaldehyde. This reaction may have occurred inside the meteorite parent bodies, and 2-deoxyribose may have been formed along with ribose, which may have been transported to the Earth and became the building blocks for life.
References
[1] Z. Iqbal et al., Curr. Org. Chem., 2012, 16, 769−788.
[2] Y. Furukawa et al., PNAS, 2019, 116, 24440-24445.
[3] S. Abe et al., ACS Earth Space Chem., 2024, 8, 1737–1744.
[4] C. Ono et al., Astrobiology, 2024, 24, 489-497.
[5] G. Cooper et al., Nature, 2001, 414, 879-883.
[6] A. Brearley, In Meteorites and the Early Solar System II, 2006, 587-624.
[7] Y. Kebukawa et al., ACS Cent. Sci., 2022, 8, 1664-1671.
[8] A. López-Islas et al., Int. J. Astrobiol., 2018, 18, 420-425.
[9] J. Oró and A. C. Cox, Fed. Proc., 1962, 21, 80.