Homochiral Selectivity in RNA Synthesis: Montmorillonite-catalyzed Quaternary Reactions of D, L-Purine with D, L- Pyrimidine Nucleotides

• Published in: Origins of life and evolution of biospheres Vol. 41; no. 3; pp. 213 - 236
• Main Authors: Joshi, Prakash C., Aldersley, Michael F., Ferris, James P.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-06-2011; Springer Nature B.V
• Subjects: Astronomy; Astrophysics and Astroparticles; Bentonite - chemistry; Biochemistry; Biomedical and Life Sciences; Biosynthesis; Catalysis; Catalysts; Chemical reactions; Chemistry; Chromatography, High Pressure Liquid; Earth Sciences; Enantiomers; Hydrolysis; Isomerism; Life Sciences; Liquid chromatography; Models, Molecular; Montmorillonite; Nucleotides; Observations and Techniques; Oligomers; Phosphorylation; Prebiotic Chemistry; Purine Nucleotides - chemistry; Pyrimidine Nucleotides - chemistry; Ribonucleic acid; RNA; RNA - chemical synthesis; Space life sciences; Transcription; Trimers; Catalysis; Prebiotic chemistry; Montmorillonite; Homochirality; RNA world
• ISSN: 0169-6149; 1573-0875
• DOI: 10.1007/s11084-010-9222-1

Selective adsorption of D, L-ImpA with D, L-ImpU on the platelets of montmorillonite demonstrates an important reaction pathway for the origin of homochirality in RNA synthesis. Our earlier studies have shown that the individual reactions of D, L-ImpA or D, L-ImpU on montmorillonite catalyst produced oligomers which were only partially inhibited by the incorporation of both D- and L-enantiomers. Homochirality in these reactions was largely due to the formation of cyclic dimers that cannot elongate. We investigated the quaternary reactions of D, L-ImpA with D, L-ImpU on montmorillonite. The chain length of these oligomers increased from 9-mer to 11-mer as observed by HPLC, with a concominant increase in the yield of linear dimers and higher oligomers in the reactions involving D, L-ImpA with D, L-ImpU as compared to the similar reactions carried out with D-enantiomers only. The formation of cyclic dimers of U was completely inhibited in the quaternary reactions. The yield of cyclic dimers of A was reduced from 60% to 10% within the dimer fraction. 12 linear dimers and 3 cyclic dimers were isolated and characterized from the quaternary reaction. The homochirality and regioselectivity of dimers were 64.1% and 71.7%, respectively. Their sequence selectivity was shown by the formation of purine-pyrimidine (54–59%) linkages, followed by purine-purine (29–32%) linkages and pyrimidine-pyrimidine (9–13%) linkages. Of the 16 trimers detected, 10 were homochiral with an overall homochirality of 73–76%. In view of the greater homochirality, sequence- and regio- selectivity, the quaternary reactions on montmorillonite demonstrate an unexpectedly favorable route for the prebiotic synthesis of homochiral RNA compared with the separate reactions of enantiomeric activated mononucleotides.