Adenine derivatives as phosphate-activating groups for the regioselective formation of 3',5'-linked oligoadenylates on montmorillonite: Possible phosphate-activating groups for the prebiotic synthesis of RNA

Methyladenine and adenine N-phosphoryl derivatives of adenosine 5'-monophosphate (5'-AMP) and uridine 5'-monophosphate (5'-UMP) are synthesized, and their structures are elucidated. The oligomerization reactions of the adenine derivatives of 5'-phosphoramidates of adenosine on montmorillonite are investigated. 1-Methyladenine and 3-methyladenine derivatives on montmorillonite yielded oligoadenylates as long as undecamer, and the 2-methyladenine and adenine derivatives on montmorillonite yielded oligomers up to hexamers and pentamers, respectively. The 1-methyladenine derivative yielded linear, cyclic, and A(5')ppA-derived oligonucleotides with a regioselectivity for the 3',5'-phosphodiester linkages averaging 84%. The effect of pK(a) and amine structure of phosphate-activating groups on the montmorillonite-catalyzed oligomerization of the S-phosphoramidate of adenosine are discussed. The binding and reaction of methyladenine and adenine N-phosphoryl derivatives of adenosine are described.