Oligomerization reactions of ribonucleotides: The reaction of the 5′ -phosphorimidazolide of adenosine with diadenosine pyrophosphate on montmorillonite and other minerals

Abstract

The reaction of the 5′ -phosphorimidazolide of adenosine (5′-ImpA) with diadenosine pyrophosphate (A5′ppA) in the presence of Na+-montmorillonite in aqueous, pH 8 solution results in the regiospecific formation of A5′ppA3′pA and A5ppA3′pA3′ pA. The formation of oligomers of general structure (pA)n decreases in the presence of A5′ppA. A5′ppA3′pA is the principal reaction product when a 1:1 ratio of ImpA and A5′ppA is used. The yield of A5′ppA3′pA3′pA is optimal when 9:1 or 4:1 ratios of ImpA: A5′ppA are used. The overall regiospecificity of formation of 3′,5′-links is about 80%. The reaction between ImpA and A5′ppA on montmorillonite differs from the self-condensation of ImpA in that it proceeds in the absence of Mg2+ and there are only small differences in oligomer yields when Na+, Li+ Ca2+, and NH4+ are the exchangeable cations on the montmorillonite. The reaction is inhibited by 0.4 M imidazole but the inhibition is suppressed with 0.4 M Mg2+. Little or no phosphodiester bond formation was observed with Mg2+- or Al3+-montmorillonite. Montmorillonites other than 22A and Volclay exhibited no catalysis for the formation of adducts between ImpA and A5′ppA and no catalysis was exhibited in ferrugenous smectite, nontronite, allophane, or sepiolite.