Magnesium Ion Catalyzed P-N Bond Hydrolysis in Imidazolide-Activated Nucleotides. Relevance to Template-Directed Synthesis of Polynucleotides

Article abstract of DOI:10.1021/ja00200a053

Magnesium, an ion necessary in enzymatic as well as in nonenzymatic template-directed polynucleotide-synthesizing reaction, has been found to catalyze the hydroxide ion attack on the P-N bond of selected 5'-monophosphate imidazolide derivatives of nucleotides, such as guanosine 5'-monophosphate 2-methylimidazolide (2-MeImpG), guanosine 5'-monophosphate imidazolide (ImpG), and adenosine 5'-monophosphate 2-methylimidazolide (2-MeImpA).Calcium ion behaves similarly, but quantitatively the effects are smaller.Pseudo-first-order rate constants of 2-MeImpG and ImpG hydrolysis as a function of Mg(2+) concentration have been obtained in the range 6 +/-, imidazolide moiety protonated) with OH(1-) rather than reaction of the anionic form (S(1-), imidazolide moiety deprotonated) with water.This conclusion is based on a study of the N-methylated substrates N-MeImpG and 1,2-diMeImpG, respectively, which were generated in situ by the equilibrium reaction of ImpG with N-methylimidazole and 2-MeImpG with 1,2-dimethylimidazole, respectively.In contrast, in the absence of Mg(2+) the reaction of S(1-) with water competes with the reaction of SH^+/- with OH(1-).The present study bears on the mechanism of the Mg(2+)-catalyzed template-directed synthesis of oligo- and polynucleotides derived from 2-MeImpG and on thecompetition between oligonucleotide synthesis and hydrolysis of 2-MeImpG.