NUCLEIC ACID METHYLMERCURY(II) INTERACTIONS AND THE H-1-NMR LIFETIMES OF NUCLEO-BASE EXCHANGEABLE PROTONS

The kinetics and equilibria of methylmercury-adenine interactions were investigated by 1H NMR three-site line-shape analysis of the 360-MHz amino proton resonances of 2ʹ,3ʹ-cAMP. This involved consideration of an additional mercurated species and provided both a direct demonstration of aminomercuration and a measure of the rates of the forward and reverse aminomcrcuration reactions, which arc slow on the NMR time scale (~100 s−1). Similar rates were obtained by two-site line-shape analysis of the nonexchanging C2 and C8 protons of the nucleobase, confirming the amino line-shape analysis and eliminating amino-to-water exchange mechanisms other than that associated directly with the aminomcrcuration as factors in amino proton line shape. These results, together with line-shape chances induced by the addition of phosphate, are consistent with a concerted fourcenter mechanism for aminomercuration involving direct bond formation between the nucleobase amino and methyl mercuric hydroxide and water elimination. The effect of N1 mercuration of the nucleobase is several orders of magnitude less than the effect of N1-protonation in increasing the rates of aminomercuration and proton transfer. These conclusions are supported by preliminary results on the aminomercuration of 2ʹ,3ʹ-cGMP and l-methyladenosine. © 1979, American Chemical Society. All rights reserved.