Guanosine-methyldiazonium ion reaction: Variation of methylation product patterns with reaction variables

Abstract

Variations of the methylation product patterns in methyldiazonium ion ( CH 3− N + ≡N ) methylation of nucleic acids may be related to the varied biological effects of nine methylating carcinogens. However, there was no such demonstration of variation of product patterns for the same methylating agent and base residue with reaction variables. We have now shown for the first time in a systematic manner that the methylation product patterns of the guanosine-methyldiazonium ion reaction are sensitive to the effects of medium, polarity, temperature, salt addition, stoichiometry and pH. The percent yields of methylation at the nitrogen, oxygen, and carbon sites were determined, achieving material balance of >95%. The major products were 1-methyl, the O 6-methyl and the 7-methylguanosine. The yields of 7-methylguanosine have been adjusted for 1,7-dimethylguanosine, a secondary methylation product, as well as ring-opened products from 7-methylguanosine and 1,7-dimethylguanosine. The different methylation patterns plotted as O : N ratios of % yields of the three major products, e.g. the O 6 : N 7 product ratios ranging from a high of 1.6 ( methanol ether medium ) to the low limit of 0.2–0.0 (aqueous), indicate the likelihood that the methylation product pattern of the guanine residue in a nucleic acid will also be dictated by the reaction conditions of the CH 3− N + ≡N attack.