Methylation of adenosine in strongly alkaline medium: Preparation and Properties of o'-methyl derivatives of adenosine and N6-methyladenosine.

In strongly alkaline aqueous medium, 9-substituted adenines, including adenine nucleosides, are relatively resistant to alkylation of the ring nitrogens and the exocyclic amino group. This fact was utilized to obtain the various possible Omicron'-methyl derivatives of adenosine by dimethyl sulfate treatment of the latter in alkaline medium, followed by separation of the products on a Dowex OH-column. In strongly alkaline aqueous dimethyl sulfoxide, several derivatives additionally methylated on the amino group were obtained, including N6,O2'-dimethyladenosine, a component located recently at the 5' terminus of animal cell and viral mRNAs. The latter was also prepared by diazomethane methylation of N6-methyladenosine in the presence of SnCl2. Alkylation in alkaline medium possesses the advantage that the products are not limited to those involving etherification of cis hydroxyls and is applicable to adenine nucleosides with sugar components other than ribose. The properties of the various O'-methylderivatives, including proton magnetic resonance data, are presented in detail.