Direct C-8 Lithiation of Naturally-Occurring Purine Nucleosides. A Simple Method for the Synthesis of 8-Carbon-Substituted Purine Nucleosides

Abstract

The sugar moiety of adenosine, inosine, or guanosine was protected with a tert-butyldimethylsilyl group. The C-8 lithiation of these protected nucleosides was carried out with lithium diisopropylamide in tetrahydrofuran at below -70°C. The reactions of the C-8-lithiated species with MeI, HCO₂Me, and ClCO₂Me were examined. The resulting products having a carbon substituent at the C-8 position were converted to the corresponding 8-carbon-substituted purine nucleosides by treatment with tetrabutylammonium fluoride. The whole sequence constitutes a simple method for the preparation of 8-carbon-substituted purine nucleosides from intact purine nucleosides.