Diastereoselective synthesis of N,O-psiconucleosides, a new class of modified nucleosides

Anomeric alpha- and beta-N,O-psiconucleosides were prepared by 1,3-dipolar cycloaddition of C-ethoxycarbonyl N-methyl nitrone with ethyl 2-acetyloxyacrylate, followed by Vorbrüggen nucleosidation. The synthetic scheme has been applied to all purine and pyrimidine nucleobases. Nucleosidation can proceed under kinetic and under thermodynamiccontrol; under thermodynamic control conditions only beta-nucleosides are obtained for pyrimidine derivatives and alpha-nucleosides for purine derivatives.