Diastereoselective Synthesis of N,O-Psiconucleosides, a New Class of Modified Nucleosides

Anomeric α- and β-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 thermodynamic control; under thermodynamic control conditions only β-nucleosides are obtained for pyrimidine derivatives and α-nucleosides for purine derivatives