New Chiral Nitrones in the Synthesis of Modified Nucleosides

Abstract

New chiral nitrones 7 and 12, easily prepared from d-xylose by multistep synthetic routes, undergo regioselective 1,3-dipolar cycloadditions with N-vinylated bases (uracil, adenine) giving isoxazolidinyl nucleosides in good yields. Attack of the dipolarophile on the Z-configuration of the nitrone through exo and endo transition states from the si face of nitrone (C-1′/C-3 erythro) affords C-3/C-5 cis (exo) and C-3/C-5 trans (endo) isoxazolidines as two major isomers.