Synthesis of 2,3-dideoxy-2-fluoro-2,3-endo-methylene- and 2,3-Dideoxy-2-fluoro-3-C-hydroxymethyl-2,3-endo-methylene-pentofuranoses and their use in the preparation of conformationally locked bicyclic nucleosides.

Construction of protected 2,3-dideoxy-2-fluoro-2,3-endo-methylene-pentofuranoses from d-glyceraldehyde and 2,3-dideoxy-2-fluoro-3-C-hydroxymethyl-2,3-endo-methylene-pentofuranoses from d-isoascorbic acid, via Simmons-Smith-type stereoselective cyclopropanations on the respective fluoroallyl alcohols, is described. Synthesis of the corresponding conformationally locked sugar modified uridine and guanosine nucleosides was achieved via Vorbrüggen or Mitsunobu methodologies. Stereochemical confirmation of the novel nucleosides was performed on the basis of 2D NOESY NMR experiments.