Modified dideoxynucleosides: Synthesis of 2'-N-alkyl-3'- hydroxyalkyl-1',2'-isoxazolidinyl thymidine and 5-fluorouridine derivatives

Isoxazolidine nucleosides bearing an hydroxyl group at C3, have been prepared in only three steps, with overall high yields. The synthetic approach is based on the 1,3-dipolar cycloaddition of 3- carboxyakyl- or acylnitrones to vinyl acetate, followed by condensation with silylated thymine or 5-fluorouracil and NaBH4 reduction.