Diastereoselective synthesis of D-xylo-isoxazolidinyl nucleosides

The condensation of the acetoxyisoxazolidines with silylated uracil, thymine, cytosine, N-acetylcytosine, and guanine proceeded in good yields and with moderate to good stereoselectivity to give isoxazolidinyl beta- and alpha-nucleosides. The stereoselectivity of the addition is dependent on the structure of the substituent at C-3 originating from the starting chiral nitrone. The Vorbruggen nucleosidation of isoxazolidine 8 at 70 degrees C afforded beta-anomers as the exclusive nucleosides together with the isoxazoline 11. It was found that the nucleosidation proceeded also in methylene chloride at room temperature. (c) 2008 Elsevier Ltd. All rights reserved.