The Synthesis and Conformation of 2'- and 3'-Hypermodified Tricyclic Nucleosides and Their Use in the Synthesis of Novel 2'- or 3'-Isomeric 4(7)-Substituted Isoxazolidine-nucleosides

Article abstract of DOI:10.1016/S0040-4020(01)85027-4

Intramolecular 1,3-dipolar cycloaddition reactions of a number of C-alkenyl nitrones of nucleoside derivatives 7, 9, 19 and 28 afforded 2'- and 3'-hypermodified tricyclic nucleoside derivatives 10 (56percent), 11 (43percent), 20 (91percent) and 29 (75percent), respectively.The solution structures of these tricyclic nucleoside derivatives have been investigated using the ³J_HH (1H at 500 MHz) and the NMR-derived torsion angle constrained energy minimizations with the aid of MacroModel's AMBER force field.Subsequent Tamao oxidation of the hypermodified nucleoside derivatives 20 and 29 gave spiro-4(7)-substituted isoxazolidine-nucleoside derivatives 21 and 30, respectively.