Regioselective Synthesis of Indazole N- and N2-(b-D-Ribonucleosides)y

The regioselective synthesis of 4-nitroindazole Nand N-(b-D-ribonucleosides) (8, 9, 1b and 2b) is described. The N-regioisomers are formed under thermodynamic control of the glycosylation reaction [fusion reaction or Silyl Hilbert-Johnson glycosylation for 48 h (66%)], while the kinetic control (Silyl Hilbert-Johnson glycosylation for 5 h) afforded only the N-isomer (64%). The structures of the nucleosides 1b and 2b were assigned by single crystal X-ray analyses. The 4-aminoN-(b-D-ribofuranosyl)-1H-indazole (3b) was obtained from the nitro nucleoside 1b by catalytic hydrogenation. Compound 3b shows fluorescence while the 4nitroindazole nucleosides 1b and 2b do not possess this property.