Regioselective Synthesis of Indazole N¹‐ and N²‐(β‐d‐Ribonucleosides)

Abstract

The regioselective synthesis of 4‐nitroindazole N ¹‐ and N ²‐(β‐d‐ribonucleosides) (8, 9, 1b and 2b) is described. The N ¹‐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 ²‐isomer (64%). The structures of the nucleosides 1b and 2b were assigned by single crystal X‐ray analyses. The 4‐amino‐N ¹‐(β‐d‐ribofuranosyl)‐1H‐indazole (3b) was obtained from the nitro nucleoside 1b by catalytic hydrogenation. Compound 3b shows fluorescence while the 4‐nitroindazole nucleosides 1b and 2b do not possess this property.

^†In honor and celebration of the 70th birthday of Professor Leroy B. Townsend.

Keywords:

• Glycosylation
• 4‐Nitroindazole
• Ribonucleosides
• Flourescence
• Regioselectivity

Acknowledgments

The authors thank Dr. H. Rosemeyer and Dr. Y. He for the measurement of the ¹H‐ and ¹³C‐NMR spectra. We gratefully acknowledge financial support by the European Community (grant no.: QLRT‐2001‐00506, “Flavitherapeutics”).

Notes

^†In honor and celebration of the 70th birthday of Professor Leroy B. Townsend.