Synthesis of 3-(β-D-ribofuranosyl)pyrazolo[3,2-i]-purine derivatives and their cytotoxic activities

9-Amino-3-(β-D-ribofuranosyl)pyrazolo[3,2-i|purine (6) has been prepared from a fully protected 3-(β-D-ribofuranosyl)pyrazolo[3,2-i]purine (2) and the 9-bromo substituted derivative 3 by nitration, followed by reduction. Reaction of 9-bromo-3-(β-D-ribofuranosyl)pyrazolo[3,2-i)purine (1b) with alkali gave the (pyrazol-3-yl)imidazole derivative, followed by diazocyclization with sodium nitrate to give 9-bromo-3-(β-D-ribofuran-osyl)imidazolo[4,5-d]pyrazolo[2,3-c][1,2,3]triazine (10) after deacetylation. Compounds 6 and 10 exhibited cytotoxic activity against leukemia cells.