Regioselective glycosylation of 7-azapteridines and conversion of the 7-azapteridine nucleosides into 6-azapurine nucleosides

Abstract

The regioselective glycosylation of reumycins (3) reacted with 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranose (4) and BSTFA in acetonitrile at 90 degrees C followed by reaction of SnCl(4) in dioxane at room temperature afforded the 1-(2',3',5'-tri-O-benzoyl-beta-D-ribofuranosyl)- 6-methylpyrimido[5,4-e][1,2,4]triazine-5,7(1H,6H)-diones (5) (toxoflavin type nucleosides), while the similar alkylations with 1-bromo-2,3,5-tri-O-benzoyl-beta-D-ribofuranose (6) and KHCO(3) in DMF at 100 degrees C gave predominantly the 8-(2',3',5'-tri-O-benzoyl-beta-D-ribofuranosyl)-6-methylpyrimido[5,4-e]-[1,2,4]triazine-5,7(6H,8H)-diones (7) (fervenulin type nucleosides). On the other hand, treatment of the 7-azapteridine nucleosides (5 and 7) in alkali solution at room temperature yielded the corresponding 1-(beta-D-ribofuranosyl)-5-methyl-1H-imidazo[4,5-e][1,2,4]- triazin-6(5H)-ones (8) and 7-(beta-D-ribofuranosyl)-5-methyl-5H-imidazo[4,5-e][1,2,4]triazin-6(7H)-ones (9) [6-azapurine nucleosides] by benzilic acid rearrangement. Some 7-azapteridine nucleosides (5 and 7-9) showed antitumor activities and anti-coccidiosis activities.