A convenient synthesis of pyrazolo[3,4-b]pyridine nucleosides by convenient ring-closure procedures. X-Ray crystal and molecular structure of 4-amino-1 -(β-D-ribofuranosyl)-1,7-dihydropyrazolo[3,4-b]pyridin-6-one

Abstract

Practical syntheses of 1-(β-D-ribofuranosyl)pyrazolo[3,4-b]pyridines as purine antagonists, related to isoguanosine, guanosine, and xanthosine, are described for the first time. Ethyl 5-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazole-4-carboxylate (10) was converted into 5-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazole (12), which was in turn converted into 6-amino-1-(β-D-ribofuranosyl)-1,7-dihydropyrazolo[3,4-b]pyridin-4-one (4) in four steps, 4-Amino-1-(β-D-ribofuranosyl)-1,7-dihydropyrazolo[3,4-b]pyridin-6-one (3) was obtained in satisfactory overall yield from compound (12), prepared in four steps via a ring-closure procedure. The structure of compound (3) was established by a single-crystal X-ray study. 4-Hydroxy-1-(β-D-ribofuranosyl)-1,7-dihydropyrazolo[3,4-b]pyridin-6-one (5) was obtained in three steps from the ester (10).