C-nucleoside studies. Part 19. The synthesis of the β-D-xylofuranosyl analogue of formycin

Preparation of 1-(3-aminobenzo[d]isoxazol-5-yl)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-ones as potent, selective, and efficacious inhibitors of coagulation factor Xa

“…9b Readily available pyrazole ester 13 9a was efficiently and selectively nitrated at the pyrazole 4-position using excess ammonium nitrate and trifluoroacetic anhydride in TFA. 13 …”