Pyrazolo [3, 4-flquinazolin-9-one (prox-benzoisoallopurinol, I), an extended analogue of 7- hydroxypyrazolo-[4, 3-d] pyriinidine (isoallopurinol, 2) and a potential dimensional probe for substrates of xanthine oxidase, has been synthesized by two independent routes. The title compound, prepared by elaboration of either a suitably substituted indazole or a quinazolinone, was found to be an active substrate for and an alternative-substrate ...