Synthesis and properties of Biagra. A 5-(2,3-dihydro-7-benzofuryl) analog of Viagra((R))

The synthesis and spectral properties (IR, MS, NMR) of a substituted 5-(2,3 -dihydro-7-benzofuryl)pyrazolo[4,3-d]pyrimidin-7-one (2); an analog of Viag ra(R) (1), are described. The generally applicable route involves interacti on of 2,3-dihydro-7-benzofuranoyl chloride (3) with 4-amino-1-methyl-3-prop yl-5-pyrazolecarboxamide (4), and the resulting bis-amide (5) is cyclized t o the corresponding substituted pyrazolo[4.3-d]pyrimidin-7-one (6). Chloros ulfonylation of 6, followed by treatment with l-methylpiperazine. furnished the title compound 2 (named Biagra). Preliminary experiments "associated w ith the erectile process" on rats lend evidence of greater potency of Biagr a (2) as compared to Viagra(R) (1).