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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 Viagra® (1), are described. The generally applicable route involves interaction of 2,3-dihydro-7-benzofuranoyl chloride (3) with 4-amino-l-methyl-3-propyl-5-pyrazolecarboxamide (4), and the resulting bis-amide (5) is cyclized to the corresponding substituted pyrazolo[4,3-d]pyrimidin-7-one (6). Chlorosulfonylation of 6, followed by treatment with 1-methylpiperazine, furnished the title compound 2 (named Biagra). Preliminary experiments “associated with the erectile process” on rats lend evidence of greater potency of Biagra (2) as compared to Viagra® (1).

Synthesis and Properties of Biagra . A 5-(2,3-Dihydro-7-benzofuryl) Analog of Viagra®