Synthesis and vasorelaxant potency of monagra. A chiral 5-(2-methyl-2,3-dihydro-7-benzofuryl)-pyrazolopyrimidone analog of viagra®

Synthesis and properties of a chiral 5-(2-methyl-2,3-dihydro-7-benzofuryl)pyrazolo[4,3-d]pyrimidin-7-one (3), an analog of Viagra® (1) and Biagra (2), are described. The key material, (±)-3-methyl-2,3-dihydrobenzofuran-7-carboxylic acid (8a) was resolved into the (S)-8b (95% ee) and (R)-8c (99% ee) enantiomers using, respectively, (-)-cinchonidine and (+)-cinchonine. The absolute configuration of 8c was determined as R by X-Ray measurements. Preliminary in vitro experiments on rat isolated thoracic aorta show that the vasorelaxant potency of 3b,c is truly higher than that of 1 and 2.