Synthesis and cardiotonic activity of pyrazolylpyrimidines

A series of pyrazolylpyrimidines was prepared by the reaction of hydrazinopyrimidines and pyrimidinecarbohydrazides with acetylacetone, and was screened for cardiotonic activity in papillary muscles and atrium of guinea-pig hearts. Many of these compounds were found to be active, and 2-(4,5-dimethyl-pyrazol-1-yl)-4-thioxo-6-methyl-4 H-pyrimidine (1c), 2-methylthio-pyrimidine-4-yl-hydroxyacet-(5-hydroxy-3,5-dimethyl)- 1-5 H-pyrazolide (7a) and 2-methylthio-4-oxo-4 H-pyrimidine-3-yl-acet-(5-hydroxy-3,5-dimethyl)-1-5 H-pyrazolide (7b) showed the most positive-inotropic effects. The ED50 values are close to those of milrinone.