Serotonin 5-HT6 receptor antagonists. II. Synthesis and structure—activity relationship of 3-arylsulfonyl-2-methylthiopyrazolo[1,5-a]pyrimidines with substituents containing an amine in the 6-position

3-(Arylsulfonyl)-2-(methylthio)pyrazolo[1,5-a]pyrimidines containing substituents with an amine in the 6-position were synthesized. Their structure—activity (antagonist) relationship was studied with respect to serotonin 5-HT6 receptors. It was shown that 2-(methylthio)-3-(phenylsulfonyl)- and 2-(methylthio)-3-(3-chlorophenylsulfonyl)pyrazolo[1,5-a]pyrimidin-6-amines, the activity of which was comparable with 3-(arylsulfonyl)-2-(methylamino)pyrazolo[1,5-a]pyrimidin-6-amines and 3-(arylsulfonyl)-2-(methylamino)-and 3-(arylsulfonyl)-2-(methylthio)pyrazolo[1,5-a]pyrimidin-7-amines that were reported earlier, were the most active picomolar ligands.