New 2,3-substituted 4,7-dihydro-6-(1'H-pyrazol-3'-yl)pyrazolo[1,5-a] pyrimidin-7-ones and related compounds: synthesis and benzodiazepine receptor binding study.

The reaction between two series of 7-dimethylaminovinyl pyrazolo[1,5-a]pyrimidines 4(a-r) 7a, 7d, 7f, 7(h-j) and hydrazine in acetic acid is investigated. The structure of 4,7-dihydro-6-(1'H-pyrazol-3'-yl)pyrazolo[1,5-a]pyrimidin-7- ones 5(a-r) and 7-methyl-6-(1'H-pyrazol-3'-yl)pyrazolo[1,5-a]pyrimidines 8a, 8d, 8f, 8(h-j) are attributed to the isolated products and the pathway of this reaction is suggested. The in vitro benzodiazepine receptor (BzR) affinity of the title compounds are determined by testing their ability to displace 3H-flunitrazepam from its specific binding in bovine brain membranes. The IC50 and GABA (gamma-aminobutyric acid) ratio values give valuable indications about affinity and behavioural profile of these new BzR ligands. Included in this investigation are indicated several structure-affinity relationships of the title compounds.