2-arylpyrazolo[1,5-a]pyrimidin-3-yl acetamides. New potent and selective peripheral benzodiazepine receptor ligands

A new class of N,N-diethyl-(2-arylpyrazolo[1,5-a]pyrimidin-3-yl)acetamides (3f-y), as azaisosters of Alpidem, was prepared following a novel synthetic method and their affinities for both the peripheral (PBR) and the central (CBR) benzodiazepine receptors were evaluated. Binding assays were carried out using both [H-3]PK 11195 and [H-3]Ro 5-4864 as radioligands for PBR, wh ereas [H-3]Ro 15-1788 was used for CBR, in rat kidney and rat cortex, respe ctively. The tested compounds exhibited a broad range of binding affinities from as low as 0.76 nM to inactivity and most of them proved to be high se lective ligands for PBR. The preliminary SAR studies suggested some of the structural features required for high affinity and selectivity; particularl y the substituents on the pyrimidine moiety seemed to play an important rol e in PBR versus CBR selectivity. A subset of the highest affinity compounds was also tested for their ability to stimulate steroid biosynthesis in C6 glioma rat cells and some of these were found to increase pregnenolone form ation with potency similar to Ro 5-4864 and PK 11195. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.