Synthesis of New GABA_A Receptor Modulator with Pyrazolo[1,5-a]quinazoline (PQ) Scaffold

We previously published a series of 8-methoxypirazolo[1,5-a]quinazolines (PQs) and their 4,5-dihydro derivatives (4,5(H)PQ) bearing the (hetero)arylalkylester group at position 3 as ligands at the γ-aminobutyric type A (GABA_A) subtype receptor. Continuing the study in this field, we report here the design and synthesis of 3-(hetero)arylpyrazolo[1,5-a]quinazoline and 3-(hetero)aroylpyrazolo[1,5-a]quinazoline 8-methoxy substituted as interesting analogs of the above (hetero)arylalkylester, in which the shortening or the removal of the linker between the 3-(hetero)aryl ring and the PQ was performed. Only compounds that are able to inhibit radioligand binding by more than 80% at 10 μM have been selected for electrophysiological studies on recombinant α1β2γ2L GABA_A receptors. Some compounds show a promising profile. For example, compounds 6a and 6b are able to modulate the GABA_AR in an opposite manner, since 6b enhances and 6a reduces the variation of the chlorine current, suggesting that they act as a partial agonist and an inverse partial agonist, respectively. The most potent derivative was 3-(4-methoxyphenylcarbonyl)-8-methoxy-4,5-dihydropyrazolo[1,5-a] quinazoline 11d, which reaches a maximal activity at 1 μM (+54%), and it enhances the chlorine current at ≥0.01 μM. Finally, compound 6g, acting as a null modulator at α1β2γ2L, shows the ability to antagonize the full agonist diazepam and the potentiation of CGS 9895 on the new α+/β- 'non-traditional' benzodiazepine site.