Fabrizio Bruni

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 [3H]PK 11195 and [3H]Ro 5-4864 as radioligands for PBR, whereas [3H]Ro 15-1788 was used for CBR, in rat kidney and rat cortex, respectively. 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 selective ligands for PBR. The preliminary SAR studies suggested some of the structural features required for high affinity and selectivity; particularly the substituents on the pyrimidine moiety seemed to play an important role 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 formation with potency similar to Ro 5-4864 and PK 11195.

Pyrazolo[1,5-a]pyrido[3,4-e]pyrimidine : a new heterocyclic ring system

Treatment of 6-acetyl-7-(2-dimethylaminovinyl)pyrazolo[1,5a]pyrimidine (1) with hydroxylamine afforded in high yields the pyridine N-oxide (2), a key intermediate in the preparation of new functionalized pyrazolo[1,5-a]pyrido[3,4e]pyrimidine as well as in the synthesis of the parent ring system (8)

New Fluoro Derivatives of the Pyrazolo[5,1-c][1,2,4]benzotriazine 5-Oxide System: Evaluation of Fluorine Binding Properties in the Benzodiazepine Site on γ-Aminobutyrric Acid Type A (GABAA) Receptor. Design, Synthesis, Biological, and Molecular Modeling Investigation

In the search for potent ligands at the benzodiazepine site on the GABA(A) receptor, new fluoro derivatives of the pyrazolo[5,1-c][1,2,4]benzotriazine system were synthesized to evaluate the importance of the introduction of a fluorine atom in this system. Biological and pharmacological studies indicate that the substitution at position 8 with a trifluoromethyl group confers pharmacological activity due to potential metabolic stability in comparison to inactive 8-methyl substituted analogues. In particular, the compound 3-(2-methoxybenzyloxycarbonyl)-8-trifluoromethylpyrazolo[5,1-c][1,2,4]benzotriazine 5-oxide (21) emerges because of its selective anxiolytic profile without side effects. An analysis of all the newly synthesized compounds in our pharmacophoric map confirms the essential interaction points for binding recognition and the important areas for affinity modulation. The fluorine atom was able to form a hydrogen bond interaction only when it is not in position 3.

Benzodiazepine receptor ligands. Synthesis and pharmacological evaluation of 3-, 7- and 8-substituted [5,1-c][1,2,4]benzotriazines and 5-oxide derivatives. Part I

Summary A new series of 3-, 7- and 8-substituted pyrazolo[5,1-c][1,2,4]benzotriazine 5-oxides and a series of pyrazolo[5,1- c ] [1,2,4]benzotriazines were synthesized and their benzodiazepine receptor affinities were evaluated in vitro. A study of structureaffinity relationships within the series is briefly discussed, considering the role of various substituents at the 3-, 7- and 8-positions and the role of N 5 -oxide. Compounds 1b, 1c, 1cR, 4c, 4cR, 9d, 12d and 12dR were evaluated in vivo for their anticonvulsant effects.

A new entry to pyrazolo[1,5-a]pyrido[3,4-e]pyrimidine derivatives

Treatment of 3-aminopyrazoles derivatives with 3-ethoxymethylenpentane-2,4-dione afforded new pyrazol[1,5-a]pyrimidines derivatives which were then converted into enamines by reaction with dimethylformamide dimethyl acetal; ring closure of these latter compounds led to pyrazolo[1,5-a]pyrido[3,4-e]pyrimidines

Synthesis and BZR affinity of pyrazolo[1,5-a]pyrimidine derivatives. Part 1: study of the structural features for BZR recognition

Examination of the pharmacophoric points of the pyrazolo[1,5-a]pyrimidine derivatives, ligands for BZR, previously published led us to the design of a novel class of 3,6-diaryl-4,7-dihydro-pyrazolo[1,5-a]pyrimidin-7-ones and to determine the groups involved in the BZR recognition.

Synthesis, in Vivo Evaluation, and Molecular Modeling Studies of New Pyrazolo[5,1-c][1,2,4]benzotriazine 5-Oxide Derivatives. Identification of a Bifunctional Hydrogen Bond Area Related to the Inverse Agonism

A new series of pyrazolo[5,1-c][1,2,4]benzotriazine 5-oxide 8-alkyloxy-/aryloxy-/arylalkyloxy and 8-aryl-/arylalkylderivatives variously substituted at the 3-position were synthesized and binding studies at the benzodiazepine site on GABA(A) receptor were carried out. The pharmacological profile was identified for compounds 10, 11, 16(+), 16(-), and 17 by considering six potential benzodiazepine actions: motor coordination, anticonvulsant action, spontaneous motility and explorative activity, potential anxiolytic-like effects, mouse learning and memory modulation, and finally, ethanol-potentiating action. Compound 17 stands out as the compound that improves mouse memory processes selectively, safely, and in a statistically significant manner. From a ligand-based pharmacophoric model, we identified a hydrogen bond interaction area HBp-3 near the lipophilic area. This new pharmacophoric model allowed us to identify four structural compound typologies and thus to rationalize the affinity data of all compounds.

New 3-, 8-disubstituted pyrazolo[5,1-c][1,2,4]benzotriazines useful for studying the interaction with the HBp-3 area (hydrogen bond point area) in the benzodiazepine site on the γ-aminobutyric acid type A (GABAA) receptor

The pharmacophoric model using ADLR procedure, based on pyrazolo[5,1-c][1,2,4]benzotriazine system, studied in our laboratory, allowed us to identify the essential interaction points (HBp-1, HBp-2, and Lp-1) and the important areas for affinity modulation (HBp-3 and Lp-2) for binding recognition at benzodiazepine (Bzs) site of GABA(A) receptors (GABA(A)-Rs). In this work ADLR method is used to rationalize the affinity data of 23 new compounds and to improve the knowledge on HBp-3 area, hydrogen bond area. Among these new compounds emerge the pyrrolo derivatives (18, 25, 28, 34, and 37) for their good affinity value (14.9>K(i)(nM)>63.0). In the orientations proposed by ADLR, the NH moiety of the pyrrole ring, independently of the position in the pyrazolobenzotriazine core, fits in HBp-3 area and points out the acceptor feature of this hydrogen bond area, already known as donor area. Unexpectedly, the oxygen atom of the furane ring does not form efficient hydrogen bond with the same area, probably for an imperfect distance. The size of substituent at position 8 is important but not necessary for the receptor recognition, in fact the interdependence between the features of the 3- and 8-substituents is again verified, (i.e., compound 20 vs 32).

Development of ligands at γ-aminobutyrric acid type A (GABAA) receptor subtype as new agents for pain relief

The identification of compounds with selective anxiolytic-like effects, exerted through the benzodiazepine site on γ-aminobutyric acid type A (GABA(A)) receptors, and that show pronounced antihyperalgesia in several pain models, has oriented research towards the development of new agents for the relief of pain. Starting from our previously reported ligands at the benzodiazepine site on GABA(A) receptors showing selective anxiolytic-like effects, we have designed new compounds with the aim of identifying those devoid of the typical side effects of the classical benzodiazepines. Our preliminary results indicate that compounds 4, 10(±) and 11 have a very promising antihyperalgesic profile in different animal pain models (peripheral mono-neuropathy, STZ-induced hyperalgesia). In particular 11 exhibits high potency since it exerted its protective effect starting from the dose of 3mg/kg po, after single injection.

Benzodiazepine receptor ligands — Part II. Synthesis and biological evaluation of pyrazolo[5,1-c][1,2,4]benzotriazine 4-oxide

Abstract A new series of 3-, 8-substituted pyrazolo[5,1-c][1,2,4]benzotriazine 4-oxides 3 were synthesized and their benzodiazepine receptor (BZR) affinities were evaluated in vitro in comparison with their 5-oxide isomers 2. The 4-oxide compounds 3c,m,n,o showed a better receptor affinity than their corresponding 5-oxide isomers, with an efficacy trend of antagonist/partial inverse agonist. From a structure—affinity relationship point of view some insight in the role played by N-4 and N-oxide is gained.