Benzodiazepine receptor ligands. 8: synthesis and pharmacological evaluation of new pyrazolo[5,1-c] [1,2,4]benzotriazine 5-oxide 3- and 8-disubstituted: high affinity ligands endowed with inverse-agonist pharmacological efficacy

Functional Selectivity and Antinociceptive Effects of a Novel KOPr Agonist

Kappa opioid receptor (KOPr) agonists represent alternative analgesics for their low abuse potential, although relevant adverse effects have limited their clinical use. Functionally selective KOPr agonists may activate, in a pathway-specific manner, G protein-mediated signaling, that produces antinociception, over β-arrestin 2-dependent induction of p38MAPK, which preferentially contributes to adverse effects. Thus, functionally selective KOPr agonists biased toward G protein-coupled intracellular signaling over β-arrestin-2-mediated pathways may be considered candidate therapeutics possibly devoid of many of the typical adverse effects elicited by classic KOPr agonists. Nonetheless, the potential utility of functionally selective agonists at opioid receptors is still highly debated; therefore, further studies are necessary to fully understand whether it will be possible to develop more effective and safer analgesics by exploiting functional selectivity at KOPr. In the present study we investigated in vitro functional selectivity and in vivo antinociceptive effects of LOR17, a novel KOPr selective peptidic agonist that we synthesized. LOR17-mediated effects on adenylyl cyclase inhibition, ERK1/2, p38MAPK phosphorylation, and astrocyte cell proliferation were studied in HEK-293 cells expressing hKOPr, U87-MG glioblastoma cells, and primary human astrocytes; biased agonism was investigated via cAMP ELISA and β-arrestin 2 recruitment assays. Antinociception and antihypersensitivity were assessed in mice via warm-water tail-withdrawal test, intraperitoneal acid-induced writhing, and a model of oxaliplatin-induced neuropathic cold hypersensitivity. Effects of LOR17 on locomotor activity, exploratory activity, and forced-swim behavior were also assayed. We found that LOR17 is a selective, G protein biased KOPr agonist that inhibits adenylyl cyclase and activates early-phase ERK1/2 phosphorylation. Conversely to classic KOPr agonists as U50,488, LOR17 neither induces p38MAPK phosphorylation nor increases KOPr-dependent, p38MAPK-mediated cell proliferation in astrocytes. Moreover, LOR17 counteracts, in a concentration-dependent manner, U50,488-induced p38MAPK phosphorylation and astrocyte cell proliferation. Both U50,488 and LOR17 display potent antinociception in models of acute nociception, whereas LOR17 counteracts oxaliplatin-induced thermal hypersensitivity better than U50,488, and it is effective after single or repeated s.c. administration. LOR17 administered at a dose that fully alleviated oxaliplatin-induced thermal hypersensitivity did not alter motor coordination, locomotor and exploratory activities nor induced pro-depressant-like behavior. LOR17, therefore, may emerge as a novel KOPr agonist displaying functional selectivity toward G protein signaling and eliciting antinociceptive/antihypersensitivity effects in different animal models, including oxaliplatin-induced neuropathy.

Synthesis, crystal structure and Hirshfeld surface analysis of 3-(4,4-dimethyl-2,3,4,5-tetra-hydro-1H-1,5-benzodiazepin-2-yl-idene)-6-methyl-3,4-di-hydro-2H-pyran-2,4-dione

The title compound, C17H18N2O3, is constructed from a benzodiazepine ring system linked to a pendant di-hydro-pyran ring, where the benzene and pendant di-hydro-pyran rings are oriented at a dihedral angle of 15.14 (4)°. Intra-molecular N-HDiazp⋯ODhydp and C-HDiazp⋯ODhydp (Diazp = diazepine and Dhydp = di-hydro-pyran) hydrogen bonds link the seven-membered diazepine ring to the pendant di-hydro-pyran ring, enclosing S(6) ring motifs. In the crystal, N-HDiazp⋯ODhydp hydrogen bonds link the mol-ecules into infinite chains along [10]. These chains are further linked via C-HBnz⋯ODhydp, C-HDhydp⋯ODhydp and C-HMth⋯ODhydp (Bnz = benzene and Mth = meth-yl) hydrogen bonds, forming a three-dimensional network. The observed weak C-HDiazp ⋯ π inter-action may further stabilize the structure. Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (51.1%), H⋯C/C⋯H (25.3%) and H⋯O/O⋯H (20.3%) inter-actions. Hydrogen bonding and van der Waals inter-actions are the dominant inter-actions in the crystal packing.

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

The condensation of 5-aminopyrazole with various bielectrophilic moieties results in the formation of pyrazoloazines, an interesting array of fused heterocyclic systems. The development of new synthetic routes towards pyrazoloazines for their biological and medicinal exploration is an attractive area for researchers throughout the world. The present review focuses on various synthetic methods developed in the last decade for the synthesis of differently substituted pyrazoloazines by a broad range of organic reactions by means of 5-aminopyrazole as a precursor.

Novel 4-thiazolidinone derivatives as agonists of benzodiazepine receptors: Design, synthesis and pharmacological evaluation

A new series of 4-chloro-N-(2-(substitutedphenyl)-4-oxothiazolidin-3-yl)-2-phenoxybenzamide derivatives were designed, synthesized and biologically evaluated as anticonvulsant agents. The designed compounds have the main essential functional groups for binding to the benzodiazepine receptors and 4-thiazolidinone ring as an anticonvulsant pharmacophore. Some of the new synthesized compounds showed considerable anticonvulsant activity in electroshock and pentylenetetrazole-induced lethal convulsion tests. Compound 5i, 4-chloro-N-(2-(4-methoxyphenyl)-4-oxothiazolidin-3-yl)-2-phenoxybenzamide, with the best activity was selected for evaluation of other benzodiazepine pharmacological effects. This compound induced significant sedative-hypnotic activity. However, it does not impair the learning and memory in the experimental condition. Flumazenil was able to antagonize the sedative-hypnotic and anticonvulsant effects of compound 5i indicating that benzodiazepine receptors are highly involved in the pharmacological properties of the novel compounds.

Design, Synthesis, and Biological Evaluation of Imidazo[1,5-a]quinoline as Highly Potent Ligands of Central Benzodiazepine Receptors

A series of imidazo[1,5-a]quinoline derivatives was designed and synthesized as central benzodiazepine receptor (CBR) ligands. Most of the compounds showed high CBR affinity with Ki values within the submicromolar and subnanomolar ranges with interesting modulations in their structure-affinity relationships. In particular, fluoroderivative 7w (Ki = 0.44 nM) resulted in the most potent ligand among the imidazo[1,5-a]quinoline derivatives described so far. Overall, these observations confirmed the assumption concerning the presence of a large though apparently saturable lipophilic pocket in the CBR binding site region interacting with positions 4 and 5 of the imidazo[1,5-a]quinoline nucleus. The in vivo biological characterization revealed that compounds 7a,c,d,l,m,q,r,w show anxiolytic and antiamnestic activities without the unpleasant myorelaxant side effects of the classical 1,4-BDZ. Furthermore, the effect of 7l,q,r, and 8i in lowering lactate dehydrogenase (LDH) release induced by ischemia-like conditions in rat brain slices suggested neuroprotective properties for these imidazo[1,5-a]quinoline derivatives.

Beyond conventional routes, an unprecedented metal-free chemoselective synthesis of anthranilate esters via a multicomponent reaction (MCR) strategy

A hitherto unreported route for the synthesis of anthranilate esters is demonstrated using 2-nitrobenzaldehyde, malonitrile and an alcohol or amine via a metal and oxidant free multicomponent reaction (MCR) strategy.

Antidepressant-like effect of artemin in mice: a mechanism for acetyl-L-carnitine activity on depression

RATIONALE

Depression may be associated with altered plasticity of the nervous system. The importance of neurotrophic factor levels is strongly suggested, and the neuronal-related family is extensively studied with respect to glial-derived one.

OBJECTIVES

Aimed to contribute to the study of nervous plasticity modulation as therapeutical target in mood disorders, the role of the glial-derived factor artemin (ARTN) in depression and in the pharmacodynamics of the antidepressant and trophic compound acetyl-L: -carnitine (ALCAR) was evaluated.

METHODS

Male mice were treated with 100 mg kg(-1) ALCAR daily for 7 days; 0.6 μg/mouse ARTN was acutely injected intracerebroventricularly. Gene knockdown of ARTN and GDNF family receptor alpha (GFRalpha3) was obtained by oligonucleotide antisense strategy. The forced swimming test was performed to evaluate antidepressant-like effects.

RESULTS

Repeated ALCAR administration increased ARTN levels in spinal cord, hippocampus, and prefrontal cortex. No modulatory effect was detected on BDNF and glial cell line-derived neutrotrophic factor (GDNF). ARTN, 30 min after administration, showed a dose-dependent antidepressant-like effect. ALCAR needed a 7-day treatment to reach a comparable effect; nevertheless, both substances were able to induce a phosphorylation of the GDNF family receptor Ret. A decrease of the free ARTN level by a specific ARTN antibody impaired the antidepressant-like effect of acute ARTN and repeated ALCAR. Gene knockdown of ARTN or, alternatively, of its receptor GFRalpha3 fully prevented ALCAR effectiveness.

CONCLUSIONS

A mechanism for the antidepressant property of ALCAR is proposed, and the novelty of the possible role of ARTN in depression is suggested.

New insight into the central benzodiazepine receptor-ligand interactions: design, synthesis, biological evaluation, and molecular modeling of 3-substituted 6-phenyl-4H-imidazo[1,5-a][1,4]benzodiazepines and related compounds

3-Substituted 6-phenyl-4H-imidazo[1,5-a][1,4]benzodiazepines and related compounds were synthesized as central benzodiazepine receptor (CBR) ligands. Most of the compounds showed high affinity for bovine and human CBR, their K(i) values spanning from the low nanomolar to the submicromolar range. In particular, imidazoester 5f was able to promote a massive flow of (36)Cl(-) in rat cerebrocortical synaptoneurosomes overlapping its efficacy profile with that of a typical full agonist. Compound 5f was then examined in mice for its pharmacological effects where it proved to be a safe anxiolytic agent devoid of the unpleasant myorelaxant and amnesic effects of the classical 1,4-benzodiazepines. Moreover, the selectivity of some selected compounds has been assessed in recombinant α(1)β(2)γ(2)L, α(2)β(1)γ(2)L, and α(5)β(2)γ(2)L human GABA(A) receptors. Finally, some compounds were submitted to molecular docking calculations along with molecular dynamics simulations in the Cromer's GABA(A) homology model.

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 (GABA(A)) 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.

Neuropharmacological screening of two 1,5-benzodiazepine compounds in mice

This work investigates whether the two 1,5-benzodiazepine compounds: 4-(2-hydroxyphenyl)-1,5-benzodiazepin-2-one (RG0501) and Benzopyrano [4,3-c] 1,5-benzodiazepine (RG0502) have any neuropharmacological activities. Diazepam and Flunitrazepam were used as drug references. The investigational 1,5-BDZ were tested in vivo for potentiating hexobarbital-induced sleep and pentylenetetrazole (PTZ)-induced seizures. Our study demonstrated that the increase of sleep duration was significantly higher with RG0501 as compared to RG0502. However, RG0502 anticonvulsant effect was more pronounced than that of RG0501 in the range dose of 6.25-37.5 mg.kg(-1). From the 50 mg.kg(-1) dose, RG0502 offered a protection against clonic-tonic seizures as well as lethality (p< or =0.05). The results showed that the required doses to obtain a pharmacological activity were more than those of the references. This difference could be related to the lack of specific substituants responsible for the pharmacological activity in the tested compounds.

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.

Novel 3-iodo-8-ethoxypyrazolo[5,1-c][1,2,4]benzotriazine 5-oxide as promising lead for design of α5-inverse agonist useful tools for therapy of mnemonic damage

The synthesis and the binding study of new 3-iodiopyrazolo[5,1-c][1,2,4] benzotriazine 5-oxides 8-alkyloxy substituted are reported. The replacement at position 3 with an iodine atom, with respect to substituents capable to form a three centered hydrogen bond and/or to form pi-pi stacking interaction with receptor protein, gave high affinity ligands, independently of the 8-alkyloxy substituent. High-affinity ligands were studied in mice in vivo for their pharmacological effects, considering five potential benzodiazepine actions: anxiolytic-like effects, motor coordination, anticonvulsant action, mouse learning and memory impairment, and ethanol-potentiating action. Compounds 5c and 5'c have an inverse agonist profile and for the first time is evidenced a pro-mnemonic activity. These compounds were evaluated also for their binding at Benzodiazepine site on GABA(A) receptor complex (GABA(A)/BzR complex) subtype to evaluate their subtype selectivity.