Indoles and 1-(3-(benzyloxy)benzyl)piperazines: Reversible and selective monoamine oxidase B inhibitors identified by screening an in-house compound library.

The therapeutic indications for monoamine oxidases A and B (MAO-A and MAO-B) inhibitors that have emerged from biological studies on animal and cellular models of neurological and oncological diseases have focused drug discovery projects upon identifying reversible MAO inhibitors. Screening of our in-house academic compound library identified two hit compounds that inhibit MAO-B with IC50 values in micromolar range. Two series of indole (23 analogues) and 3-(benzyloxy)benzyl)piperazine (16 analogues) MAO-B inhibitors were derived from hits, and screened for their structure-activity relationships. Both series yielded low micromolar selective inhibitors of human MAO-B, namely indole 2 (IC50 = 12.63 ± 1.21 µM) and piperazine 39 (IC50 = 19.25 ± 4.89 µM), which is comparable to selective MAO-B inhibitor isatin (IC50 = 6.10 ± 2.81 µM), yet less potent in comparison to safinamide (IC50 = 0.029 ± 0.002 µM). Selective MAO-B inhibitors 2, 14, 38 and 39 exhibited favourable permeation of the blood-brain barrier and low cytotoxicity in the human neuroblastoma cell line SH-SY5Y.

2-(2-Hydroxyethyl)piperazine derivatives as potent human carbonic anhydrase inhibitors: Synthesis, enzyme inhibition, computational studies and antiglaucoma activity.

Targeting Carbonic Anhydrases (CAs) represents a strategy to treat several diseases, from glaucoma to cancer. To widen the structure-activity relationships (SARs) of our series of piperazines endowed with potent human carbonic anhydrase (hCA) inhibition, a new series of chiral piperazines carrying a (2-hydroxyethyl) group was prepared. The Zn-binding function, the 4-sulfamoylbenzoyl moiety, was connected to one piperazine N-atom, while the other nitrogen was decorated with alkyl substituents. In analogy to the approach used for the synthesis of the previously reported series, the preparation of the new compounds started with (R)- and (S)-aspartic acid. A partial racemization occurred during the synthesis. In order to overcome this problem, other chemical strategies were investigated. The inhibitory activity of the new polar derivatives against four hCAs isoforms I, II, IV and IX using a stopped flow CO2 hydrase assay was determined. Some compounds showed potency in the nanomolar range and a preference for inhibiting hCA IX.

Histamine H3 receptor antagonists with peptidomimetic (keto)piperazine structures to inhibit Aß oligomerisation.

Alzheimers disease (AD) is the most prominent neurodegenerative disorder with high medical need. Protein-protein-interactions (PPI) interactions have a critical role in AD where ß-amyloid structures (Aß) build toxic oligomers. Design of disease modifying multi target directed ligand (MTDL) has been performed, which disable PPI on the one hand and on the other hand, act as procognitive antagonists at the histamine H3 receptor (H3R). The synthetized compounds are structurally based on peptidomimetic amino acid-like structures mainly as keto, diketo-, or acyl variations of a piperazine moiety connected to an H3R pharmacophore. Most of them showed low nanomolar affinities at H3R and some with promising affinity to Aß-monomers. The structure-activity relationships (SAR) described offer new possibilities for MTDL with an optimized profile combining symptomatic and potential causal therapeutic approaches in AD.

Piperazine squaric acid diamides, a novel class of allosteric P2X7 receptor antagonists.

The P2X7 receptor (P2X7R) stands out among the purinergic receptors due to its strong involvement in the regulation of tumor growth and metastasis formation as well as in innate immune responses and afferent signal transmission. Numerous studies have pointed out the beneficial effects of P2X7R antagonism for the treatment of a variety of cancer types, inflammatory diseases, and chronic pain. Herein we describe the development of novel P2X7R antagonists, incorporating piperazine squaric diamides as a central element. Besides improving the antagonists' potency from pIC50 values of 5.7-7.6, ADME properties (logD7.4 value, plasma protein binding, in vitro metabolic stability) of the generated compounds were investigated and optimized to provide novel P2X7R antagonists with drug-like properties. Furthermore, docking studies revealed the antagonists binding to the allosteric binding pocket in two distinct binding poses, depending on the substitution of the central piperazine moiety.

Novel piperazine urea derivatives as highly potent transient receptor potential vanilloid 1 (TRPV1) antagonists.

Transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel with high permeability to Ca2+, which can be activated by low pH, noxious heat and vanilloid compounds such as capsaicin. TRPV1 has been proved to be very important in the process of pain production and is considered to be a highly effective analgesic target. In this work, three series of new piperazine urea TRPV1 antagonists were designed, synthesized and evaluated based on classical TRPV1 antagonists BCTC and GRT12360. Among them, N-(4,6-dimethylpyridin-2-yl)-4-(2-(pyrrolidin-1-yl)benzyl)piperazine-1-carboxamide (5ac) was finally identified, which had excellent TRPV1 antagonistic activity (IC50 (CAP) = 9.80 nM), good bioavailability and did not cause side effects of hyperthermia. In the study of molecular docking, the compound 5ac fitted well with the amino acid residues on rTRPV1 through hydrophobic interaction. Collectively, compound 5ac is an efficient TRPV1 antagonist and can be used as a candidate for the development of analgesic drugs.

Evaluation of 4-(4-Fluorobenzyl)piperazin-1-yl]-Based Compounds as Competitive Tyrosinase Inhibitors Endowed with Antimelanogenic Effects.

There is a considerable attention for the development of inhibitors of tyrosinase (TYR) as therapeutic strategy for the treatment of hyperpigmentation disorders in humans. Continuing in our efforts to identify TYR inhibitors, we describe the design, synthesis and pharmacophore exploration of new small molecules structurally characterized by the presence of the 4-fluorobenzylpiperazine moiety as key pharmacophoric feature for the inhibition of TYR from Agaricus bisporus (AbTYR). Our investigations resulted in the discovery of the competitive inhibitor [4-(4-fluorobenzyl)piperazin-1-yl]-(3-chloro-2-nitro-phenyl)methanone 26 (IC50 =0.18 µM) that proved to be ∼100-fold more active than reference compound kojic acid (IC50 =17.76 µM). Notably, compound 26 exerted antimelanogenic effect on B16F10 cells in absence of cytotoxicity. Docking analysis suggested its binding mode into AbTYR and into modelled human TYR.

Optimization and SAR research at the piperazine and phenyl rings of JNJ4796 as new anti-influenza A virus agents, part 1.

JNJ4796, a small molecule fuse inhibitor targeting the conserved stem region of hemagglutinin, effectively neutralized a broad spectrum of group 1 influenza A virus (IAV), and protected mice against lethal and sublethal influenza challenge after oral administration. In this study, we reported the modification and structure-activity relationship (SAR) of C (piperazine ring) and E (phenyl ring) rings of JNJ4796. Compound (R)-2c was identified to show excellent in vitro activity against IAV H1N1 and Oseltamivir-resistant IAV H1N1 stains (IC50: 0.03-0.06 µM), low cytotoxicity (CC50 > 200 µM), accepted oral PK profiles and low inhibition rate of hERG (13.2%, at 10 µM). Evaluation for the in vivo anti-IAV efficacy of (R)-2c will begin soon.

Piperazine, a Key Substructure for Antidepressants: Its Role in Developments and Structure-Activity Relationships.

Depression is the single largest contributor to global disability with a huge economic and social burden on the world. There are a number of antidepressant drugs on the market, but treatment-resistant depression and relapse of depression in a large number of patients have increased problems for clinicians. One peculiarity observed in most of the marketed antidepressants is the presence of a piperazine substructure. Although piperazine is also used in the optimization of other pharmacological agents, it is almost extensively used for the development of novel antidepressants. One common understanding is that this is due to its favorable CNS pharmacokinetic profile; however, in the case of antidepressants, piperazine plays a much bigger role and is involved in specific binding conformations of these agents. Therefore, in this review, a critical analysis of the significance of the piperazine moiety in the development of antidepressants has been performed. An overview of current developments in the designing and synthesis of piperazine-based antidepressants (2015 onwards) along with SAR studies is also provided. The various piperazine-based therapeutic agents in early- or late-phase human testing for depression are also discussed. The preclinical compounds discussed in this review will help researchers understand how piperazine actually influences the design and development of novel antidepressant compounds. The SAR studies discussed will provide crucial clues about the structural features and optimizations required to enhance the efficacy and potency of piperazine-based antidepressants.

Design, Synthesis, and Evaluation of Small Molecule Gαq/11 Protein Inhibitors for the Treatment of Uveal Melanoma.

Uveal melanoma is the ocular malignancy and mainly driven by oncogenic mutations of Gαq/11 proteins. Previous targeted therapy for melanoma treatment was limited to specific downstream signaling pathway, and inhibiting the "molecular switches" G proteins for melanoma treatment therapy was rarely described. We herein report the discovery of imidazopiperazine derivatives as Gαq/11 protein inhibitors. The most promising compound GQ127 showed good efficacy and safety in inositol monophosphate (IP1) assay by directly inhibiting Gαq/11 proteins. GQ127 induced uveal melanoma cells apoptosis and displayed potent antitumor activities in uveal melanoma cells viability, migration, and invasion. The effects of GQ127 on Gαq/11 signaling pathway were confirmed by analyzing the downstream effectors yes-associated protein (YAP) and extracellular signal-regulated kinase (ERK). More importantly, GQ127 significantly suppressed UM xenograft growth in mouse model without severe toxicity at the testing dose. These findings provide a lead compound that directly targets the Gαq/11 proteins for uveal melanoma treatment.

Synthesis, docking studies, and pharmacological evaluation of 2-hydroxypropyl-4-arylpiperazine derivatives as serotoninergic ligands.

A new series of norbornene and exo-N-hydroxy-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide derivatives was prepared, and their affinities to the 5-HT1A , 5-HT2A , and 5-HT2C receptors were evaluated and compared with a previously synthesized series of derivatives characterized by the same nuclei, to identify selective ligands for the subtype receptors. Arylpiperazines represent one of the most important classes of 5-HT1A R ligands, and the research of new derivatives has been focused on the modification of one or more portions of this pharmacophore. The combination of structural elements (heterocyclic nucleus, hydroxyalkyl chain, and 4-substituted piperazine), known to be critical for the affinity to 5-HT1A receptors, and the proper selection of substituents resulted in compounds with high specificity and affinity toward serotoninergic receptors. The most active compounds were selected for further in vivo assays to determine their functional activity. Finally, to rationalize the obtained results, molecular docking studies were performed. The results of the pharmacological studies showed that 3e, 4j, and 4n were the most active and promising derivatives for the serotonin receptor considered in this study.

Synthesis of Novel Triazolyl/Oxadiazolyl/Thiadiazolyl-Piperazine as Potential Anticonvulsant Agents.

Reaction of piperazine with chloroacetylchloride in dry acetone yield compound 1: , which on reaction with hydrazine hydrate yielded compound 2: , which was further reacted with various substituted phenylisothiocyanates in absolute alcohol to afford compounds 3-8: i. e. 2-(carbazolylacetyl)-N-(substitutedphenyl)-hydrazinepiperazinothioamides. Compounds 3-8: on reaction with aqueous NaOH, ethanolic NaOH and conc. H2SO4 afford triazoles 9-14: , oxadiazoles 15-20: and thiadiazoles 21-26: respectively. Twenty four newly synthesized compounds were evaluated for their anticonvulsant activity and acute toxicity. The structures of these compounds were established on the basis of analytical and spectral data.

Design, Synthesis, and Biological Evaluation of Pyridazinones Containing the (2-Fluorophenyl) Piperazine Moiety as Selective MAO-B Inhibitors.

Twelve pyridazinones (T1-T12) containing the (2-fluorophenyl) piperazine moiety were designed, synthesized, and evaluated for monoamine oxidase (MAO) -A and -B inhibitory activities. T6 was found to be the most potent MAO-B inhibitor with an IC50 value of 0.013 µM, followed by T3 (IC50 = 0.039 µM). Inhibitory potency for MAO-B was more enhanced by meta bromo substitution (T6) than by para bromo substitution (T7). For para substitution, inhibitory potencies for MAO-B were as follows: -Cl (T3) > -N(CH3)2 (T12) > -OCH3 (T9) > Br (T7) > F (T5) > -CH3 (T11) > -H (T1). T6 and T3 efficiently inhibited MAO-A with IC50 values of 1.57 and 4.19 µM and had the highest selectivity indices (SIs) for MAO-B (120.8 and 107.4, respectively). T3 and T6 were found to be reversible and competitive inhibitors of MAO-B with Ki values of 0.014 and 0.0071, respectively. Moreover, T6 was less toxic to healthy fibroblast cells (L929) than T3. Molecular docking simulations with MAO binding sites returned higher docking scores for T6 and T3 with MAO-B than with MAO-A. These results suggest that T3 and T6 are selective, reversible, and competitive inhibitors of MAO-B and should be considered lead candidates for the treatment of neurodegenerative disorders like Alzheimer's disease.

Novel piperazine-2,5-dione analogs bearing 1H-indole: Synthesis and biological effects.

In this work, a series of novel piperazine-2,5-dione derivatives bearing indole analogs (2a-2q) was designed and synthesized. The synthesized compounds were characterized by IR, 1H NMR, 13C NMR spectroscopy, and ESI-MS. They were then evaluated for their anti-depressant, anti-inflammatory, and analgesic activities in vivo. The experimental results revealed that all the compounds showed clear anti-depressant, anti-inflammatory, and analgesic effects at a dose of 10 mg/kg. Among them, compounds 2e and 2q exhibited the best anti-depressant effects (the percent decreases in the duration of immobility were 70.2% and 71.2%, respectively), which were similar to that of fluoxetine (67.9%) in the forced swim test. Additionally, compounds 2e and 2q also displayed good anti-inflammatory and analgesic activities. Literature reports have highlighted the anti-inflammatory and analgesic effects of anti-depressant drugs, suggesting that they may have a similar mechanism of action. Therefore, further studies to investigate the possible mechanisms of action of compounds 2e and 2q are warranted.

Newly Synthesized Fluorinated Cinnamylpiperazines Possessing Low In Vitro MAO-B Binding.

Herein, we report on the synthesis and pharmacological evaluation of ten novel fluorinated cinnamylpiperazines as potential monoamine oxidase B (MAO-B) ligands. The designed derivatives consist of either cinnamyl or 2-fluorocinnamyl moieties connected to 2-fluoropyridylpiperazines. The three-step synthesis starting from commercially available piperazine afforded the final products in overall yields between 9% and 29%. An in vitro competitive binding assay using l-[3H]Deprenyl as radioligand was developed and the MAO-B binding affinities of the synthesized derivatives were assessed. Docking studies revealed that the compounds 8-17 were stabilized in both MAO-B entrance and substrate cavities, thus resembling the binding pose of l-Deprenyl. Although our results revealed that the novel fluorinated cinnamylpiperazines 8-17 do not possess sufficient MAO-B binding affinity to be eligible as positron emission tomography (PET) agents, the herein developed binding assay and the insights gained within our docking studies will certainly pave the way for further development of MAO-B ligands.

Design and synthesis of purine connected piperazine derivatives as novel inhibitors of Mycobacterium tuberculosis.

A series of novel purine linked piperazine derivatives were synthesized to identify new, potent inhibitors of Mycobacterium tuberculosis. The compounds were designed to target MurB disrupting the biosynthesis of the peptidoglycan and exert antiproliferative effects. The first series of purine-2,6-dione linked piperazine derivatives were synthesized using an advanced intermediate 1-(3,4-difluorobenzyl)-7-(but-2-ynyl)-3-methyl-8-(piperazin-1-yl)-1H-purine-2,6(3H,7H)-dione hydrochloride (6) which was coupled with varied carboxylic acid chloride derivatives. Following this piperazine linked derivatives were also synthesized from 6 using diverse isocyanate partners. The anti-mycobacterial activity of the analogues was tested againstMycobacterium tuberculosis H37Rv which revealed a cluster of six analogues (11, 24,27, 32, 33 and34), possessed promising activity. In comparison, a set of these new compounds possessed greater potencies relative to current drugs used in the clinic such as Ethambutol. These results were also correlated with computational molecular docking analysis, providing models for strong interactions of the inhibitors with MurB providing a template for the future development of preclinical agents against Mycobacterium tuberculosis.

Synthesis and pharmacological evaluation of piperidine (piperazine)-amide substituted derivatives as multi-target antipsychotics.

We report the optimisation of a series of novel amide-piperidine (piperazine) derivatives using the multiple ligand approach with dopamine and serotonin receptors. Of the derivatives, compound 11 exhibited high affinity for the D2, 5-HT1A, and 5-HT2A receptors, but low affinity for the 5-HT2C and histamine H1 receptors and human ether-a-go-go-related gene (hERG) channels. In vivo, compound 11 reduced apomorphine-induced climbing, MK-801-induced hyperactivity and DOI-induced head twitching without observable catalepsy, even at the highest dose tested. In addition, it exhibited suppression in a CAR test. Furthermore, in a novel object recognition task, it displayed procognition properties. Therefore, compound 11 is a promising candidate multi-target antipsychotic.

Discovery of 5-(4-methylpiperazin-1-yl)-2-nitroaniline derivatives as a new class of SIRT6 inhibitors.

SIRT6 is a deacetylase of histone H3 and inhibitors of SIRT6 have been thought as potential agents for treatment of diabetes. Herein we report the discovery of a series of new SIRT6 inhibitors containing the skeleton 1-phenylpiperazine. Among them, compound 5-(4-methylpiperazin-1-yl)-2-nitroaniline (6d) is the most potent one, which showed an IC50 value of 4.93 µM against SIRT6 in the Fluor de Lys (FDL) assay. It displayed KD values of 9.76 µM and 10 µM in surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC) assays, respectively. In selectivity assay, 6d showed no activity against other members of the HDAC family (SIRT1-3 and HDAC1-11) at concentrations up to 200 µM. In a mouse model of type 2 diabetes, 6d could significantly increase the level of glucose transporter GLUT-1, thereby reducing blood glucose. Overall, this study provides a promising lead compound for subsequent drug discovery targeting SIRT6.

Synthesis and evaluation of sulfonyl piperazine LpxH inhibitors.

The UDP-2,3-diacylglucosamine pyrophosphate hydrolase LpxH is essential in lipid A biosynthesis and has emerged as a promising target for the development of novel antibiotics against multidrug-resistant Gram-negative pathogens. Recently, we reported the crystal structure of Klebsiella pneumoniae LpxH in complex with 1 (AZ1), a sulfonyl piperazine LpxH inhibitor. The analysis of the LpxH-AZ1 co-crystal structure and ligand dynamics led to the design of 2 (JH-LPH-28) and 3 (JH-LPH-33) with enhanced LpxH inhibition. In order to harness our recent findings, we prepared and evaluated a series of sulfonyl piperazine analogs with modifications in the phenyl and N-acetyl groups of 3. Herein, we describe the synthesis and structure-activity relationship of sulfonyl piperazine LpxH inhibitors. We also report the structural analysis of an extended N-acyl chain analog 27b (JH-LPH-41) in complex with K. pneumoniae LpxH, revealing that 27b reaches an untapped polar pocket near the di-manganese cluster in the active site of K. pneumoniae LpxH. We expect that our findings will provide designing principles for new LpxH inhibitors and establish important frameworks for the future development of antibiotics against multidrug-resistant Gram-negative pathogens.

Design, synthesis and evaluation of novel nonquaternary and 3 non-oxime reactivators for acetylcholinesterase inhibited by organophosphates.

A new series of novel nonquaternary conjugates and non-oxime reactivators for reactivation of both nerve agents and pesticides inhibited hAChE were described in this paper. Conjugates with piperazine linked to the substituted salicylaldoxime emerged as efficient reactivators for VX inhibited hAChE. The in vitro reactivation experiment showed that some of them were equal or more efficient reactivators for pesticides inhibited hAChE than obidoxime. It was also found that some non-oxime derivatives of Mannich phenols displayed obvious reactivation potency for VX, sarin and pesticides inhibited hAChE even in very low concentration. It has been proved that introduction of peripheral site ligands with widespread aromatic system and amide substitutions could increase binding affinity for inhibited hAChE in most cases, which contribute to the reactivation efficiency.

6-Acetyl-5-hydroxy-4,7-dimethylcoumarin derivatives: Design, synthesis, modeling studies, 5-HT1A, 5-HT2A and D2 receptors affinity.

Molecular docking studies using appropriate 5-HT1A, 5-HT2A and D2 receptors models were used to design sixteen new 5-hydroxycoumarin derivatives with piperazine moiety (3-18). The microwave radiation have been used to synthesize them and their structures have been confirmed using mass spectrometry, 1H and 13C NMR. All newly prepared derivatives were evaluated for their 5-HT1A, 5-HT2A and D2 receptor affinity. Seven of the synthesized derivatives showed very high affinities to 5-HT1A receptor (3-4.0 nM, 6-4.0 nM, 7-1.0 nM, 9-6.0 nM, 15-4.3 nM, 16-1.0 nM, 18-3.0 nM) and one of them showed high affinities to 5-HT2A receptor (16-8.0 nM). In the case of the D2 receptor none of the tested derivatives showed high affinity. Compounds 7 and 16 were identified as potent antagonists of the 5-HT1A receptor as shown by the [35S]GTPcS binding assay but they didn't show any antidepressant effect at the single dose tested (10 mg/kg) in the tail suspension tests.