Synthesis, Molecular Properties Estimations, and Dual Dopamine D2 and D3 Receptor Activities of Benzothiazole-Based Ligands

Aromatic linker variations in novel dopamine D2 and D3 receptor ligands

Dopamine D2-like receptors, especially D2 and D3 receptor subtypes, are important targets of antipsychotic agents. Many of these antipsychotics share an aliphatic linker element between a protonable amine group and an acyl-like moiety. Here, we have modified this aliphatic linker into phenylmethyl and phenylethyl linkers substituted in different positions. The design, synthesis, and in vitro evaluation of 18 dopamine D2 and D3 receptor ligands were performed in this study. Using a radioligand displacement assay, all ligands were found to have modest nanomolar affinity to D2R and D3R. N-(4-{2-[4-(2-Methoxyphenyl)piperazin-1-yl]ethyl}phenyl)acetamide (6c) demonstrates the highest D3R and D2R affinity values (pKi values of 7.83 [D2R] and 8.04 [D3R]), featuring a slight preference to D3R. This derivative can be taken as a reference structure for the development of a new class of D2R and D3R ligands.

Design, Synthesis, Antifungal Evaluation, Structure-Activity Relationship (SAR) Study, and Molecular Docking of Novel Spirotryprostatin A Derivatives

Phytopathogenic fungi cause plant diseases and economic losses in agriculture. To efficiently control plant pathogen infections, a total of 19 spirotryprostatin A derivatives and 26 spirooxindole derivatives were designed, synthesized, and tested for their antifungal activity against ten plant pathogens. Additionally, the intermediates of spirooxindole derivatives were investigated, including proposing a mechanism for diastereoselectivity and performing amplification experiments. The bioassay results demonstrated that spirotryprostatin A derivatives possess good and broad-spectrum antifungal activities. Compound 4d exhibited excellent antifungal activity in vitro, equal to or higher than the positive control ketoconazole, against Helminthosporium maydis, Trichothecium roseum, Botrytis cinerea, Colletotrichum gloeosporioides, Fusarium graminearum, Alternaria brassicae, Alternaria alternate, and Fusarium solan (MICs: 8-32 µg/mL). Compound 4k also displayed remarkable antifungal activity against eight other phytopathogenic fungi, including Fusarium oxysporium f. sp. niveum and Mycosphaerella melonis (MICs: 8-32 µg/mL). The preliminary structure-activity relationships (SARs) were further discussed. Moreover, molecular docking studies revealed that spirotryprostatin A derivatives anchored in the binding site of succinate dehydrogenase (SDH). Therefore, these compounds showed potential as natural compound-based chiral fungicides and hold promise as candidates for further enhancements in terms of structure and properties.

Recent advances in dopamine D2 receptor ligands in the treatment of neuropsychiatric disorders

Dopamine is a biologically active amine synthesized in the central and peripheral nervous system. This biogenic monoamine acts by activating five types of dopamine receptors (D_1-5 Rs), which belong to the G protein-coupled receptor family. Antagonists and partial agonists of D₂ Rs are used to treat schizophrenia, Parkinson's disease, depression, and anxiety. The typical pharmacophore with high D₂ R affinity comprises four main areas, namely aromatic moiety, cyclic amine, central linker and aromatic/heteroaromatic lipophilic fragment. From the literature reviewed herein, we can conclude that 4-(2,3-dichlorophenyl), 4-(2-methoxyphenyl)-, 4-(benzo[b]thiophen-4-yl)-1-substituted piperazine, and 4-(6-fluorobenzo[d]isoxazol-3-yl)piperidine moieties are critical for high D₂ R affinity. Four to six atoms chains are optimal for D₂ R affinity with 4-butoxyl as the most pronounced one. The bicyclic aromatic/heteroaromatic systems are most frequently occurring as lipophilic appendages to retain high D₂ R affinity. In this review, we provide a thorough overview of the therapeutic potential of D₂ R modulators in the treatment of the aforementioned disorders. In addition, this review summarizes current knowledge about these diseases, with a focus on the dopaminergic pathway underlying these pathologies. Major attention is paid to the structure, function, and pharmacology of novel D₂ R ligands, which have been developed in the last decade (2010-2021), and belong to the 1,4-disubstituted aromatic cyclic amine group. Due to the abundance of data, allosteric D₂ R ligands and D₂ R modulators from patents are not discussed in this review.

Design and Synthesis of Arylpiperazine Serotonergic/Dopaminergic Ligands with Neuroprotective Properties

Long-chain arylpiperazine scaffold is a versatile template to design central nervous system (CNS) drugs that target serotonin and dopamine receptors. Here we describe the synthesis and biological evaluation of ten new arylpiperazine derivatives designed to obtain an affinity profile at serotonin 5-HT_1A, 5-HT_2A, 5-HT₇ receptor, and dopamine D₂ receptor of prospective drugs to treat the core symptoms of autism spectrum disorder (ASD) or psychosis. Besides the structural features required for affinity at the target receptors, the new compounds incorporated structural fragments with antioxidant properties to counteract oxidative stress connected with ASD and psychosis. All the new compounds showed CNS MultiParameter Optimization score predictive of desirable ADMET properties and cross the blood–brain barrier. We identified compound 12a that combines an affinity profile compatible with antipsychotic activity (5-HT_1AK_i = 41.5 nM, 5-HT_2AK_i = 315 nM, 5-HT₇K_i = 42.5 nM, D₂K_i = 300 nM), and compound 9b that has an affinity profile consistent with studies in the context of ASD (5-HT_1AK_i = 23.9 nM, 5-HT_2AK_i = 39.4 nM, 5-HT₇K_i = 45.0 nM). Both compounds also had antioxidant properties. All compounds showed low in vitro metabolic stability, the only exception being compound 9b, which might be suitable for studies in vivo.

A Review on the Arylpiperazine Derivatives as Potential Therapeutics for the Treatment of Various Neurological Disorders

Abstract:

Neurological disorders are disease conditions related to the neurons and central nervous system (CNS). Any kind of structural, electrical, biochemical and functional abnormalities in neurons can lead to various types of disorders like Alzheimer’s disease (AD), depression, Parkinson’s disease (PD), epilepsy, stroke, etc. Currently available medicines are symptomatic and do not treat the disease state. Thus, novel CNS active agents with the potential of complete treatment of an illness are highly desired. A range of small organic molecules are being explored as potential drug candidates for the cure of different neurological disorders. In this context, arylpiperazine has been found to be a versatile scaffold and indispensable pharmacophore in many CNS active agents. A number of molecules with arylpiperazine nucleus have been developed as potent leads for the treatment of AD, PD, depression and other disorders. The arylpiperazine nucleus can be optionally substituted at different chemical structures and offer flexibility for the synthesis of large number of derivatives. In the current review article, we have explored the role of various arylpiperazine containing scaffolds against different neurological disorders, including AD, PD, and depression. The structure-activity relationship studies were conducted for recognizing potent lead compounds. This review article may provide important clues on the structural requirements for the design and synthesis of effective molecules as curative agents for different neurological disorders.

Adenosine A2AR/A1R Antagonists Enabling Additional H3R Antagonism for the Treatment of Parkinson's Disease

Adenosine A1/A2A receptors (A1R/A2AR) represent targets in nondopaminergic treatment of motor disorders such as Parkinson's disease (PD). As an innovative strategy, multitargeting ligands (MTLs) were developed to achieve comprehensive PD therapies simultaneously addressing comorbid symptoms such as sleep disruption. Recognizing the wake-promoting capacity of histamine H3 receptor (H3R) antagonists in combination with the "caffeine-like effects" of A1R/A2AR antagonists, we designed A1R/A2AR/H3R MTLs, where a piperidino-/pyrrolidino(propyloxy)phenyl H3R pharmacophore was introduced with overlap into an adenosine antagonist arylindenopyrimidine core. These MTLs showed distinct receptor binding profiles with overall nanomolar H3R affinities (Ki < 55 nM). Compound 4 (ST-2001, Ki (A1R) = 11.5 nM, Ki (A2AR) = 7.25 nM) and 12 (ST-1992, Ki (A1R) = 11.2 nM, Ki (A2AR) = 4.01 nM) were evaluated in vivo. l-DOPA-induced dyskinesia was improved after administration of compound 4 (1 mg kg-1, i.p. rats). Compound 12 (2 mg kg-1, p.o. mice) increased wakefulness representing novel pharmacological tools for PD therapy.

Synthesis, in silico, and in vitro studies of novel dopamine D2 and D3 receptor ligands

Dopamine is an important neurotransmitter in the human brain and its altered concentrations can lead to various neurological diseases. We studied the binding of novel compounds at the dopamine D₂ (D₂ R) and D₃ (D₃ R) receptor subtypes, which belong to the D₂ -like receptor family. The synthesis, in silico, and in vitro characterization of 10 dopamine receptor ligands were performed. Novel ligands were docked into the D₂ R and D₃ R crystal structures to examine the precise binding mode. A quantum mechanics/molecular mechanics study was performed to gain insights into the nature of the intermolecular interactions between the newly introduced pentafluorosulfanyl (SF₅ ) moiety and D₂ R and D₃ R. A radioligand displacement assay determined that all of the ligands showed moderate-to-low nanomolar affinities at D₂ R and D₃ R, with a slight preference for D₃ R, which was confirmed in the in silico studies. N-{4-[4-(2-Methoxyphenyl)piperazin-1-yl]butyl}-4-(pentafluoro-λ6-sulfanyl)benzamide (7i) showed the highest D₃ R affinity and selectivity (pK_i values of 7.14 [D₂ R] and 8.42 [D₃ R]).

Synthesis, Antimicrobial Activity, Structure-Activity Relationship, and Molecular Docking Studies of Indole Diketopiperazine Alkaloids

Strategies for the synthesis of indole diketopiperazine alkaloids (indole DKPs) have been described and involve three analogs of indole DKPs. The antimicrobial activity and structure-activity relationship (SAR) of 24 indole DKPs were explored. Compounds 3b and 3c were found to be the most active, with minimum inhibitory concentrations (MIC) values in the range of 0.94–3.87 μM (0.39–1.56 μg/mL) against the four tested bacteria (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, and Escherichia coli). Furthermore, compounds 4a and 4b displayed broad-spectrum antimicrobial activity with MIC values of 1.10–36.9 μM (0.39–12.5 μg/mL) against all tested bacteria and plant pathogenic fungi (Colletotrichum gloeosporioides, Valsa mali, Alternaria alternata and Alternaria brassicae). According to the in silico study, compounds 3c showed significant binding affinity to the FabH protein from Escherichia coli, which has been identified as the key target enzyme of fatty acid synthesis (FAS) in bacteria. Therefore, these compounds are not only promising new antibacterial agents but also potential FabH inhibitors.

Talipexole variations as novel bitopic dopamine D2 and D3 receptor ligands

We linked 5,6,7,8-tetrahydro-4H-thiazoloazepine scaffolds with phenylpiperazine pharmacophores to generate bitopic dopamine receptor ligands.

Binding kinetics of cariprazine and aripiprazole at the dopamine D3 receptor

The dissociation behaviours of aripiprazole and cariprazine at the human D₂ and D₃ receptor are evaluated. A potential correlation between kinetics and in vivo profiles, especially cariprazine’s action on negative symptoms in schizophrenia, is investigated. The binding kinetics of four ligands were indirectly evaluated. After the receptor preparations were pre-incubated with the unlabelled ligands, the dissociation was initiated with an excess of [³H]spiperone. Slow dissociation kinetics characterizes aripiprazole and cariprazine at the D₂ receptor. At the D₃ receptor, aripiprazole exhibits a slow monophasic dissociation, while cariprazine displays a rapid biphasic behaviour. Functional ß-arrestin assays and molecular dynamics simulations at the D₃ receptor confirm a biphasic binding behaviour of cariprazine. This may influence its in vivo action, as the partial agonist could react rapidly to variations in the dopamine levels of schizophrenic patients and the ligand will not quantitatively dissociate from the receptor in one single step. With these findings novel agents may be developed that display rapid, biphasic dissociation from the D₃R to further investigate this effect on in vivo profiles.