Structurally constrained hybrid derivatives containing octahydrobenzo[g or f]quinoline moieties for dopamine D2 and D3 receptors: binding characterization at D2/D3 receptors and elucidation of a pharmacophore model

Synthesis and biological evaluation as well as in silico studies of arylpiperazine-1,2-benzothiazine derivatives as novel anti-inflammatory agents

Novel arylpiperazine-1,2-benzothiazine derivatives have been designed and synthesized as potential anti-inflammatory agents. Their structure and properties have been studied using spectroscopic techniques (¹H NMR, ¹³C NMR, FT-IR), MS, elemental analyses, and single-crystal X-ray diffraction (SCXRD, for compound 7b). This study aimed to evaluate the inhibitory activity of new derivatives against both cyclooxygenase isoforms COX-1 and COX-2 due to the similarity of new compounds to oxicams drugs from the NSAIDs group. All new compounds were divided into two series - A and B - with a different linker between thiazine and piperazines nitrogens. Series A included the three-carbon aliphatic linker and series B - two-carbon with a carbonyl group. According to in vitro and molecular docking studies all new compounds exhibited cyclooxygenase inhibitory activity. The series of A compounds included COX-1 inhibitors only. In contrast, the B series showed inhibition of both COX-1 and COX-2, which suggested the importance of the acetoxy linker for COX-2 inhibition. Moreover, the most selective compound 7b, towards COX-2, was non-toxic for the normal human cell line (in concentration of 10 µM) comparable to reference drug meloxicam. Additionally, investigation of influence on model membranes confirmed the ability of the compound 7b to penetrate lipid bilayers which seemed to be important to the influence with membrane protein-cyclooxygenase.

Evaluation of 1,2-Benzothiazine 1,1-dioxide Derivatives In Vitro Activity towards Clinical-Relevant Microorganisms and Fibroblasts

The global concern related with growing number of bacterial pathogens, resistant to numerous antibiotics, prone scientific environment to search for new antimicrobials. Antiseptics appear to be suitable candidates as adjunctive agents to antibiotics or alternative local treatment option aiming to prevent and treat infections. 1,2-benzothiazines are considered one the most promising of them. In this research twenty 1,2-benzothiazine 1,1-dioxide derivatives were scrutinized with regard to their biological activity. Three of them are new. For evaluation of compounds' activity against microbial pathogens, disk diffusion method and serial microdilution method was applied. To establish the cytotoxicity profile of tested 1,2-benzothiazines 1,1-dioxides derivatives, the cytotoxicity assay using fibroblasts L292 was performed. Antimicrobial activity of all tested compounds against Gram-positive Staphylococcus aureus and Enterococcus faecalis strains was higher than antimicrobial activity of DMSO solvent, which possesses antimicrobial activity itself. Gram-negative P. aeruginosa, E. coli and K. pneumoniae have shown susceptibility only to compounds 3e, 7i and 7l. None of tested compounds was effective against C. albicans. Compound 6g has demonstrated the strongest antimicrobial potency (MIC = 0.00975 mg/mL) among compounds of series 6. Compounds of series 7, namely 7d, 7f, 7g had the lowest minimum inhibitory concentration (MIC). Compound 7f displayed also the lowest cytotoxic effect against fibroblast cell line among series 7 compounds. All tested derivatives displayed lower MIC against Gram-positive bacteria than commercially applied antiseptic, povidone iodine, which MIC value range for tested Gram-positive bacteria was 1.56-6.25 mg/mL.

Synthesis of 3-(3-hydroxyphenyl)pyrrolidine dopamine D3 receptor ligands with extended functionality for probing the secondary binding pocket

A series of 3-(3-hydroxyphenyl)pyrrolidine analogues which incorporate N-alkyl groups and N-butylamide-linked benzamide functionality have been synthesized and their in vitro binding affinities at human dopamine receptors have been evaluated. Our ligand design strategy was to take the 3-(3-hydroxyphenyl)pyrrolidine scaffold and extend functionality from the orthosteric binding site to the secondary binding pocket for enhancing affinity and selectivity for the D₃ receptor. The N-alkyl analogues constitute a homologous series from N-pentyl to N-decyl to probe the length/bulk tolerance of the secondary binding pocket of the D₃ receptor. Enantiomeric 3-(3-hydroxyphenyl)pyrrolidine analogues were also prepared in order to test the chirality preference of the orthosteric binding site for this scaffold. Benzamide analogues were prepared to enhance affinity and/or selectivity based upon the results of the homologous series.

Advances and challenges in the search for D2 and D3 dopamine receptor-selective compounds

Compounds that target D2-like dopamine receptors (DRs) are currently used as therapeutics for several neuropsychiatric disorders including schizophrenia (antagonists) and Parkinson's disease (agonists). However, as the D₂R and D₃R subtypes are highly homologous, creating compounds with sufficient subtype-selectivity as well as drug-like properties for therapeutic use has proved challenging. This review summarizes the progress that has been made in developing D₂R- or D₃R-selective antagonists and agonists, and also describes the experimental conditions that need to be considered when determining the selectivity of a given compound, as apparent selectivity can vary widely depending on assay conditions. Future advances in this field may take advantage of currently available structural data to target alternative secondary binding sites through creating bivalent or bitopic chemical structures. Alternatively, the use of high-throughput screening techniques to identify novel scaffolds that might bind to the D₂R or D₃R in areas other than the highly conserved orthosteric site, such as allosteric sites, followed by iterative medicinal chemistry will likely lead to exceptionally selective compounds in the future. More selective compounds will provide a better understanding of the normal and pathological functioning of each receptor subtype, as well as offer the potential for improved therapeutics.

Chloroquinoline–acetamide hybrids: a promising series of potential antiprotozoal agents

In an endeavour to develop efficacious antiprotozoal agents chloroquinoline–acetamide hybrids were synthesized and screened in vitro against E. histolytica and P. falciparum and molecular docking studies were performed against PfDHFR.

Revision of the classical dopamine D2 agonist pharmacophore based on an integrated medicinal chemistry, homology modelling and computational docking approach

The scientific advances during the 1970ies and 1980ies within the field of dopaminergic neurotransmission enabled the development of a pharmacophore that became the template for design and synthesis of dopamine D2 agonists during the following four decades. A major drawback, however, is that this model fails to accommodate certain classes of restrained dopamine D2 agonists including ergoline structures. To accommodate these, a revision of the original model was required. The present study has addressed this by an extension of the original model without compromising its obvious qualities. The revised pharmacophore contains an additional hydrogen bond donor feature, which is required for it to accommodate ergoline structures in a low energy conformation and in accordance with the steric restrictions dictated by the original model. The additional pharmacophore feature suggests ambiguity in the binding mode for certain compounds, including a series of ergoline analogues, which was reported recently. The ambiguity was confirmed by docking to a homology model of the D2 receptor as well as by pharmacological characterization of individual enantiomers of one of the analogues. The present research also addresses the potential of designing ligands that interact with the receptor in a large, distal cavity of the dopamine D2 receptor that has not previously been studied systematically. The pharmacological data indicate that this area may be a major determinant for both the dopamine D2 affinity and efficacy, which remains to be explored in future studies.

Pharmacophore-based screening and identification of novel human ligase I inhibitors with potential anticancer activity

Human DNA ligases are enzymes that are indispensable for DNA replication and repair processes. Among the three human ligases, ligase I is attributed to the ligation of thousands of Okazaki fragments that are formed during lagging strand synthesis during DNA replication. Blocking ligation therefore can lead to the accumulation of thousands of single strands and subsequently double strand breaks in the DNA, which is lethal for the cells. The reports of the high expression level of ligase I protein in several cancer cells (versus the low ligase expression level and the low rate of division of most normal cells in the adult body) support the belief that ligase I inhibitors can target cancer cells specifically with minimum side effects to normal cells. Recent publications showing exciting data for a ligase IV inhibitor exhibiting antitumor activity in mouse models also strengthens the argument for ligases as valid antitumor targets. Keeping this in view, we performed a pharmacophore-based screening for potential ligase inhibitors in the Maybridge small molecule library and procured some of the top-ranking compounds for enzyme-based and cell-based in vitro screening. We report here the identification of novel ligase I inhibitors with potential anticancer activity against a colon cancer cell line.

Understanding the Structural Requirements of Hybrid (S)-6-((2-(4-Phenylpiperazin-1-yl)ethyl)(propyl)amino)-5,6,7,8-tetrahydronaphthalen-1-ol and its Analogs as D2/D3 Receptor Ligands: A Three-Dimensional Quantitative Structure-Activity Relationship (3D QSAR) Investigation

To gain insights into the structural requirements for dopamine D2 and D3 agonists in the treatment of Parkinson's disease (PD) and to elucidate the basis of selectivity for D3 over D2 (D2/D3), 3D quantitative structure-activity relationship (3D QSAR) investigations using CoMFA (comparative molecular field analysis) and CoMSIA (comparative molecular similarity indices analysis) methods were performed on a series of 45 structurally related D2 and D3 dopaminergic ligands. Two alignment methods (atom-based and flexible) and two charge calculation methods (Gasteiger-Hückel and AM1) were used in the present study. Overall, D2 affinity and selectivity (D2/D3) models performed better with r²_cv values of 0.71 and 0.63 for CoMFA and 0.71 and 0.79 for CoMSIA, respectively. The corresponding predictive r² values for the CoMFA and CoMSIA models were 0.92 and 0.86 and 0.91 and 0.78, respectively. The CoMFA models generated using flexible alignment outperformed the models with the atom-based alignment in terms of relevant statistics and interpretability of the generated contour maps while CoMSIA models obtained using atom-based alignment showed superiority in terms of internal and external predictive abilities. The presence of carbonyl group (C=O) attached to the piperazine ring and the hydrophobic biphenyl ring were found to be the most important features responsible for the D3 selectivity over D2. This study can be further utilized to design and develop selective and potent dopamine agonists to treat PD.

Modification of agonist binding moiety in hybrid derivative 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-1-ol/-2-amino versions: impact on functional activity and selectivity for dopamine D2/D3 receptors

The goal of the present study was to explore, in our previously developed hybrid template, the effect of introduction of additional heterocyclic rings (mimicking catechol hydroxyl groups as bioisosteric replacement) on selectivity and affinity for the D3 versus D2 receptor. In addition, we wanted to explore the effect of derivatization of functional groups of the agonist binding moiety in compounds developed by us earlier from the hybrid template. Binding affinity (K(i)) of the new compounds was measured with tritiated spiperone as the radioligand and HEK-293 cells expressing either D2 or D3 receptors. Functional activity of selected compounds was assessed in the GTPγS binding assay. In the imidazole series, compound 10a exhibited the highest D3 affinity whereas the indole derivative 13 exhibited similar high D3 affinity. Functionalization of the amino group in agonist (+)-9d with different sulfonamides derivatives improved the D3 affinity significantly with (+)-14f exhibiting the highest affinity. However, functionalization of the hydroxyl and amino groups of 15 and (+)-9d, known agonist and partial agonist, to sulfonate ester and amide in general modulated the affinity. In both cases loss of agonist potency resulted from such derivatization.

High-affinity and selective dopamine D₃ receptor full agonists

We have designed, synthesized and evaluated a series of new compounds with the goal to identify potent and selective D(3) ligands. The two most potent and selective new D(3) ligands are compounds 38 and 52, which bind to the D(3) receptors with a K(i) value of <nM and display a selectivity of 450-494 times over the D(2) receptors and >10,000 times over the D(1) receptors. Both 38 and 52 are full agonists with high potency at the D(3) receptor in a D(3) functional assay.

Interaction of novel hybrid compounds with the D3 dopamine receptor: Site-directed mutagenesis and homology modeling studies

The dopamine D3 receptor has been implicated as a potential target for drug development in various complex psychiatric disorders including psychosis, drug dependence, and Parkinson's disease. In our overall goal to develop molecules with preferential affinity at D3 receptors, we undertook a hybrid drug development approach by combining a known dopamine agonist moiety with a substituted piperazine fragment. In the present study, three compounds produced this way with preferential D3 agonist activity, were tested at D3 receptors with mutations in the agonist binding pocket of three residues known to be important for agonist binding activity. At S192A and T369V, the hybrid agonist compounds produced an interaction profile in [(3)H]spiperone binding assays similar to that of the parent 5-OH-DPAT and 7-OH-DPAT molecules. The loss of affinity at the S192A mutant was most prominent for 5-OH-DPAT and its corresponding hybrid compound D237. D110N did not show any radioligand binding. Homology modeling indicated that 7-OH-DPAT-derived D315 uniquely shares H-bonding with Tyr365 which produced favorable interaction and no loss of H-bonding in the S192A mutant, suggesting that agonist activity may not be solely controlled by residues in the binding pocket.

Further delineation of hydrophobic binding sites in dopamine D(2)/D(3) receptors for N-4 substituents on the piperazine ring of the hybrid template 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-2-ol

Here we report a structure-activity relationship (SAR) study of analogues of 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-2-ol. Our SAR is focused on introduction of various substitutions in the piperazine ring of the hybrid template. The goal behind this study is to delineate the nature of the binding pocket for N-aryl substitution in the piperazine ring by observing the effect of various hydrophobic and other heteroaromatic substitutions on binding affinity (K(i)), as measured with tritiated spiperone and HEK-293 cells expressing either D(2) or D(3) receptors. Functional activity of selected compounds was assessed with the GTPgammaS binding assay. Compound 8d was the most selective for the D(3) receptor in the spiperone binding assay. An interesting similarity in binding affinity was observed between isoquinoline derivative D-301 and the 2-substituted pyridine derivative 8d, suggesting the importance of relative spatial relationships between the N-atom of the ligand and the molecular determinants of the binding pocket in D(2)/D(3) receptors. Functional activity assays demonstrated high potency and selectivity of (+)-8a and (-)-28b (D(2)/D(3) (ratio of EC(50)): 105 and 202, respectively) for the D(3) receptor and both compounds were more selective compared to the reference drug ropinirole (D(2)/D(3) (ratio of EC(50)): 29.5).

Current perspectives on selective dopamine D(3) receptor antagonists as pharmacotherapeutics for addictions and related disorders

Repeated exposure to drugs of abuse produces long-term molecular and neurochemical changes that may explain the core features of addiction, such as the compulsive seeking and taking of the drug, as well as the risk of relapse. A growing number of new molecular and cellular targets of addictive drugs have been identified, and rapid advances are being made in relating those targets to specific behavioral phenotypes in animal models of addiction. In this context, the pattern of expression of the dopamine (DA) D(3) receptor in the rodent and human brain and changes in this pattern in response to drugs of abuse have contributed primarily to direct research efforts toward the development of selective DA D(3) receptor antagonists. Growing preclinical evidence indicates that these compounds may actually regulate the motivation to self-administer drugs and disrupt drug-associated cue-induced craving. This report will be divided into three parts. First, preclinical evidence in support of the efficacy of selective DA D(3) receptor antagonists in animal models of drug addiction will be reviewed. The effects of mixed DA D(2)/D(3) receptor antagonists will not be discussed here because most of these compounds have low selectivity at the D(3) versus D(2) receptor, and their efficacy profile is related primarily to functional antagonism at D(2) receptors and possibly interactions with other neurotransmitter systems. Second, major advances in medicinal chemistry for the identification and optimization of selective DA D(3) receptor antagonists and partial agonists will be analyzed. Third, translational research from preclinical efficacy studies to so-called proof-of-concept studies for drug addiction indications will be discussed.

Novel method for generating structure-based pharmacophores using energetic analysis

We describe a novel method to develop energetically optimized, structure-based pharmacophores for use in rapid in silico screening. The method combines pharmacophore perception and database screening with protein-ligand energetic terms computed by the Glide XP scoring function to rank the importance of pharmacophore features. We derive energy-optimized pharmacophore hypotheses for 30 pharmaceutically relevant crystal structures and screen a database to assess the enrichment of active compounds. The method is compared to three other approaches: (1) pharmacophore hypotheses derived from a systematic assessment of receptor-ligand contacts, (2) Glide SP docking, and (3) 2D ligand fingerprint similarity. The method developed here shows better enrichments than the other three methods and yields a greater diversity of actives than the contact-based pharmacophores or the 2D ligand similarity. Docking produces the most cases (28/30) with enrichments greater than 10.0 in the top 1% of the database and on average produces the greatest diversity of active molecules. The combination of energy terms from a structure-based analysis with the speed of a ligand-based pharmacophore search results in a method that leverages the strengths of both approaches to produce high enrichments with a good diversity of active molecules.