Structure-activity studies on the nociceptin/orphanin FQ receptor antagonist 1-benzyl-N-{3-[spiroisobenzofuran-1(3H),4'-piperidin-1-yl]propyl} pyrrolidine-2-carboxamide

seco-1-Azacubane-2-carboxylic acid-Amide Bond Comparison to Proline

seco-1-Azacubane-2-carboxylic acid, an unusual and sterically constrained amino acid, was found to undergo amide bond formation at both the N- and C-termini using proline based bioactive molecule templates as a concept platform.

Exploring Highly Functionalized Tetrahydropyridine as a Dual Inhibitor of Monoamine Oxidase A and B: Synthesis, Structural Analysis, Single Crystal XRD, Supramolecular Assembly Exploration by Hirshfeld Surface Analysis, and Computational Studies

Ethyl 4-(4-fluorophenylamino)-2,6-bis(4-(trifluoromethyl)phenyl)-1-(4-fluoro-phenyl)-1,2,5,6-tetrahydropyridine-3-carboxylate (FTEAA) has been synthesized efficiently in an iodine-catalyzed five-component reaction of 4-fluoroaniline, 4-trifluoromethyl benzaldehyde, and ethyl acetoacetate in methanol at 55 °C for 12 h. Various spectro-analytical techniques such as ¹H and ¹³C NMR and Fourier-transform infrared spectroscopy have validated the structure of FTEAA. Further confirmation of the structure of FTEAA has been established on the basis of single-crystal X-ray diffraction analysis. The supramolecular assembly of FTEAA in terms of strong and comparatively weak noncovalent interactions is fully investigated by Hirshfeld surface analysis, the interaction energy between pairs of molecules, and energy frameworks. The void analysis is conducted to explore the strength and stability of the crystal structure. Furthermore, molecular docking analysis was computationally performed to see the potential intermolecular interactions between the selected proteins and FTEAA. The binding interaction energies are found to be -8.8 and -9.6 kcal/mol for the proteins MAO-B (PDB ID: 2V5Z) and MAO-A (PDB ID: 2Z5X), respectively. These reasonably good binding energies (more negative values) indicate the efficient associations between the FTEAA and target proteins. The proteins and FTEAA were also analyzed for intermolecular interactions. FTEAA and proteins interact in a variety of ways, like conventional hydrogen bonds, carbon-hydrogen bonds, alkyl, π-alkyl, and halide interactions.

In silico analysis of energy interactions between nociceptin/orfanin FQ receptor and two antagonists with potential antidepressive action

This study addresses the binding energies of NOPR-ligand complexes and presents the main amino acid residues involved in the interaction between these complexes.

Azide-Functionalized Naphthoxyloside as a Tool for Glycosaminoglycan Investigations

We present a xylosylated naphthoxyloside carrying a terminal azide functionality that can be used for conjugation using click chemistry. We show that this naphthoxyloside serves as a substrate for β4GalT7 and induces the formation of soluble glycosaminoglycan (GAG) chains with physiologically relevant lengths and sulfation patterns. Finally, we demonstrate its usefulness by conjugation to the Alexa Fluor 647 and TAMRA fluorophores and coupling to a surface plasmon resonance chip for interaction studies with the hepatocyte growth factor known to interact with the GAG heparan sulfate.

Embelin as Lead Compound for New Neuroserpin Polymerization Inhibitors

Familial encephalopathy with neuroserpin inclusion bodies (FENIB) is a severe and lethal neurodegenerative disease. Upon specific point mutations in the SERPINI1gene-coding for the human protein neuroserpin (NS) the resulting pathologic NS variants polymerize and accumulate within the endoplasmic reticulum of neurons in the central nervous system. To date, embelin (EMB) is the only known inhibitor of NS polymerization in vitro. This molecule is capable of preventing NS polymerization and dissolving preformed polymers. Here, we show that lowering EMB concentration results in increasing size of NS oligomers in vitro. Moreover, we observe that in cells expressing NS, the polymerization of G392E NS is reduced, but this effect is mediated by an increased proteasomal degradation rather than polymerization impairment. For these reasons we designed a systematic chemical evolution of the EMB scaffold aimed to improve its anti-polymerization properties. The effect of EMB analogs against NS polymerization was assessed in vitro. None of the EMB analogs displayed an anti-polymerization activity better than the one reported for EMB, indicating that the EMB–NS interaction surface is very specific and highly optimized. Thus, our results indicate that EMB is, to date, still the best candidate for developing a treatment against NS polymerization.

Green Synthesis and Antimicrobial Activity of Some Novel N-Arylimidazo[1,2-a]pyrazine-2-Carboxamide Derivatives

The article deals with the synthesis of some novel N-arylimidazo[1,2-a]pyrazine-2-carboxamides (7a-l) by condensation reaction of imidazo[1,2-a]pyrazine-2-carboxylic acid (5) with different aliphatic/aromatic amines (6a-l) by using 1-methylimidazole, Mukaiyama’s reagent and 2-chloro-1-methylpyridinium iodide under microwave irradiation conditions. A new series of compounds 7 have been prepared from 2-iodopyrazine (1). Compound 1 on purged with ammonia gas in the presence of Cu2O and K2CO3 furnishes pyrazin-2-amine (2), which is treated with ethyl 3-bromo-2-oxopropanoate (3) to produce ethyl imidazo[1,2-a]pyrazine-2-carboxylate (4), which on hydrolysis with NaOH yields imidazo[1,2-a]pyrazine-2-carboxylic acid (5). The structures of the newly synthesized compounds have been elucidated on the basis of spectral (IR, 1H and 13C NMR and MS) and analytical data. Compounds 7a-l have also been screened for their antimicrobial activity. Some of the compounds exhibit promising antimicrobial activity

Pharmacological profile of the neuropeptide S receptor: Dynamic mass redistribution studies

Neuropeptide S (NPS) is the endogenous ligand of the neuropeptide S receptor (NPSR). NPS modulates several biological functions including anxiety, wakefulness, pain, and drug abuse. The aim of this study was the investigation of the pharmacological profile of NPSR using the dynamic mass redistribution (DMR) assay. DMR is a label-free assay that offers a holistic view of cellular responses after receptor activation. HEK293 cells stably transfected with the murine NPSR (HEK293mNPSR) have been used. To investigate the nature of the NPS-evoked DMR signaling, FR900359 (Gq inhibitor), pertussis toxin (Gi inhibitor), and rolipram (phosphodiesterase inhibitor) were used. To determine the pharmacology of NPSR, several selective ligands (agonists, partial agonists, antagonists) have been tested. NPS, through selective NPSR activation, evoked a robust DMR signal with potency in the nanomolar range. This signal was predominantly, but not completely, blocked by FR900359, suggesting the involvement of the Gq-dependent signaling cascade. NPSR ligands (agonists and antagonists) displayed potency values in DMR experiments similar, but not identical, to those reported in the literature. Furthermore, partial agonists produced a higher efficacy in DMR than in calcium experiments. DMR can be successfully used to study the pharmacology and signaling properties of novel NPSR ligands. This innovative approach will likely increase the translational value of in vitro pharmacological studies.

NOP receptor pharmacological profile - A dynamic mass redistribution study

The Nociceptin/Orphanin FQ (N/OFQ) peptide NOP receptor is coupled to pertussis toxin (PTX)-sensitive G proteins (G_i/o) whose activation leads to the inhibition of both cAMP production and calcium channel activity, and to the stimulation of potassium currents. The label free dynamic mass redistribution (DMR) approach has been demonstrated useful for investigating the pharmacological profile of G protein-coupled receptors. Herein, we employ DMR technology to systematically characterize the pharmacology of a large panel of NOP receptor ligands. These are of peptide and non-peptide nature and display varying degrees of receptor efficacy, ranging from full agonism to pure antagonism. Using Chinese hamster ovary (CHO) cells expressing the human NOP receptor we provide rank orders of potency for full and partial agonists as well as apparent affinities for selective antagonists. We find the pharmacological profile of NOP receptor ligands to be similar but not identical to values reported in the literature using canonical assays for G_i/o-coupled receptors. Our data demonstrate that holistic label-free DMR detection can be successfully used to investigate the pharmacology of the NOP receptor and to characterize the cellular effects of novel NOP receptor ligands.

High-affinity ligands of the colchicine domain in tubulin based on a structure-guided design

Microtubule-targeting agents that bind at the colchicine-site of tubulin are of particular interest in antitumoral therapy due to their dual mechanism of action as antimitotics and vascular disrupting agents. Cyclohexanediones derivatives have been described as a new family of colchicine-domain binders with an association constant to tubulin similar to that of colchicine. Here, the high-resolution structures of tubulin in complex with cyclohexanediones TUB015 and TUB075 were solved by X-ray crystallography. A detailed analysis of the tubulin-TUB075 interaction by means of computational affinity maps allowed the identification of two additional regions at the binding site that were addressed with the design and synthesis of a new series of cyclohexanediones with a distal 2-substituted benzofurane. These new compounds showed potent antiproliferative activity with IC50 values in the nM range, arrested cell cycle progression at the G2/M phase and induced apoptosis at sub μM concentrations. Moreover, they caused the destruction of a preformed vascular network in vitro and inhibited the migration of endothelial cells at non-toxic concentrations. Finally, these compounds displayed high affinity for tubulin as substantiated by a K b value of 2.87 × 108 M-1 which, to the best of our knowledge, represents the highest binding constant measured to date for a colchicine-domain ligand.

Modified synthesis of NOP receptor antagonist SB612111

SB612111 ((5S,7S)-7-{[4-(2,6-dichlorophenyl)piperidin-1-yl]methyl}-1-methyl-6,7,8,9-tetrahydro-5H-benzo[7]annulen-5-ol) is a potent and selective antagonist of the nociception/orphanin FQ peptide (NOP) receptor. In the process of synthesizing cis-SB612111 to support ongoing animal studies, several key steps of the published syntheses in the patent literature proceeded in low yields in our hands, particularly with the route to the key intermediate piperidine 3, the reduction of amide 14, lactone 17 formation and the final reductive amination between 18 and 3 in the diastereoselective synthesis. We have thus explored various reaction conditions and successfully improved the yields for the necessary synthetic steps. We herein report our modified synthesis of SB612111 as the cis-diastereomers.

The Importance of Ligand-Receptor Conformational Pairs in Stabilization: Spotlight on the N/OFQ G Protein-Coupled Receptor

Understanding the mechanism by which ligands affect receptor conformational equilibria is key in accelerating membrane protein structural biology. In the case of G protein-coupled receptors (GPCRs), we currently pursue a brute-force approach for identifying ligands that stabilize receptors and facilitate crystallogenesis. The nociceptin/orphanin FQ peptide receptor (NOP) is a member of the opioid receptor subfamily of GPCRs for which many structurally diverse ligands are available for screening. We observed that antagonist potency is correlated with a ligand's ability to induce receptor stability (Tm) and crystallogenesis. Using this screening strategy, we solved two structures of NOP in complex with top candidate ligands SB-612111 and C-35. Docking studies indicate that while potent, stabilizing antagonists strongly favor a single binding orientation, less potent ligands can adopt multiple binding modes, contributing to their low Tm values. These results suggest a mechanism for ligand-aided crystallogenesis whereby potent antagonists stabilize a single ligand-receptor conformational pair.

Pharmacological characterization of endomorphin-2-based cyclic pentapeptides with methylated phenylalanine residues

As part of our continuing studies on the structure-activity relationships of cyclic pentapeptides based on the structure of endomorphin-2, we report here the synthesis and biological activities of a new series of analogs incorporating 2', 3' or 4'-methylphenylalanine (MePhe) residues into positions 3 or 4 of the parent cyclopeptide, Dmt-c[d-Lys-Phe-Phe-Asp]NH2 (Dmt=2',6'-dimethyltyrosine). Analogs with MePhe in position 4 showed a row of magnitude increased μ-opioid receptor (MOP receptor) affinity as compared with a parent compound. The in vitro potencies of the new analogs were determined in calcium mobilization assay performed in Chinese Hamster Ovary (CHO) cells expressing human recombinant opioid receptors and chimeric G proteins. All analogs were strong μ/κ (MOP/KOP) receptor agonists and weak δ (DOP) receptor agonists. In the in vivo hot-plate test in mice, the MePhe(4)-modified peptides showed remarkable antinociceptive activity after intracerebroventricular (i.c.v.) administration which was most likely due to the concomitant activation of more than one opioid receptor type.

Chimeric G proteins in fluorimetric calcium assays: experience with opioid receptors

High throughput calcium mobilization assays are extensively used for pharmacological characterization of GPCR ligands. These approaches, initially developed for G(q)-coupled receptors, can be extended to G(i) coupled GPCRs using chimeric G proteins. Here we used the Gα(qi5) protein to force the nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor, as well as the classical opioid receptors to signal through the PLC-IP(3)-Ca(2+) pathway in CHO cells. Calcium levels were monitored using the fluorometric imaging plate reader FlexStation II and the Ca(2+) dye Fluo 4 AM. For investigating the pharmacology of the NOP receptor a panel of full and partial agonists and antagonists were assessed, while a small panel of agonists and antagonists was used for evaluating the pharmacological profile of opioid receptors. Some limitations of this assay and differences in the results obtained in comparison with those with G(i) based biochemical assays are described. Overall, the present results confirm that the chimeric G protein strategy is useful for studying the pharmacological activity of G(i) coupled receptor ligands and that the aberrant signaling does not produce any measurable change in the pharmacological profile of the receptor under study. Thus, this G protein strategy is extremely useful for setting up primary screening assays for NOP and classical opioid receptors and likely for other members of the GPCR family.

Structure of the nociceptin/orphanin FQ receptor in complex with a peptide mimetic

Members of the opioid receptor family of G-protein-coupled receptors (GPCRs) are found throughout the peripheral and central nervous system, where they have key roles in nociception and analgesia. Unlike the 'classical' opioid receptors, δ, κ and μ (δ-OR, κ-OR and μ-OR), which were delineated by pharmacological criteria in the 1970s and 1980s, the nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP, also known as ORL-1) was discovered relatively recently by molecular cloning and characterization of an orphan GPCR. Although it shares high sequence similarity with classical opioid GPCR subtypes (∼60%), NOP has a markedly distinct pharmacology, featuring activation by the endogenous peptide N/OFQ, and unique selectivity for exogenous ligands. Here we report the crystal structure of human NOP, solved in complex with the peptide mimetic antagonist compound-24 (C-24) (ref. 4), revealing atomic details of ligand-receptor recognition and selectivity. Compound-24 mimics the first four amino-terminal residues of the NOP-selective peptide antagonist UFP-101, a close derivative of N/OFQ, and provides important clues to the binding of these peptides. The X-ray structure also shows substantial conformational differences in the pocket regions between NOP and the classical opioid receptors κ (ref. 5) and μ (ref. 6), and these are probably due to a small number of residues that vary between these receptors. The NOP-compound-24 structure explains the divergent selectivity profile of NOP and provides a new structural template for the design of NOP ligands.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Modulation of silent and constitutively active nociceptin/orphanin FQ receptors by potent receptor antagonists and Na+ ions in rat sympathetic neurons

The pharmacology of G protein-coupled receptors can be influenced by factors such as constitutive receptor activation and Na(+) ions. In this study, we examined the coupling of natively and heterologously expressed nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptors with voltage-dependent Ca(2+) channels after exposure to four high-affinity NOP receptor blockers [[Nphe(1)Arg(14)Lys(15)]N/OFQ-NH(2) (UFP-101), 1-[1-(cyclooctylmethyl)-1,2,3,6-tetrahydro-5-(hydroxymethyl)-4-pyridinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (Trap-101), 1-benzyl-N-{3-[spiroisobenzofuran-1(3H),4'-piperidin-1-yl]propyl}pyrrolidine-2-carboxamide (compound 24), and N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl)benzamide hydrochloride (JTC-801)] in sympathetic neurons. The enhanced tonic inhibition of Ca(2+) currents in the absence of agonists, indicative of constitutively active NOP receptors in transfected neurons, was abolished after pretreatment with pertussis toxin. In control neurons, the four antagonists did not exert any effects when applied alone but significantly blocked the N/OFQ-mediated Ca(2+) current inhibition. Exposure of transfected neurons to UFP-101 resulted in partial agonist effects. In contrast, Trap-101, compound 24, and JTC-801 exerted inverse agonism, as measured by the loss of tonic Ca(2+) current inhibition. In experiments designed to measure the N/OFQ concentration-response relationship under varying Na(+) concentrations, a leftward shift of IC(50) values was observed after Na(+) exposure. Although similar N/OFQ efficacies were measured with all solutions, a significant decrease of Hill coefficient values was obtained with increasing Na(+) concentrations. Examination of the allosteric effects of Na(+) on heterologously overexpressed NOP receptors showed that the tonic Ca(2+) current inhibition was abolished in the presence of the monovalent cation. These results demonstrate that constitutively active NOP receptors exhibit differential blocker pharmacology and allosteric regulation by Na(+). Data are also presented demonstrating that heterologously expressed mu opioid receptors in sympathetic neurons are similarly modulated.