Azulene-based compounds for targeting orexin receptors

A library of 70 000 synthetically accessible azulene-based compounds was virtually screened at the OX2 receptor. Based on the results, a series of azulene derivatives was synthesized and the binding to and activation of both orexin receptor subtypes were assessed. Two most promising binders were determined to have inhibition constants in the 3-9 mu M range and two other compounds showed weak OX2 receptor agonism. Furthermore, three compounds exhibited a concentration-dependent potentiation of the response to orexin-A at the OX1 but not the OX2 receptors. Altogether this data opens new approaches for further development of antagonists, agonists, and potentiators of orexin response based on the azulene scaffold. (C) 2018 Elsevier Masson SAS. All rights reserved.Peer reviewe

Stapled truncated orexin peptides as orexin receptor agonists

The peptides orexin-A and -B, the endogenous agonists of the orexin receptors, have similar 19-amino-acid C-termini which retain full maximum response as truncated peptides with only marginally reduced potency, while further N-terminal truncations successively reduce the activity. The peptides have been suggested to bind in an α‐helical conformation, and truncation beyond a certain critical length is likely to disrupt the overall helical structure. In this study, we set out to stabilize the α‐helical conformation of orexin‐A15–33 via peptide stapling at four different sites. At a suggested hinge region, we varied the length of the cross-linker as well as replaced the staple with two α-aminoisobutyric acid residues. Modifications close to the peptide C‐terminus, which is crucial for activity, were not allowed. However, central and N‐terminal modifications yielded bioactive peptides, albeit with decreased potencies. This provides evidence that the orexin receptors can accommodate and be activated by α-helical peptides. The decrease in potency is likely linked to a stabilization of suboptimal peptide conformation or blocking of peptide backbone–receptor interactions at the hinge region by the helical stabilization or the modified amino acids.Peer reviewe

Synthesis of carboxyimidamide-substituted benzo[c][1,2,5]oxadiazoles and their analogs, and evaluation of biological activity against Leishmania donovani

A facile synthesis route to carboxyimidamide-substituted benzoxadiazoles and related derivatives was developed. A total of 25 derivatives were synthesized. They were evaluated for antileishmanial activity by inhibition of Leishmania donovani axenic amastigote growth using a fluorescent viability microplate assay. The most promising derivative (14) demonstrated an antileishmanial EC50 of 4.0 mu M, and it also showed activity in infected macrophages (EC50 5.92 mu M) without signs of cytotoxicity.Peer reviewe

Pharmacological characterization of the orexin/hypocretin receptor agonist Nag 26

One promising series of small-molecule orexin receptor agonists has been described, but the molecular pharmacological properties, i.e. ability and potency to activate the different orexin receptor-regulated signal pathways have not been reported for any of these ligands. We have thus here assessed these properties for the most potent ligand of the series, 4'-methoxy-N,N-dimethyl-3'4N-(3-{[2-(3-methylbenzamido)ethyl]amino}phenyl sulfamoy1]-(1,1'-biphenyl)-3-carboxamide (Nag 26). Chinese hamster ovary-K1 cells expressing human orexin receptor subtypes OX1 and OX2 were used. Ca2+ elevation and cell viability and death were assessed by fluorescent methods, the extracellular signal-regulated kinase pathway by a luminescent Elk-1 reporter assay, and phospholipase C and adenylyl cyclase activities by radioactive methods. The data suggest that for the G(q)-dependent responses, Ca2+, phospholipase C and Elk-1, Nag 26 is a full agonist for both receptors, though of much lower potency. However, saturation was not always reached for OX1, partially due to Nag 26s low solubility and partially because the response decreased at high concentrations. The latter occurs in the same range as some reduction of cell viability, which is independent of orexin receptors. Based on the EC50, Nag 26 was OX2 selective by 20-200 fold in different assays, with some indication of biased agonism (as compared to orexin-A). Nag 26 is a potent orexin receptor agonist with a largely similar pharmacological profile as orexin-A. However, its weaker potency (low-mid micromolar) and low water solubility as well as the non-specific effect in the mid-micromolar range may limit its usefulness under physiological conditions.Peer reviewe

Pharmacophore Model To Discover OX₁ and OX₂ Orexin Receptor Ligands

Small molecule agonists and antagonists of the orexinergic system have key implications for research and therapeutic purposes. We report a pharmacophore model trained on ∼200 antagonists and prospectively validated by screening a collection of ∼137,000 compounds. The resulting hit list, 395 compounds, was tested for OX₁ and OX₂ receptor activity using calcium mobilization assay in recombinant cell lines. Validation was conducted using both calcium mobilization and [¹²⁵I]-orexin‑A competition binding. Compounds <b>4</b>–<b>7</b> have weak agonist activity and K_i’s in the 1–30 μM range; compounds <b>8</b>–<b>14</b> are antagonists with K_i’s in the 0.1–10 μM range for OX₂ and 1–50 μM for the OX₁ receptor. Docking simulations were used to devise a working hypothesis where two subpockets are important for activation, one between TM5 and TM6 lined by Phe5.42, Tyr5.47, and Tyr6.48 and another above the orthosteric pocket lined by Asp2.65 and Tyr7.32

Azulene as a biphenyl mimetic in orexin/hypocretin receptor agonists

Azulene is a rare ring structure in drugs, and we investigated whether it could be used as a biphenyl mimetic in known orexin receptor agonist Nag 26, which is binding to both orexin receptors OX1 and OX2 with preference towards OX2. The most potent azulene-based compound was identified as an OX1 orexin receptor agonist (pEC50 = 5.79 +/- 0.07, maximum response = 81 +/- 8% (s.e.m. of five independent experiments) of the maximum response to orexin-A in Ca2+ elevation assay). However, the azulene ring and the biphenyl scaffold are not identical in their spatial shape and electron distribution, and their derivatives may adopt different binding modes in the binding site.Peer reviewe

Nonpeptidic Oxazole-Based Prolyl Oligopeptidase Ligands with Disease-Modifying Effects on alpha-Synuclein Mouse Models of Parkinson's Disease

Prolyl oligopeptidase (PREP) is a widely distributedserine proteasein the human body cleaving proline-containing peptides; however, recentstudies suggest that its effects on pathogenic processes underlyingneurodegeneration are derived from direct protein-protein interactions(PPIs) and not from its regulation of certain neuropeptide levels.We discovered novel nonpeptidic oxazole-based PREP inhibitors, whichdeviate from the known structure-activity relationship forPREP inhibitors. These new compounds are effective modulators of thePPIs of PREP, reducing alpha-synuclein (alpha Syn) dimerizationand enhancing protein phosphatase 2A activity in a concentration-responsemanner, as well as reducing reactive oxygen species production. Fromthe best performing oxazoles, HUP-55 was selected for in vivo studies. Its brain penetration was evaluated, andit was tested in alpha Syn virus vector-based and alpha Syn transgenicmouse models of Parkinson's disease, where it restored motorimpairment and reduced levels of oligomerized alpha Syn in the striatumand substantia nigra.Peer reviewe

A Developability-Focused Optimization Approach Allows Identification of in Vivo Fast-Acting Antimalarials: <i>N</i>‑[3-[(Benzimidazol-2-yl)amino]propyl]amides

Malaria continues to be a major global health problem, being particularly devastating in the African population under the age of five. Artemisinin-based combination therapies (ACTs) are the first-line treatment recommended by the WHO to treat Plasmodium falciparum malaria, but clinical resistance against them has already been reported. As a consequence, novel chemotypes are urgently needed. Herein we report a novel, in vivo active, fast-acting antimalarial chemotype based on a benzimidazole core. This discovery is the result of a medicinal chemistry plan focused on improving the developability profile of an antichlamydial chemical class previously reported by our group