Positive allosteric modulation of the mu-opioid receptor produces analgesia with reduced side effects.

Positive allosteric modulators (PAMs) of the mu-opioid receptor (MOR) have been hypothesized as potentially safer analgesics than traditional opioid drugs. This is based on the idea that PAMs will promote the action of endogenous opioid peptides while preserving their temporal and spatial release patterns and so have an improved therapeutic index. However, this hypothesis has never been tested. Here, we show that a mu-PAM, BMS-986122, enhances the ability of the endogenous opioid Methionine-enkephalin (Met-Enk) to stimulate G protein activity in mouse brain homogenates without activity on its own and to enhance G protein activation to a greater extent than ß-arrestin recruitment in Chinese hamster ovary (CHO) cells expressing human mu-opioid receptors. Moreover, BMS-986122 increases the potency of Met-Enk to inhibit GABA release in the periaqueductal gray, an important site for antinociception. We describe in vivo experiments demonstrating that the mu-PAM produces antinociception in mouse models of acute noxious heat pain as well as inflammatory pain. These effects are blocked by MOR antagonists and are consistent with the hypothesis that in vivo mu-PAMs enhance the activity of endogenous opioid peptides. Because BMS-986122 does not bind to the orthosteric site and has no inherent agonist action at endogenously expressed levels of MOR, it produces a reduced level of morphine-like side effects of constipation, reward as measured by conditioned place preference, and respiratory depression. These data provide a rationale for the further exploration of the action and safety of mu-PAMs as an innovative approach to pain management.

Discovery and SAR of aryl hydroxy pyrimidinones as potent small molecule agonists of the GPCR APJ.

This article describes the discovery of aryl hydroxy pyrimidinones and the medicinal chemistry efforts to optimize this chemotype for potent APJ agonism. APJ is a G-protein coupled receptor whose natural agonist peptide, apelin, displays hemodynamic improvement in the cardiac function of heart failure patients. A high throughput screen was undertaken to identify small molecule hits that could be optimized to mimic the apelin in vitro response. A potent and low molecular weight aryl hydroxy pyrimidinone analog 30 was identified through optimization of an HTS hit and medicinal chemistry efforts to improve its properties.

2,6-Bis(benzimidazol-2-yl)pyridine complexes of group 14 elements.

Treatment of MCl2 (M = Ge or Sn) with 2,6-bis(benzimidazol-2-yl)pyridine (G-BZIMPY, G = NBn, N(3,5-CF3)Bn, NAllyl and O) yielded the self-ionization products [G-BZIMPYMCl][MCl3] (1-6) in high yields (75-98%). Reduction reactions are examined and the nickel complexes 8 and 9 ([(NBn-BZIMPY)2Ni][MCl3]2) are isolated from the reaction of Ni(COD)2 with 1 and 2 respectively. [NBn-BZIMPYSnCl][SnCl3] shows a significantly stronger MLCT band in the UV-vis absorption spectrum than its germanium counterparts, with germanium complexes exhibiting negative solvatochromism that is not observed in tin complexes.

Identification and biochemical analyses of selective CB2 agonists.

Cannabinoid CB1 and CB2 receptors are activated by Δ9-tetrahydrocannabinol, a psychoactive component of marijuana. The cannabinoid CB1 receptor is primarily located in the brain and is responsible for the psychoactive side effects, whereas the cannabinoid CB2 receptor is located in immune cells and is an attractive target for immune-related maladies. We identify small molecules that selectively bind to the cannabinoid CB2 receptor and can be further developed into therapeutics. The affinity of three molecules, ABK5, ABK6, and ABK7, to the cannabinoid CB2 receptor was determined with radioligand competition binding. The potency of G-protein coupling was determined with GTPγS binding. The three compounds bound selectively to the cannabinoid CB2 receptor, and no binding to the cannabinoid CB1 receptor was detected up to 10 µM. Immunoblotting studies show that the amount of ERK1/2 and MEK phosphorylation increased in a Gi/o-dependent manner. Furthermore, an immune cell line (Jurkat cells) was treated with ABK5, and as a result, inhibited cell proliferation. These three compounds are novel cannabinoid CB2 receptor agonists and hold promise to be further developed to treat inflammation and the often-associated pain.

Halogen and Sulfur Oxidation of Germanium and Tin Dications.

Herein we present the oxidation of base-stabilized tetrelII dications [LM][OTf]2 [L = BIMEt3 = tris(1-ethyl-benzoimidazol-2-ylmethyl)amine and M = Ge, Sn] with PCl5, SeCl4, Br2, and I2 to access dicationic dihalides [LMX2][OTf]2. The addition of oxygen-rich donor molecules (picoline N-oxide, OPEt3) to dications [LM][OTf]2 yielded donor-acceptor complexes bearing a tetrel(II) dication adjacent to a pnictogen(V) moiety. The addition of elemental sulfur to [LGe][OTf]2 yielded [(LGeS)2][OTf]4 containing a dimeric tetracation.

2,6-Bis(benzimidazol-2-yl)pyridines as more electron-rich and sterically accessible alternatives to 2,6-bis(imino)pyridine for group 13 coordination chemistry.

Treatment of GaCl3 with 2,6-bis(benzimidazol-2-yl)pyridine (G-BZIMPY, G = NBz, N(3,5-CF3)Bz, N-allyl and O) yielded the autoionization products [G-BZIMPYGaCl2][GaCl4] (1-4) in great yields. The Ga(iii) complex 1 was reduced to Ga(i) using K2[Fe(CO)4], resulting in the complex [(NBzBZIMPY)(Cl)Ga-Fe(CO)4] (7). GaCl3 and AlCl3 were complexed by the structurally similar bis(imino)pyridine (DIMPY) and the resulting complexes are compared to those of G-BZIMPY.

Synthesis, characterization and mass-spectrometric analysis of [LSn(IV)F4-x]x+ salts [L = tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine, x = 1-4].

A series of complexes with the formulae [(BIMEt3)SnF4-x][OTf]x with x = 1-4 has been synthesized by successive fluoride abstraction from SnF4 with TMSOTf in the presence of the tetradentate nitrogen donor BIMEt3 (tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine). Single crystal X-ray diffraction and heteronuclear NMR spectroscopic analysis provided insight into these new main group cations. Electrospray ionization mass spectrometric analysis on solutions containing the different salts allowed for successful detection of the cations [(BIMEt3)SnF]3+, [(BIMEt3)SnF2]2+ and [(BIMEt3)SnF3]+.

Tris(benzoimidazol)amine (L) complexes of pnictogen(iii) and pnictogen(v) cations and assessment of the [LP]3+/[LPF2]3+ redox couple.

A series of cationic complexes involving a pnictogen(iii) (Pn = P, As, Sb) centre and the tetradentate ligand tris((1-ethyl-benzoimidazol-2-yl)methyl)amine (BIMEt3) have been synthesized and comprehensively characterized. Oxidation of [P(BIMEt3)]3+ with XeF2 provides access to [PF2(BIMEt3)]3+ representing the first structurally characterized example of a phosphorus(v) centred trication.

Oxidation of a germanium(ii) dication to access cationic germanium(iv) fluorides.

The synthesis and characterization of the tris(1-ethyl-benzoimidazol-2-ylmethyl)amine (BIMEt3 = L) complex of Ge(ii)2+ is described. Oxidation of [LGe]2+ with Selectfluor gives [LGeF2]2+, in a process that is envisaged to involve a tricationic complex [LGeF]3+ as an intermediate, which has been isolated by fluoride ion abstraction from [LGeF2]2+.

Tris(1-methyl-imidazol-2-yl)phosphane Complexes of Pnictogen, Tetrel, and Triel Cations.

cations gallium indium nitrogen ligands pnictogens tetrelThe synthesis and characterization of salts with the generic formula [P(Im)3 M][OTf]x (Im=1-methyl-imidazol-2-yl; M=P, As or Sb and x=3; M=Ge or Sn and x=2) are reported. In all cases, the cations adopt a cage structure with two chemically and energetically distinct apical lone pairs. In contrast, complexes of gallium and indium engage two P(Im)3 ligands resulting in a distorted octahedral geometry for the triel center in compounds of the generic formula [{P(Im)3 }2 M][OTf]3 (M=Ga or In). An assessment of the acidity and basicity of the new compounds is presented.

Complexes of Stiboranium Mono-, Di-, and Trications.

Reaction of Ph2 SbCl3 with 2,2'-bipyridine and Me3 SiOSO2 CF3 releases chlorobenzene, which is interpreted as a reductive (SbV /SbIII ) elimination from a complex of a stiboranium cation. Conversely, reactions of Ph2 SbCl3 with 4-methylpyridine-N-oxide and AgOSO2 CF3 give redox-resistant complexes with the generic formulae [Ph2 SbCl3-x Lx+1 ][OTf]x , including a compound containing a pnictogen(V) trication.

Discovery of Selective Cannabinoid CB2 Receptor Agonists by High-Throughput Screening.

The endocannabinoid system (ECS) plays a diverse role in human physiology ranging from the regulation of mood and appetite to immune modulation and the response to pain. Drug development that targets the cannabinoid receptors (CB1 and CB2) has been explored; however, success in the clinic has been limited by the psychoactive side effects associated with modulation of the neuronally expressed CB1 that are enriched in the CNS. CB2, however, are expressed in peripheral tissues, primarily in immune cells, and thus development of CB2-selective drugs holds the potential to modulate pain among other indications without eliciting anxiety and other undesirable side effects associated with CB1 activation. As part of a collaborative effort among industry and academic laboratories, we performed a high-throughput screen designed to discover selective agonists or positive allosteric modulators (PAMs) of CB2. Although no CB2 PAMs were identified, 167 CB2 agonists were discovered here, and further characterization of four select compounds revealed two with high selectivity for CB2 versus CB1. These results broaden drug discovery efforts aimed at the ECS and may lead to the development of novel therapies for immune modulation and pain management with improved side effect profiles.

Pharmacologic Evidence for a Putative Conserved Allosteric Site on Opioid Receptors.

Allosteric modulators of G protein-coupled receptors, including opioid receptors, have been proposed as possible therapeutic agents with enhanced selectivity. BMS-986122 is a positive allosteric modulator (PAM) of the µ-opioid receptor (µ-OR). BMS-986187 is a structurally distinct PAM for the δ-opioid receptor (δ-OR) that has been reported to exhibit 100-fold selectivity in promoting δ-OR over µ-OR agonism. We used ligand binding and second-messenger assays to show that BMS-986187 is an effective PAM at the µ-OR and at the κ-opioid receptor (κ-OR), but it is ineffective at the nociceptin receptor. The affinity of BMS-986187 for δ-ORs and κ-ORs is approximately 20- to 30-fold higher than for µ-ORs, determined using an allosteric ternary complex model. Moreover, we provide evidence, using a silent allosteric modulator as an allosteric antagonist, that BMS-986187 and BMS-986122 bind to a similar region on all three traditional opioid receptor types (µ-OR, δ-OR, and κ-OR). In contrast to the dogma surrounding allosteric modulators, the results indicate a possible conserved allosteric binding site across the opioid receptor family that can accommodate structurally diverse molecules. These findings have implications for the development of selective allosteric modulators.

Reversible Oxidative Se-Se Coupling of Phosphine Selenides by Ph3 Sb(OTf)2.

Salts of diphosphoniumdiselenide dications ([R3 PSeSePR3 ][OTf]2 ) have been isolated from reactions of trialkylphosphine selenides with triphenylantimony bistriflate. The redox process is speculated to proceed via a cationic coordination complex [Ph3 SbL2 ][OTf]2 (L=Me3 PSe, iPr3 PSe), which is also formed in the reaction of [R3 PSeSePR3 ][OTf]2 with Ph3 Sb. The observations indicate that the reductive elimination of [R3 PSeSePR3 ]2+ from [Ph3 Sb(SePR3 )2 ]2+ is reversible through the oxidative addition of [R3 PSeSePR3 ]2+ to Ph3 Sb.

Standard Curves Are Necessary to Determine Pharmacological Properties for Ligands in Functional Assays Using Competition Binding Technologies.

Homogeneous functional assays that utilize competition binding technology are widely used for determining pharmacological properties such as intrinsic activity and potency. One example is time-resolved fluorescence resonance energy transfer (TR-FRET) 3',5'-cyclic adenosine monophosphate (cAMP) assays, where labeled cAMP (tracer) and a labeled anti-cAMP antibody bind together to produce a TR-FRET signal when the two constituents are proximal to each other. This signal is disrupted when unlabeled and cellularly generated cAMP competes with the tracer cAMP for binding to the labeled antibody. It is important that the resulting assay signal, usually expressed as a TR-FRET ratio, be transformed to cAMP concentration using a cAMP standard curve. However, examples are still generated in the literature wherein investigators have used the ratiometric signal (not transformed using a standard curve) to determine values for intrinsic activity and potency of ligands. Untransformed raw data often produce reasonable looking sigmoidal concentration response curves, perhaps tempting investigators to use the raw data instead of the transformed data for applying pharmacological models. In this article, we describe the correct procedure for determining the potency and intrinsic activity of ligands that result in changes in cAMP levels using a lysate dilution assay of GLP-1 (7-36)-mediated TR-FRET cAMP accumulation and simulated data. We also highlight how the inappropriate use of raw signal data can dramatically affect interpretation of intrinsic activity and potency of ligands, and how this can adversely affect drug discovery programs. These findings apply not only to cAMP functional assays but also to other functional cellular signaling assays that utilize competition binding technologies.

Substitution Reactions at Dipp BIAN Supported Fluoroantimony Cations Yielding Cyanoantimony and Azidoantimony Cations.

This work presents new cationic coordination complexes of antimony with the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (Dipp BIAN) ligand system. The fluoroantimony complexes [SbF(Dipp BIAN)][OTf]2 and [SbF2 (Dipp BIAN)][OTf] have been successfully isolated and characterized. The fluorine substituent in the Lewis acidic complex [SbF(Dipp BIAN)][OTf]2 can be selectively replaced without degradation of the Sb-Dipp BIAN interaction to give the first dicationic azido and cyano derivatives, [Sb(CN)(Dipp BIAN)][OTf]2 and [Sb(N3 )(Dipp BIAN)][OTf]2 , which have been isolated and structurally characterized.

Tris(2-pyridyl)phosphine as a versatile ligand for pnictogen acceptors.

We report cationic complexes of arsenic and antimony with the tris(2-pyridyl)phosphine ligand. Chloride ion abstraction from AsCl3 using TMSOTf in the presence of the ligand gives [P(Pyr)3As][OTf]3, in which the trication adopts a C3v symmetric cage structure. The reaction proceeds via the intermediate [P(Pyr)3AsCl][OTf]2, which undergoes chloride exchange to give [P(Pyr)3As][OTf]3 and [P(Pyr)3AsCl2][OTf]. The rearrangement reaction has been supported by the isolation of the antimony mono fluoride derivative [P(Pyr)3SbF][OTf]2. The asymmetric axial lone pairs in derivatives of [P(Pyr)3Pn]3+ are electronically separated. The HOMO-1 (for arsenic) and HOMO (for antimony) represent the major contribution to the phosphine lone pair indicating the possibility for nucleophilic behaviour despite the +3 charge. Less accessible is the HOMO-7, which represents the lone pair at arsenic or antimony, respectively.

Cationic 2,2'-bipyridine complexes of germanium(ii) and tin(ii).

We present the first systematic study of 2,2'-bipyridine complexes of E(ii) cationic acceptors (E = Ge, Sn). The complexes were comprehensively characterized by spectroscopic and crystallographic methods to yield complexes of ECl1+ and E2+. Computational DFT methods were also employed to survey the bonding in the cations, along with an examination of their molecular orbitals (MOs).

Endogenous opioids regulate moment-to-moment neuronal communication and excitability.

Fear and emotional learning are modulated by endogenous opioids but the cellular basis for this is unknown. The intercalated cells (ITCs) gate amygdala output and thus regulate the fear response. Here we find endogenous opioids are released by synaptic stimulation to act via two distinct mechanisms within the main ITC cluster. Endogenously released opioids inhibit glutamate release through the δ-opioid receptor (DOR), an effect potentiated by a DOR-positive allosteric modulator. Postsynaptically, the opioids activate a potassium conductance through the µ-opioid receptor (MOR), suggesting for the first time that endogenously released opioids directly regulate neuronal excitability. Ultrastructural localization of endogenous ligands support these functional findings. This study demonstrates a new role for endogenously released opioids as neuromodulators engaged by synaptic activity to regulate moment-to-moment neuronal communication and excitability. These distinct actions through MOR and DOR may underlie the opposing effect of these receptor systems on anxiety and fear.

Condensation Reactions of Chlorophosphanes with Chalcogenides.

A high-yielding and facile synthesis for diphosphane monochalcogenides (1(Ch)((R))) and their constitutional isomers, diphosphanylchalcoganes (2(Ch)((R))), was developed, featuring a condensation reaction between chlorophosphanes (R2PCl) and sodium chalcogenides (Na2Ch, Ch = S, Se, (Te)). The optimized protocol selectively yields either 1(Ch)((R)) (R2(Ch)PPR2) or 2(Ch)((R)) (Ch(PR2)2) depending upon the steric demand of the substituents R. Reaction pathways consistent with the distinct reaction outcomes are proposed. The application of 1(Ch)((R)) and 2(Ch)((R)) as an interesting class of ligands is exemplarily demonstrated by the preparation of selected transition metal complexes.