From pyrroles to 1-oxo-2,3,4,9-tetrahydro-1H-β-carbolines: A new class of orally bioavailable mGluR1 antagonists

Exploiting the SAR of the known pyrrole derivatives, a new class of mGluR1 antagonists was designed by replacement of the pyrrole core with an indole scaffold and consequent cyclization of the C-2 position into a tricyclic beta-carboline template. The appropriate exploration of the position C-6 with a combination of H-bond acceptor groups coupled with bulky/lipophilic moieties led to the discovery of a new series of mGluR1 antagonists. These compounds exhibited a non-competitive behavior, excellent pharmacokinetic properties, and good in vivo activity in animal models of acute and chronic pain, after oral administration.

13C bis-labeled pyrroles: A tool for the identification of the rat metabolism of 3-methyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester

Following the recent disclosure of 3-methyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester as a potent and selective mGluR1 non-competitive antagonist, the use of a doubly (13)C-labeled analogue to identify, and consequently prevent, metabolically labile positions is reported.

Structure-activity studies on neuropeptide S: identification of the amino acid residues crucial for receptor activation

Neuropeptide S (NPS) has been recently recognized as the endogenous ligand for the previous orphan G-protein-coupled receptor GPR154, now referred to as the NPS receptor (NPSR). The NPS-NPSR receptor system regulates important biological functions such as sleeping/wakening, locomotion, anxiety, and food intake. To collect information on the mechanisms of interaction between NPS and its receptor, a classical structure-activity relationship study was performed. Human (h) NPS derivatives obtained by Ala and d-scan and N- and C-terminal truncation were assessed for their ability to stimulate calcium release in HEK293 cells expressing the human recombinant NPSR. The results of this study indicate that (i) the effect of hNPS is mimicked by the fragment hNPS-(1-10); (ii) Phe(2), Arg(3), and Asn(4) are crucial for biological activity; (iii) the sequence Thr(8)-Gly(9)-Met(10) is important for receptor activation, although with non-stringent chemical requirements; and (iv) the sequence Val(6)-Gly(7) acts as a hinge region between the two above-mentioned domains. However, the stimulatory effect of hNPS given intracerebroventricularly on mouse locomotor activity was not fully mimicked by hNPS-(1-10), suggesting that the C-terminal region of the peptide maintains importance for in vivo activity. In conclusion, this study identified the amino acid residues of this peptide most important for receptor activation.

From pyrroles to pyrrolo[1,2-a]pyrazinones: A new class of mGluR1 antagonists

Exploiting the SAR of the known pyrrole derivatives, a new class of mGluR1 antagonists was developed through a cyclization of the C-2 position on the pyrrole N-1 nitrogen. The resulting pyrrolo[1,2-a]pyrazinones are potent and noncompetitive antagonists.

In vitro and in vivo pharmacological characterization of the novel UT receptor ligand [Pen5,DTrp7,Dab8]urotensin II(4-11) (UFP-803)

The novel urotensin-II (U-II) receptor (UT) ligand, [Pen(5),DTrp(7),Dab(8)]U-II(4-11) (UFP-803), was pharmacologically evaluated and compared with urantide in in vitro and in vivo assays. In the rat isolated aorta, UFP-803 was inactive alone but, concentration dependently, displaced the contractile response to U-II to the right, revealing a competitive type of antagonism and a pA(2) value of 7.46. In the FLIPR [Ca(2+)](i) assay, performed at room temperature in HEK293(hUT) and HEK293(rUT) cells, U-II increased [Ca(2+)](i) with pEC(50) values of 8.11 and 8.48. Urantide and UFP-803 were inactive as agonists, but antagonized the actions of U-II by reducing, in a concentration-dependent manner, the agonist maximal effects with apparent pK(B) values in the range of 8.45-9.05. In a separate series of experiments performed at 37 degrees C using a cuvette-based [Ca(2+)](i) assay and CHO(hUT) cells, urantide mimicked the [Ca(2+)](i) stimulatory effect of U-II with an intrinsic activity (alpha) of 0.80, while UFP-803 displayed a small (alpha=0.21) but consistent residual agonist activity. When the same experiments were repeated at 22 degrees C (a temperature similar to that in FLIPR experiments), urantide displayed a very small intrinsic activity (alpha=0.11) and UFP-803 was completely inactive as an agonist. In vivo in mice, UFP-803 (10 nmol kg(-1)) antagonized U-II (1 nmol kg(-1))-induced increase in plasma extravasation in various vascular beds, while being inactive alone. In conclusion, UFP-803 is a potent UT receptor ligand which displays competitive/noncompetitive antagonist behavior depending on the assay. While UFP-803 is less potent than urantide, it displayed reduced residual agonist activity and as such may be a useful pharmacological tool.

3-Methyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester: an exploration of the C-2 position. Part I

Following the recent disclosure of 3-methyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester, a potent and selective mGluR1 non-competitive antagonist, we report here a detailed exploration of the C-2 position of this scaffold with the preparation of differently substituted amides. Great improvement of the pharmacokinetic properties has been achieved through this exercise.

3-Methyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester: an exploration of the C-2 position. Part II, A solid-phase approach

Following the recent disclosure (Part I of this paper) of 3-methyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) amides and of their improved pharmacokinetic profile with respect to the originally reported esters, a further exploration of the C-2 position through a solid-phase approach is reported here.

Stereoselective synthesis and preliminary evaluation of (+)- and (–)-3-methyl-5-carboxy-thien-2-yl-glycine (3-MATIDA): identification of (+)-3-MATIDA as a novel mGluR1 competitive antagonist

The synthesis of the (+)- and (-)-isomers of 3-methyl-5-carboxy-thyen-2-yl-glycine (3-MATIDA), heterocyle isosters of carboxyphenylglycines (CPGs), a known class of competitive metabotropic glutamate receptors, was accomplished by a stereoselective Ugi condensation. The two isomers were tested as potential rat mGluR1 ligand and the (+) isomer was found to be a moderately potent antagonist, while the (-) one was inactive.

Evidence that the metabotropic glutamate receptor 5 antagonist MPEP may act as an inhibitor of the norepinephrine transporter in vitro and in vivo

The mechanisms through which blockade of metabotropic glutamate receptors 5 (mGluR5) results in anxiolytic and antidepressant effects are currently unknown. In the present study, we therefore hypothesized that the anxiolytic- and antidepressant-like profile of the noncompetitive mGluR5 receptor antagonist 2-ethyl-6-(phenylethynyl)-pyridine (MPEP) may be mediated by inhibition of the norepinephrine transporter (NET). Accordingly, we first examined the potency of MPEP to bind to or inhibit uptake at the NET as well as the dopamine and serotonin transporters (DAT and SERT, respectively). We also examined the simultaneous in vivo effects of MPEP and desipramine (DMI) on both NE-like oxidation current in the amygdala (AMY) and cell firing in the locus coeruleus (LC) by means of differential pulse voltammetry (DPV) coupled with electrophysiology. MPEP completely displaced the binding of [3H]-nisoxetine on human NET with a pKi of 6.63 +/- 0.02. In addition, MPEP was able to inhibit [3H]-NE uptake in LLCPK cells expressing human NET, with a pIC50 of 5.55 +/- 0.09. In vivo DPV data revealed that both MPEP (30 mg/kg i.p.) and DMI (10 mg/kg i.p.) significantly increased NE-like voltammetric responses levels in the AMY, whereas both compounds also significantly decreased cell firing monitored concomitantly from the second microelectrode in the LC. Collectively, the results of the present study provide potential new mechanisms through which MPEP exerts its anxiolytic and antidepressant effects.

2,4-Dicarboxy-pyrroles as selective non-competitive mGluR1 antagonists: an exploration of the role of the pyrrolic scaffold

Following the disclosure of 3-(1,2,2-trimethylpropyl) 4-[3,5-dimethyl-2-propyloxycarbonyl]pyrrolecarboxylate as a potent and selective mGluR1 non-competitive antagonist, the role and the importance of the pyrrole template were investigated. Different aromatic moieties were investigated as possible bio-isosteric replacement of the original scaffold and some of them were shown to be partially able to mimic the properties of the original pyrrole ring.

2,4-Dicarboxy-pyrroles as selective non-competitive mGluR1 antagonists: further characterization of 3,5-dimethyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester and structure-activity relationships

Following the disclosure of 3,5-dimethyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester [3,5-dimethyl PPP] as a potent and selective mGluR1 non-competitive antagonist, we report here further in vivo characterization of this important tool and disclose the investigation of the C-5 position, which led to very potent compounds.

Synthesis and pharmacological characterisation of 2,4-dicarboxy-pyrroles as selective non-competitive mGluR1 antagonists

Metabotropic glutamate receptors (mGluRs) are an unusual family of G-protein coupled receptor (GPCR), and are characterised by a large extracellular N-terminal domain that contains the glutamate binding site. We have identified a new class of non-competitive metabotropic glutamate receptor 1 (mGluR1) antagonists, 2,4-dicarboxy-pyrroles which are endowed with nanomolar potency. They interact within the 7 transmembrane (7TM) domain of the receptor and show antinociceptive properties when tested in a number of different animal models.

Purification and Biological Characterization of Host-Specific SV-Toxins from Stemphylium vesicarium Causing Brown Spot of European Pear

ABSTRACT Culture filtrates of a pathogenic isolate (IT37) of Stemphylium vesicarium, causing brown spot of European pear, induced veinal necrosis only on pear leaves susceptible to the pathogen. Two host-specific toxins, SV-toxins I and II, were purified from culture filtrates of IT37 by successively using Amberlite XAD-2 resin adsorption, cellulose thin-layer chromatography, and high-performance liquid chromatography under three different sets of conditions. Susceptible cultivars showed veinal necrosis at a SV-toxin I concentration of 0.01 to 0.1 mug/ml, whereas resistant cultivars were insensitive to the toxin at 1,000 mug/ml. SV-toxins I and II caused a dose-dependent increase in electrolyte loss from susceptible leaf tissues. No increase in electrolyte loss was detected in leaf tissues from resistant cultivars. The results of physiological studies indicated that SV-toxins appear to have an early effect on plasma membranes of susceptible leaves. Spores of a nonpathogenic isolate induced necrotic lesions on susceptible leaves in the presence of a small amount of toxin. SV-toxins were detected in intercellular fluids obtained from diseased leaves after inoculation with the pathogen. The results indicate that SV-toxins I and II produced by S. vesicarium can be characterized as host-specific toxins.

Pharmacological analysis of carboxyphenylglycines at metabotropic glutamate receptors

Three carboxyphenylglycine derivatives were examined for their activity on glutamate metabotropic receptors negatively linked to adenylate cyclase. Chinese hamster ovary cells stably expressing mGlu2 and mGlu4 were utilised for this study. A receptor binding analysis was also performed for the main classes of glutamate ionotropic receptors and for the glycine binding site on the NMDA-receptor complex. In mGlu2 expressing cells (S)4-carboxy-3-hydroxyphenylglycine and (S)4-carboxy-phenylglycine antagonized forskolin-stimulated cAMP levels, with EC50 of 21 and 970 microM, respectively, acting as agonists at this receptor subtype, whereas (RS) alpha-methyl-4-carboxyphenylglycine antagonized glutamate response in these cells. None of these compounds showed any agonistic or antagonistic activity on mGlu4 expressing cells. No affinity for the ionotropic receptors (NMDA, AMPA and kainate) and for the glycine site of the NMDA-receptor complex was found using the receptor binding approach, except for (RS)4-carboxy-3-hydroxyphenylglycine which showed a pKi of 5.68 in ((+/-)2-carboxypiperazin-4-yl)propyl-1-phosphonic acid binding for NMDA receptor, although this can be ascribed to the (R) form of the racemic mixture.

Competitive antagonism by phenylglycine derivatives at type I metabotropic glutamate receptors

The metabotropic glutamate receptors (mGluRs) form a family of G-protein-coupled receptors which consists of at least seven members termed mGluR1-mGluR7. These members are classified into subfamilies according to their sequence similarities, signal transduction mechanisms and agonist selectivities. mGluR1 and mGluR5 are coupled to the phosphoinositide hydrolysis/Ca2+ signal transduction and efficiently respond to quisqualate. In this study, we have stably expressed mGluR1 in Chinese hamster ovary cells on which the activation of the phosphoinositide signal transduction pathway was evaluated by means of two methods and their degree of correspondence was analyzed. These two methods involve the Li(+)-dependent accumulation of [3H]inositol-labeled inositol phosphates or the [3H]cytidine-labeled phospholiponucleotide cytidine diphospho (CDP)- diacylglycerol (DAG). The correlation between the two measures was found to be generally uniform for the different agonists evaluated. However, the levels of CDP-DAG were found to be consistently higher. Furthermore, quisqualate showed a differential activity on the two methods behaving as a partial agonist and as a full agonist on the inositol phosphate and the CDP-DAG responses, respectively. On the same cells the activity of a series of carboxyphenylglycines recently described as possible new tools for investigating the role of mGluRs has been evaluated. Three phenylglycine derivatives were tested and found to be competitive antagonists at this mGluR subtype. They inhibited both the phosphoinositide signal transduction pathway and the release of intracellular Ca2+ induced by quisqualate the most potent agonist at mGluR1. The pharmacological nature of these compounds and their relative potencies in antagonizing mGluR1 activation are described.

Smooth muscle myosin light chain kinase: rapid purification by anion exchange high-performance liquid chromatography

A rapid procedure for the purification of myosin light chain kinase present in chicken gizzard smooth muscle using anion exchange high-performance liquid chromatography is described. The procedure allows preparation of microgram amounts of the protein directly from the extract of gizzard myofibrils and then is suitable for the study of myosin light chain kinase in small muscles. The protein was judged to be greater than 95% pure by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The enzyme retains its activity since it catalyzes the calcium-calmodulin-dependent phosphorylation of the 20,000-Da myosin light chain.

Caldesmon: anomalous electrophoretic behaviour in polyacrylamide gel

In SDS gels caldesmon (Mr = 140 kDa) and myosin light chain kinase (Mr = 130 kDa) migrate as a closely separated doublet. When glycerol is added to the gel caldesmon is characterized by an anomalous migration. In fact under this latter condition, the distance between caldesmon and myosin light chain kinase is enhanced by two-three times. The nature of putative caldesmon and myosin light chain kinase was confirmed by physicochemical, enzymatic and immunological methods.