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An array of six pyridyl-substituted fused bicyclic piperidines was prepared as novel cores for medicinal chemistry. For maximum diversity, the size of the fused ring varied from three to six atoms and contained up to two oxygen atoms. The pyridine ring was incorporated to improve physicochemical properties and to challenge the robustness of the chemistry. The presence of the pyridine did interfere with our initial approaches to these molecules, and in several instances, a blocking strategy had to be employed. These new scaffolds possess high sp3 character and may prove useful in multiple medicinal chemistry applications.

A novel GPR119 agonist based on the 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole scaffold was designed through lead optimization starting from pyrazole-based GPR119 agonist 1. The design is centered on the conformational restriction of the core scaffold, while minimizing the change in spatial relationships of two key pharmacophoric elements (piperidine-carbamate and aryl sulfone)., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Research on phosphodiesterases both in academic labs and in the pharmaceutical industry has remained steady over the past 35 years. Although there have been some clinical successes, they have been clustered around just a couple of PDE isoforms, and disproportionate to the huge investment put forth against what seem like very druggable targets. This review attempts to uncover the reasons for the lack of productivity in PDE drug discovery, and summarizes the current hot areas of research. In addition, new insights gathered about structure-function relationships are highlighted, in particular those relating to enzyme regulation. Lastly, novel strategies for targeting the activation or inactivation of selected PDEs are proposed that may allow for a more targeted approach for PDE modulation., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

PDE8B is a cAMP-specific isoform of the broader class of phosphodiesterases (PDEs). As no selective PDE8B inhibitors had been reported, a high throughput screen was run with the goal of identifying selective tools for exploring the potential therapeutic utility of PDE8B inhibition. Of the numerous hits, one was particularly attractive since it was amenable to rapid deconstruction leading to inhibitors with very high ligand efficiency (LE) and lipophilic ligand efficiency (LLE). These triazolopyrimidines were optimized for potency, selectivity and ADME properties ultimately leading to compound 42. This compound was highly potent and selective with good bioavailability and advanced into pre-clinical development., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The first highly potent and selective PDE8 inhibitors are disclosed. The initial tetrahydroisoquinoline hit was transformed into a nipecotic amide series in order to address a reactive metabolite issue. Reduction of lipophilicity to address metabolic liabilities uncovered an interesting diastereomer-dependent trend in turnover by human microsomes., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The synthesis and properties of the bridged piperidine (oxaazabicyclo) compounds 8, 9, and 11 are described. A conformational analysis of these structures is compared with the representative GPR119 ligand 1. These results and the differences in agonist pharmacology are used to formulate a conformation-based hypothesis to understand activation of the GPR119 receptor. We also show for these structures that the agonist pharmacology in rat masks the important differences in human pharmacology.

Background: Abolishing the inhibitory signal of intracellular cAMP by phosphodiesterases (PDEs) is a prerequisite for effector T (Teff) cell function. While PDE4 plays a prominent role, its control of cAMP levels in Teff cells is not exclusive. T cell activation has been shown to induce PDE8, a PDE isoform with 40- to 100-fold greater affinity for cAMP than PDE4. Thus, we postulated that PDE8 is an important regulator of Teff cell functions., Methodology/principal Findings: We found that Teff cells express PDE8 in vivo. Inhibition of PDE8 by the PDE inhibitor dipyridamole (DP) activates cAMP signaling and suppresses two major integrins involved in Teff cell adhesion. Accordingly, DP as well as the novel PDE8-selective inhibitor PF-4957325-00 suppress firm attachment of Teff cells to endothelial cells. Analysis of downstream signaling shows that DP suppresses proliferation and cytokine expression of Teff cells from Crem-/- mice lacking the inducible cAMP early repressor (ICER). Importantly, endothelial cells also express PDE8. DP treatment decreases vascular adhesion molecule and chemokine expression, while upregulating the tight junction molecule claudin-5. In vivo, DP reduces CXCL12 gene expression as determined by in situ probing of the mouse microvasculature by cell-selective laser-capture microdissection., Conclusion/significance: Collectively, our data identify PDE8 as a novel target for suppression of Teff cell functions, including adhesion to endothelial cells.

Starting from a non-selective pyrazolo-pyrimidone lead, the sequential use of parallel medicinal chemistry and directed synthesis led to the discovery of potent, highly selective, and orally bioavailable PDE9 inhibitors. The availability of these tools allowed for a thorough evaluation of the therapeutic potential of PDE9 inhibition.

Using a combination of parallel and directed synthesis, the discovery of a highly potent and selective series of adenosine A3 agonists was achieved. High aqueous solubility, required for the intended parenteral route of administration, was achieved by the presence of one or two basic amine functional groups.

Clinical use of the nonsteroidal anti-inflammatory drug diclofenac (DF) is associated with an incidence of idiosyncratic hepatoxicity. The formation of reactive metabolites of DF in vivo has been proposed to be responsible for such toxicity. One type of reactive metabolite, a benzoquinone imine of DF formed through oxidation by cytochromes P450, can be trapped by glutathione in vitro in liver microsomes to form glutathione (GS) adducts. Three GS adducts from DF were reported in the literature, namely, 5-hydroxy (OH)-4-glutathione-DF, 4'-OH-3'-glutathione-DF and 5-OH-6-glutathione-DF, and they all have the same molecular weight of 616. Recently, we developed a sensitive and high throughput method for the detection of GS adducts from liver microsome incubation. This method uses a constant neutral loss scan of m/z 129, a "structure-characteristic" fragment for GS adduct, on an automated chip-based nanoelectrospray (Advion NanoMate 100) attached to a tandem mass spectrometer (Sciex API 3000). The analysis of GS adducts from human liver microsome incubation with DF by the NanoMate 100-API 3000 method unambiguously revealed a new adduct ion with m/z 583 (MH+), in addition to the known adduct peak with m/z 617 (MH+). This new adduct was further confirmed to be 4'-OH-2'-glutathion-deschloro-diclofenac by liquid chromatography (LC) tandem mass spectrometry (MS), LC/MS-NMR, and comparison to a synthetic standard.

KB-R7943 and SEA0400 are Na(+)/Ca(2+) exchanger (NCX) inhibitors with differing potency and selectivity. The cardioprotective efficacy of these NCX inhibitors was examined in isolated rabbit hearts (Langendorff perfused) subjected to regional ischemia (coronary artery ligation) and reperfusion. KB-R7943 and SEA0400 elicited concentration-dependent reductions in infarct size (SEA0400 EC(50): 5.7 nM). SEA0400 was more efficacious than KB-R7943 (reduction in infarct size at 1 microM: SEA0400, 75%; KB-R7943, 40%). Treatment with either inhibitor yielded similar reductions in infarct size whether administered before or after regional ischemia. SEA0400 (1 microM) improved postischemic recovery of function (+/-dP/dt), whereas KB-R7943 impaired cardiac function at >/=1 microM. At 5-20 microM, KBR-7943 elicited rapid and profound depressions of heart rate, left ventricular developed pressure, and +/-dP/dt. Thus the ability of KB-R7943 to provide cardioprotection is modest and limited by negative effects on cardiac function, whereas the more selective NCX inhibitor SEA0400 elicits marked reductions in myocardial ischemic injury and improved +/-dP/dt. NCX inhibition represents an attractive approach for achieving clinical cardioprotection.

Selective adenosine A(3) agonists have potential utility for the prevention of perioperative myocardial ischemic injury. Herein, we report on the discovery and synthesis of compound 7. This amino nucleoside agonist possesses unprecedented levels of selectivity for the human adenosine A(3) receptor.

Intramolecular endo-cyclization reactions of N-acyliminium ions have seen wide application for the synthesis of heterocyclic compounds. The corresponding exocyclic variant, which would provide 1-aminotetralin derivatives, for example, has little precedent. We have discovered that acyclic N-acylcarbamates can be readily reduced to the corresponding N-acylhemiaminal derivatives in high yield using DIBAL as the reducing agent. These intermediates are remarkably stable and, if desired, can be purified and stored. The acyclic N-acylhemiaminals undergo both intra- and intermolecular nucleophilic addition reactions mediated by strong Lewis acids, such as TiCl(4). Diastereoselectivity, induced either by a substituent on the newly formed ring, or by utilizing a chiral ester on the carbamic acid, was disappointingly low. This methodology was successfully applied to the synthesis of the racemic form of the marketed antidepressant sertraline.

The hypocholesterolemic activities of pamaqueside and tiqueside, two structurally similar saponins, were evaluated in cholesterol-fed rabbits. The pharmacological profiles of the saponins were virtually identical: both dose-dependently decreased the intestinal absorption of labeled cholesterol 25-75%, increased fecal neutral sterol excretion up to 2.5-fold, and decreased hepatic cholesterol content 10-55%. High doses of pamaqueside (>5 mg/kg) or tiqueside (>125 mg/kg) completely prevented hypercholesterolemia. Decreases in plasma and hepatic cholesterol levels were strongly correlated with increased neutral sterol excretion. Ratios of neutral sterol excreted to pamaqueside administered were greater than 1:1 at all doses, in opposition to the formation of a stoichiometric complex previously suggested for tiqueside and other saponins. Ratios in tiqueside-treated rabbits were less than unity, a reflection of its lower potency. Pamaqueside-treated rabbits exhibited a more rapid decline in plasma cholesterol concentrations than control animals fed a cholesterol-free diet, indicating that the compound also inhibited the absorption of biliary cholesterol. Intravenous administration of pamaqueside had no effect on plasma cholesterol levels despite plasma levels twice those observed in rabbits given pamaqueside orally. These data indicate that pamaqueside and tiqueside induce hypocholesterolemia by blocking lumenal cholesterol absorption via a mechanism that apparently differs from the stoichiometric complexation of cholesterol hypothesized for other saponins.

Cholesterol absorption inhibition remains an attractive approach for the treatment of hypercholesterolemia. We have continued our SAR development in the spirostanyl cellobioside class of agents seeking a greater understanding of the role carbamoyl substitution has on the potency in this series. In this regard, a series of differentially substituted carbamate analogs were made with and without deoxygenations. From this study, it was determined that the minimal requirements for optimal potency was a lone carbamate at C4" and deoxygenation at the C6" position.

We have explored the use of steroidal glycosides as cholesterol absorption inhibitors which act through an unknown mechanism. The lead for this program was tigogenin cellobioside (1, tiqueside) which is a weak inhibitor (ED50 = 60 mg/kg) as measured in an acute hamster cholesterol absorption assay. Modification of the steroid portion of the molecule led to the discovery of 11-ketotigogenin cellobioside (5, pamaqueside) which has an ED50 of 2 mg/kg. Replacement of the cellobiose with other sugars failed to provide more potent analogs. However, large improvements in potency were realized through modification of the hydroxyl groups on the cellobiose. This strategy ultimately led to the 4", 6"-bis[(2-fluorophenyl)carbamoyl]-beta-D-cellobiosyl derivative of 11-ketotigogenin (51) with an ED50 of 0.025 mg/kg in the hamster assay, as well as the corresponding hecogenin analog 64 (ED50 = 0.07 mg/kg).

A-77636, ((1R,3S) 3-(1'-adamantyl)-1-aminomethyl-3,4-dihydro-5,6-dihydroxy-1H-2-benz opyran hydrochloride), is a selective dopamine D1 receptor agonist. In a battery of receptor binding assays, A-77636 shows the highest affinity (pKi = 7.40 +/- 0.09; Ki = 39.8 nM) for the dopamine D1 receptor. A-77636 is an agonist at the dopamine D1 receptors in the fish retina (pEC50 = 8.13; EC50 = 1.1 nM; intrinsic activity = 102% of dopamine) and the rat caudate-putamen (pEC50 = 8.97; intrinsic activity = 134% of dopamine). The compound is functionally inactive at dopamine D2 receptors (EC50 > 10 microM). In rats with unilateral 6-OHDA (6-hydroxydopamine) lesions of the nigro-striatal dopaminergic pathway, A-77636 elicits prolonged (> 20 h) contralateral turning that is blocked by SCH 23390, a D1 receptor antagonist, but not by haloperidol at doses selective for the dopamine D2 receptor. Higher doses of A-77636 produce forelimb clonus in rats and mice. When tested in marmosets treated with MPTP to induce a parkinsonian-like state, A-77636 increases locomotor activity and decreases the severity of the parkinsonian-like symptoms: the compound is active after either subcutaneous or oral administration. A-77641, the optical antipode of A-77636, has a lower affinity towards the dopamine D1 receptor (pKi = 5.14, Ki = 7200 nM), is less potent as a dopamine D1 receptor agonist (pEC50 = 5.65; EC50 = 2200 nM), fails to elicit turning in the 6-OHDA-lesioned rat, and lacks antiparkinsonian efficacy in the MPTP-treated marmoset.(ABSTRACT TRUNCATED AT 250 WORDS)

A68930, [1R, 3S] 1-aminomethyl-5,6-dihydroxy-3-phenylisochroman HCl, is a potent, partial agonist in the dopamine-sensitive adenylate cyclase model of the D1 dopamine receptor in fish retina. In the rat caudate-putamen model of the D1 dopamine receptor, A68930 is a potent (EC50 2.1 nM) full agonist. In contrast, A68930 is a much weaker (EC50 = 3,920 nM) full agonist in a biochemical model of the D2 dopamine receptor. A68930 also displays weak 2 agonist activity but the molecule is virtually inactive at the 1 and beta-adrenoceptors. When tested in rats bearing a unilateral 6-OHDA lesion of the nigro-neostriatal neurons, A68930 elicits prolonged (> 20 hr) contralateral turning.

The synthesis and dopaminergic activity of a series of C3 and nitrogen-substituted 1-(aminomethyl)-3,4-dihydro-5,6-dihydroxy-1H-2-benzopyrans (isochromans) is described. The synthesis of the compounds was stereospecific for the 1,3 cis isomer, and the enantioselective synthesis of both enantiomers of one of the analogues (20) was achieved. It was determined that all of the dopaminergic activity resides in the [1R,3S] isomer. Generally, substitution at the C3 position provided compounds with very high potency (less than 10 nm EC50) and selectivity for the D1 receptor, with a wide range of intrinsic activities (60-160%). Analogues containing C3 substituents including aryl, arylalkyl, and cyclic and acyclic alkyl groups showed a marked enhancement of dopaminergic activity compared to the unsubstituted compound. As a class, the drugs were orally active in the rat rotation model with a very long duration of action.

A68930, (1R,3S)-1-aminomethyl-5,6-dihydroxy-3-phenylisochroman HCl, is a potent (EC50 = 2.5 nM), partial (intrinsic activity = 66% of dopamine) agonist in the fish retina dopamine-sensitive adenylate cyclase model of the D1 dopamine receptor. In the rat caudate-putamen model of the D1 dopamine receptor, A68930 is a potent (EC50 = 2.1 nM) full agonist. In contrast, A68930 is a much weaker (EC50 = 3920 nM) full agonist in a biochemical model of the dopamine D2 receptor. The orientation of the 3-phenyl substituent in the molecule is critical for the affinity and selectivity of the molecule towards the dopamine D1 receptor. A68930 also displays weak alpha 2-agonist activity but the molecule is virtually inactive at the alpha 1- and beta-adrenoceptors. When tested in rats bearing a unilateral 6-OHDA lesion of the nigro-neostriatal neurons, A68930 elicits prolonged (greater than 20 h) contralateral turning that is antagonized by dopamine D1 receptor selective doses of SCH 23390 but not by D2 receptor selective doses of haloperidol. In this lesioned rat model, A68930 increases 2-deoxyglucose accumulation in the lesioned substantia nigra, pars reticulata. When tested in normal rats, A68930 elicits hyperactivity and, at higher doses, produces a forelimb clonus.