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Positive modulation of cAMP signalling by phosphodiesterase (PDE) inhibitors has recently been explored as a potential target for the reversal of cognitive and behavioural deficits implicating the corticoaccumbal circuit. Previous studies show that PDE type 1 isoform B (PDE1B) inhibition may improve memory function in rodent models; however, the contribution of PDE1B inhibition to impulsivity, attentional and motivational functions as well as its neurophysiological effects have not been investigated. To address this, we recorded single unit activity in medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) in Lister Hooded rats treated with the PDE1B inhibitor Lu AF64386 and tested in the 5-choice serial reaction time task (5-CSRTT). We also asked whether PDE1B inhibition modulates neurophysiological deficits produced by subchronic phencyclidine (PCP) treatment, a rat pharmacological model of schizophrenia. Lu AF64386 significantly affected behavioural parameters consistent with a reduction in goal-directed behaviour, however without affecting accuracy. Additionally, it reduced mPFC neuronal activity. Pre-treatment with PCP did not affect behavioural parameters, however it significantly disrupted overall neuronal firing while increasing phasic responses to reward-predicting cues and disrupting mPFC-NAc cross-talk. The latter two effects were reversed by Lu AF64386. These findings suggest PDE1B inhibition may be beneficial in disorders implicating a dysfunction of the mPFC-NAc network.

Two series of novel chiral hexahydro-2H-furo[3,2-b]pyrroles, 4-(7,8-dimethoxyquinazolin-4-yl) series A and 4-(6,7- dimethoxyquinazolin-4-yl) series B, were synthesized in enantiomerically pure form and evaluated for their inhibitory effects on phosphodiesterase 1 (PDE1) and phosphodiesterase 4 (PDE4) as well as for their inhibitory activity on cell proliferation in A375 melanoma and 3T3 fibroblast cells in vitro. Key steps of synthesis were (i) diastereoselective nucleophilic addition of vinylmagnesium bromide to N-allylimine derived from conveniently protected d-glyceraldehyde, (ii) ring-closing metathesis, (iii) debenzylative cycloetherification, and (iv) aromatic nucleophilic substitution. Some of the obtained compounds were proven to be active as inhibitors of PDE1 isoforms, with IC50 values in the high nanomolar/low micromolar concentration range, and showed antiproliferative activity on A375 melanoma cells., This work was financially supported by the Government of Aragon (E45_17R research group). A.C. thanks the Government of Aragon for an EPIF grant.

The calcium-regulated phosphodiesterase 1 (PDE1) family is highly expressed in the brain, but its functional role in neurones is poorly understood. Using the selective PDE1 inhibitor Lu AF64196 and biosensors for cyclic nucleotides including a novel biosensor for cGMP, we analyzed the effect of PDE1 on cAMP and cGMP in individual neurones in brain slices from male newborn mice. Release of caged NMDA triggered a transient increase of intracellular calcium, which was associated with a decrease in cAMP and cGMP in medium spiny neurones in the striatum. Lu AF64196 alone did not increase neuronal cyclic nucleotide levels, but blocked the NMDA-induced reduction in cyclic nucleotides indicating that this was mediated by calcium-activated PDE1. Similar effects were observed in the prefrontal cortex and the hippocampus. Upon corelease of dopamine and NMDA, PDE1 was shown to down-regulate the D1-receptor mediated increase in cAMP. PDE1 inhibition increased long-term potentiation in rat ventral striatum, showing that PDE1 is implicated in the regulation of synaptic plasticity. Overall, our results show that PDE1 reduces cyclic nucleotide signaling in the context of glutamate and dopamine coincidence. This effect could have a therapeutic value for treating brain disorders related to dysfunctions in dopamine neuromodulation.

Background and Purpose PDE1, a subfamily of cyclic nucleotide PDEs consisting of three isoforms, PDE1A, PDE1B and PDE1C, has been implicated in the regulation of vascular tone. The PDE1 isoform(s) responsible for tone regulation is unknown. This study used isoform-preferring PDE1 inhibitors, Lu AF58027, Lu AF64196, Lu AF66896 and Lu AF67897, to investigate the relative contribution of PDE1 isoforms to regulation of vascular tone. Experimental Approach In rat mesenteric arteries, expression and localization of Pde1 isoforms were determined by quantitative PCR and in situ hybridization, and physiological impact of PDE1 inhibition was evaluated by isometric tension recordings. Key Results In rat mesenteric arteries, Pde1a mRNA expression was higher than Pde1b and Pde1c. In situ hybridization revealed localization of Pde1a to vascular smooth muscle cells (VSMCs) and only minor appearance of Pde1b and Pde1c. The potency of the PDE1 inhibitors at eliciting relaxation showed excellent correlation with their potency at inhibiting PDE1A. Thus, Lu AF58027 was the most potent at inhibiting PDE1A and was also the most potent at eliciting relaxation in mesenteric arteries. Inhibition of NOS with l-NAME, soluble GC with ODQ or PKG with Rp-8-Br-PET-cGMP all attenuated the inhibitory effect of PDE1 on relaxation, whereas PKA inhibition with H89 had no effect. Conclusions and Implications Pde1a is the dominant PDE1 isoform present in VSMCs, and relaxation mediated by PDE1A inhibition is predominantly driven by enhanced cGMP signalling. These results imply that isoform-selective PDE1 inhibitors are powerful investigative tools allowing examination of physiological and pathological roles of PDE1 isoforms.

Background and purpose Phosphodiesterase enzymes (PDE1-11) break down cyclic nucleotides and are important in the regulation of the cardiovascular system. The purpose of the present study was to investigate the effect on the cardiovascular system of two novel selective PDE1 inhibitors, Lu AF41228 and Lu AF58027. Experimental approach We used rat mesenteric small arteries (internal diameters of 200-300 µm), RT-PCR and measurement of isometric wall tension. The effect of Lu AF41228 and Lu AF58027 on heart rate and blood pressure was assessed in both anesthetized and conscious male rats. Key results Nanomolar concentrations of Lu AF41228 and Lu AF58027 inhibited PDE1A, PDE1B, and PDE1C enzyme activity, while micromolar concentrations were required to observe inhibitory effects at other PDEs. RT-PCR revealed expression of PDE1A, PDE1B, and PDE1C in rat brain, heart, and aorta, but only PDE1A and PDE1B in mesenteric arteries. In rat isolated mesenteric arteries contracted with phenylephrine or U46619, Lu AF41228 and Lu AF58027 induced concentration-dependent relaxations which were markedly reduced by inhibitors of guanylate cyclase, ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), and adenylate cyclase, SQ22536 (9-(tetrahydro-2-furanyl)-9H-purin-6-amine, 9-THF-Ade), and in preparations without endothelium. In anesthetized rats Lu AF41228 and Lu AF58027 dose-dependently lowered mean blood pressure and increased heart rate. In conscious rats with telemetric pressure transducers, repeated dosing of Lu AF41228 lowered mean arterial blood pressure 10-15 mmHg and increased heart rate. Conclusions and implications The findings that these novel PDE1 inhibitors induce vasodilation and blood pressure lowering suggest a potential use of these vasodilators in the treatment of hypertension and vasospasm.

Therapeutic interest in augmentation of 5-hydroxytryptamine2A (5-HT2A) receptor signaling has been renewed by the effectiveness of psychedelic drugs in the treatment of various psychiatric conditions. In this study, we have further characterized the pharmacological properties of the recently developed 5-HT2 receptor agonist N-2-hydroxybenzyl)-2,5-dimethoxy-4-cyanophenylethylamine (25CN-NBOH) and three structural analogs at recombinant 5-HT2A, 5-HT2B, and 5-HT2C receptors and investigated the pharmacokinetic properties of the compound. 25CN-NBOH displayed robust 5-HT2A selectivity in [3H]ketanserin/[3H]mesulergine, [3H]lysergic acid diethylamide and [3H]Cimbi-36 binding assays (Ki2C/Ki2A ratio range of 52–81; Ki2B/Ki2A ratio of 37). Moreover, in inositol phosphate and intracellular Ca2+ mobilization assays 25CN-NBOH exhibited 30- to 180-fold 5-HT2A/5-HT2C selectivities and 54-fold 5-HT2A/5-HT2B selectivity as measured by Δlog(Rmax/EC50) values. In an off-target screening 25CN-NBOH (10 μM) displayed either substantially weaker activity or inactivity at a plethora of other receptors, transporters, and kinases. In a toxicological screening, 25CN-NBOH (100 μM) displayed a benign acute cellular toxicological profile. 25CN-NBOH displayed high in vitro permeability (Papp = 29 × 10−6 cm/s) and low P-glycoprotein-mediated efflux in a conventional model of cellular transport barriers. In vivo, administration of 25CN-NBOH (3 mg/kg, s.c.) in C57BL/6 mice mice produced plasma and brain concentrations of the free (unbound) compound of ∼200 nM within 15 minutes, further supporting that 25CN-NBOH rapidly penetrates the blood-brain barrier and is not subjected to significant efflux. In conclusion, 25CN-NBOH appears to be a superior selective and brain-penetrant 5-HT2A receptor agonist compared with (±)-2,5-dimethoxy-4-iodoamphetamine (DOI), and thus we propose that the compound could be a valuable tool for future investigations of physiologic functions mediated by this receptor.

Gabazine, a γ-aminobutyric acid type A (GABAA) receptor antagonist, has previously been reported to inhibit the binding of [3H]NCS-382, a representative ligand of the high-affinity binding site for the neuroactive substance γ-hydroxybutyric acid (GHB). We herein report a study on the structural determinants of gabazine for binding to (i) the orthosteric binding site of the GABAA receptor and (ii) the high-affinity GHB binding site. Expanding the structural diversity of available ligands for the high-affinity GHB binding sites, this study identified 2-(imidazo[1,2-b]pyridazin-2-yl)acetic acid as a novel ligand-scaffold leading to analogues with relatively high affinity (Ki 0.19–2.19 μM) and >50 times selectivity for the [3H]NCS-382 over [3H]muscimol binding sites. These results highlight that gabazine interacts with the high-affinity GHB and orthosteric GABAA receptor binding sites differently and that distinct analogues can be generated to select between them. To facilitate further in vivo studies, a prom...

The ρ-containing γ-aminobutyric acid type A receptors (GABAA Rs) play an important role in controlling visual signaling. Therefore, ligands that selectively target these GABAA Rs are of interest. In this study, we demonstrate that the partial GABAA R agonist imidazole-4-acetic acid (IAA) is able to penetrate the blood-brain barrier in vivo; we prepared a series of α- and N-alkylated, as well as bicyclic analogues of IAA to explore the structure-activity relationship of this scaffold focusing on the acetic acid side chain of IAA. The compounds were prepared via IAA from l-histidine by an efficient minimal-step synthesis, and their pharmacological properties were characterized at native rat GABAA Rs in a [(3) H]muscimol binding assay and at recombinant human α1 β2 γ2S and ρ1 GABAA Rs using the FLIPR™ membrane potential assay. The (+)-α-methyl- and α-cyclopropyl-substituted IAA analogues ((+)-6 a and 6 c, respectively) were identified as fairly potent antagonists of the ρ1 GABAA R that also displayed significant selectivity for this receptor over the α1 β2 γ2S GABAA R. Both 6 a and 6 c were shown to inhibit GABA-induced relaxation of retinal arterioles from porcine eyes.

The toxic hallucinogen 25B-NBOMe is very rapidly degraded by human liver microsomes and has low oral bioavailability. Herein we report on the synthesis, microsomal stability, and 5-HT2A/5-HT2C receptor profile of novel analogues of 25B-NBOMe modified at the primary site of metabolism. Although microsomal stability could be increased while maintaining potent 5-HT2 receptor agonist properties, all analogues had an intrinsic clearance above 1.3 L/kg/h predictive of high first-pass metabolism.

The scientific advances during the 1970ies and 1980ies within the field of dopaminergic neurotransmission enabled the development of a pharmacophore that became the template for design and synthesis of dopamine D2 agonists during the following four decades. A major drawback, however, is that this model fails to accommodate certain classes of restrained dopamine D2 agonists including ergoline structures. To accommodate these, a revision of the original model was required. The present study has addressed this by an extension of the original model without compromising its obvious qualities. The revised pharmacophore contains an additional hydrogen bond donor feature, which is required for it to accommodate ergoline structures in a low energy conformation and in accordance with the steric restrictions dictated by the original model. The additional pharmacophore feature suggests ambiguity in the binding mode for certain compounds, including a series of ergoline analogues, which was reported recently. The ambiguity was confirmed by docking to a homology model of the D2 receptor as well as by pharmacological characterization of individual enantiomers of one of the analogues. The present research also addresses the potential of designing ligands that interact with the receptor in a large, distal cavity of the dopamine D2 receptor that has not previously been studied systematically. The pharmacological data indicate that this area may be a major determinant for both the dopamine D2 affinity and efficacy, which remains to be explored in future studies.

By introducing distal substituents on a tetracyclic scaffold resembling the ergoline structure, two series of analogues were achieved exhibiting subnanomolar receptor binding affinities for the dopamine D2 and serotonin 5-HT6 receptor subtype, respectively. While the 5-HT6 ligands were antagonists, the D2 ligands displayed intrinsic activities ranging from full agonism to partial agonism with low intrinsic activity. These structures could potentially be interesting for treatment of neurological diseases such as schizophrenia, Parkinson’s disease, and cognitive deficits.

A series of bioisosteric 4-(aminomethyl)-1-hydroxypyrazole (4-AHP) analogues of muscimol, a GABA(A) receptor agonist, has been synthesized and pharmacologically characterized at native and selected recombinant GABA(A) receptors. The unsubstituted 4-AHP analogue (2a) (EC(50) 19 μM, R(max) 69%) was a moderately potent agonist at human α(1)β(2)γ(2) GABA(A) receptors, and in SAR studies substitutions in the 3- and/or 5-position were found to be detrimental to binding affinities. Ligand-receptor docking in an α(1)β(2)γ(2) GABA(A) receptor homology model along with the obtained SAR indicate that 2a and muscimol share a common binding mode, which deviates from the binding mode of the structurally related antagonist series based on 4-(piperidin-4-yl)-1-hydroxypyrazole (4-PHP, 1). Selectivity for α(1)β(2)γ(2) over ρ(1) GABA(A) receptors was observed for the 5-chloro, 5-bromo, and 5-methyl substituted analogues of 2a illustrating that even small differences in structure can give rise to subtype selectivity.

Inhibitors of the phosphodiesterase enzyme PDE10A have been the target for extensive investigations and huge drug discovery research efforts during the recent years. Although PDE10A with its 13 years history is a relatively newly discovered target, it has been paradigmatic for the new generation of 'high efficiency drug discovery'. Several companies now have clinical programs aiming at validating the clinical potential of PDE10A inhibitors. The majority of companies have been focusing on the treatment of schizophrenia since preclinical evidence suggests that a PDE10A inhibitor could provide antipsychotic, pro-cognitive and negative symptom efficacy.This article highlights and reviews research advances published in the patent literature since mid-2009 until mid-2012. The article is supplemented with selected publications from the scientific literature, emphasizing the possible involvement of PDE10A inhibitors in the treatment of schizophrenia.Several compounds from various companies are currently undergoing clinical testing, dominated by compounds in clinical Phase I. Focus is mainly on CNS diseases and schizophrenia is the leading target indication.

A 5-HT3 receptor agonist based on a benzamide scaffold was identified in a screening of a small commercial compound library, and an elaborate SAR study originating from this hit was performed. The design, synthesis, and functional characterisation of benzamide analogues at the 5-HT3A receptor yielded substantial information concerning the analogues as 5-HT3 receptor agonists. However, the potencies of the derived analogues were not significantly improved over that of the initial hit. The benzamide scaffold constitutes a novel type of 5-HT3 receptor agonist, as it does not possess a positively charged functionality, which is essential for the binding of all orthosteric ligands to the receptor. Preliminary investigations suggest that the compounds may exert their effects on 5-HT3 receptors by binding to an allosteric site in the receptor complex.

A novel direct, flexible, and robust approach to the iso-ergoline tetracyclic system in which a five or six-membered ring is established by intramolecular carbene C–H insertion is reported. The protocol involves a two step conversion of an aromatic aldehyde to the corresponding hydrazone and without purification further conversion to the diazo-compound followed by thermal carbene formation and C–H insertion α to a nitrogen.

PDE10A inhibition has generated much excitement as a potential novel mechanism for the treatment of the positive symptoms of schizophrenia. PDE10A is only '10 years old' as a drug discovery target since it was first discovered in 1999, and thus PDE10A is an example of the modern drug discovery paradigm demonstrating the highly increased speed by which novel targets can be validated, hits identified, lead-optimization performed and compounds progressed into clinical trials. At least one PDE10A inhibitor compound has been progressed to clinical Phase II for the treatment of schizophrenia. And preclinical evidence suggests that a PDE10A inhibitor could provide antipsychotic, pro-cognitive and negative symptom efficacy in the same dose range.The review surveys advances in the medicinal chemistry of PDE10A through the patent literature since 2007. The article is supplemented with selected publications from the scientific literature.Readers will gain an up to date overview of all patents published in the PDE10A field within the last 2 years and be able to judge about the structure-activity relationship and drugability of most progressed PDE10A compounds.PDE10A inhibitors will possibly be involved in the treatment of schizophrenia. The field is rapidly approaching a clinical validation of PDE10A inhibitors.

The discovery of the first class of subtype-selective inhibitors of the human excitatory amino acid transporter subtype 1 (EAAT1) and its rat orthologue GLAST is reported. An opening structure-activity relationship of 25 analogues is presented that addresses the influence of substitutions at the 4- and 7-positions of the parental skeleton 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile. The most potent analogue 1o displays high nanomolar inhibitory activity at EAAT1 and a >400-fold selectivity over EAAT2 and EAAT3, making it a highly valuable pharmacological tool. The excitatory amino acid transporters (EAATs) belong to the solute carrier family 1 (SLC1), and carry out the concentra- tive uptake of (S)-glutamate (Glu) (and aspartate (Asp)) from the glutamatergic synaptic cleft. 1-3 Five EAAT subtypes have been identified to date, in humans termed EAAT1-EAAT5. For historical reasons the nomenclature differs in rodents: the orthologues of human EAAT1, EAAT2 and EAAT3 subtypes are termed GLAST, GLT-1 and EAAC-1, respectively, whereas the nomenclature for EAAT4,5 is conserved across the species. The EAATs display differential localization and overall distribution patterns in the adult rodent brain. Whereas GLAST (EAAT1) and GLT-1 (EAAT2) are astroglial transporters, EAAC-1 (EAAT3) and EAAT4 are predominantly found in neurons. 4 GLT-1 (EAAT2) is the predominantly expressed subtype, found throughout the brain and spinal cord, and has been shown to be responsible for >90% of the Glu uptake in the adult brain. 4-6 GLAST (EAAT1) is found at the highest levels in the cerebellum with lower levels in the cortex and spinal cord, 7 and EAAC-1 (EAAT3) is expressed in high densities at postsynaptic terminals in the whole brain, particu- larly in the hippocampus, cerebellum, and basal ganglia. 4 EAAT4 is highly enriched in the Purkinje cells of the cerebel- lum, but the transporter has also been detected in the rat fore- and midbrain albeit in dramatically lower levels. 4,5,8,9 Finally, EAAT5 is found exclusively in the retina. 4,5,10 In agreement with the distribution and densities of the CNS subtypes, EAAT2 knockout mice have displayed pronounced loss of hippocampal neurons, seizures, and 50% mortality at 6 weeks of age. In contrast, knockout of GLAST (EAAT1), EAAC-1 (EAAT3), or EAAT4 in mice have been reported not to cause significant abnormalities in anatomy or in CNS-related phenotypes. 4,6 However, such studies may not be fully conclusive when it comes to elucidation of the physiological importance of the specific transporter subtype, as the absence of physiologic and phenotypic effects in the knockout mice may also be ascribed to compensatory mechanisms. Hence, we believe that valuable information about the physiological functions and thus thera- peutic potentials of a specific EAAT subtype may be addressed in a more subtle way by studying the actions of a selective ligand. 4

A series of Milnacipran analogs with variation in the aromatic moiety were prepared in high enantiomeric excess. Structure-activity relationships for two parallel enantiomeric series are described. The (-)-(1R,2S)-naphthyl analog (8h) showed the highest potency in the two series and is a triple reuptake inhibitor of the SERT, NET, and DAT.

The discovery of the enzyme phosphodiesterase 10A (PDE10A) was reported simultaneously in 1999 by three independent groups. PDE10A has been shown by localisation studies to have the most restricted distribution of all the 11 known PDE families, with the PDE10A mRNA highly expressed only in the brain and testes. In the brain, mRNA and protein are highly enriched in the striatum and, together with increased pharmacological characterisation, this unique distribution of PDE10A in the brain indicates a potential use of PDE10A inhibitors for treating neurological and psychiatric disorders, in particular, psychotic disorders like schizophrenia. However, PDE10A inhibitors have also been claimed to be useful as treatment for cancer, diabetes and especially obesity. Two years after the reported discovery of PDE10A, Bayer filed the first patent application claiming PDE10A inhibitors, followed shortly thereafter by Pfizer. Since then, a number of scientific publications and filed patents testify to an increasing phar...

A number of amino acids bioisosterically derived from the specific GABA A agonist, isonipecotic acid, were electrophysiologically characterized as antagonists at GABA C ρ 1 receptors expressed in Xenopus oocytes. The phosphinic acid analogue of isonipecotic acid, piperidin-4-ylphosphinic acid ( 2 ), was comparable with the standard GABA C antagonist, (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA), in terms of potency and GABA C versus GABA A receptor selectivity. Whereas the phosphonic acid analogue, piperidin-4-ylphosphonic acid ( 4 ), was at least an order of magnitude weaker than piperidin-4-ylphosphinic acid as a GABA C antagonist, the seleninic acid analogue, piperidin-4-ylseleninic acid (SEPI, 6 ), was the most potent and selective GABA C antagonist within the group of isonipecotic acid derived amino acids studied.

A versatile procedure for the synthesis of optically pure 1-amino-3-aryl indanes is presented, exemplified by the synthesis of the triple uptake inhibitor (+)-indatraline (1).

Phosphodiesterase 10A (PDE10A) plays a key role in the regulation of brain striatal signaling, and several pharmaceutical companies currently investigate PDE10A inhibitors in clinical trials for various central nervous system diseases. A PDE10A PET ligand may provide evidence that a clinical drug candidate reaches and binds to the target. Here we describe the successful discovery and initial validation of the novel radiolabeled PDE10A ligand 5,8-dimethyl-2-[2-((1- 11 C-methyl)-4phenyl-1H-imidazol-2-yl)-ethyl]-[1,2,4]triazolo[1,5-a]pyridine ( 11 C-Lu AE92686) and its tritiated analog 3 H-Lu AE92686. Methods: Initial in vitro experiments suggested Lu AE92686 as a promising radioligand, and the corresponding tritiated and 11 C-labeled compounds were synthesized. 3 H-Lu AE92686 was evaluated as a ligand for in vivo occupancy studies in mice and rats, and 11 C-Lu AE92686 was evaluated as a PET tracer candidate in cynomolgus monkeys and in humans. Results: 11C-Lu AE92686 displayed high specificity and selectivity for PDE10A-expressing regions in the brain of cynomolgus monkeys and humans. Similar results were found in rodents using 3H-Lu AE92686. The binding of 11C-Lu AE92686 and 3H-Lu AE92686 to striatum was completely and dose-dependently blocked by the structurally different PDE10A inhibitor 2-[4-(1-methyl-4-pyridin-4yl-1H-pyrazol-3-yl)-phenoxymethyl]-quinoline (MP-10) in rodents and in monkeys. In all species, specific binding of the radioligand was seen in the striatum but not in the cerebellum, supporting the use of the cerebellum as a reference region. The binding potentials (BPND )o f11C-Lu AE92686 in the striatum of both cynomolgus monkeys and humans were evaluated by the simplified reference tissue model with the cerebellum as the reference tissue, and BPND was found to be high and reproducible—that is, BPNDs were 6.5 ± 0.3 (n 5 3) and 7.5 ± 1.0 (n 5 12) in monkeys and humans, respectively. Conclusion: Rodent, monkey, and human tests of labeled Lu AE92686 suggest that 11 C-Lu AE92686 has great potential as a human PET tracer for the PDE10A enzyme.

The voltage-gated potassium channels of the KV7 family (KV7.1–5) play important roles in controlling neuronal excitability and are therefore attractive targets for treatment of CNS disorders linked to hyperexcitability. One of the main challenges in developing KV7 channel active drugs has been to identify compounds capable of discriminating between the neuronally expressed subtypes (KV7.2–5), aiding the identification of the subunit composition of KV7 currents in various tissues, and possessing better therapeutic potential for particular indications. By taking advantage of the structure-activity relationship of acrylamide KV7 channel openers and the effects of these compounds on mutant KV7 channels, we have designed and synthesized a novel KV7 channel modulator with a unique profile. The compound, named SMB-1, is an inhibitor of KV7.2 and an activator of KV7.4. SMB-1 inhibits KV7.2 by reducing the current amplitude and increasing the time constant for the slow component of the activation kinetics. The activation of KV7.4 is seen as an increase in the current amplitude and a slowing of the deactivation kinetics. Experiments studying mutant channels with a compromised binding site for the KV7.2–5 opener retigabine indicate that SMB-1 binds within the same pocket as retigabine for both inhibition of KV7.2 and activation of KV7.4. SMB-1 may serve as a valuable tool for KV7 channel research and may be used as a template for further design of better subtype selective KV7 channel modulators. A compound with this profile could hold novel therapeutic potential such as the treatment of both positive and cognitive symptoms in schizophrenia.

Piperidin-4-ylphosphinic acid, methyl(piperidin-4-yl)phosphinic acid and piperidin-4-ylphosphonic acid analogues of the GABAA agonist piperidin-4-ylcarboxylic acid (isonipecotic acid) were synthesised. The acid groups were introduced using a sequential Pudovik addition followed by a Barton deoxygenation procedure and finally followed by acidic hydrolysis. The mild and efficient procedure gave the target amino acids in good yields.

PDE10A is a recently identified phosphodiesterase with a quite remarkable localization since the protein is abundant only in brain tissue. Based on this unique localization, research has focused extensively on using PDE10A modulators as a novel therapeutic approach for dysfunction in the basal ganglia circuit including Parkinson’s disease, Huntington’s disease, schizophrenia, addiction and obsessive compulsive disorder. Medicinal chemistry efforts identified the N -methyl- N -[4-(quinolin-2-ylmethoxy)-phenyl]-isonicotinamide ( 8 ) as a nanomolar PDE10A inhibitor. A subsequent Lead-optimization program identified analogous N -methylanilides and their corresponding N -methylbenzamides ( 29 ) as potent PDE10A inhibitors, concurrently some interesting and unexpected binding modes were identified.

Although superficially similar, the currently most advanced inhibitors of PDE2, PDE9, and PDE10 for central nervous system disorders differ in a number of ways. PDE9 appears to be very restrictive in its binding motif requirements: in essence only one chemotype, emulating the GMP bidentate-binding motif, covers the known PDE9 chemical space. A much larger diversity of compounds is described for inhibitors of PDE2: it appears as if the less stringent requirements for binding to the invariant glutamine (Gln) in combination with the induced hydrophobic (selectivity) pocket allow a much broader variety of inhibitor chemotypes. PDE10 also has less stringent structural requirements and accepts more structurally diverse inhibitors compared to PDE9. The PDE10-unique Q2 pocket provides an additional opportunity for diversity in compounds targeting this enzyme. In special cases, high affinities can be obtained without even interacting with the central Gln.

Disturbances of the basal ganglia processes is heavily involved in schizophrenia. Phosphodiesterase 10A (PDE10A) is a basal ganglia specific hydrolase, which plays an essential role in regulating cAMP/PKA and cGMP/PKG signalling cascades by controlling the magnitude, duration and cellular location of cAMP/cGMP elevation. Biochemical and behavioral data indicate that PDE10A inhibition activates cAMP/PKA signalling in the basal ganglia, leading to the potentiation of dopamine D₁ receptor signalling, and concomitant inhibition of dopamine D₂ receptor signalling. Preclinical evidence in a range of animal models suggests that a PDE10A inhibitor could provide efficacy on positive, cognitive and negative symptoms of schizophrenia and PDE10A inhibitors are currently being evaluated in clinical trials for the treatment of schizophrenia.

Papaverine, an inhibitor of phosphodiesterase (PDE) 10A, is gaining attention for its potential in the treatment of neuropsychiatric diseases such as schizophrenia. However, the precise mechanisms underlying the putative neuroprotective/neurotrophic actions of papaverine remain unclear. Thus, we investigated the effects of papaverine on nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells. Papaverine potentiated NGF-induced neurite outgrowth in PC12 cells in a concentration-dependent manner. In contrast, the selective PDE10A inhibitor MP-10 had no effect on NGF-induced neurite outgrowth. The potentiation of NGF-induced neurite outgrowth by papaverine was blocked by the PLC-γ inhibitor U73122. Furthermore, papaverine's potentiation of NGF-induced neurite outgrowth was also blocked by the co-administration of inositol 1,4,5-trisphosphate (IP(3)) receptor antagonists (xestospongin C and 2-aminoethoxydiphenyl borate (2-APB)) and by reduced expression of IP(3) receptor gene (i.e., itpr1 and itpr3) by siRNA. Our findings suggest that papaverine could potentiate NGF-induced neurite outgrowth, and that activation of PLC-γ and IP(3) receptors might be involved in the mechanism underlying papaverine's potentiation of neurite outgrowth in PC12 cells.

Piperidin-4-ylphosphinic acid, methyl(piperidin-4-yl)phosphinic acid and piperidin-4-ylphosphonic acid analogues of the GABAA agonist piperidin-4-ylcarboxylic acid (isonipecotic acid) were synthesised. The acid groups were introduced using a sequential Pudovik addition followed by a Barton deoxygenation procedure and finally followed by acidic hydrolysis. The mild and efficient procedure gave the target amino acids in good yields.

The first seleninic acid analogues of γ-aminobutyric acid (GABA) and of the specific GABAA agonist piperidine-4-carboxylic acid (isonipecotic acid), 1 and 2, respectively, have been synthesized and shown to be potent agonists at the GABA receptors.

5-Substituted 1-pyrazolol analogues of ibotenic acid have been synthesized and pharmacologically characterized on ionotropic and metabotropic glutamate receptors (iGluRs and mGluRs). The syntheses involved introduction of bromide, alkyls, phenyl and arylalkyls in the 5-position of 1-benzyloxypyrazole leading to 5-substituted (RS)-2-amino-(1-hydroxy-4-pyrazolyl)acetic acids (5a-l). The pharmacological activities of the synthesized analogues ranged from the 5-cyclopropylmethyl analogue (5f) with weak but selective affinity for NMDA receptors (IC(50)=35 microM), over the 5-n-propyl analogue (5c), which was a selective mGluR2 agonist (EC(50)=72 microM), to the 5-cyclohexylmethyl analogue (5g), which was a selective mGluR2 antagonist (K(i)=32 microM), and the 5-phenylethyl analogue (5j), which was a weak but apparently selective mGluR1 antagonist (K(i)=230 microM). This series of compounds afforded GluR ligands with a broad spectrum of pharmacological profiles, and showing potential for development of new compounds with subtype-selective activities at various GluRs.

The potency and efficacy of a series of bioisosterically modified GABA analogues were determined electrophysiologically using heteromeric GABA(A) receptors expressed in Xenopus oocytes. These agonist parameters were shown to be strongly dependent on the receptor subunit combination. On the other hand, the antagonist potencies of the classical GABA(A) antagonists SR 95531 (7) and BMC (8) and also of 5g and the phosphinic acid bioisosteres of 5a, compounds 5f and 6, were essentially independent of the receptor subunit combinations.

1-Propylbutylphosphinic acid 2, (1-propylbutyl)methylphosphinic acid 3 and 1-propylbutylphosphonic acid 4 have been synthesized as bioisosteres of the corresponding carboxylic acid valproate 1, which is a potent anticonvulsant. The novel phosphinic and phosphonic acids were tested for their anticonvulsant activity and were found to be inactive.

[structure: see text] The first seleninic acid analogues of gamma-aminobutyric acid (GABA) and of the specific GABA(A) agonist piperidine-4-carboxylic acid (isonipecotic acid), 1 and 2, respectively, have been synthesized and shown to be potent agonists at the GABA receptors.