Diazaspirononane Nonsaccharide Inhibitors of O-GlcNAcase (OGA) for the Treatment of Neurodegenerative Disorders.

O-GlcNAcylation is a post-translational modification of tau understood to lower the speed and yield of its aggregation, a pathological hallmark of Alzheimer's disease (AD). O-GlcNAcase (OGA) is the only enzyme that removes O-linked N-acetyl-d-glucosamine (O-GlcNAc) from target proteins. Therefore, inhibition of OGA represents a potential approach for the treatment of AD by preserving the O-GlcNAcylated tau protein. Herein, we report the multifactorial optimization of high-throughput screening hit 8 to a potent, metabolically stable, and orally bioavailable diazaspirononane OGA inhibitor (+)-56. The human OGA X-ray crystal structure has been recently solved, but bacterial hydrolases are still widely used as structural homologues. For the first time, we reveal how a nonsaccharide series of inhibitors binds bacterial OGA and discuss the suitability of two different bacterial orthologues as surrogates for human OGA. These breakthroughs enabled structure-activity relationships to be understood and provided context and boundaries for the optimization of druglike properties.

[1,2,4]Triazolo[1,5-a]pyrimidine Phosphodiesterase 2A Inhibitors: Structure and Free-Energy Perturbation-Guided Exploration.

We describe the hit-to-lead exploration of a [1,2,4]triazolo[1,5-a]pyrimidine phosphodiesterase 2A (PDE2A) inhibitor arising from high-throughput screening. X-ray crystallography enabled structure-guided design, leading to the identification of preferred substructural components. Further rounds of optimization used relative binding free-energy calculations to prioritize different substituents from the large accessible chemical space. The free-energy perturbation (FEP) calculations were performed for 265 putative PDE2A inhibitors, and 100 compounds were synthesized representing a relatively large prospective application providing unexpectedly active molecules with IC50's from 2340 to 0.89 nM. Lead compound 46 originating from the FEP calculations showed PDE2A inhibition IC50 of 1.3 ± 0.39 nM, ∼100-fold selectivity versus other PDE enzymes, clean cytochrome P450 profile, in vivo target occupancy, and promise for further lead optimization.

1,3,5-Trisubstituted Pyrazoles as Potent Negative Allosteric Modulators of the mGlu2/3 Receptors.

The metabotropic glutamate subtype 2 (mGlu2 ) receptor is a presynaptic membrane receptor distributed widely in brain that provides feedback inhibitory control of glutamate release. Inhibition of the mGlu2 receptor function with a negative allosteric modulator (NAM) enhances activity-dependent glutamate release, which may be of therapeutic benefit for the treatment of neurological and psychiatric disorders. An attractive pyrazole hit was identified after a high-throughput screening (HTS) campaign. The evolution of this hit is described by structure-activity relationship (SAR) studies on specific parts of the molecule. From near micromolar potency we could obtain compounds with single-digit nanomolar activity in the mGlu2 NAM GTPγS assay. In addition to SAR on in vitro potency, a more detailed overview is given with a specific set of compounds on the excellent agreement between in vitro potency, free brain concentration, and ex vivo mGlu2 receptor occupancy. Finally, to obtain improved drug-like compounds, plans for future research are suggested toward increasing free brain concentration while maintaining high in vitro potency.

Discovery of 8-Trifluoromethyl-3-cyclopropylmethyl-7-[(4-(2,4-difluorophenyl)-1-piperazinyl)methyl]-1,2,4-triazolo[4,3-a]pyridine (JNJ-46356479), a Selective and Orally Bioavailable mGlu2 Receptor Positive Allosteric Modulator (PAM).

Positive allosteric modulators of the metabotropic glutamate 2 receptor have generated great interest in the past decade. There is mounting evidence of their potential as therapeutic agents in the treatment of multiple central nervous system disorders. We have previously reported substantial efforts leading to potent and selective mGlu2 PAMs. However, finding compounds with the optimal combination of in vitro potency and good druglike properties has remained elusive, in part because of the hydrophobic nature of the allosteric binding site. Herein, we report on the lead optimization process to overcome the poor solubility inherent to the advanced lead 6. Initial prototypes already showed significant improvements in solubility while retaining good functional activity but displayed new liabilities associated with metabolism and hERG inhibition. Subsequent subtle modifications efficiently addressed those issues leading to the identification of compound 27 (JNJ-46356479). This new lead represents a more balanced profile that offers a significant improvement on the druglike attributes compared to previously reported leads.

Pyrido[4,3-e][1,2,4]triazolo[4,3-a]pyrazines as Selective, Brain Penetrant Phosphodiesterase 2 (PDE2) Inhibitors.

A novel series of pyrido[4,3-e][1,2,4]triazolo[4,3-a]pyrazines is reported as potent PDE2/PDE10 inhibitors with drug-like properties. Selectivity for PDE2 was obtained by introducing a linear, lipophilic moiety on the meta-position of the phenyl ring pending from the triazole. The SAR and protein flexibility were explored with free energy perturbation calculations. Rat pharmacokinetic data and in vivo receptor occupancy data are given for two representative compounds 6 and 12.

Identification of a novel orally bioavailable phosphodiesterase 10A (PDE10A) inhibitor with efficacy in animal models of schizophrenia.

We report the continuation of a focused medicinal chemistry program aimed to further optimize a series of imidazo[1,2-a]pyrazines as a novel class of potent and selective phosphodiesterase 10A (PDE10A) inhibitors. In vitro and in vivo pharmacokinetic and pharmacodynamic evaluation allowed the selection of compound 25a for its assessment in preclinical models of psychosis. The evolution of our medicinal chemistry program, structure-activity relationship (SAR) analysis, as well as a detailed pharmacological profile for optimized lead 25a are described.

Discovery of a potent, selective, and orally active phosphodiesterase 10A inhibitor for the potential treatment of schizophrenia.

We report the discovery of a series of imidazo[1,2-a]pyrazine derivatives as novel inhibitors of phosphodiesterase 10A (PDE10A). In a high-throughput screening campaign we identified the imidazopyrazine derivative 1, a PDE10A inhibitor with limited selectivity versus the other phosphodiesterases (PDEs). Subsequent investigation of 1 and replacement of the trimethoxyphenyl group by a (methoxyethyl)pyrazole moiety maintained PDE10A inhibition but enhanced selectivity against the other PDEs. Systematic examination and analysis of structure-activity and structure-property relationships resulted in the discovery of 2, an in vitro potent and selective inhibitor of PDE10A with high striatal occupancy of PDE10A, promising in vivo efficacy in different rodent behavioral models of schizophrenia, and a good pharmacokinetic profile in rats.

Pharmacology of JNJ-42314415, a centrally active phosphodiesterase 10A (PDE10A) inhibitor: a comparison of PDE10A inhibitors with D2 receptor blockers as potential antipsychotic drugs.

The new phosphodiesterase 10A inhibitor (PDE10AI) JNJ-42314415 [3-[6-(2-methoxyethyl)pyridin-3-yl]-2-methyl-8-morpholin-4-ylimidazo[1,2-a]pyrazine] was compared with three reference PDE10AIs and eight dopamine 2 (D(2)) receptor blockers. Despite displaying relatively low PDE10A activity in vitro, JNJ-42314415 was found to be a relatively potent and specific PDE10AI in vivo. The compound was devoid of effects on prolactin release and of receptor interactions associated with other commonly observed adverse effects of available antipsychotics. Similar to D(2) receptor blockers, the tested PDE10AIs antagonized stimulant-induced behavior and inhibited conditioned avoidance behavior; these effects were observed at doses close to the ED(50) for striatal PDE10A occupancy. Relative to the ED(50) for inhibition of apomorphine-induced stereotypy, PDE10AIs blocked conditioned avoidance behavior and behaviors induced by nondopaminergic stimulants (phencyclidine, scopolamine) more efficiently than did D(2) receptor blockers; however, they blocked behaviors induced by dopaminergic stimulants (apomorphine, d-amphetamine) less efficiently. PDE10AIs also induced less pronounced catalepsy than D(2) receptor blockers. The effects of PDE10A inhibition against dopaminergic stimulants and on catalepsy were potentiated by the D(1) antagonist SCH-23390 (8-chloro-3-methyl-5-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepin-7-ol), suggesting that enhancement of D(1) receptor-mediated neurotransmission contributes to the behavioral profile of PDE10AIs. By reducing dopamine D(2) and concomitantly potentiating dopamine D(1) receptor-mediated neurotransmission, PDE10AIs may show antipsychotic activity with an improved side-effect profile relative to D(2) receptor blockers. However, the clinical implications of this dual mechanism must be further explored.

Inhibitor-based validation of a homology model of the active-site of tripeptidyl peptidase II.

A homology model of the active site region of tripeptidyl peptidase II (TPP II) was constructed based on the crystal structures of four subtilisin-like templates. The resulting model was subsequently validated by judging expectations of the model versus observed activities for a broad set of prepared TPP II inhibitors. The structure-activity relationships observed for the prepared TPP II inhibitors correlated nicely with the structural details of the TPP II active site model, supporting the validity of this model and its usefulness for structure-based drug design and pharmacophore searching experiments.

JNJ16259685, a highly potent, selective and systemically active mGlu1 receptor antagonist.

We examined the pharmacological profile of (3,4-dihydro-2H-pyrano[2,3]b quinolin-7-yl) (cis-4-methoxycyclohexyl) methanone (JNJ16259685). At recombinant rat and human metabotropic glutamate (mGlu) 1a receptors, JNJ16259685 non-competitively inhibited glutamate-induced Ca2+ mobilization with IC50 values of 3.24+/-1.00 and 1.21+/-0.53 nM, respectively, while showing a much lower potency at the rat and human mGlu5a receptor. JNJ16259685 inhibited [3H]1-(3,4-dihydro-2H-pyrano[2,3-b]quinolin-7-yl)-2-phenyl-1-ethanone ([3H]R214127) binding to membranes prepared from cells expressing rat mGlu1a receptors with a Ki of 0.34+/-0.20 nM. JNJ16259685 showed no agonist, antagonist or positive allosteric activity toward rat mGlu2, -3, -4 or -6 receptors at concentrations up to 10 microM and did not bind to AMPA or NMDA receptors, or to a battery of other neurotransmitter receptors, ion channels and transporters. In primary cerebellar cultures, JNJ16259685 inhibited glutamate-mediated inositol phosphate production with an IC50 of 1.73+/-0.40 nM. Subcutaneously administered JNJ16259685 exhibited high potencies in occupying central mGlu1 receptors in the rat cerebellum and thalamus ( ED50=0.040 and 0.014 mg/kg, respectively). These data show that JNJ16259685 is a selective mGlu1 receptor antagonist with excellent potencies in inhibiting mGlu1 receptor function and binding and in occupying the mGlu1 receptor after systemic administration.

Synthesis and biological evaluation of imidazol-2-one and 2-cyanoiminoimidazole derivatives: novel series of PDE4 inhibitors.

This communication describes the synthesis and in vitro PDE4 inhibitory activity of a novel series of imidazol-2-one and 2-cyanoiminoimidazole derivatives. The compounds described were also tested in in vivo models to evaluate their anti-inflammatory activity after topical administration as well as their gastro-intestinal side effects. Several compounds proved to be potent PDE4 inhibitors and some 2-cyanoiminoimidazoles showed less pronounced gastro-intestinal side effects than reference compounds but maintained anti-inflammatory activity after topical administration.