In vitro characterization of AR-A000002, a novel 5-hydroxytryptamine(1B) autoreceptor antagonist

2-Phenethylamines in Medicinal Chemistry: A Review

A concise review covering updated presence and role of 2-phenethylamines in medicinal chemistry is presented. Open-chain, flexible alicyclic amine derivatives of this motif are enumerated in key therapeutic targets, listing medicinal chemistry hits and appealing screening compounds. Latest reports in discovering new bioactive 2-phenethylamines by research groups are covered too.

Synthesis and structure-activity relationships for a new class of tetrahydronaphthalene amide inhibitors of Mycobacterium tuberculosis

Drug resistant tuberculsosis (TB) is global health crisis that demands novel treatment strategies. Bacterial ATP synthase inhibitors such as bedaquiline and next-generation analogues (such as TBAJ-876) have shown promising efficacy in patient populations and preclinical studies, respectively, suggesting that selective targeting of this enzyme presents a validated therapeutic strategy for the treatment of TB. In this work, we report tetrahydronaphthalene amides (THNAs) as a new class of ATP synthase inhibitors that are effective in preventing the growth of Mycobacterium tuberculosis (M.tb) in culture. Design, synthesis and comprehensive structure-activity relationship studies for approximately 80 THNA analogues are described, with a small selection of compounds exhibiting potent (in some cases MIC₉₀ <1 μg/mL) in vitro M.tb growth inhibition taken forward to pharmacokinetic and off-target profiling studies. Ultimately, we show that some of these THNAs possess reduced lipophilic properties, decreased hERG liability, faster mouse/human liver microsomal clearance rates and shorter plasma half-lives compared with bedaquiline, potentially addressing of the main concerns of persistence and phospholipidosis associated with bedaquiline.

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Tetrahydronaphthalene amides are novel inhibitors of M.tb in culture.

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Selective and potent inhibitors of the mycobacterial ATP synthase.

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Improved hERG liability, clearance and half-life compared to bedaquiline.

Morpholine as a privileged structure: A review on the medicinal chemistry and pharmacological activity of morpholine containing bioactive molecules

Morpholine is a heterocycle featured in numerous approved and experimental drugs as well as bioactive molecules. It is often employed in the field of medicinal chemistry for its advantageous physicochemical, biological, and metabolic properties, as well as its facile synthetic routes. The morpholine ring is a versatile and readily accessible synthetic building block, it is easily introduced as an amine reagent or can be built according to a variety of available synthetic methodologies. This versatile scaffold, appropriately substituted, possesses a wide range of biological activities. There are many examples of molecular targets of morpholine bioactive in which the significant contribution of the morpholine moiety has been demonstrated; it is an integral component of the pharmacophore for certain enzyme active-site inhibitors whereas it bestows selective affinity for a wide range of receptors. A large body of in vivo studies has demonstrated morpholine's potential to not only increase potency but also provide compounds with desirable drug-like properties and improved pharamacokinetics. In this review we describe the medicinal chemistry/pharmacological activity of morpholine derivatives on various therapeutically related molecular targets, attempting to highlight the importance of the morpholine ring in drug design and development as well as to justify its classification as a privileged structure.

Regioisomerism in the synthesis of a chiral aminotetralin drug compound: unraveling mechanistic details and diastereomer-specific in-depth NMR investigations

During chemical process development of a novel 2-aminotetralin derivative intended for use as an antidepressant, scrutiny of the byproduct present in the drug molecule revealed a set of regioisomers. Detailed studies showed that this impurity issue originated from an early synthetic step in which a brominated tetralone motif was generated in a ring-closing protocol. It was found that this reaction was accompanied by a migration of the aromatic bromo substituent via different bromonium species along two discrete pathways. This example of the halogen dance reaction resulted in the formation of a series of tetralone impurities with a bromine distributed across all available aromatic positions of the tetralin nucleus. Subsequently, when subjected to reductive amination conditions, each of these tetralones gave rise to pairs of aminotetralins in a diastereomeric relationship. NMR investigations revealed that the alicyclic portion of the compounds thus formed displayed very complex signal patterns, which required further in-depth studies using a variety of sophisticated techniques. As a result, a deep insight into the structural features of the current 2-aminotetralin family was obtained, which is emphasized by the definition of a novel "0.2 ppm rule" allowing the absolute configuration at tetralin C-2 to be determined.

Preclinical pharmacology and pharmacokinetics of AZD3783, a selective 5-hydroxytryptamine 1B receptor antagonist

The preclinical pharmacology and pharmacokinetic properties of (2R)-6-methoxy-8-(4-methylpiperazin-1-yl)-N-(4-morpholin-4-ylphenyl)chromane-2-carboxamide (AZD3783), a potent 5-hydroxytryptamine 1B (5-HT(1B)) receptor antagonist, were characterized as part of translational pharmacokinetic/pharmacodynamic hypothesis testing in human clinical trials. The affinity of AZD3783 to the 5-HT(1B) receptor was measured in vitro by using membrane preparations containing recombinant human or guinea pig 5-HT(1B) receptors and in native guinea pig brain tissue. In vivo antagonist potency of AZD3783 for the 5HT(1B) receptor was investigated by measuring the blockade of 5-HT(1B) agonist-induced guinea pig hypothermia. The anxiolytic-like potency was assessed using the suppression of separation-induced vocalization in guinea pig pups. The affinity of AZD3783 for human and guinea pig 5-HT(1B) receptor (K(i), 12.5 and 11.1 nM, respectively) was similar to unbound plasma EC(50) values for guinea pig receptor occupancy (11 nM) and reduction of agonist-induced hypothermia (18 nM) in guinea pig. Active doses of AZD3783 in the hypothermia assay were similar to doses that reduced separation-induced vocalization in guinea pig pups. AZD3783 demonstrated favorable pharmacokinetic properties. The predicted pharmacokinetic parameters (total plasma clearance, 6.5 ml/min/kg; steady-state volume of distribution, 6.4 l/kg) were within 2-fold of the values observed in healthy male volunteers after a single 20-mg oral dose. This investigation presents a direct link between AZD3783 in vitro affinity and in vivo receptor occupancy to preclinical disease model efficacy. Together with predicted human pharmacokinetic properties, we have provided a model for the quantitative translational pharmacology of AZD3783 that increases confidence in the optimal human receptor occupancy required for antidepressant and anxiolytic effects in patients.

[N-methyl-3H3]AZ10419369 binding to the 5-HT1B receptor: in vitro characterization and in vivo receptor occupancy

Radiotracers suitable for positron emission tomography studies often serve as preclinical tools for in vivo receptor occupancy. The serotonin 1B receptor (5-HT(1B)) subtype is a pharmacological target used to discover treatments for various psychiatric and neurological disorders. In psychiatry, 5-HT(1B) antagonists may provide novel therapeutics for depression and anxiety. We report on the in vitro and in vivo evaluation of tritiated 5-methyl-8-(4-methyl-piperazin-1-yl)-4-oxo-4H-chromene-2-carboxylicacid (4-morpholin-4-yl-phenyl)-amide ([N-methyl-(3)H(3)]AZ10419369), a potent 5-HT(1B) radiotracer. [N-methyl-(3)H(3)]-AZ10419369 showed saturable single-site high-affinity in vitro binding (guinea pig, K(d) = 0.38 and human, K(d) = 0.37) to guinea pig or human 5-HT(1B) receptors in recombinant membranes and high-affinity (K(d) = 1.9 nM) saturable (B(max) = 0.099 pmol/mg protein) binding in membranes from guinea pig striatum. When [N-methyl-(3)H(3)]AZ10419369 was administered to guinea pigs by intravenous bolus, the measured radioactivity was up to 5-fold higher in brain areas containing the 5-HT(1B) receptor (striatum/globus pallidus, midbrain, hypothalamus, and frontal cortex) compared with the cerebellum, the nonspecific binding region. Specific uptake peaked 30 min after injection with slow dissociation from target regions, as suggested by the in vitro binding kinetic profile. Pretreatment with 6-fluoro-8-(4-methyl-piperazin-1-yl)-4-oxo-4H-chromene-2-carboxylic acid [4-(4-propionyl-piperazin-1-yl)-phenyl]-amide (AZD1134) and 2-aminotetralin (AR-A000002), 5-HT(1B)-selective ligands, inhibited [N-methyl-(3)H(3)]AZ10419369-specific binding in a dose-dependent manner. In the guinea pig striatum, AZD1134 (ED(50) = 0.017 mg/kg) occupies a greater percentage of the 5-HT(1B) receptors at a lower administered dose than AR-A000002 (ED(50) = 2.5 mg/kg). In vivo receptor occupancy is an essential component to build binding-efficacy-exposure relationships and compare novel compound pharmacology. [N-methyl-(3)H(3)]AZ10419369 is a useful preclinical tool for investigating 5-HT(1B) receptor occupancy for novel compounds targeting this receptor.

[11C]AZ10419369: a selective 5-HT1B receptor radioligand suitable for positron emission tomography (PET). Characterization in the primate brain

The 5-HT1B receptor has been implicated in several psychiatric disorders and is a potential pharmacological target in the treatment of depression. Here we report the synthesis of a novel PET radioligand, [11C]AZ10419369 (5-methyl-8-(4-methyl-piperazin-1-yl)-4-oxo-4H-chromene-2-carboxylic acid (4-morpholin-4-yl-phenyl)-amide), for in vivo visualization of 5-HT1B receptors in the brains of macaques and humans subjects. [11C]AZ10419369 was prepared by N-methylation of (8-(1-piperazinyl)-5-methylchrom-2-en-4-one-2-(4-morpholinophenyl) carboxamide, using carbon-11 methyl triflate. Regional brain uptake patterns of [11C]AZ10419369 were characterized by PET measurements in two macaques and a preliminary study in two human subjects. In addition, AZ10419369 was prepared in tritium labeled form for in vitro autoradiography studies in macaque brain tissue sections. The radiochemical purity of [11C]AZ10419369 was >99% and specific radioactivity was >3600 Ci/mmol. After iv injection of [11C]AZ10419369, 3-4% was in brain after 7.5 min. The regional brain distribution of radioactivity was similar in humans and macaques showing the highest uptake of radioactivity in the occipital cortex and the basal ganglia, in accord with autoradiographic studies performed using [3H]AZ10419369. Uptake was moderate in the temporal and frontal cortical regions, lower in the thalamus and lowest in the cerebellum. In macaques pre-treated with the selective 5-HT1B receptor antagonist, AR-A000002, binding was reduced in a dose-dependent manner, consistent with specific binding to 5-HT1B receptors. These data support [11C]AZ10419369 as a suitable radioligand for labeling 5-HT1B receptors in the primate brain. This radioligand may be useful in future studies evaluating drug-induced receptor occupancy and measurement of brain 5-HT1B receptor levels in patients with psychiatric disorders.

Synthesis of novel quinolone and quinoline-2-carboxylic acid (4-morpholin-4-yl-phenyl)amides: A late-stage diversification approach to potent 5HT1B antagonists

Multiparallel amenable syntheses of 6-methoxy-8-amino-4-oxo-1,4-dihydroquinoline-2-carboxylic acid-(4-morpholin-4-yl-phenyl)amides (I) and 4-amino-6-methoxy-8-(4-methyl-piperazin-1-yl)-quinoline-2-carboxylic acid (4-morpholin-4-yl-phenyl)amides (II) which facilitate late-stage diversification at the 8-position of (I) and at the 4- and 8-positions of (II) are described. The resulting novel series were determined to contain potent 5HT(1B) antagonists. Preliminary SAR data are presented.

Characterisation of the selective 5-HT1B receptor antagonist SB-616234-A (1-[6-(cis-3,5-dimethylpiperazin-1-yl)-2,3-dihydro-5-methoxyindol-1-yl]-1-[2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]methanone hydrochloride): In vivo neurochemical and behavioural evidence of anxiolytic/antidepressant activity

The 5-HT1B receptor has attracted significant interest as a potential target for the development of therapeutics for the treatment of affective disorders such as anxiety and depression. Here we present the in vivo characterisation of a novel, selective and orally bioavailable 5-HT1B receptor antagonist, SB-616234-A (1-[6-(cis-3,5-dimethylpiperazin-1-yl)-2,3-dihydro-5-methoxyindol-1-yl]-1-[2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]methanone hydrochloride). SB-616234-A reversed the 5-HT1/7 receptor agonist, SKF-99101H-induced hypothermia in guinea pigs in a dose related manner with an ED50 of 2.4 mg/kg p.o. Using in vivo microdialysis in freely moving guinea pigs, SB-616234-A (3-30 mg/kg p.o.) caused a dose-related increase in extracellular 5-HT in the dentate gyrus. Evaluation of antidepressant- and anxiolytic-like effects of this 5-HT1B receptor antagonist was performed in a variety of models and species. SB-616234-A produced a decrease in immobility time in the mouse forced swim test; an effect suggestive of antidepressant activity. Furthermore, SB-616234-A produced dose-related anxiolytic effects in both rat and guinea pig maternal separation-induced vocalisation models with an ED50 of 1.0 and 3.3 mg/kg i.p., respectively (vs fluoxetine treatment ED50 = 2.2 mg/kg i.p. in both species). Also a significant reduction in posturing behaviours was observed in the human threat test in marmosets; an effect indicative of anxiolytic activity. In summary, SB-616234-A is a novel, potent and orally bioavailable 5-HT1B receptor antagonist which exhibits a neurochemical and behavioural profile that is consistent with both anxiolytic- and antidepressant-like activity in a variety of species. Taken together these data suggest that SB-616234-A may have therapeutic efficacy in the treatment of affective disorders.

Synthesis and SAR of highly potent dual 5-HT1A and 5-HT1B antagonists as potential antidepressant drugs

Novel 5-HT(1) autoreceptor ligands based on the N-4-aryl-piperazinyl-N'-ethyl-5,6,7,8-tetrahydropyrido[4', 3':4,5]thieno[2,3-d]pyrimidin-4(3H)-one core are described. Aiming at antidepressants with a novel mode of action our objective was to identify potent antagonists showing balanced affinities and high selectivity for the 5-HT(1A) and 5-HT(1B) receptors. Strategies for the development of dual 5-HT(1A) and 5-HT(1B) antagonists based on 1 and 2 as leads and the corresponding results are discussed. Isoquinoline analogue 33 displayed high affinity and an antagonistic mode of action for the 5-HT(1A) and the 5-HT(1B) receptors and was characterized further with respect to selectivity, electrically stimulated [(3)H]5-HT release and in vivo efficacy.

Identification of a potent and selective 5-HT1B receptor antagonist

An SAR study around the mixed 5-HT1ABD receptor antagonist SB-272183 found that introduction of cis-2,6-dimethyl substitution onto the piperazine ring was a key structural change, which imparted a combination of both excellent selectivity over the 5-HT1A and 5-HT1D receptors and low intrinsic activity. This led to the identification of the selective 5-HT1B receptor antagonist SB-616234.