2,6-Diaryl-4-phenacylaminopyrimidines as potent and selective adenosine A(2A) antagonists with reduced hERG liability

In this report, the design and synthesis of a series of pyrimidine based adenosine A(2A) antagonists are described. The strategy and outcome of expanding SAR exploration to attenuate hERG and improve selectivity over A(1) are discussed. Compound 33 exhibited excellent potency, selectivity over A(1), and reduced hERG liability.     

Overcoming hERG activity in the discovery of a series of 4-azetidinyl-1-aryl-cyclohexanes as CCR2 antagonists

A series of 4-azetidinyl-1-aryl-cyclohexanes as potent CCR2 antagonists with high selectivity over activity for the hERG potassium channel is discovered through divergent SARs of CCR2 and hERG.     

A molecular switch driving inactivation in the cardiac k(+) channel HERG

K(+) channels control transmembrane action potentials by gating open or closed in response to external stimuli. Inactivation gating, involving a conformational change at the K(+) selectivity filter, has recently been recognized as a major K(+) channel regulatory mechanism. In the K(+) channel hERG, inactivation controls the length of the human cardiac action potential. Mutations impairing hERG inactivation cause life-threatening cardiac arrhythmia, which also occur as undesired side effects of drugs. In this paper, we report atomistic molecular dynamics simulations, complemented by mutational and electrophysiological studies, which suggest that the selectivity filter adopts a collapsed conformation in the inactivated state of hERG. The selectivity filter is gated by an intricate hydrogen bond network around residues S620 and N629. Mutations of this hydrogen bond network are shown to cause inactivation deficiency in electrophysiological measurements. In addition, drug-related conformational changes around the central cavity and pore helix provide a functional mechanism for newly discovered hERG activators.     

Aminomethyl tetrahydronaphthalene ketopiperazine MCH-R1 antagonists--Increasing selectivity over hERG

A direct correlation between hERG binding and QTc prolongation was established for a series of aminomethyl tetrahydronaphthalene ketopiperazine MCH-R1 antagonists. Compounds within this class with greater selectivity over hERG were developed. Compound 4h proved to have the best profile, with MCH-R1 Ki = 16 nm and hERG IC50 = 25 microM.     

Optimization of piperidin-4-yl-urea-containing melanin-concentrating hormone receptor 1 (MCH-R1) antagonists: Reducing hERG-associated liabilities

The discovery and optimization of piperidin-4-yl-urea derivatives as MCH-R1 antagonists is herein described. Previous work around the piperidin-4-yl-amides led to the discovery of potent MCH-R1 antagonists. However, high affinity towards the hERG potassium channel proved to be an issue. Different strategies to increase hERG selectivity were implemented and resulted in the identification of piperidin-4-yl-urea compounds as potent MCH-R1 antagonists with minimized hERG inhibition.     

Stoichiometry of altered hERG1 channel gating by small molecule activators

Voltage-gated K⁺ channels are tetramers formed by coassembly of four identical or highly related subunits. All four subunits contribute to formation of the selectivity filter, the narrowest region of the channel pore which determines K⁺ selective conductance. In some K⁺ channels, the selectivity filter can undergo a conformational change to reduce K⁺ flux by a mechanism called C-type inactivation. In human ether-a-go-go–related gene 1 (hERG1) K⁺ channels, C-type inactivation is allosterically inhibited by ICA-105574, a substituted benzamide. PD-118057, a 2-(phenylamino) benzoic acid, alters selectivity filter gating to enhance open probability of channels. Both compounds bind to a hydrophobic pocket located between adjacent hERG1 subunits. Accordingly, a homotetrameric channel contains four identical activator binding sites. Here we determine the number of binding sites required for maximal drug effect and determine the role of subunit interactions in the modulation of hERG1 gating by these compounds. Concatenated tetramers were constructed to contain a variable number (zero to four) of wild-type and mutant hERG1 subunits, either L646E to inhibit PD-118057 binding or F557L to inhibit ICA-105574 binding. Enhancement of hERG1 channel current magnitude by PD-118057 and attenuated inactivation by ICA-105574 were mediated by cooperative subunit interactions. Maximal effects of the both compounds required the presence of all four binding sites. Understanding how hERG1 agonists allosterically modify channel gating may facilitate mechanism-based drug design of novel agents for treatment of long QT syndrome.     

Structure-activity relationships of trimethoxybenzyl piperazine N-type calcium channel inhibitors

We previously reported the small organic N-type calcium channel blocker NP078585 that while efficacious in animal models for pain, exhibited modest L-type calcium channel selectivity and substantial off-target inhibition against the hERG potassium channel. Structure-activity studies to optimize NP078585 preclinical properties resulted in compound 16, which maintained high potency for N-type calcium channel blockade, and possessed excellent selectivity over the hERG (~120-fold) and L-type (~3600-fold) channels. Compound 16 shows significant anti-hyperalgesic activity in the spinal nerve ligation model of neuropathic pain and is also efficacious in the rat formalin model of inflammatory pain.     

The discovery and structure–activity relationships of 2-(piperidin-3-yl)-1H-benzimidazoles as selective,CNS penetrating H1-antihistamines for insomnia

A series of 2-(3-aminopiperidine)-benzimidazoles were identified as selective H₁-antihistamines for evaluation as potential sedative hypnotics. Representative compounds showed improved hERG selectivity over a previously identified 2-aminobenzimidazole series. While hERG activity could be modulated via manipulation of the benzimidazole N1 substituent, this approach led to a reduction in CNS exposure for the more selective compounds. One example, 9q, retained a suitable selectivity profile with CNS exposure equivalent to known centrally active H₁-antihistamines.     

Design, synthesis and SAR of indazole and benzoisoxazole containing 4-azetidinyl-1-aryl-cyclohexanes as CCR2 antagonists

A novel series of 4-azetidinyl-1-aryl-cyclohexanes containing indazole or benzoisoxazole moiety have been identified as potent CCR2 antagonists with high selectivity versus hERG.     

Discovery of orally active,pyrrolidinone-based progesterone receptor partial agonists

We have designed and synthesized a novel series of pyrrolidinones as progesterone receptor partial agonists. Compounds from this series had improved AR selectivity, rat pharmacokinetic properties, and in vivo potency compared to the lead compound. In addition, these compounds had improved selectivity against hERG channel inhibition.     

Discovery of a novel melanin concentrating hormone receptor 1 (MCHR1) antagonist with reduced hERG inhibition

An initial SAR study resulted in the identification of the novel, potent MCHR1 antagonist 2. After further profiling, compound 2 was discovered to be a potent inhibitor of the hERG potassium channel, which prevented its further development. Additional optimization of this structure resulted in the discovery of the potent MCHR1 antagonist 11 with a dramatically reduced hERG liability. The decrease in hERG activity was confirmed by several in vivo preclinical cardiovascular studies examining QT prolongation. This compound demonstrated good selectivity for MCHR1 and possessed good pharmacokinetic properties across preclinical species. Compound 11 was also efficacious in reducing body weight in two in vivo mouse models. This compound was selected for clinical evaluation and was given the code AMG 076.     

Optimisation of 2-cyano-pyrimidine inhibitors of cathepsin K: Improving selectivity over hERG

Several structure-guided optimisation strategies were explored in order to improve the hERG selectivity profile of cathepsin K inhibitor 1, whilst maintaining its otherwise excellent in vitro and in vivo profile. Ultimately, attenuation of c log P and pK_a properties proved a successful approach and led to the discovery of a potent analogue 23, which, in addition to the desired selectivity over hERG (>1000-fold), displayed a highly attractive overall profile.     

Novel 6,7,8,9-tetrahydro-5H-1,4,7,10a-tetraaza-cyclohepta[f]indene analogues as potent and selective 5-HT(2C) agonists for the treatment of metabolic disorders

The discovery of a novel series of 5-HT_2C agonists based on a tricyclic pyrazolopyrimidine scaffold is described. Compounds with good levels of in vitro potency and moderate to good levels of selectivity with respect to the 5-HT_2A and 5-HT_2B receptors were identified. One of the analogues (7g) was found to be efficacious in a sub-chronic weight loss model. A key limitation of the series of compounds was that they were found to be potent inhibitors of the hERG ion channel. Some compounds, bearing polar side chains were identified which showed a much reduced hERG liability however these compounds were sub-optimal in terms of their in vitro potency or selectivity.     

Substituted azaquinazolinones as modulators of GHSr-1a for the treatment of type II diabetes and obesity

Substituted azaquinazolinones were identified as antagonists of the GHSr-1A receptor for the treatment of type II diabetes and obesity. Optimisation for potency and LogD lead to the identification of orally bioavailable, potent antagonists with improved selectivity over hERG.     

Discovery of 3-morpholino-imidazole[1,5-a]pyrazine BTK inhibitors for rheumatoid arthritis

8-Amino-imidazo[1,5-a]pyrazine-based Bruton’s tyrosine kinase (BTK) inhibitors, such as 6, exhibited potent inhibition of BTK but required improvements in both kinase and hERG selectivity (Liu et al., 2016; Gao et al., 2017). In an effort to maintain the inhibitory activity of these analogs and improve their selectivity profiles, we carried out SAR exploration of groups at the 3-position of pyrazine compound 6. This effort led to the discovery of the morpholine group as an optimized pharmacophore. Compounds 13, 23 and 38 displayed excellent BTK potencies, kinase and hERG selectivities, and pharmacokinetic profiles.     

The identification, and optimisation of hERG selectivity, of a mixed NET/SERT re-uptake inhibitor for the treatment of pain

Hit compound 1, a selective noradrenaline re-uptake transporter (NET) inhibitor was optimised to build in potency at the serotonin re-uptake transporter (SERT) whilst maintaining selectivity against the dopamine re-uptake transporter (DAT). During the optimisation of 1 it became clear that selectivity against the Kv11.1 potassium ion channel (hERG) was also a parameter for optimisation within the series. Discrete structural changes to the molecule as well as a lowering of global cLogP successfully increased the hERG selectivity to afford compound 11m, which was efficacious in a mouse model of inflammatory pain, complete Freund’s adjuvant (CFA) induced thermal hyperalgesia and a rat model of neuropathic pain, spinal nerve ligation (SNL) induced mechanical allodynia.     

Scaffold-hopping with zwitterionic CCR3 antagonists: Identification and optimisation of a series with good potency and pharmacokinetics leading to the discovery of AZ12436092

The discovery and optimisation of a series of zwitterionic CCR3 antagonists is described. Optimisation of the structure led to AZ12436092, a compound with excellent selectivity over activity at hERG and outstanding pharmacokinetics in preclinical species.     

Effects of outer mouth mutations on hERG channel function: a comparison with similar mutations in the Shaker channel.

The fast-inactivation process in the hERG channel can be affected by mutations in the pore or S6 domain, similar to the C-type inactivation in the Shaker channel. However, differences in the kinetics and voltage dependence of inactivation between these two channels suggest that different structural determinants may be involved. To explore this possibility, we mutated a serine in the outer mouth region of hERG (S631) to residues of different physicochemical properties and compared the resulting changes in the channel's inactivation process with those resulting from mutations of an equivalent position in the Shaker channel (T449). The most dramatic differences are seen when this position is occupied by a charged residue: S631K and S631E disrupted C-type inactivation in hERG, whereas T449K and T449E facilitate C-type inactivation in Shaker. S631K and S631E also disrupted the K selectivity of hERG pore, a change not seen in T449K or T449E of Shaker. To further study why there are such differences, we replaced S631 with cysteine. This allowed us to manipulate the properties of thiol groups at position 631 and correlate side-chain properties here with changes in channel function. S631C behaved like the wild-type channel when the thiol groups were in the reduced state. Oxidizing thiol groups with H2O2 or modifying them with MTSET or MTSES disrupted C-type inactivation and K selectivity, similar to the phenotype of S631K and S631E. The same thiol-modifying maneuvers did not affect the wild-type channel function. Our results suggest differences in the outer mouth structure between hERG and Shaker, and we propose a "molecular spring" hypothesis to explain these differences.     

The discovery of aminopyrazines as novel, potent Na(v)1.7 antagonists: hit-to-lead identification and SAR

Herein the discovery of a novel class of aminoheterocyclic Na(v)1.7 antagonists is reported. Hit compound 1 was potent but suffered from poor pharmacokinetics and selectivity. The compact structure of 1 offered a modular synthetic strategy towards a broad structure-activity relationship analysis. This analysis led to the identification of aminopyrazine 41, which had vastly improved hERG selectivity and pharmacokinetic properties.     

1-(2-Phenoxyphenyl)methanamines: SAR for dual serotonin/noradrenaline reuptake inhibition, metabolic stability and hERG affinity

A novel series of 1-(2-phenoxyphenyl)methanamines is disclosed, which possess selective dual 5-HT and NA reuptake pharmacology. Analogues with good human in vitro metabolic stability, hERG selectivity and passive membrane permeability were identified.