Structure–activity relationships of diphenylpiperazine N-type calcium channel inhibitors

A novel series of compounds derived from the previously reported N-type calcium channel blocker NP118809 (1-(4-benzhydrylpiperazin-1-yl)-3,3-diphenylpropan-1-one) is described. Extensive SAR studies resulted in compounds with IC₅₀ values in the range of 10–150 nM and selectivity over the L-type channels up to nearly 1200-fold. Orally administered compounds 5 and 21 exhibited both anti-allodynic and anti-hyperalgesic activity in the spinal nerve ligation model of neuropathic pain.     

Synthesis and biological evaluation of oxazole derivatives as T-type calcium channel blockers

T-type calcium channel is one of therapeutic targets for the treatment of cardiovascular diseases and neuropathic pain. In this study, as a part of our ongoing efforts to develop potent T-type calcium channel blockers, we designed oxazole derivatives substituted with arylpiperazinylalkylamines. The oxazoles were synthesized in a convenient convergent synthetic method, and biologically evaluated against α_1G (Ca_V3.1) T-type calcium channel. Among total 41 oxazole compounds synthesized, the most active one was the compound 10-35 with an IC₅₀ value of 0.65 μM, which is comparable with that of mibefradil.     

Discovery of tetrahydropyrido[4,3-d]pyrimidine derivatives for the treatment of neuropathic pain

A series of tetrahydropyridopyrimidine derivatives were synthesized and evaluated for neurotoxicity and peripheral analgesic activity followed by assessment of antiallodynic and antihyperalgesic potential in two peripheral neuropathic pain models, the chronic constriction injury (CCI) and partial sciatic nerve ligation (PSNL). Compounds (4b and 4d) exhibiting promising efficacies in four behavioral assays of allodynia and hyperalgesia (spontaneous pain, tactile allodynia, cold allodynia and mechanical hyperalgesia) were quantified for their ED₅₀ values (15.12–65.10 mg/kg). Studies carried out to assess the underlying mechanism revealed that the compounds suppressed the inflammatory component of the neuropathic pain and prevented oxidative and nitrosative stress.     

Large conductance Ca2+-activated K+ channel (BKCa) activating properties of a series of novel N-arylbenzamides: Channel subunit dependent effects

Large conductance calcium activated potassium channels (BK_Ca) are fundamental in the control of cellular excitability. Thus, compounds that activate BK_Ca channels could provide potential therapies in the treatment of pathologies of the cardiovascular and central nervous system. A series of novel N-arylbenzamide compounds, and the reference compound NS1619, were evaluated for BK_Ca channel opener properties in Human Embryonic Kidney (HEK293) cells expressing the human BK_Ca channel α-subunit alone or α + β1-subunit complex.Channel activity was determined using a non-radioactive Rb⁺ efflux assay to construct concentration effect curves for each compound. All N-arylbenzamide compounds and NS1619 evoked significant (p <0.05) concentration related increases in Rb⁺ efflux both in cells expressing α-subunit alone or α + β1-subunits. Co-expression of the β1-subunit modified the Rb⁺ efflux responses, relative to that obtained in cells expressing the α-subunit alone, for most of the N-arylbenzamide compounds, in contrast to NS1619. The EC₄₀ values of NS1619, BKMe1 and BKOEt1 were not significantly affected by the co-expression of the BK_Ca channel α + β1-subunits. In contrast, 5 other N-arylbenzamides (BKPr2, BKPr3, BKPr4, BKH1 and BKVV) showed a significant (p <0.05) 2- to 10-fold increase in EC₄₀ values when tested on the BK_Ca α + β1-subunit expressing cells compared to BK_Ca α-subunit expressing cells. Further, the E_max values for BKPr4, BKVV and BKH1 were lower in the BK_Ca channel α + β1-subunit expressing cells.In conclusion, the N-arylbenzamides studied, like NS1619, were able to activate BK_Ca channels formed of the α-subunit only. The co-expression of the β1-subunit, however, modified the ability of certain compounds to active the channel leading to differentiated pharmacodynamic profiles.     

Bioavailable pyrrolo-benzo-1,4-diazines as Nav1.7 sodium channel blockers for the treatment of pain

A series of pyrrolo-benzo-1,4-diazine analogs have been synthesized to improve the profile of the previous lead compound 1. The syntheses, structure–activity relationships, and selected pharmacokinetic data of these analogs are described. The optimization efforts allowed the identification of 33, a quinoline amide exhibiting potent Na_v1.7 inhibitory activity and moderate selectivity over Na_v1.5. Compound 33 displayed anti-nociceptive oral efficacy in a rat CFA inflammatory pain model at 100 mpk and in a rat spinal nerve ligation neuropathic pain model with an EC₅₀ 75 μM.     

Synthesis and evaluation of aminobenzothiazoles as blockers of N- and T-type calcium channels

Both N- and T-type calcium ion channels have been implicated in pain transmission and the N-type channel is a well-validated target for the treatment of neuropathic pain. An SAR investigation of a series of substituted aminobenzothiazoles identified a subset of five compounds with comparable activity to the positive control Z160 in a FLIPR-based intracellular calcium response assay measuring potency at both Ca_V2.2 and Ca_V3.2 channels. These compounds may form the basis for the development of drug leads and tool compounds for assessing in vivo effects of variable modulation of Ca_V2.2 and Ca_V3.2 channels.     

Synthesis and in vitro evaluation of 2,4-diamino-1,3,5-triazine derivatives as neuronal voltage-gated sodium channel blockers

Neuronal sodium channels blockers interfere with ion flux and have been used for managing neuropathic pain, epilepsy, and cerebral ischemic disorders. In the current study, four groups of 2,4-diamino-1,3,5-triazine derivatives were synthesized and investigated for their neuronal sodium channels binding activity. 5-Aryl-1,3,5-triazaspiro[5.5]undeca-1,3-diene-2,4-diamines (4a–4j) were found to have the best neuronal sodium binding activity among the four groups of triazines evaluated. Derivatives 4a–4j blocked the sodium channels with IC₅₀ values ranged from 4.0 to 14.7 μM. The result from this study showed that analogues of 2,4-diamino-1,3,5-triazines could be used as leads for the discovery of neuronal sodium channels blockers for managing central nervous system related disorders.     

A stereo-controlled synthesis of 2,4-dimethyl-4-hydroxy-16-phenylhexadecanoic acid 1,4-lactone and its PPAR activities

A novel class of natural PPAR agonists, 2,4-dimethyl-4-hydroxy-16-phenylhexadecanoic acid 1,4-lactone (1), were discovered in marine natural product libraries. The synthesis of 1 was accomplished starting from vinylmethyl ketone. Ring formation of the α,γ dialkyl γ-lactone was achieved via the stereo-controlled reaction of a ketyl radical anion with a chiral methacrylate. In the PPAR agonistic assay, the most potent of the four stereoisomers had EC₅₀ values of 12 μM for mPPARα, 9 μM for mPPARδ and >100 μM for mPPARγ.     

Synthesis,in vitro evaluation and molecular docking studies of novel amide linked triazolyl glycoconjugates as new inhibitors of α-glucosidase

A series of N-substituted amide linked triazolyl β-d-glucopyranoside derivatives (4a-l) were synthesized and their in vitro inhibitory activity against yeast α-glucosidase enzyme [EC.3.2.1.20] was assessed. Compounds 4e (IC₅₀ = 156.06 μM), 4f (IC₅₀ = 147.94 μM), 4k (IC₅₀ = 127.71 μM) and 4l (IC₅₀ = 121.33 μM) were identified as the most potent inhibitors for α-glucosidase as compared to acarbose (IC₅₀ = 130.98 μM) under the same in vitro experimental conditions. Kinetic study showed that both 4e and 4f inhibit the enzyme in a competitive manner with p-nitrophenyl α-d-glucopyranoside as substrate. Molecular docking studies of 4e, 4f, 4k and 4l were also carried out using homology model of α-glucosidase to find out the binding modes responsible for the inhibitory activity. This study revealed that the binding affinity of compounds 4e, 4f, 4k and 4l for α-glucosidase were −8.2, −8.6, −8.3 and −8.5 kcal/mol respectively, compared to that of acarbose (−8.9 kcal/mol). The results suggest that the N-substituted amide linked triazole glycoconjugates can reasonably mimic the substrates for the yeast α-glucosidase.     

Synthesis and structure–activity relationships of 4-fluorophenyl-imidazole p38α MAPK,CK1δ and JAK2 kinase inhibitors

The synthesis and structure–activity relationships of novel 4-(4′-fluorophenyl)imidazoles as selective p38α MAPK, CK1δ and JAK2 inhibitors with improved water solubility are described. Microwave-assisted multicomponent reactions afforded 4-fluorophenyl-2,5-disubstituted imidazoles. Carboxylate and phosphonate groups were introduced via ‘click’ reactions. The kinase selectivity was influenced by the heteroaryl group at imidazole C-5 and the position of a carboxylic acid or tetrazole at imidazole C-2. For example, pyrimidines 15 and 34 inhibited p38α MAPK with IC₅₀ = 250 nM and 96 nM, respectively. Pyridine 3 gave CK1δ inhibition with IC₅₀ = 89 nM and pyridin-2-one 31 gave JAK2 inhibition with IC₅₀ = 62 nM.     

Discovery of novel tetrahydroisoquinoline derivatives as orally active N-type calcium channel blockers with high selectivity for hERG potassium channels

N-type calcium channels represent a promising target for the treatment of neuropathic pain. The selective N-type calcium channel blocker ziconotide ameliorates severe chronic pain but has a narrow therapeutic window and requires intrathecal administration. We identified tetrahydroisoquinoline derivative 1a as a novel potent N-type calcium channel blocker. However, this compound also exhibited potent inhibitory activity against hERG channels. Structural optimizations led to identification of (1S)-(1-cyclohexyl-3,4-dihydroisoquinolin-2(1H)-yl)-2-{[(1-hydroxycyclohexyl)methyl]amino}ethanone ((S)-1h), which exhibited high selectivity for hERG channels while retaining potency for N-type calcium channel inhibition. (S)-1h went on to demonstrate in vivo efficacy as an orally available N-type calcium channel blocker in a rat spinal nerve ligation model of neuropathic pain.     

Synthesis,biological evaluation and molecular docking study of N-arylbenzo[d]oxazol-2-amines as potential α-glucosidase inhibitors

A novel series of N-arylbenzo[d]oxazol-2-amines (4a–4m) were synthesized and evaluated for their α-glucosidase inhibitory activity. Compounds 4f–4i, 4k and 4m displayed potent inhibitory activity against α-glucosidase with IC₅₀ values in the range of 32.49 ± 0.17–120.24 ± 0.51 μM as compared to the standard drug acarbose. Among all tested compounds, compound 4g having 4-phenoxy substitution at the phenyl ring was found to be the most active inhibitor of α-glucosidase with an IC₅₀ value of 32.49 ± 0.17 μM. Analysis of the kinetics of enzyme inhibition indicated that compound 4g is a noncompetitive inhibitor of α-glucosidase with a K_i value of 31.33 μM. Binding interaction of compound 4g with α-glucosidase was explored by molecular docking simulation.     

The discovery of potent glycine transporter type-2 inhibitors: Design and synthesis of phenoxymethylbenzamide derivatives

We describe the discovery of phenoxymethylbenzamide derivatives as a novel class of glycine transporter type-2 (GlyT-2) inhibitors. We found hit compound 1 (human GlyT-2, IC₅₀ = 4040 nM) in our library and converted its 1-(1-(naphthalen-2-ylmethyl)piperidin-4-yl)pyrrolidin-3-yl group to an 1-(N,N-dimethylaminopropyl)piperidyl group and its tert-butyl group to a trifluoromethyl group to obtain N-(1-(3-(dimethylamino)propyl)piperidin-4-yl)-4-((4-(trifluoromethyl)phenoxy)methyl)benzamide (20). Compound 20 showed good inhibitory activity against human GlyT-2 (IC₅₀ = 15.3 nM) and exhibited anti-allodynia effects in a mouse neuropathic pain model.     

Pyridine sulfonamide as a small key organic molecule for the potential treatment of type-II diabetes mellitus and Alzheimer’s disease: In vitro studies against yeast α-glucosidase,acetylcholinesterase and butyrylcholinesterase

This paper presents the efficient high yield synthesis of novel pyridine 2,4,6-tricarbohydrazide derivatives (4a–4i) along with their α-glucosidase, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition activities. The enzymes inhibition results showed the potential of synthesized compounds in controlling both type-II diabetes mellitus and Alzheimer’s disease. In vitro biological investigations revealed that most of compounds were more active against yeast α-glucosidase than the reference compound acarbose (IC₅₀ 38.25 ± 0.12 μM). Among the tested series the compound 4c bearing 4-flouro benzyl group was noted to be the most active (IC₅₀ 25.6 ± 0.2 μM) against α-glucosidase, and it displayed weak inhibition activities against AChE and BChE. Compound 4a exhibited the most desired results against all three enzymes, as it was significantly active against all the three enzymes; α-glucosidase (IC₅₀ 32.2 ± 0.3 μM), AChE (IC₅₀ 50.2 ± 0.8 μM) and BChE (IC₅₀ 43.8 ± 0.8 μM). Due to the most favorable activity of 4a against the tested enzymes, for molecular modeling studies this compound was selected to investigate its pattern of interaction with α-glucosidase and AChE targets.     

Functional interactions between voltage-gated Ca2 + channels and Rab3-interacting molecules (RIMs): New insights into stimulus–secretion coupling

Stimulus–secretion coupling is a complex set of intracellular reactions initiated by an external stimulus that result in the release of hormones and neurotransmitters. Under physiological conditions this signaling process takes a few milliseconds, and to minimize delays cells have developed a formidable integrated network, in which the relevant molecules are tightly packed on the nanometer scale. Active zones, the sites of release, are composed of several different proteins including voltage-gated Ca^2 + (Ca_V) channels. It is well acknowledged that hormone and neurotransmitter release is initiated by the activation of these channels located close to docked vesicles, though the mechanisms that enrich channels at release sites are largely unknown. Interestingly, Rab3 binding proteins (RIMs), a diverse multidomain family of proteins that operate as effectors of the small G protein Rab3 involved in secretory vesicle trafficking, have recently identified as binding partners of Ca_V channels, placing both proteins in the center of an interaction network in the molecular anatomy of the active zones that influence different aspects of secretion. Here, we review recent evidences providing support for the notion that RIMs directly bind to the pore-forming and auxiliary β subunits of Ca_V channels and with RIM-binding protein, another interactor of the channels. Through these interactions, RIMs regulate the biophysical properties of the channels and their anchoring relative to active zones, significantly influencing hormone and neurotransmitter release.     

Improvement of water-solubility of biarylcarboxylic acid peroxisome proliferator-activated receptor (PPAR) δ-selective partial agonists by disruption of molecular planarity/symmetry

To elucidate the molecular basis of peroxisome proliferator-activated receptor (PPAR) δ partial agonism, X-ray crystal structures of complexes of the PPARδ ligand-binding site with partial agonists are required. Unfortunately, reported PPARδ partial agonists, biphenylcarboxylic acids 1 and 2, possess insufficient aqueous solubility to allow such crystals to be obtained. To improve the aqueous solubility of 1 and 2, substituents were introduced at the 2-position of the biaryl moiety, focusing on disruption of molecular planarity and symmetry. All 2-substituted biphenyl analogs examined showed more potent PPARδ agonistic activity with greater aqueous solubility than 1 or 2. Among these biphenyls, 25 showed potent and selective PPARδ partial agonistic activity (EC₅₀: 5.7 nM), with adequate solubility in phosphate buffer (0.022 mg/mL). The 2-substituted pyridyl analog 27 showed weaker PPARδ partial agonistic activity (EC₅₀: 76 nM) with excellent solubility in phosphate buffer (2.7 mg/mL; at least 2700 times more soluble than 2). Our results indicate that two strategies to improve aqueous solubility, that is, introduction of substituent(s) to modify the dihedral angle and to disrupt molecular symmetry, may be generally applicable to bicyclic molecules. Combination of these approaches with the traditional approach of reducing the molecular hydrophobicity may be particularly effective.     

Solvatomorphs of dimeric transition metal complexes based on the V4O12 cyclic anion as building block: Crystalline packing and magnetic properties

Dinuclear [{M(phen)₂}₂V₄O₁₂] · C₆H₁₂O · H₂O (M = Co^II 1, Mn^II 2, Ni^II 3 and Cu^II 4) and [{Cu(phen)₂}₂V₄O₁₂] · 3.5H₂O 5 has been prepared by biphasic and hydrothermal syntheses, respectively. All five structures exhibit the {V₄O₁₂}^4? cluster in a chair-like configuration, covalently bonded to two [M(phen)₂]²⁺ fragments, producing a super-exchange magnetic phenomenon. The magnetic study of complexes 1–5 shows that they are very weak antiferromagnetically coupled systems, with J values of ?0.14, 2; ?0.64, 3 and ?0.23, 4 cm^?1. Complexes 1 to 3 correspond to isostructural compounds in which the cyclovanadate group acts as a bidentate bridged ligand. In the copper complexes (4 and 5) the {V₄O₁₂}^4? anion presents the novel monodentate bridging mode, and therefore a more significant distortion from the chair-like configuration. The mentioned complexes, together with that reported in the literature, permit to conclude that it is quite common for a single molecular species to exist in more than one crystalline arrangement. A detailed analysis of the structures of 1–4 shows that the crystal symmetry cannot be strictly centrosymmetric, due to the presence of the cyclohexanol molecule with a single –OH group in the lattice.     

Lobeline esters as novel ligands for neuronal nicotinic acetylcholine receptors and neurotransmitter transporters

Vesicular monoamine transporter-2 (VMAT2) is a viable target for development of pharmacotherapies for psychostimulant abuse. Lobeline (1) is a potent antagonist at α4β21 nicotinic acetylcholine receptors, has moderate affinity (K_i = 5.46 μM) for VMAT2, and is being investigated currently as a clinical candidate for treatment of psychostimulant abuse. A series of carboxylic acid and sulfonic acid ester analogs 2–20 of lobeline were synthesized and evaluated for interaction with α4β21 and α71 neuronal nicotinic acetylcholine receptors (nAChRs), the dopamine transporter (DAT), serotonin transporter (SERT) and VMAT2. Both carboxylic acid and sulfonic acid esters had low affinity at α71 nAChRs. Similar to lobeline (K_i = 4 nM), sulfonic acid esters had high affinity at α4β21 (K_i = 5–17 nM). Aromatic carboxylic acid ester analogs of lobeline (2–4) were 100–1000-fold less potent than lobeline at α4β21 nAChRs, whereas aliphatic carboxylic acid ester analogs were 10–100-fold less potent than lobeline at α4β21. Two representative lobeline esters, the 10-O-benzoate (2) and the 10-O-benzenesulfonate (10) were evaluated in the ³⁶Rb⁺ efflux assay using rat thalamic synaptosomes, and were shown to be antagonists with IC₅₀ values of 0.85 μM and 1.60 μM, respectively. Both carboxylic and sulfonic acid esters exhibited a range of potencies (equipotent to 13–45-fold greater potency compared to lobeline) for inhibiting DAT and SERT, respectively, and like lobeline, had moderate affinity (K_i = 1.98–10.8 μM) for VMAT2. One of the more interesting analogs, p-methoxybenzoic acid ester 4, had low affinity at α4β21 nAChRs (K_i = 19.3 μM) and was equipotent with lobeline, at VMAT2 (K_i = 2.98 μM), exhibiting a 6.5-fold selectivity for VMAT2 over α4β2 nAChRs. Thus, esterification of the lobeline molecule may be a useful structural modification for the development of lobeline analogs with improved selectivity at VMAT2.     

Second generation 4-(4-methyl-1H-indol-5-ylamino)-2-phenylthieno[2,3-b]pyridine-5-carbonitrile PKCθ inhibitors

Thieno[2,3-b]pyridine-5-carbonitrile 16 with a 4-methyl-5-indolylamine at C-4 and a 5-methoxy-2-(dimethylamino)-methylphenyl group at C-2 had an IC₅₀ value of 16 nM for the inhibition of PKCθ. While moderate inhibition of PKCδ was also observed (IC₅₀ = 130 nM), 16 had IC₅₀ values of greater than 5 μM against Lyn and other members of the Src kinase family.     

2,4(5)-Diarylimidazoles as inhibitors of hNaV1.2 sodium channels: Pharmacological evaluation and structure–property relationships

Sodium (Na) channels continue to represent an important target for the development of novel anticonvulsants. We have synthesized and evaluated a series of 2,4(5)-diarylimidazoles for inhibition of the human neuronal Na_V1.2 Na channel isoform. Starting with the unsubstituted lead compound previously published 3, SAR studies were performed introducing substituents with different physico-chemical properties. Lipophilicity (log D_7.4) and basicity (pK_a) of the compounds were measured and submitted for QSPR investigations. Some of the active compounds described had IC₅₀ values that were considerably lower than our lead compound. In particular, the m-CF₃ disubstituted 22 was the most active compound, inhibiting hNa_V1.2 currents within the nanomolar concentration range (IC₅₀ = 200 nM). In comparison, lamotrigine and phenytoin, two clinically used anticonvulsant drugs known to inhibit Na channels, had IC₅₀’s values that were greater than 100 μM.