Redox cycloisomerization approach to 1,2-dihydropyridines

The phosphine-catalyzed synthesis of 1,2-dihydropyridines via an alkyne isomerization/electrocyclization sequence is described. Propargylidenecarbamate substrates were prepared following a one-pot procedure between a terminal alkyne, a benzonitrile, and a chloroformate in the presence of trimethylaluminum. This methodology gives access to a diverse set of 2,6-disubstituted 1,2-dihydropyridines in high yield. The products can be easily converted into substituted piperidines or pyridines, and this methodology was applied to the synthesis of indolizidines.

Synthesis, structural and spectral analysis of 1-(pyrazin-2-yl) piperidin-2-ol by density functional theory

The organic compound 1-(pyrazin-2-yl) piperidin-2-ol (abbreviated as PPOL) has been synthesized and characterized by IR, Raman, (1)H NMR and UV-Vis spectroscopy. The Fourier-transform Raman (3500-50cm(-1)) and infrared spectra (4000-400cm(-1)) were recorded in the solid state and interpreted by comparison with theoretical spectra derived from density functional theory (DFT) calculations. The optimized geometry, frequency and intensity of the vibrational bands of the compound was obtained by the density functional theory using 6-31G(d,p) basis set. In the optimized geometry results shows that geometry parameters are good agreement with XRD values. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. In calculation of electronic absorption spectra, TD-DFT calculations were carried out in the both gas and solution phases. (1)H NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. (1)H NMR analysis is evident for O-H⋯O intermolecular interaction of the title molecule. The thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (Cp,m), standard entropies (Sm) and standard enthalpy changes (Hm) increase with rise in temperature. In addition, HOMO and LUMO energies and the first-order hyperpolarizability have been computed.

Improving selectivity preserving affinity: new piperidine-4-carboxamide derivatives as effective sigma-1-ligands

We report the design, synthesis and binding evaluation against σ1 and σ2 receptors of a series of new piperidine-4-carboxamide derivatives variously substituted on the amide nitrogen atom. Specifically, we assessed the effects exerted on σ receptor affinity by substituting the N-benzylcarboxamide group present on a series of compounds previously synthesized in our laboratory with different cyclic or linear moieties. The synthesized compounds 2a-o were tested to estimate their affinity and selectivity toward σ1 and σ2 receptors. Very high σ1 affinity (Ki = 3.7 nM) and Kiσ2/Kiσ1 selectivity ratio (351) were found for the tetrahydroquinoline derivative 2k, featuring a 4-chlorobenzyl moiety linked to the piperidine nitrogen atom.

Halofuginone - the multifaceted molecule

Halofuginone is an analog of febrifugine-an alkaloid originally isolated from the plant Dichroa febrifuga. During recent years, halofuginone has attracted much attention because of its wide range of beneficial biological activities, which encompass malaria, cancer, and fibrosis-related and autoimmune diseases. At present two modes of halofuginone actions have been described: (1) Inhibition of Smad3 phosphorylation downstream of the TGFβ signaling pathway results in inhibition of fibroblasts-to-myofibroblasts transition and fibrosis. (2) Inhibition of prolyl-tRNA synthetase (ProRS) activity in the blood stage of malaria and inhibition of Th17 cell differentiation thereby inhibiting inflammation and the autoimmune reaction by activation of the amino acid starvation and integrated stress responses. This review deals with the history and origin of this natural product, its synthesis, its known modes of action, and it's various biological activities in pre-clinical animal models and in humans.

Synthesis, Anticonvulsant and Binding Interaction Study of Novel Piperamides with Bovine Serum Albumin by Fluorescence Spectroscopy

A series of piperamides (PA) 8a-j were designed, synthesized and evaluated for their antimicrobial and anticonvulsant activity. Compounds 8a and 8h showed considerable antibacterial activity against B. subtilis with minimum inhibitory concentration (MIC) of 8 and 10 µg/mL, respectively. Compounds 8a and 8h showed advanced anticonvulsant activity as well as lower neurotoxicity than the reference drugs. The interaction between bovine serum albumin (BSA) and PA was investigated using fluorescence quenching and UV-vis absorption spectroscopy. Results showed that PA could strongly quinch the intrensic fluorescence of BSA through a static quencing procedure. The binding constant and number of binding sites of PA with BSA were obtained. The binding distance was calculated based on Forster non-radiative energy transfer theory.

Synthesis and biological evaluation of novel sigma-1 receptor antagonists based on pyrimidine scaffold as agents for treating neuropathic pain

The discovery and synthesis of a new series of pyrimidines as potent sigma-1 receptor (σ1R) antagonists, associated with pharmacological antineuropathic pain activity, are the focus of this article. The new compounds were evaluated in vitro in σ-1 and σ-2 receptor binding assays. The nature of the pyrimidine scaffold was crucial for activity, and a basic amine was shown to be necessary according to the known pharmacophoric model. The most promising derivative was 5-chloro-2-(4-chlorophenyl)-4-methyl-6-(3-(piperidin-1-yl)propoxy)pyrimidine (137), which exhibited a high binding affinity to σ1R receptor (Ki σ1 = 1.06 nM) and good σ-1/2 selectivity (1344-fold). In in vivo tests, compound 137 exerted dose-dependent antinociceptive effects in mice formalin model and rats CCI models of neuropathic pain. In addition, no motor impairments were found in rotarod tests; acceptable pharmacokinetic properties were also noted. These data suggest compound 137 may constitute a novel class of drugs for the treatment of neuropathic pain.

Concise and straightforward asymmetric synthesis of a cyclic natural hydroxy-amino acid

An enantioselective total synthesis of the natural amino acid (2S,4R,5R)-4,5-di-hydroxy-pipecolic acid starting from D-glucoheptono-1, 4-lactone is presented. The best sequence employed as a key step the intramolecular nucleophilic displacement by an amino function of a 6-O-p-toluene-sulphonyl derivative of a methyl D-arabino-hexonate and involved only 12 steps with an overall yield of 19%. The structures of the compounds synthesized were elucidated on the basis of comprehensive spectroscopic (NMR and MS) and computational analysis.

Vascular effects of diphenylmethoxypiperidine-derived dopamine uptake inhibitors

Vascular effects of 4-aryl methoxypiperidinol compounds previously shown to share with cocaine the ability to inhibit the dopamine transporter are described. All the compounds tested inhibit KCl-induced and noradrenaline-dependent contractions in mesenteric arteries ex vivo. Thus, diphenylpyraline and its analogs may have a role as therapeutic options for the treatment of some of the cardiotoxic effects of cocaine intoxications.

Synthesis of an Optically Pure Synthetic Intermediate of Aloperine from a Yeast-Reductive Product

Optically pure (S)- and (R)-vinylpiperidine 2 and (S)- and (R)-(hydroxyethyl)piperidine 3, which were key intermediates for the synthesis of aloperine, were synthesized from yeast-reductive products.

Synthesis and identification of chiral aminomethylpiperidine carboxamides as inhibitor of collagen induced platelet activation

A series of chiral lactam carboxamides of aminomethylpiperidine were synthesized and investigated for the collagen induced in vitro anti-platelet efficacy and collagen plus epinephrine induced in vivo pulmonary thromboembolism. The compound 31a (30 μM/kg) displayed a remarkable antithrombotic efficacy (60% protection) which was sustained for more than 24 h and points to its excellent bioavailability. The compounds 31a (IC50 = 6.6 μM) and 32a (IC50 = 37 μM), as well as their racemic mixture 28i (IC50 = 16 μM) significantly inhibited collagen-induced human platelet aggregation in vitro. Compound 34c displayed dual mechanism of action against both collagen (IC50 = 3.3 μM) and U46619 (IC50 = 2.7 μM) induced platelet aggregation. The pharmacokinetic study of 31a indicated very faster absorption, prolonged and constant systemic exposure and thereby exhibiting better therapeutic response.

Novel GlyT1 inhibitor chemotypes by scaffold hopping. Part 2: development of a [3.3.0]-based series and other piperidine bioisosteres

This Letter describes the development and SAR of a novel series of GlyT1 inhibitors derived from a scaffold hopping approach, in lieu of an HTS campaign, which provided intellectual property position. Members within this new [3.3.0]-based series displayed excellent GlyT1 potency, selectivity, free fraction, and modest CNS penetration. Moreover, enantioselective GlyT1 inhibition was observed, within this novel series and a number of other piperidine bioisosteric cores.

[A novel dipeptidyl peptidase IV inhibitors developed through scaffold hopping and drug splicing strategy]

Though all the marketed drugs of dipeptidyl peptidase IV inhibitors are structurally different, their inherent correlation is worthy of further investigation. Herein we rapidly discovered a novel DPP-IV inhibitor 8g (IC50 = 4.9 nmol.L-1) which exhibits as good activity and selectivity as the market drugs through scaffold hopping and drug splicing strategies based on alogliptin and linagliptin. This study demonstrated that the employment of classic medicinal chemistry strategy to the marketed drugs with specific target is an efficient approach to discover novel bioactive molecules.

Syntheses of precursors and reference compounds of the melanin-concentrating hormone receptor 1 (MCHR1) tracers [¹¹C]SNAP-7941 and [¹⁸F]FE@SNAP for positron emission tomography

The MCH receptor has been revealed as a target of great interest in positron emission tomography imaging. The receptor's eponymous substrate melanin-concentrating hormone (MCH) is a cyclic peptide hormone, which is located predominantly in the hypothalamus with a major influence on energy and weight regulation as well as water balance and memory. Therefore, it is thought to play an important role in the pathophysiology of adiposity, which is nowadays a big issue worldwide. Based on the selective and high-affinity MCH receptor 1 antagonist SNAP-7941, a series of novel SNAP derivatives has been developed to provide different precursors and reference compounds for the radiosyntheses of the novel PET radiotracers [(11)C]SNAP-7941 and [(18)F]FE@SNAP. Positron emission tomography promotes a better understanding of physiologic parameters on a molecular level, thus giving a deeper insight into MCHR1 related processes as adiposity.

Ring expansion of vinylaziridines through the strain-release pericyclic reaction: recent developments and applications

Recent syntheses of azetidines, pyrrolidines, piperidines and azepines through cycloaddition or sigmatropic rearrangements of vinylaziridines are described. Applications to natural product synthesis and mechanistic investigations are also summarized.

Discovery of TD-8954, a clinical stage 5-HT(4) receptor agonist with gastrointestinal prokinetic properties

The discovery of a series of 5-HT4 receptor agonists based on a novel 2-alkylbenzimidazole aromatic core is described. Optimization of the 2-substituent of the benzimidazole ring led to a series of agonists with subnanomolar binding affinity and moderate-to-high intrinsic activity relative to that of 5-HT. Consistent with our previously described multivalent design approach to this target, subsequent optimization of the linker and secondary binding group regions of the series afforded compound 18 (TD-8954), a potent and selective 5-HT4 receptor agonist in vitro with demonstrated prokinetic activity in multiple species.

Designing bifunctional NOP receptor-mu opioid receptor ligands from NOP receptor-selective scaffolds. Part I

The nociceptin receptor (NOP) and its endogenous agonist, nociceptin/orphanin FQ (N/OFQ), members of the opioid receptor and peptide families respectively, modulate the pharmacological effects of classical opioids, particularly opioid-induced reward and nociception. We hypothesized that compounds containing both NOP and opioid receptor activity in a single molecule may have useful pharmacological profiles as non-addicting analgesics or as drug abuse medications. We report here our forays into the structure-activity relationships for discovering 'bifunctional' NOP-mu opioid receptor (MOP) ligands, starting from our NOP-selective scaffolds. This initial SAR suggests pharmacophoric elements that may be modified to modulate/increase opioid affinity, while maintaining high affinity for the NOP receptor, to result in potent bifunctional small-molecule NOP/MOP ligands.

Synthesis of biologically active O-substituted derivatives of 1-[(3, 5-dichloro-2-hydroxyphenyl)sulfonyl]piperidine

In the present work, a series of 2-O-substituted derivatives of 1-[(3,5-dichloro-2-hydroxy phenyl) sulfonyl]piperidine (5a-j) were synthesized. These derivatives were geared up by the coupling of 3,5-dichloro-2-hydroxy benzenesulfonyl chloride (1) with piperidine (2) under dynamic pH control in aqueous media to form parent compound 1-[(3,5-dichloro-2-hydroxyphenyl)sulfonyl]piperidine (3), followed by the substitution at oxygen atom with different electrophiles (4a-j) in the presence of sodium hydride (NaH) and dimethyl formamide (DMF) to give a series of O-substituted derivatives of sulfonamides bearing piperidine nucleus 5a-j. The synthesized O-substituted sulfonamides were spectrally characterized. The bioactivity of all the synthesized compounds were evaluated against lipoxygenase (LOX), acetylcholinesterae (AChE) and butyrylcholinesterase (BChE) enzymes and found to be having talented activity against butyrylcholinesterase enzyme.

Novel substituted heteroaromatic piperazine and piperidine derivatives as inhibitors of human enterovirus 71 and coxsackievirus a16

A series of substituted heteroaromatic piperazine and piperidine derivatives were found through virtual screening based on the structure of human enterovirus 71 capsid protein VP1. The preliminary biological evaluation revealed that compounds 8e and 9e have potent activity against EV71 and Coxsackievirus A16 with low cytotoxicity.

Effect of anchoring 4-anilidopiperidines to opioid peptides

We report here the design, synthesis, and in vitro characterization of new opioid peptides featuring a 4-anilidopiperidine moiety. Despite the fact that the chemical structures of fentanyl surrogates have been found suboptimal per se for the opioid activity, the corresponding conjugates with opioid peptides displayed potent opioid activity. These studies shed an instructive light on the strategies and potential therapeutic values of anchoring the 4-anilidopiperidine scaffold to different classes of opioid peptides.

Proton donor acidity controls selectivity in nonaromatic nitrogen heterocycle synthesis

Piperidines are prevalent in natural products and pharmaceutical agents and are important synthetic targets for drug discovery and development. We report on a methodology that provides highly substituted piperidine derivatives with regiochemistry selectively tunable by varying the strength of acid used in the reaction. Readily available starting materials are first converted to dihydropyridines via a cascade reaction initiated by rhodium-catalyzed carbon-hydrogen bond activation. Subsequent divergent regio- and diastereoselective protonation of the dihydropyridines under either kinetic or thermodynamic control provides two distinct iminium ion intermediates that then undergo highly diastereoselective nucleophilic additions. X-ray structural characterization of both the kinetically and thermodynamically favored iminium ions along with density functional theory calculations provide a theoretical underpinning for the high selectivities achieved for the reaction sequences.

Design, synthesis and evaluation of novel heterodimers of donepezil and huperzine fragments as acetylcholinesterase inhibitors

Four series of novel heterodimers comprised of donepezil and huperzine A (HupA) fragments were designed, synthesized, and evaluated in search of potent acetylcholinesterase (AChE) inhibitors as potential therapeutic treatment for Alzheimer's disease. Heterodimers comprised of dimethoxyindanone (from donepezil), hupyridone (from HupA), and connected with a multimethylene linker, were identified as potent and selective inhibitors of AChE. Diastereomeric heterodimers (RS,S)-17b (with a tetramethylene linker) exhibited the highest potency of inhibition towards AChE with an IC(50) value of 9 nM and no detectable inhibitory effect on butyrylcholinesterase at 1mM.

Design, synthesis and evaluation of novel heterodimers of donepezil and huperzine fragments as acetylcholinesterase inhibitors

Four series of novel heterodimers comprised of donepezil and huperzine A (HupA) fragments were designed, synthesized, and evaluated in search of potent acetylcholinesterase (AChE) inhibitors as potential therapeutic treatment for Alzheimer's disease. Heterodimers comprised of dimethoxyindanone (from donepezil), hupyridone (from HupA), and connected with a multimethylene linker, were identified as potent and selective inhibitors of AChE. Diastereomeric heterodimers (RS,S)-17b (with a tetramethylene linker) exhibited the highest potency of inhibition towards AChE with an IC(50) value of 9 nM and no detectable inhibitory effect on butyrylcholinesterase at 1mM.

σ-1 receptor at the mitochondrial-associated endoplasmic reticulum membrane is responsible for mitochondrial metabolic regulation

The mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) is a small section of the outer mitochondrial membrane tethered to the ER by lipid and protein filaments. One such MAM protein is the σ-1 receptor, which contributes to multiple signaling pathways. We found that short interfering RNA-mediated knockdown of σ-1 reduced pregnenolone synthesis by 95% without affecting expression of the inner mitochondrial membrane resident enzyme, 3-β-hydroxysteroid dehydrogenase 2. To explore the underlying mechanism of this effect, we generated a series of σ-receptor ligands: 5,6-dimethoxy-3-methyl-N-phenyl-N-(3-(piperidin-1-yl)propyl)benzofuran-2-carboxamide (KSCM-1), 3-methyl-N-phenyl-N-(3-(piperidin-1-yl)propyl)benzofuran-2-carboxamide (KSCM-5), and 6-methoxy-3-methyl-N-phenyl-N-(3-(piperidin-1-yl) propyl)benzofuran-2-carboxamide (KSCM-11) specifically bound to σ-1 in the nanomolar range, whereas KSCM-5 and KSCM-11 also bound to σ-2. Treatment of cells with the KSCM ligands led to decreased cell viability, with KSCM-5 having the most potent effect followed by KSCM-11. KSCM-1 increased σ-1 expression by 4-fold and progesterone synthesis, whereas the other compounds decreased progesterone synthesis. These differences probably are caused by ligand molecular structure. For example, KSCM-1 has two methoxy substituents at C-5 and C-6 of the benzofuran ring, whereas KSCM-11 has one at C-6. KSCM ligands or σ-1 knockdown did not alter the expression of ER resident enzymes that synthesize steroids. However, coimmunoprecipitation of the σ-1 receptor pulled down voltage-dependent anion channel 2 (VDAC2), whose expression was enhanced by KSCM-1. VDAC2 plays a key role in cholesterol transport into the mitochondria, suggesting that the σ-1 receptor at the MAM coordinates with steroidogenic acute regulatory protein for cholesterol trafficking into the mitochondria for metabolic regulation.

Structural, vibrational and DSC investigations of the bis-4-benzyl piperidinium tetraoxoselenate monohydrate crystal

A new organic-inorganic salt, bis-4-benzyl piperidinium tetraoxoselenate monohydrate has been synthesized and characterized by X-ray diffraction, FT-IR and FT-Raman spectroscopies. The title compound crystallizes in the monoclinic system P2(1)/c at room temperature with the following parameters: a=8.617(3)Å, b=27.140(9)Å, c=10.926(5)Å, β=96.46(4)° and Z=4. Its vibrational spectra have been discussed on the basis on quantum chemical density theory (DFT) calculation using B3LYP/6-31G(*) approach. The role of the intermolecular interaction in this crystal is analyzed. Acidic protons of the selenate group were transferred to the organic cation giving the singly-protonated cation. The ability of ions to form spontaneous three-dimensional structure through O-H···O and N-H···O hydrogen bond is fully utilized. These hydrogen bonds give notable vibrational effects.

Design and synthesis of inhibitors of Plasmodium falciparum N-myristoyltransferase, a promising target for antimalarial drug discovery

Design of inhibitors for N-myristoyltransferase (NMT), an enzyme responsible for protein trafficking in Plasmodium falciparum , the most lethal species of parasites that cause malaria, is described. Chemistry-driven optimization of compound 1 from a focused NMT inhibitor library led to the identification of two early lead compounds 4 and 25, which showed good enzyme and cellular potency and excellent selectivity over human NMT. These molecules provide a valuable starting point for further development.