Design, synthesis, and pharmacological evaluation of phenoxy pyridyl derivatives as dual norepinephrine reuptake inhibitors and 5-HT1A partial agonists

Multitarget-Directed Ligands Hitting Serotonin Receptors: A Medicinal Chemistry Survey

Serotonin (5-hydroxytryptamine, 5-HT) is a ubiquitous neurotransmitter in the human body. In the central nervous system, 5-HT affects sleep, pain, mood, appetite, and attention, while in the peripheral nervous system, 5-HT modulates peristalsis, mucus production, and blood vessel dilation. Fourteen membrane receptors mediate 5-HT activity. In agreement with the crucial roles played by 5-HT, many drugs target 5-HT receptors (5-HTRs). Therefore, it is unsurprising that many efforts have been devoted to discovering multitarget-directed ligands (MTDLs) capable of engaging one or more 5-HTRs plus another target phenotypically linked to a particular disease. In this review, we will describe medicinal chemistry efforts in designing MTDLs encompassing activity for one or more 5-HTRs, starting with atypical antipsychotics and moving to dual 5-HT1AR/serotonin transporter ligands, 5-HT6R antagonists/acetyl cholinesterases inhibitors, and 5-HT4R agonists/acetyl cholinesterases inhibitors. We will also provide an outlook on the most recent efforts made in the field.

Effect of "magic chlorine" in drug discovery: an in silico approach

The chlorine atom plays a vital role in drug design, yet the benefits of chlorine in 250 FDA-approved chlorine-containing drugs have not been studied properly. To see the "magic chloro" effect, computational studies have been carried out for 35 inhibitors, which are numbered as 12 complexes with (parent (-H), one chlorine, or two chlorine) substituents. The physicochemical properties are studied by conceptual density functional theory (CDFT). The pharmacokinetics, toxicity and metabolic properties of the studied inhibitors are estimated using chemoinformatics tools. SwissTargetPrediction is used to predict the multitarget activities of the studied inhibitors. Four FDA-approved drugs, diazepam, chloroquine, chloramphenicol, and bendamustine, are referenced to validate the studies. A higher HOMO-LUMO gap predicted high stability for the studied one and two chlorine-substituted analogues. Most of the studied inhibitors show "drug likeliness", nontoxicity, and high gastrointestinal (GI) absorption. The addition of one or two chloro substituents has increased the physicochemical properties and stability of most of the inhibitors compared to the parent analogues, whereas the toxicity is not affected. No change in metabolic properties is observed on addition of one or two chlorine substituents. The multi-target activities of all the studied inhibitors are validated by the reference drugs and experimental results.

"Magic Chloro": Profound Effects of the Chlorine Atom in Drug Discovery

Chlorine is one of the most common atoms present in small-molecule drugs beyond carbon, hydrogen, nitrogen, and oxygen. There are currently more than 250 FDA-approved chlorine-containing drugs, yet the beneficial effect of the chloro substituent has not yet been reviewed. The seemingly simple substitution of a hydrogen atom (R = H) with a chlorine atom (R = Cl) can result in remarkable improvements in potency of up to 100,000-fold and can lead to profound effects on pharmacokinetic parameters including clearance, half-life, and drug exposure in vivo. Following the literature terminology of the "magic methyl effect" in drugs, the term "magic chloro effect" has been coined herein. Although reports of 500-fold or 1000-fold potency improvements are often serendipitous discoveries that can be considered "magical" rather than planned, hypotheses made to explain the magic chloro effect can lead to lessons that accelerate the cycle of drug discovery.

Data-Driven Analysis of Fluorination of Ligands of Aminergic G Protein Coupled Receptors

Currently, G protein-coupled receptors are the targets with the highest number of drugs in many therapeutic areas. Fluorination has become a common strategy in designing highly active biological compounds, as evidenced by the steadily increasing number of newly approved fluorine-containing drugs. Herein, we identified in the ChEMBL database and analysed 1554 target-based FSAR sets (non-fluorinated compounds and their fluorinated analogues) comprising 966 unique non-fluorinated and 2457 unique fluorinated compounds active against 33 different aminergic GPCRs. Although a relatively small number of activity cliffs (defined as a pair of structurally similar compounds showing significant differences of activity -ΔpPot > 1.7) was found in FSAR sets, it is clear that appropriately introduced fluorine can increase ligand potency more than 50-fold. The analysis of matched molecular pairs (MMPs) networks indicated that the fluorination of the aromatic ring showed no clear trend towards a positive or negative effect on affinity; however, a favourable site for a positive potency effect of fluorination was the ortho position. Fluorination of aliphatic fragments more often led to a decrease in biological activity. The results may constitute the rules of thumb for fluorination of aminergic receptor ligands and provide insights into the role of fluorine substitutions in medicinal chemistry.

Introducing an α-Keto Ester Functional Group through Pt-Catalyzed Direct C-H Acylation with Ethyl Chlorooxoacetate

Platinum-catalyzed selective C-H acylation of 2-aryloxypyridines with ethyl chlorooxoacetate provides an efficient way of introducing an α-keto ester functional group. The reaction is oxidant-free, additive-free, and, more significantly, free of any decarbonylative side reactions. The reaction tolerates a variety of substituents from strongly electron-donating to strongly electron-withdrawing groups. Double acylation is feasible for 2-phenoxypyridine and its derivatives with only one substituent at the para position. Although the reaction of 2-(2-methylphenoxy)pyridine with ethyl malonyl chloride did not produce the desired β-keto ester, the reaction with ethyl succinyl chloride proceeded smoothly to give the γ-keto ester. Ethyl chlorooxoacetate is much more reactive than ethyl succinyl chloride in this Pt-catalyzed C-H acylation reaction.

Mechanism-based pharmacokinetic/pharmacodynamic modeling of rat prefrontal cortical dopamine response to dual acting norepinephrine reuptake inhibitor and 5-HT1A partial agonist

Evidence suggests that compounds possessing both norepinephrine reuptake inhibition and 5-HT(1A) partial agonism (NRI/5-HT(1A)) activities may have a greater efficacy in treating neuropsychiatric disorders than compounds possessing either activity alone. The objectives of the present study were first to characterize the pharmacokinetic/pharmacodynamic (PK/PD) relationship of the plasma concentrations of atomoxetine (NRI) and buspirone (5-HT(1A) partial agonist), administered alone and in combination, on the prefrontal cortex dopamine levels in rats, and second to use the model developed to characterize the PK/PD relationship of novel NRI/5-HT(1A) compounds, PF-04269339 and PF-03529936, in a NRI/5-HT(1A) drug discovery program. Maximal dopamine elevation was twofold higher after administration of atomoxetine and buspirone in combination, PF-04269339, or PF-03529936 than after administration of atomoxetine or buspirone alone. A mechanism-based extended indirect response model characterized the time profiles of the prefrontal cortex dopamine response to atomoxetine and buspirone, administered alone or in combination. After fixing three mechanism-specific pharmacodynamic parameters (I (max) and γ2 for NRI and γ1 for 5-HT(1A)) based on the model for atomoxetine and/or buspirone, the model fitted the exposure-response profiles of PF-04269339 and PF-03529936 well. Good in vitro-to-in vivo correlation was demonstrated with the compound-specific pharmacodynamic parameters (IC(50) for NRI and SC(50) and S (max) for 5-HT(1A)) across the compounds. In summary, a piecewise modeling approach was used successfully for the characterization of the PK/PD relationship of novel NRI/5-HT(1A) compounds on prefrontal cortex dopamine levels in rats. The application and value of the mechanism-based modeling in the dual pharmacology drug discovery program are also discussed.

In vivo brain microdialysis: advances in neuropsychopharmacology and drug discovery

INTRODUCTION: Microdialysis is an important in vivo sampling technique, useful in the assay of extracellular tissue fluid. The technique has both pre-clinical and clinical applications but is most widely used in neuroscience. The in vivo microdialysis technique allows measurement of neurotransmitters such as acetycholine (ACh), the biogenic amines including dopamine (DA), norepinephrine (NE) and serotonin (5-HT), amino acids such as glutamate (Glu) and gamma aminobutyric acid (GABA), as well as the metabolites of the aforementioned neurotransmitters, and neuropeptides in neuronal extracellular fluid in discrete brain regions of laboratory animals such as rodents and non-human primates. AREAS COVERED: In this review we present a brief overview of the principles and procedures related to in vivo microdialysis and detail the use of this technique in the pre-clinical measurement of drugs designed to be used in the treatment of chemical addiction, neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD) and as well as psychiatric disorders such as attention-deficit/hyperactivity disorder (ADHD) and schizophrenia. This review offers insight into the tremendous utility and versatility of this technique in pursuing neuropharmacological investigations as well its significant potential in rational drug discovery. EXPERT OPINION: In vivo microdialysis is an extremely versatile technique, routinely used in the neuropharmacological investigation of drugs used for the treatment of neurological disorders. This technique has been a boon in the elucidation of the neurochemical profile and mechanism of action of several classes of drugs especially their effects on neurotransmitter systems. The exploitation and development of this technique for drug discovery in the near future will enable investigational new drug candidates to be rapidly moved into the clinical trial stages and to market thus providing new successful therapies for neurological diseases that are currently in demand.