Design, synthesis and in vitro evaluation of bridgehead fluoromethyl analogs of N-{2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl}-N-(pyridin-2-yl)cyclohexanecarboxamide (WAY-100635) for the 5-HT1A receptor

Silver(I)-Catalyzed Synthesis of Cuneanes from Cubanes and their Investigation as Isosteres

Bridged or caged polycyclic hydrocarbons have rigid structures that project substituents into precise regions of 3D space, making them attractive as linking groups in materials science and as building blocks for medicinal chemistry. The efficient synthesis of new or underexplored classes of such compounds is, therefore, an important objective. Herein, we describe the silver(I)-catalyzed rearrangement of 1,4-disubstituted cubanes to cuneanes, which are strained hydrocarbons that have not received much attention since they were first described in 1970. The synthesis of 2,6-disubstituted or 1,3-disubstituted cuneanes can be achieved with high regioselectivities, with the regioselectivity being dependent on the electronic character of the cubane substituents. A preliminary assessment of cuneanes as scaffolds for medicinal chemistry suggests cuneanes could serve as isosteric replacements of trans-1,4-disubstituted cyclohexanes and 1,3-disubstituted benzenes. An analogue of the anticancer drug sonidegib was synthesized, in which the 1,2,3-trisubstituted benzene was replaced with a 1,3-disubstituted cuneane.

Photoinduced Diastereoselective Aminoalkylation of Cubanes

The unique properties of rigid, nonconjugated hydrocarbons provide many opportunities to design molecular building blocks for a variety of applications, but the development of suitable conditions for alkylation of cubanes is quite challenging. Herein, a photoinduced method for aminoalkylation of cubanes is reported. The benign conditions reported allow the incorporation of a wide variety of (hetero)arylimine reaction partners with broad functional group tolerance and high diastereoselectivity.

Nonconjugated Hydrocarbons as Rigid-Linear Motifs: Isosteres for Material Sciences and Bioorganic and Medicinal Chemistry

Nonconjugated hydrocarbons, like bicyclo[1.1.1]pentane, bicyclo[2.2.2]octane, triptycene, and cubane are a unique class of rigid linkers. Due to their similarity in size and shape they are useful mimics of classic benzene moieties in drugs, so-called bioisosteres. Moreover, they also fulfill an important role in material sciences as linear linkers, in order to arrange various functionalities in a defined spatial manner. In this Review article, recent developments and usages of these special, rectilinear systems are discussed. Furthermore, we focus on covalently linked, nonconjugated linear arrangements and discuss the physical and chemical properties and differences of individual linkers, as well as their application in material and medicinal sciences.

Cubanes in Medicinal Chemistry

Cubane is a highly strained saturated hydrocarbon system that has historically been of interest in theoretical organic chemistry. More recently it has become a molecule of interest for biological applications due to its inherent stability and limited toxicity. Of greater significance is the ability to potentially functionalize cubane at each of its carbon atoms, providing complex biologically active molecules with unique spatial arrangements for probing active sites. These characteristics have led to an increased use of cubane in pharmaceutically relevant molecules. In this Perspective we describe synthetic methodology for accessing a range of functionalized cubanes and their applications in pharmaceuticals. We also provide some perspectives on challenges and future directions in the advancement of this field.

Structural Insights into 5-HT1A/D4 Selectivity of WAY-100635 Analogues: Molecular Modeling, Synthesis, and in Vitro Binding

The resurgence of interest in 5-HT1A receptors as a therapeutic target requires the existence of highly selective 5-HT1A ligands. To date, WAY-100635 has been the prototypical antagonist of these receptors. However, this compound also has significant affinity for and activity at D4 dopamine receptors. In this context, this work was aimed at better understanding the 5-HT1A/D4 selectivity of WAY-100635 and analogues from a structural point of view. In silico investigations revealed two key interactions for the 5-HT1A/D4 selectivity of WAY-100635 and analogues. First, a hydrogen bond only found with the Ser 7.36 of D4 receptor appeared to be the key for a higher D4 affinity for newly synthesized aza analogues. The role of Ser 7.36 was confirmed as the affinity of aza analogues for the mutant D4 receptor S7.36A was reduced. Then, the formation of another hydrogen bond with the conserved Ser 5.42 residue appeared to be also critical for D4 binding.

Comparative assessment of (18) F-Mefway as a serotonin 5-HT1A receptor PET imaging agent across species: Rodents, nonhuman primates, and humans

We have developed (18) F-trans-Mefway ((18) F-Mefway) for positron emission tomography (PET) imaging studies of serotonin 5-HT1A receptors which are implicated in various brain functions. Translation of imaging the 5-HT1A receptor in animal models to humans will facilitate an understanding of the role of the receptor in human brain disorders. We report comparative brain distribution of (18) F-Mefway in normal mice, rats, monkeys, and healthy human volunteers. Mefway was found to be very selective, with subnanomolar affinity for the 5-HT1A receptor. Affinities of >55 nM were found for all other human-cloned receptor subtypes tested. Mefway was found to be a poor substrate (>30 μM) for the multidrug resistance 1 protein, suggesting low likelihood of brain uptake being affected by P-glycoprotein. Cerebellum was used as a reference region in all imaging studies across all species due to the low levels of (18) F-Mefway binding. Consistent binding of (18) F-Mefway in cortical regions, hippocampus, and raphe was observed across all species. (18) F-Mefway in the human brain regions correlated with the known postmortem distribution of 5-HT1A receptors. Quantitation of raphe was affected by the resolution of the PET scanners in rodents, whereas monkeys and humans showed a raphe to cerebellum ratio of approximately 3. (18) F-Mefway appears to be an effective 5-HT1A receptor imaging agent in all models, including humans. (18) F-Mefway therefore may be used to quantify 5-HT1A receptor distribution in brain regions for the study of various CNS disorders. J. Comp. Neurol. 524:1457-1471, 2016. © 2015 Wiley Periodicals, Inc.

Synthesis, preclinical evaluation and molecular modelling of macrocyclic appended 1-(2-methoxyphenyl)piperazine for 5-HT1A neuroreceptor imaging

An efficient approach in the design and synthesis of a multi-functional chelating agent based on 1-(2-methoxyphenyl)piperazine for targeting 5-HT_1A receptors in brain was envisaged.

Synthesis and Evaluation of Mefway Analogs as Ligands for Serotonin 5HT1A Receptors

¹⁸F-Mefway (N-{2-[4-(2'-methoxyphenyl)piperazinyl]ethyl}-N-(2-pyridyl)-N-(4'-¹⁸F-fluoro-methylcyclohexane)carboxamide) was developed and evaluated for use as a PET ligand for imaging 5-HT_1A receptors. Ongoing studies of ¹⁸F-Mefway have shown it to be an effective PET radiotracer. We have synthesized isomers of Mefway by changing the position of the methyl-group in attempts to evaluate stability for imaging purposes. 2-Methyl-, 3-methyl-, and 4-methyl-cyclohexane-1-carboxylic acids and 3-carbomethoxy-, 4-carbomethoxycyclohexane-1-carboxylic acids were coupled with WAY-100634 to provide the methylcyclohexyl derivatives (2-, 3- and 4-methyl). Mefway and 3-Mefway analogs were prepared by reduction of carbomethoxy-derivatives followed by fluorination. In vitro binding affinities for the methylated derivatives in rat brain homogenates was found to be 10.4 nM (2-methyl), 77 nM (3-methyl) and 21.5 nM (4-methyl). Binding affinity of 3-Mefway and 4-Mefway was found to be 17.4 nM and 6.26 nM, respectively. Our results suggest that 3-methyl/3-fluoromethyl substituent has approx. 3-fold lower affinities compared to the 4-methyl/4-fluoromethyl substituent.

N-(4-[(18)F]-fluoropyridin-2-yl)-N-{2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl}carboxamides as analogs of WAY100635. New PET tracers of serotonin 5-HT(1A) receptors

N-(4-[(18)F]-Fluoropyridin-2-yl)-N-{2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl}-carboxamides were prepared by labeling their 4-nitropyridin-2-yl precursors through nitro substitution by the (18)F anion. In vitro and in vivo tests showed that the cyclohexanecarboxamide derivative is a reversible, selective and high affinity 5-HT1A receptor antagonist (IC50 = 0.29 nM, ki = 0.18 nM) with high brain uptake, slow brain clearance and stability to defluorination when compared with conventional standards. This PET radioligand is a promising candidate for an improved in vivo quantification of 5-HT1A receptors in neuropsychiatric disorders.

Synthesis, radiolabeling and bioevaluation of a novel arylpiperazine derivative containing triazole as a 5-HT1A receptor imaging agents

INTRODUCTION

It has been recognized that serotonin plays a main role in various pathological conditions such as anxiety, depression, aggressiveness, schizophrenia, suicidal behavior, panic and autism. 1-(2-Methoxyphenyl) piperazine pharmacophore, a fragment of the true 5-HT(1A) antagonist WAY100635, is found in numerous selective 5-HT(1A) imaging agents. In this paper, we have reported the synthesis of a novel derivative of 1-(2-methoxyphenyl) piperazine that is labeled with (99m)Tc (CO)(3) via click chemistry.

METHODS

The bidentate alkyne, propargylglycine was reacted with phenyl piperazine triazole derivative in the presence of a catalytic amount of Cu (I) to form tridentate ligand. The ligand was radiolabeled with the precursor [(99m)Tc] [(H(2)O)(3) (CO)(3)](+) and characterized by HPLC. The bioevaluation of radio labeled ligand was carried out in rats.

RESULTS

Triazole complex was labeled by (99m)Tc-tricarbonyl and its radiochemical yield was more than >95% which was determined by HPLC. In vivo stability studies in human serum albumin show a 93% ratio of complex after a 24h period. The calculated partition coefficient (logP) was 0.34±0.02. Receptor binding assays indicated about 70% specific binding of radioligand to 5-HT(1A) receptors. Biodistribution studies have shown brain hippocampus uptake of 0.40±0.08 %ID/g at 30 min post injection.

CONCLUSIONS

Results indicate that this (99m)Tc-tricabonyl-arylpiperazine derivative has specific binding to 5-HT(1A) receptors and presented suitable characters for its use as a CNS imaging agent.

4-Benzyl-N-methyl-piperazine-1-carbothio-amide

The asymmetric unit in the title thio­urea derivative, C₁₃H₁₉N₃S, comprises three independent mol­ecules (A, B and C). The thio­urea groups are superimposable for the three mol­ecules, but there are significant conformational differences. Mol­ecules A and B are approximate mirror images of each other, and mol­ecule C has an inter­mediate conformation. The dihedral angles between the thio­urea groups and the phenyl rings are 52.10 (5), 63.29 (5) and 66.46 (6)° in mol­ecules A, B and C, respectively. Each independent mol­ecule self-associates into a supra­molecular chain along [100] via N—H⋯S hydrogen bonds. Mol­ecules of A and B assemble into layers four mol­ecules thick in the ac plane via C—H⋯S and C—H⋯π inter­actions. Mol­ecules of C self-assemble into layers in the ac plane via C—H⋯S inter­actions. The layers stack along the b axis with no specific inter­actions between them.