Deciphering the Supramolecular Organization of Multiple Guests Inside a Microporous MOF to Understand their Release Profile.

Metal-organic frameworks (MOFs) give the opportunity of confining guest molecules into their pores even by a post-synthetic protocol. PUM168 is a Zn-based MOF characterized by microporous cavities that allows the encapsulation of a significant number of guest molecules. The pores engineered with different binding sites show a remarkable guest affinity towards a series of natural essential oils components, such as eugenol, thymol and carvacrol, relevant for environmental applications. Exploiting single crystal X-ray diffraction, it was possible to step-wisely monitor the rather complex three-components guest exchange process involving dimethylformamide (DMF, the pristine solvent) and binary mixtures of the flavoring agents. A picture of the structural evolution of the DMF-to-guest replacement occurring inside the MOF crystal was reached by a detailed single-crystal-to-single-crystal monitoring. The relation of the supramolecular arrangement in the pores with selective guests release was then investigated as a function of time and temperature by static headspace GC-MS analysis.

Structure-activity relationship study towards non-peptidic positron emission tomography (PET) radiotracer for gastrin releasing peptide receptors: Development of [18F] (S)-3-(1H-indol-3-yl)-N-[1-[5-(2-fluoroethoxy)pyridin-2-yl]cyclohexylmethyl]-2-methyl-2-[3-(4-nitrophenyl)ureido]propionamide.

Gastrin-releasing peptide receptors (GRP-Rs, also known as bombesin 2 receptors) are overexpressed in a variety of human cancers, including prostate cancer, and therefore they represent a promising target for in vivo imaging of tumors using positron emission tomography (PET). Structural modifications of the non-peptidic GRP-R antagonist PD-176252 ((S)-1a) led to the identification of the fluorinated analog (S)-3-(1H-indol-3-yl)-N-[1-[5-(2-fluoroethoxy)pyridin-2-yl]cyclohexylmethyl]-2-methyl-2-[3-(4-nitrophenyl)ureido]propionamide ((S)-1m) that showed high affinity and antagonistic properties for GRP-R. This antagonist was stable in rat plasma and towards microsomal oxidative metabolism in vitro. (S)-1m was successfully radiolabeled with fluorine-18 through a conventional radiochemistry procedure. [18F](S)-1m showed high affinity and displaceable interaction for GRP-Rs in PC3 cells in vitro.

Radiosynthesis and in vivo Evaluation of Carbon-11 (2S)-3-(1H-Indol-3-yl)-2-{[(4-methoxyphenyl)carbamoyl]amino}-N-{[1-(5-methoxypyridin-2-yl)cyclohexyl]methyl}propanamide: An Attempt to Visualize Brain Formyl Peptide Receptors in Mouse Models of Neuroinflammation.

Here, we describe the very first attempt to visualize in vivo formyl peptide receptors (FPRs) in mouse brain by positron emission tomography (PET). FPRs are expressed in microglial cells where they mediate chemotactic activity of ß-amyloid peptide in Alzheimer disease and, thus, are involved in neuroinflammatory processes. To this purpose, we have selected (2S)-3-(1H-Indol-3-yl)-2-{[(4-methoxyphenyl)carbamoyl]amino}-N-{[1-(5-methoxypyridin-2-yl)cyclohexyl]methyl}propanamide ((S)-1), that we have previously identified as a potent non-peptidic FPR agonist. (S)-[(11) C]-1 has been prepared in high radiochemical yield. (S)-[(11) C]-1 showed very low penetration of blood-brain barrier and, thus, was unable to accumulate into the brain. In addition, (S)-[(11) C]-1 was not able to label FPRs receptors in brain slices of PS19 and APP23 mice, two animal models of Alzheimer disease. Although (S)-[(11) C]-1 was not suitable to visualize FPRs in the brain, this study provides useful information for the design and characterization of future potential PET radioligands for visualization of brain FPRs by PET.

Functionalized Coumarine Fragment to Obtain Fluorescent and Selective P-Glycoprotein Ligands.

Starting from our lead compound MC70 displaying high P-glycoprotein (P-gp) inhibition activity but low selectivity, a new class of coumarine derivatives was studied to develop selective and fluorescent P-gp ligands. In this series, the biphenyl moiety of MC70 was replaced with the coumarine fluorophore as a bioisostere of the biphenyl nucleus in order to improve the selectivity toward P-gp and the fluorescent properties for in vitro studies. Moreover, the presence and position of substituents on the coumarine nucleus were probed to develop suitable fluorescent probes to study the expression and activity of P-gp in living cells. The best result was found for compound 4c, which exerts a good P-gp activity profile (EC50 = 13 µM) as substrate and a high selectivity toward the pump since it is inactive toward MRP1.

Arylpiperazine agonists of the serotonin 5-HT1A receptor preferentially activate cAMP signaling versus recruitment of ß-arrestin-2.

G protein-coupled receptors (GPCRs) mediate biological signal transduction through complex molecular pathways. Therapeutic effects of GPCR-directed drugs are typically accompanied by unwanted side effects, owing in part to the parallel engagement of multiple signaling mechanisms. The discovery of drugs that are 'functionally selective' towards therapeutic effects, based on their selective control of cellular responses through a given GPCR, is thus a major goal in pharmacology today. In the present study, we show that several arylpiperazine ligands of the serotonin 5-HT1A receptor (5-HT1AR) preferentially activate 3',5'-cyclic adenosine monophosphate (cAMP) signaling versus ß-arrestin-2 recruitment. The pharmacology of these compounds is thus qualitatively different from the endogenous agonist serotonin, indicating functional selectivity of 5-HT1AR-mediated response pathways. Preliminary evidence suggests that phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) downstream of 5-HT1AR is a substrate of functionally selective signaling by partial agonists. We propose that the compounds described in the present study are useful starting points for the development of signaling pathway-selective drugs targeting 5-HT1AR.

Novel 3-(1H-indol-3-yl)-2-[3-(4-methoxyphenyl)ureido]propanamides as selective agonists of human formyl-peptide receptor 2.

N-Formyl peptide receptors (FPRs) are G protein-coupled receptors (GPCRs) that play critical roles in inflammatory reactions, and FPR-specific interactions can possibly be used to facilitate the resolution of pathological inflammatory reactions. We here report the synthesis and biological evaluation of six pairs of chiral ureidopropanamido derivatives as potent and selective formyl peptide receptor-2 (FPR2) agonists that were designed starting from our lead agonist (S)-3-(1H-indol-3-yl)-2-[3-(4-methoxyphenyl)ureido]-N-[[1-(5-methoxy-2-pyridinyl)cyclohexyl]methyl]propanamide ((S)-9a). The new compounds were obtained in overall yields considerably higher than (S)-9a. Several of the new compounds showed agonist properties comparable to that of (S)-9a along with higher selectivity over FPR1. Molecular modeling was used to define chiral recognition by FPR2. In vitro metabolic stability of selected compounds was also assessed to obtain preliminary insight on drug-like properties of this class of compounds.

Selective agonists for serotonin 7 (5-HT7) receptor and their applications in preclinical models: an overview.

The serotonin 7 (5-HT7) receptor was the last serotonin receptor subtype to be discovered in 1993. This receptor system has been implicated in several central nervous system (CNS) functions, including circadian rhythm, rapid eye movement sleep, thermoregulation, nociception, memory and neuropsychiatric symptoms and pathologies, such as anxiety, depression and schizophrenia. In 1999, medicinal chemistry efforts led to the identification of SB-269970, which became the gold standard selective 5-HT7 receptor antagonist, and later of various selective agonists such as AS-19, LP-44, LP-12, LP-211 and E-55888. In this review, we summarize the preclinical pharmacological studies performed using these agonists, highlighting their strengths and weaknesses. The data indicate that 5-HT7 receptor agonists can have neuroprotective effects against N-methyl-d-aspartate-induced toxicity, modulate neuronal plasticity in rats, enhance morphine-induced antinociception and alleviate hyperalgesia consecutive to nerve lesion in neuropathic animals.

Design, synthesis, radiolabeling and in vivo evaluation of potential positron emission tomography (PET) radioligands for brain imaging of the 5-HT7 receptor.

Here we describe the design, synthesis, and pharmacological evaluation of a set of compounds structurally related to the high affinity serotonin 5-HT7 receptor agonist N-(4-cyanophenylmethyl)-4-(2-diphenyl)-1-piperazinehexanamide (6, LP-211). Specific structural modifications were performed in order to maintain affinity for the target receptor and to improve the selectivity over 5-HT1A and adrenergic α1 receptors. The synthesized compounds have chemical features that could enable labeling with a positron emitter radioisotope (carbon-11 or fluorine-18) and lipophilicity within the range considered optimal for brain penetration and low non-specific binding. 4-[2-(4-Methoxyphenyl)phenyl]-N-(pyridin-4-ylmethyl)piperazinehexanamide (23a) and N-pyridin-4-ylmethyl-3-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]ethoxy]propanamide (26a) were radiolabeled on the methoxy group with carbon-11. Positron emission tomography (PET) analysis revealed that [(11)C]-23a and [(11)C]-26a were P-glycoprotein (P-gp) substrates and rapidly metabolized, resulting in poor brain uptake. These features were not predicted by in vitro tests.

Design, synthesis, lipophilic properties, and binding affinities of potential ligands in positron emission tomography (PET) for visualization of brain dopamine D4 receptors.

We report the synthesis of compounds structurally related to the high-affinity dopamine D4 receptor ligand N-{2-[4-(3-cyanopyridin-2-yl)piperazin-1-yl]ethyl}-3-methoxybenzamide (1e). All compounds were specifically designed as potential PET radioligands for brain D4 receptor visualization, having lipophilicity within a range for brain uptake and weak non-specific binding (0.75100-fold), but its D4 receptor affinity was suboptimal for imaging of brain D4 receptors (Ki =30 nM).

Potent and selective tariquidar bioisosters as potential PET radiotracers for imaging P-gp.

Compounds 8a-d have been designed as bioisosters of tariquidar for imaging P-gp expression and density by PET. The results displayed that compounds 8b and 8d could be considered potential P-gp/BCRP ligands suitable as (11)C and (18)F radiotracers, respectively.

Activity-lipophilicity relationship studies on P-gp ligands designed as simplified tariquidar bulky fragments.

A series of alkyloxyquinoline derivatives has been developed to evaluate the relationship between P-gp potency and lipophilicity. The results show a satisfactory lipophilicity-activity correlation although a series of derivatives showing higher P-gp potency is needed in order to confirm this hypothesis.

Novel highly potent serotonin 5-HT7 receptor ligands: structural modifications to improve pharmacokinetic properties.

Here we report the synthesis, pharmacological and pharmacokinetic evaluation of a pilot set of compounds structurally related to the potent and selective 5-HT7 ligand LP-211. Among the studied compounds, N-pyridin-3-ylmethyl-3-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]ethoxy]propanamide (4b) showed high affinity for 5-HT7 receptors (K(i)=23.8 nM), selectivity over 5-HT1A receptors (>50-fold), in vitro metabolic stability (82%) and weak interaction with P-glycoprotein (BA/AB=3.3). Compound 4b was injected ip in mice to preliminarily evaluate its distribution between blood and brain.

Towards metabolically stable 5-HT7 receptor ligands: a study on 1-arylpiperazine derivatives and related isosters.

Serotonin 7 (5-hydroxytryptamine7 or 5-HT7) is the most recently identified serotonin receptor. It is involved in mood disorders and is studied as a target for antidepressants. Here, we report on the structural manipulation of the 5-HT7 receptor ligand 4-[2-(3-methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine (1a) aimed at obtaining 5-HT7 receptor ligands endowed with good in vitro metabolic stability. A set of N-[3-methoxyphenyl)ethyl-substituted] 1-arylpiperazine, 4-arylpiperidine and 1-aryl-4-aminopiperidine was synthesized and tested in radioligand binding assays at human cloned 5-HT7 and 5-HT1A receptors. In vitro metabolic stability of the target compounds was assessed after incubation with rat hepatic S9 microsomal fraction. Among the new compounds, 1-(2-biphenyl)-4-[2-(3-methoxyphenyl)ethyl]piperazine (1d) and 4-(2-biphenyl)-1-[2-(3-methoxyphenyl)ethyl]piperidine (2d) showed a good compromise between affinity at 5-HT7 receptor (K i = 7.5 nM and 13 nM, respectively) and in vitro metabolic stability (26 and 65 % recovery of parent compound, respectively) but were poorly selective over 5-HT1A receptor.

Investigation of σ receptors agonist/antagonist activity through N-(6-methoxytetralin-1-yl)- and N-(6-methoxynaphthalen-1-yl)alkyl derivatives of polymethylpiperidines.

A series of polymethyl-substituted piperidines linked to either a 6-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl or a 6-methoxynaphthalen-1-yl moiety was generated with the aim of verifying a previously generated hypothesis: tetralin and naphthalene nuclei confer opposite activity at the σ1 receptor. Compounds 6, 9 and 10 displayed appreciable affinity at both σ subtypes, but none of the novel compounds displayed significant antiproliferative activity in MCF7wt and MCF7σ1 cell lines. The effect on bradikynin-triggered Ca(2+) mobilization was studied as a methodology to suggest σ receptors mediated activity.

Naphthalenyl derivatives for hitting P-gp/MRP1/BCRP transporters.

Substituted naphthalenyl derivatives bearing oxazole, or thiazole or furyl heteronuclei have been carried out as bioisosters of aryl-oxazoles and -thiazoles derivatives previously reported in order to investigate the role of the hindrance on the activity towards P-gp/BCRP/and MRP1 transporters. In addition, the role of naphthalenyl group to modulate P-gp intrinsic activity of these compounds was ascertained. The results demonstrated that all naphthalenyl derivatives displayed comparable P-gp activity with respect to lead compounds previously characterized in our SAR studies but were less active towards BCRP and MRP1 pumps. In terms of intrinsic activity, the replacement of aryl with naphthalenyl moiety led to P-gp inhibitors, unambiguous or ambiguous substrates on the base of the heteronucleus and the substituent on the naphthalenyl fragment. Indeed, oxazole derivatives were: inhibitors (R=H, F, OH), unambiguous substrates (R=OCH(3)), or ambiguous substrate (R=Br); thiazole derivatives were: unambiguous substrates (R=OCH(3), Br), or ambiguous substrates (R=H, F). Finally furyl derivatives were ambiguous substrates.

Synthesis and binding assays of novel 3,3-dimethylpiperidine derivatives with various lipophilicities as σ1 receptor ligands.

Starting from two carbocyclic analogs, a series of 3,3-dimethylpiperidine derivatives was prepared and tested in radioligand binding assays at σ(1) and σ(2) receptors, and at Δ(8)-Δ(7) sterol isomerase (SI) site. The novel compounds mostly bear heterocyclic rings or bicyclic nucleus of differing lipophilicities. Compounds 18a and 19a,b demonstrated the highest σ(1) affinity (K(i)=0.14-0.38 nM) with a good selectivity versus σ(2) binding. Among them, 18a had the lowest ClogD value (3.01) and only 19b was selective versus SI too. Generally, it was observed that more planar and hydrophilic heteronuclei conferred a decrease in affinity for both σ receptor subtypes.

Identification of a red-emitting fluorescent ligand for in vitro visualization of human serotonin 5-HT(1A) receptors.

The 5-HT(1A) receptor subtype is the most thoroughly studied serotonin receptor subtype. We report here the design, synthesis and characterization of two new fluorescent ligands for the 5-HT(1A) receptor. The new 1-arylpiperazine-based red-emitting fluorescent compound 6 displayed good binding affinity at the 5-HT(1A) receptor (K(i)=35 nM) and was able to label specifically the human 5-HT(1A) receptor stably expressed in CHO cells visualized using confocal laser scanning microscopy.

Radiosynthesis and in vivo evaluation of [(11)C]MC80 for P-glycoprotein imaging.

P-glycoprotein (P-gp) is an ATP-dependent efflux pump protecting the body against xenobiotics. The in vitro characterized modulator 6,7-dimethoxy-2-(6-methoxy-naphthalen-2-ylmethyl)-1,2,3,4-tetrahydroisoquinoline (MC80) of the P-gp pump was labelled with (11)C and evaluated in vivo for its potential to image P-gp function and expression. Radiochemical pure (>98%) [(11)C]MC80 was obtained within 25 min starting from [(11)C]methyl iodide with radiochemical yield of 26%. Biodistribution studies in FVB mice demonstrated a high baseline brain uptake (7.66 + or - 1.38%ID/g at 1 min pi). Cerebral uptake was increased in mdr1a knock-out mice as well as after CsA pretreatment. Pre-administration of an excess of non-radioactive MC80 caused a reduced uptake in several target organs including brain, pancreas and intestines. The results indicate that [(11)C]MC80 kinetics are modulated by P-gp. Reversed phase-HPLC analysis of brain revealed an excellent metabolic profile (>90% intact [(11)C]MC80).

Why PB28 Could Be a Covid 2019 Game Changer?

PB28, a cyclohexylpiperazine derivative, could be a potential strategy for Covid 19 because in a recent study it has been found more active than hydroxychloroquine without interaction with cardiac proteins. PB28 has been designed, developed, and biologically evaluated in the past decade in our research group. A possible mechanism to explain its surprising anti-COVID-19 activity is suggested..

Determination of 1-aryl-4-propylpiperazine pKa values: the substituent on aryl modulates basicity.

In order to design a potential drug, it is important to know its pK(a) because the protonation state of the molecule will be critical for ligand-receptor interaction and for the pharmacokinetic of the molecule. pK(a) values of a series of 1-(substitutedphenyl)-4-propylpiperazines were measured to study how the presence of a substituent on the phenyl ring modulates the basicity of N-4 nitrogen. pK(a) values indicated that the position of the substituent was crucial. In general, the introduction of the substituent in ortho-position of the phenyl ring increased the basicity of the molecule. This effect appeared to be related to steric and conformational effects and not to the electronic properties of the substituent. On the other hand, meta- and para-substituted derivatives showed a slight decrease of pK(a) that was qualitatively consistent with the electronic properties of the substituent.