Heliotropiumides A and B, new phenolamides with N-carbamoyl putrescine moiety from Heliotropium foertherianum collected in Hawaii and their biological activities.

Two new compounds heliotropiumides A (1) and B (2), phenolamides each with an uncommon carbamoyl putrescine moiety, were isolated from the seeds of a naturalized Hawaiian higher plant, Heliotropium foertherianum Diane & Hilger in the borage family, which is widely used for the treatment of ciguatera fish poisoning. The structures of compounds 1 and 2 were characterized based on MS spectroscopic and NMR analysis, and DP4+ calculations. The absolute configuration (AC) of compound 1 was determined by comparison of its optical rotation with those reported in literature. Compound 2 showed inhibition against NF-κB with an IC50 value of 36µM.

Carbazole Scaffold in Medicinal Chemistry and Natural Products: A Review from 2010-2015.

9H-carbazole is an aromatic molecule that is tricyclic in nature, with two benzene rings fused onto a 5-membered pyrrole ring. Obtained from natural sources or by synthetic routes, this scaffold has gained much interest due to its wide range of biological activity upon modifications, including antibacterial, antimalarial, anticancer, and anti-Alzheimer properties. This review reports a survey of the literature on carbazole-containing molecules and their medicinal activities from 2010 through 2015. In particular, we focus on their in vitro and in vivo activities and summarize structure-activity relationships (SAR), mechanisms of action, and/or cytotoxicity/selectivity findings when available to provide future guidance for the development of clinically useful agents from this template.

Bispidine as a Privileged Scaffold.

Thediazabicyclic molecule bispidine named by the chemist Carl Mannich in 1930, is a naturally occurring scaffold with interesting features. Bispidine can form different conformers, has high basicity, can attack dichloromethane, has metal ion coordination properties and interacts with nicotinic acetylcholine receptors. In this review we will discuss important properties, synthetic pathways and biological activities of bispidine and some derivatives. Bispidine can function as a scaffold for compounds with very diverse biological activities, e.g. interacting with ion channels, G-protein coupled receptors, and enzymes, and is even used for the development of new in vivo radiotracers.

The twin drug approach for novel nicotinic acetylcholine receptor ligands.

The association of two pharmacophoric entities generates so-called 'twin drugs' or dimer derivatives. We applied this approach for the design of a small compound library for the interaction with α4ß2(∗) nicotinic acetylcholine receptors (nAChRs). In this compound series, the nAChR ligand N,N-dimethyl-2-(pyridin-3-yloxy)ethan-1-amine 9 served as one pharmacological entity and it was initially kept constant as one part of the 'twin' compound. 'Twin' compounds with identical or non-identical entities using the 'no linker mode' or 'overlap' mode were synthesized and evaluated for their nAChR affinities. Compound 17a showed the highest affinity for the α4ß2(∗) nAChR subtype (Ki=0.188 nM) and its (di)fluoro analogs could retain nanomolar affinities, when replacing pyridine as the hydrogen bond acceptor system by mono- or difluoro-phenyls. The 'twin drug' approach proved to provide compounds with high affinity and subtype selectivity for α4ß2(∗) nAChRs.

Semisynthetic analogues of toxiferine I and their pharmacological properties at α7 nAChRs, muscle-type nAChRs, and the allosteric binding site of muscarinic M2 receptors.

A new series of analogues of the calabash curare alkaloid toxiferine I was prepared and pharmacologically evaluated at α7 and muscle-type nAChRs and the allosteric site of muscarinic M2 receptors. The new ligands differ from toxiferine I by the absence of one (2a-c) or two (3a-c) hydroxy groups, saturation of the exocyclic double bonds, and various N-substituents (methyl, allyl, 4-nitrobenzyl). At the muscle-type nAChRs, most ligands showed similar binding to the muscle relaxant alcuronium, indicating neuromuscular blocking activity, with the nonhydroxylated analogues 3b (Ki = 75 nM) and 3c (Ki = 82 nM) displaying the highest affinity. At α7 nAChRs, all ligands showed a moderate to low antagonistic effect, suggesting that the alcoholic functions are not necessary for antagonistic action. Compound 3c exerted the highest preference for the muscle-type nAChRs (Ki = 82 nM) over α7 (IC50 = 21 µM). As for the allosteric site of M2 receptors, binding was found to be dependent on N-substitution rather than on the nature of the side chains. The most potent ligands were the N-allyl analogues 2b and 3b (EC0.5,diss = 12 and 36 nM) and the N-nitrobenzyl derivatives 2c and 3c (EC0.5,diss = 32 and 49 nM). The present findings should help delineate the structural requirements for activity at different types of AChRs and for the design of novel selective ligands.

The 3,7-diazabicyclo[3.3.1]nonane scaffold for subtype selective nicotinic acetylcholine receptor (nAChR) ligands. Part 1: the influence of different hydrogen bond acceptor systems on alkyl and (hetero)aryl substituents.

3,7-Diazabicyclo[3.3.1]nonane is a naturally occurring scaffold interacting with nicotinic acetylcholine receptors (nAChRs). When one nitrogen of the 3,7-diazabicyclo[3.3.1]nonane scaffold was implemented in a carboxamide motif displaying a hydrogen bond acceptor (HBA) functionality, compounds with higher affinities and subtype selectivity for α4ß2(∗) were obtained. The nature of the HBA system (carboxamide, sulfonamide, urea) had a strong impact on nAChR interaction. High affinity ligands for α4ß2(∗) possessed small alkyl chains, small un-substituted hetero-aryl groups or para-substituted phenyl ring systems along with a carboxamide group. Electrophysiological responses of selected 3,7-diazabicyclo[3.3.1]nonane derivatives to Xenopus oocytes expressing various nAChR subtypes showed diverse activation profiles. Compounds with strongest agonistic profiles were obtained with small alkyl groups whereas a shift to partial agonism/antagonism was observed for aryl substituents.

The 3,7-diazabicyclo[3.3.1]nonane scaffold for subtype selective nicotinic acetylcholine receptor ligands. Part 2: carboxamide derivatives with different spacer motifs.

3,7-Diazabicyclo[3.3.1]nonane (bispidine) based nicotinic acetylcholine receptor (nAChR) ligands have been synthesized and evaluated for nAChRs interaction. Diverse spacer motifs were incorporated between the hydrogen bond acceptor (HBA) part and a variety of substituted (hetero)aryl moieties. Bispidine carboxamides bearing spacer motifs often showed high affinity in the low nanomolar range and selectivity for the α4ß2(∗) nAChR. Compounds 15, 25, and 47 with Ki values of about 1 nM displayed the highest affinities for α4ß2(∗) nAChR. All evaluated compounds are partial agonists or antagonists at α4ß2(∗), with reduced or no effects on α3ß4(∗) with the exception of compound 15 (agonist), and reduced or no effect at α7 and muscle subtypes.

Synthesis and evaluation of N(1)-alkylindole-3-ylalkylammonium compounds as nicotinic acetylcholine receptor ligands.

In this study thirty-three novel indole derivatives were designed and synthesized based on the structure of deformylflustrabromine B (1), a metabolite isolated from the marine bryozoan Flustra foliacea L. The syntheses were carried out using standard methodologies and in good yields. The molecules were tested for their affinities for the α4ß2(∗), α3ß4(∗), α7(∗) and (α1)(2)ß1γδ nicotinic acetylcholine receptor (nAChR) subtypes. Binding assays showed that, among these ligands, compound 7c exhibited the highest affinity with K(i)=136.1, 93.9 and 862.4nM for the α4ß2(∗), α3ß4(∗), and α7(∗) nAChRs subtypes, respectively. These results indicated that the indole core might be a useful scaffold for the development of new potent and selective nAChR ligands.

Feasibility of [18F]-2-Fluoro-A85380-PET imaging of human vascular nicotinic acetylcholine receptors in vivo.

OBJECTIVES: The aim of this feasibility study was to evaluate [(18)F]-2-Fluoro-A85380 for in vivo imaging of arterial nicotinic acetylcholine receptors (nAChRs) in humans. Furthermore, potentially different vascular uptake patterns of this new tracer were evaluated in healthy volunteers and in patients with neurodegenerative disorders. BACKGROUND: [(18)F]-2-Fluoro-A85380 was developed for in vivo positron emission tomography (PET) imaging of nAChR subunits in the human brain. These nAChRs are also found in arteries and seem to mediate the deleterious effects of nicotine as a part of tobacco smoke in the vasculature. It has been previously shown that uptake patterns of the radiotracer in the brain differs in patients with neurodegenerative disorders compared with healthy controls. METHODS: [(18)F]-2-Fluoro-A85380 uptake was quantified in the ascending and descending aorta, the aortic arch, and the carotids in 5 healthy volunteers and in 6 patients with either Parkinson's disease or multiple system atrophy, respectively, as the maximum target-to-background ratio. The maximal standardized uptake value values, the single hottest segment, and the percent active segments of the [(18)F]-2-Fluoro-A85380 uptake in the arteries were also assessed. RESULTS: [(18)F]-2-Fluoro-A85380 uptake was clearly visualized and maximum target-to-background ratio uptake values corrected for the background activity of the tracer showed specific tracer uptake in the arterial walls. Significantly higher uptake values were found in the descending aorta. Comparison between volunteers and patients revealed significant differences, with lower [(18)F]-2-Fluoro-A85380 uptake in the patient group when comparing single arterial territories but not when all arterial territories were pooled together. CONCLUSIONS: [(18)F]-2-Fluoro-A85380 can provide specific information on the nAChR distribution in human arteries. Vascular nAChR density seems to be lower in patients with Parkinson's disease or multiple system atrophy. Once confirmed in larger study populations and in the experimental setting, this approach might provide insights into the pathogenic role of nAChRs in the human vasculature.

A hydrazide linker strategy for heterobivalent compounds as ortho- and allosteric ligands of acetylcholine-binding proteins.

The occurrence of orthosteric and allosteric binding sites is a characteristic common feature of several acetylcholine- binding proteins, like acetylcholinesterase or the nicotinic and muscarinic acetylcholine receptors. These proteins are involved in a number of neurological disorders, such as Alzheimer's disease, and represent important therapeutic targets for the development of heterodimeric ligands addressing both of their binding sites. Among the pharmacophores, which have been combined in such heterodimers, the tetrahydroacridine derivative tacrine has attracted particular interest. This review discusses the chemistry behind the linker connection of tacrine to other pharmacophores and summarizes the types of linkers established to date. Especially, the development of a hydrazide linker for tacrine-derived heterodimers is highlighted by applications in the inhibition of cholinesterases, the bivalent binding to nicotinic and muscarinic acetylcholine receptors, as well as the histochemical imaging of acetylcholinesterase and amyloid-ß.

Nicotinic acetylcholine receptor ligands, a patent review (2006-2011).

INTRODUCTION: Nicotinic acetylcholine receptors (nAChRs), pentameric ligand-gated cation channels, are potential targets for the development of therapeutics for a variety of disease states. AREAS COVERED: This article is reviewing recent advances in the development of small-molecule ligands for diverse nAChR subtypes and is a continuation of an earlier review in this journal. EXPERT OPINION: The development of nAChR ligands with preference for α4ß2 or α7 subtypes for the treatment of central nervous system disorders are in the most advanced developmental stage. In addition, there is a fast growing interest to generate so-called PAMs, positive allosteric modulators, to influence the channels' functionalities.

Nicotine decreases food intake through activation of POMC neurons.

Smoking decreases appetite, and smokers often report that they smoke to control their weight. Understanding the neurobiological mechanisms underlying the anorexic effects of smoking would facilitate the development of novel treatments to help with smoking cessation and to prevent or treat obesity. By using a combination of pharmacological, molecular genetic, electrophysiological, and feeding studies, we found that activation of hypothalamic α3ß4 nicotinic acetylcholine receptors leads to activation of pro-opiomelanocortin (POMC) neurons. POMC neurons and subsequent activation of melanocortin 4 receptors were critical for nicotinic-induced decreases in food intake in mice. This study demonstrates that nicotine decreases food intake and body weight by influencing the hypothalamic melanocortin system and identifies critical molecular and synaptic mechanisms involved in nicotine-induced decreases in appetite.

Cytisine-based nicotinic partial agonists as novel antidepressant compounds.

Nicotine and other nicotinic agents are thought to regulate mood in human subjects and have antidepressant-like properties in animal models. Recent studies have demonstrated that blockade of nicotinic acetylcholine receptors (nAChRs) including those containing the beta2 subunit (beta2(*)), results in antidepressant-like effects. Previous studies have shown that cytisine, a partial agonist at alpha4/beta2(*) nAChRs, and a full agonist at alpha3/beta4(*) and alpha7 nAChRs, has antidepressant-like properties in several rodent models of antidepressant efficacy; however, it is not clear whether more selective partial agonists will also be effective in these models. We tested cytisine and two derivatives, 5-bromo-cytisine (5-Br-Cyt) and 3-(pyridin-3'-yl)-cytisine (3-pyr-Cyt) for their ability to act as a partial agonist of different nAChR subtypes and to show antidepressant-like activity in C57/BL6 mice in the tail suspension, the forced-swim, and the novelty-suppressed feeding tests. 3-pyr-Cyt was a partial agonist with very low efficacy at alpha4/beta2(*) nAChRS but had no agonist effects at other nAChRs normally targeted by cytisine, and it was effective in mouse models of antidepressant efficacy. Animals showed dose-dependent antidepressant-like effects in all three behavioral paradigms. 5-Br-Cyt was not effective in behavioral tests when administered peripherally, probably because of its inability to penetrate the blood-brain barrier, because it efficiently reduced immobility in the tail suspension test when administered intraventricularly. These results suggest that novel nicotinic partial agonists may provide new possibilities for development of drugs to treat mood disorders.

Smoking upregulates alpha4beta2* nicotinic acetylcholine receptors in the human brain.

The role of the alpha4beta2* nicotinic acetylcholine receptors (nAChR) in tobacco addiction in humans is largely unresolved. We visualized brain alpha4beta2* nicotinic acetylcholine receptors of smokers and non-smokers with positron emission tomography using 2-[(18)F]fluoro-3-(2(S)azetidinylmethoxy)pyridine, commonly known as 2-[(18)F]F-A-85380. The total brain distribution volume of 2-[(18)F]F-A-85380 was significantly increased in smokers. Statistical parametric mapping revealed that the most prominent regional differences of distribution volumes (DV) were found in cerebellum and brainstem with an increased uptake in smokers. The up-regulation of alpha4beta2* nAChR upon chronic nicotine exposure via tobacco smoking incorporates subcortical brain regions which may play an important role in nicotine addiction.

Synthetic approaches and bio-distribution studies of [11C]methyl-phenidate.

PURPOSE: The purpose of this study was a) to present a facilitated method for the preparation and workup of [11C]d-threo-methylphenidate ([11C]d-threo-MP) (a ligand that was shown to bind selectively to the presynaptic dopaminergic transporters) from [11C]methyliodide ([11C]CH3I), b) to demonstrate that the ligand can as well be produced by an alternative labeling method employing [11C]diazomethane as the labeling agent and c) to present biodistribution data for this tracer obtained in rats. METHODS: 11C-labeling with [11C]CH3I was performed using either [d-threo-1-(2-nitrophenylsulfanyl)piperidin-2-yl]phenyl-acetic acid (d-threo-N-NPS-ritalinic acid) under addition of sodium hydroxide as base or the previously prepared sodium salt of d-threo-N-NPS-ritalinic acid. The two approaches were compared with regard to radiochemical yield and purification procedures needed in order to obtain a sufficiently pure tracer solution for human use. For the alternative reaction pathway using [11C]diazo-methane as the labeling agent the reaction was performed with d-threo-N-NPS-ritalinic acid. The biodistribution of [11C]d-threo-MP was determined in rats at 5, 10 and 30 min post injection of the tracer. RESULTS: The application of the sodium salt of d-threo-N-NPS-ritalinic acid as precursor resulted in higher radiochemical yields than the use of the free acid under basic conditions, the yields were 20 +/- 8% and 6 +/- 3%, respectively for the final isolated product (based on [11C]CH3I starting activity). The alternative labeling approach by means of [11C]diazomethane as the labeling agent was demonstrated to give radiochemical yields of 76 +/- 8% (based on [11C]diazomethane starting activity, determined by HPLC analysis of the crude reaction mixture before final work-up) within shorter process times. Based on [11C]methane starting activity both approaches result in similar yields (17% and 15%, respectively) Biodistribution studies in rats revealed a low blood activity (0.09% injected dose/g (% ID/g)) at 5 min post injection (p.i.), as well as a relatively high liver uptake (15.9% ID at 30 min) compared to a lower kidney uptake (3.2% ID at 30 min). Brain uptake was 0.9% ID/g already 5 and 10 min p.i.. CONCLUSIONS: The application of the sodium salt of d-threo-N-NPS-ritalinic acid as precursor for the radiosynthesis of [11C]d-threo-MP reduces the amount of [11C]methanol formed from the reaction of [11C]CH3I with sodium hydroxide, that is added to generate the carboxylic anion of d-threo-N-NPS-ritalinic acid needed for labeling with [11C]CH3I. The purification process could be simplified (omission of one solid phase extraction step), resulting in an easily automated process for the production of the tracer. The preparation of [11C]d-threo-MP by means of [11C]diazomethane as the labeling agent appears to be an interesting alternative to the [11C]CH3I methods because of shorter overall process times and high labeling yields. Biodistribution data show a rapid extraction of the tracer from the blood pool. Tracer excretion seems to take place predominantly via the hepatic pathway since liver uptake at 30 min was considerably higher than kidney uptake. [11C]d-threo-MP exhibits a rapid and sufficiently high brain uptake in rats.

Feasibility of 2-deoxy-2-[18F]fluoro-D-glucose- A85380-PET for imaging of human cardiac nicotinic acetylcholine receptors in vivo.

Nicotinic acetylcholine receptors mediate the parasympathetic autonomic control of cardiac function. Aim of this study was the assessment of cardiac nicotinic acetylcholine receptor distribution with a novel (alpha4beta2) nicotinic acetylcholine receptor PET ligand (2-deoxy-2- [18F]fluoro-D-glucose-A85380) in humans. Five healthy volunteers without cardiac disease and six patients with either Parkinson's disease or multiple system atrophy without additional overt cardiac disease were evaluated with 2-deoxy-2-[18F]fluoro-D-glucose-A85380 PET-imaging to assess the cardiac parasympathetic innervation and the putative impact of both disorders. 2-deoxy-2- [18F]fluoro-D-glucose-A85380 whole body PET-scans were performed on a Siemens PET/CT biograph(TM) 75.4 min +/- 6.7 after i.v. injection of 371.2 +/- 58.1 MBq. Average count rate density of left ventricle ROI's and a standard ROI in the right lung were measured within three consecutive slices of 10.0 mm thickness. Heart-to-lung ratios were calculated in each volunteer and patient. Tracer uptake in the left ventricle could be measured in all of the five volunteers and the six patients. Heart-to-lung ratios in the volunteer group were not different from patients suffering from Parkinson's disease or MSA (3.2 +/- 0.5 vs 3.2 +/- 0.8 and 2.96+/-0.7, mean +/- SD), respectively. Human cardiac nicotinic acetylcholine receptors can be visualized and measured by 2-deoxy-2- [18F]fluoro-D-glucose-A85380 PET scans both in cardiac-healthy subjects and patients suffering from Parkinson's disease or multiple system atrophy. The heart- as well as the lung-tracer uptake was almost constant throughout all subjects leading to a good target-to-background ratio. These first results suggest no impact of either PD or MSA on cardiac nicotinic acetylcholine receptors.

In vitro evaluation of nicotinic acetylcholine receptors with 2-[18F]F-A85380 in Parkinson's disease.

Nicotinic acetylcholine receptors (nAChR) are involved in many physiological functions and appear to be affected in neurodegenerative diseases like Alzheimer's disease and Parkinson's disease (PD). Here, we describe the in vitro evaluation of nAChRs in PD with 2-[18F]F-A85380, a ligand with high affinity to the beta2 nAChR subunit. Autoradiography with 2-[18F]F-A85380 in untreated rat brain corresponded to the known distribution of alpha4beta2 nAChRs with high uptake in the thalamus, moderate uptake in the striatum and cortex and low uptake in the cerebellum (47%, 43% and 19% of the thalamus, respectively). The localization of alpha4beta2 nAChRs in the striatum was investigated in rodents with unilateral lesion of the substantia nigra. 2-[18F]F-A85380 binding was significantly reduced in the striatum ipsilateral to the lesion side (to 64% of the contralateral side), indicating that a fraction of alpha4beta2 nAChRs is located on dopaminergic terminals, whereas another fraction resides on striatal interneurons or cortical afferents. Similarly, in human brain sections of PD patients, 2-[18F]F-A85380 uptake was significantly reduced not only in the caudate and putamen but also in the thalamus (approximately 30% of the binding of control brain in all three regions); within the striatum, nAChRs in the putamen were significantly more severely affected as in the caudate. The observed pattern of alpha4beta2* nAChR loss demonstrates the potential of 2-[18F]F-A85380 for further investigations of this positron emission tomography ligand for in vivo studies of alpha4beta2* nAChRs in PD.

6H,13H-Pyrazino[1,2-a;4,5-a']diindole analogs: probing the pharmacophore for allosteric ligands of muscarinic M2 receptors.

A series of 6H,13H-pyrazino[1,2-a;4,5-a']diindole analogs was synthesized in order to probe the pharmacophore hypothesis for allosteric ligands of muscarinic M(2) receptors. The 3D structure of the novel ring system was determined by means of NMR spectroscopy and X-ray diffraction revealing a totally flat geometry. Low binding affinities for the [(3)H]N-methylscopolamine-occupied M(2) receptors (reflected by EC(50,diss)) indicated that the spatial arrangement of the pharmacophore elements (two aromatic rings flanked by two cationic centers) incorporated in the bisquaternary analogs 5 and 6 is unfavorable for strong ligand-receptor interactions. Due to the structural similarity of the novel compounds to neuromuscular-blocking agents, their affinities (reflected by K(i)) to the muscle type of nicotinic acetylcholine receptors were also determined. The dimethyl and diallyl analogs 5 and 6 exhibited rather high affinities to the muscle type of nicotinic acetylcholine receptors, suggesting a pronounced neuromuscular-blocking activity. Compound 5 showed a 34-fold higher affinity for the muscle type nAChR than for the allosteric site of M(2) receptors.