piperidines and benzovesamicol

[. Twenty participants of both sexes and a mean age of 73.9 ± 6.0 years, age-range [64; 86], were recruited. Highest tracer binding was present in the striatum, some thalamic nuclei, and the basal forebrain. Intermediate binding was found in most nuclei of the brainstem, thalamus, and hypothalamus; the vermis and flocculonodular lobe; and the hippocampus, amygdala, insula, cingulate, olfactory cortex, and Heschl's gyrus. Lowest binding was present in most areas of the cerebral cortex, and in the cerebellar nuclei and hemispheres. The spatial distribution of tracer correlated with immunohistochemical post-mortem data, as well as with regional expression levels of SLC18A3, the VAChT coding gene.. Our in vivo findings confirm the regional cholinergic distribution in specific brain structures as described post-mortem. A positive spatial correlation between tracer distribution and regional gene expression levels further corroborates [

Topics: Aged; Brain; Cholinergic Agents; Electrons; Female; Fluorine Radioisotopes; Humans; Male; Middle Aged; Piperidines; Positron-Emission Tomography; Vesicular Acetylcholine Transport Proteins

Herein, new ligands for the vesicular acetylcholine transporter (VAChT), based on a benzovesamicol scaffold, are presented. VAChT is acknowledged as a marker for cholinergic neurons and a positron emission tomography tracer for VAChT could serve as a tool for quantitative analysis of cholinergic neuronal density. With an easily accessible triflate precursor, aminocarbonylations were utilized to evaluate the chemical space around the C5 position on the tetrahydronaphthol ring. Synthesized ligands were evaluated for their affinity and selectivity for VAChT. Small, preferably aromatic, N-substituents proved to be more potent than larger substituents. Of the fifteen compounds synthesized, benzyl derivatives (±)-7i and (±)-7l had the highest affinities for VAChT. Compound (±)-7i was chosen to investigate the importance of stereochemistry for binding to VAChT and selectivity toward the σ

Topics: Amides; Animals; Carbon Radioisotopes; Humans; Ligands; PC12 Cells; Piperidines; Positron-Emission Tomography; Rats; Vesicular Acetylcholine Transport Proteins

Located in presynaptic cholinergic nerve terminals, the vesicular acetylcholine transporter (VAChT) represents a potential target for quantitative visualization of early degeneration of cholinergic neurons in Alzheimer's disease using PET. Benzovesamicol derivatives are proposed as radioligands for this purpose. We report QSAR studies of vesamicol and benzovesamicol derivatives taking into account the stereoselectivity of the VAChT binding site. Use of different data sets and different models in this study revealed that both enantiomers of 5-fluoro-3-(4-phenyl-piperidin-1-yl)-1,2,3,4-tetrahydro-naphthalen-2-ol (5-FBVM) are promising candidates, with predicted VAChT affinities between 6.1 and 0.05 nM. The synthesis of enantiopure (R,R)- and (S,S)-5-FBVM and their corresponding triazene precursors for future radiofluorination is reported. Both enantiomers exhibited high in vitro affinity for VAChT [(+)-5-FBVM: K(i)=6.95 nM and (-)-5-FBVM: K(i)=3.68 nM] and were selective for σ(2) receptors (∼70-fold), only (+)-5-FBVM is selective for σ(1) receptors (∼fivefold). These initial results suggest that (+)-(S,S)-5-FBVM warrants further investigation as a potential radioligand for in vivo PET imaging of cholinergic nerve terminals.

Topics: Binding Sites; Ligands; Naphthols; Piperidines; Positron-Emission Tomography; Quantitative Structure-Activity Relationship; Radiopharmaceuticals; Stereoisomerism; Vesicular Acetylcholine Transport Proteins

Vesamicol derivatives are promising candidates as ligands for the vesicular acetylcholine transporter (VAChT) to enable in vivo imaging of cholinergic deficiencies if applied as positron emission tomography radiotracers. So far, optimization of the binding affinity of vesamicol-type ligands was hampered by the lack of respective quantitative structure-activity relationships. We developed the first quantitative model to predict, from molecular structure, the binding affinity of vesamicol-type ligands toward VAChT employing comparative molecular field analysis (CoMFA) for a set of 37 ligands, covering three different structural types (4-phenylpiperidine, spiro, and tropan derivatives of vesamicol). The prediction capability was assessed by leave-one-out cross-validation (LOO) and through leaving out and predicting 50% of the compounds selected such that both the training and the prediction sets cover almost the whole range of experimental data. The statistics indicate a significant prediction power of the models ( q (2) (LOO) = 0.66, q (2) (50% out) = 0.59-0.74). The discussion includes detailed analyses of CoMFA regions critical for ligand-VAChT binding, identifying structural implications for high binding affinity.

Topics: Binding Sites; Fluorobenzenes; Iodobenzenes; Ligands; Models, Molecular; Molecular Structure; Piperidines; Quantitative Structure-Activity Relationship; Reproducibility of Results; Static Electricity; Stereoisomerism; Vesicular Acetylcholine Transport Proteins

Molecular imaging of the vesicular acetylcholine transporter (VAChT) using positron emission tomography (PET) may provide insights into early diagnosis and better understanding of Alzheimer's disease. We further characterized the VAChT ligand (2R,3R)-5-FEOBV (1) and developed new fluoropropoxy analogues. Ex vivo studies of the new nonradiolabeled analogues (2R,3R)-5-FPOBV (2) (k(D) = 0.7 nM) and (2S,3S)-5-FPOBV (3) (k(D) = 8.8 nM) were performed in rat brain and showed an enantioselective inhibition of (-)-5-[(125)I]-IBVM uptake in striatum, cortex, and hippocampus (e.g., 74% for 2 and only 54% for 3 in the cortex). Radiochemical procedures were developed to produce [(18)F]1 and [(18)F]2 as potential imaging agent for the VAChT. The radiochemistry was carried out in a one step procedure, with radiolabeling yields of 17 and 2.6% (range: 1-5.4), respectively, nondecay corrected with good specific activity: 124-338 GBq/micromol. The radiochemical purity was greater than 98%. The biological (ex vivo and in vivo) properties of these radioligands were evaluated in rats and showed a low (less then 0.1% of the injected dose) and homogeneous brain uptake. The in vivo PET study of [(18)F]2 performed in baboon also revealed rapid defluorination as the main problem. Therefore [(18)F]1 and [(18)F]2 appear to be unsuitable for in vivo imaging of the VAChT using PET.

Topics: Animals; Autoradiography; Brain; Drug Interactions; Evaluation Studies as Topic; Isotope Labeling; Male; Papio; Piperidines; Positron-Emission Tomography; Protein Binding; Radiopharmaceuticals; Rats; Rats, Wistar; Tetrahydronaphthalenes; Time Factors; Tissue Distribution; Vesicular Acetylcholine Transport Proteins; Whole Body Imaging

Our goal was to synthesize new stereospecific benzovesamicol analogues, which could potentially be used as SPECT or PET radioligands for the vesicular acetylcholine transporter (VAChT). This paper describes the chemical synthesis, resolution and determination of binding affinity for four enantiomeric pairs of derivatives. Their intrinsic affinities were determined by competition against binding of [3H]vesamicol to human VAChT. Of the eight enantiomers, (E)-(R,R)-5-AOIBV [(R,R)-3], and (R,R)-5-FPOBV [(R,R)-4] displayed the highest binding affinities for VAChT (Kd=0.45 and 0.77 nM, respectively), which indicated that an elongation of the chain from 5-idodo as in the case of 5-iodobenzovesamicol (5-IBVM), to a 5-(E)-3-iodoallyloxy or 5-fluoropropoxy substituent, as in 5-AOIBV and 5-FPOBV, respectively, was very well tolerated at the vesamicol binding site. The enantiomer (R,R)-4-MAIBV [(R,R)-16], which retains the basic structure of (-)-5-IBVM but possess an additional aminomethyl substituent in the 4-position of the piperidine ring, displayed lower binding affinity (Kd=8.8 nM). Nevertheless, the result suggests that substitution at this position may be an interesting alternative to investigate for development of new benzovesamicol analogues. As expected, the corresponding (S,S) enantiomers displayed lower Kd values, they were approximately 10-fold lower in the case of (S,S)-5-FPOBV (Kd=8.4 nM) and (E)-(S,S)-5-AOIBV (Kd=4.3 nM). (R,R)-3, and (R,R)-4 showed the same high affinity for VAChT as (-)-5-IBVM and may be suitable as imaging agents of cholinergic nerve terminals.

Topics: In Vitro Techniques; Magnetic Resonance Spectroscopy; Membrane Transport Proteins; Molecular Probes; Piperidines; Stereoisomerism; Vesicular Acetylcholine Transport Proteins