Absolute configuration of cis- and trans-2-(o-bromophenyl)cyclohexanols and (+)-cis-2-(o-bromophenyl)cyclohexylamine.
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AH5183 was studied because it inhibits acetylcholine transport into synaptic vesicles. The drug apparently is a slow-acting anti-cholinesterase, so further experiments were performed with this enzyme inhibited. Soaking for hours in AH5183 in Ringer does not decrease quantal size. However, a few minutes of tetanic nerve stimulation results in a marked decrease in quantal size. Quantal size also decreased after hours in a hypertonic Ringer containing the drug.
Stereochemical isomers with hydroxy groups were synthesized by reacting 2-(dimethoxymethyl)cyclohexanone with propargylmagnesium bromide. The stereo chemical structures were identified by NMR spectral interpretation and the geometry optimization. To assist the NMR interpretation, geometry optimization based on semi-empirical AM1 and PM3 methods was applied. Throughout this study, the structures of the two isomers were all determined and 1H and 13C NMR spectra were fully assigned. It was proven that the less polar isomer is an axial alcohol and the more polar one is an equatorial alcohol.
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A post-stimulation synthesis of acetylcholine (ACh), its incorporation into a 'stable-bound' (vesicular) compartment and subsequent release, were compared in K+-stimulated synaptosomes, in the absence and presence of 10 microM AH5183. The drug depressed by 16% the net intrasynaptosomal formation of ACh from 1 microM [3H]choline (Ch) in the medium, by competitively inhibiting (Ki approximately equal to 20 microM) the high-affinity Ch transport, but it had no direct effect on the intraterminal synthesis of ACh per se. The drug reduced incorporation of newly synthesized [3H]ACh into synaptic vesicles by 55% and subsequent K+-depolarization-induced release of [3H]ACh by 83%, although it had no effect on Ca2+ influx into synaptosomes. These results are consistent with the hypothesis that AH5183 blocks cholinergic neurotransmission presynaptically by interfering with recharging of synaptic vesicles with ACh. Since the reduction of ACh release in the presence of AH5183 had no direct effect on ACh synthesis, these results also suggest that the transmitter release is not prerequisite for enhancement of Ch uptake and ACh synthesis in stimulated nerve terminals.
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Three iodovesamicol analogs, iodinated at the ortho, meta, and para positions of the 4-phenylpiperidine moiety, were synthesized and labeled with 125I by isotopic exchange reaction. Their potencies as a vesamicol-like drug were evaluated with competitive inhibition studies using (-)[3H]vesamicol. The radiochemical yields were 40-85%, the radiochemical purities exceeded 95% and their specific activities were 370-740 GBq/mmol. The descending order of binding affinity of the tested compounds against the vesamicol receptor was m-iodovesamicol > o-iodovesamicol > p-iodovesamicol. The receptor binding affinity of m-iodovesamicol (IC50 = 133 nM) was comparable with that of vesamicol (IC50 = 109 nM). Therefore, the meta position of the 4-phenylpiperidinyl fragment of vesamicol was the optimum site for iodination, and radioiodinated m-iodovesamicol may serve as a useful radiopharmaceutical for in vitro and in vivo studies of presynaptic cholinergic neurons in rats.
Iodovesamicol analogs, radioiodinated at the ortho (1), meta(2) and para(3) positions of the 4-phenylpiperidine moiety, were evaluated as potential presynaptic cholinergic neuron mapping agents. Significant accumulation of m-[125I]iodovesamicol (mIV(2)) (about 3% of the injected dose) was noted in the rat brain with prolonged retention times. The accumulation of mIV(2) in the rat brain was decreased by 67% by 5 min pre-injection of dl-vesamicol(1 mumol/kg). Pre-injection of (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperdine[(+)-3-PPP](0.75 mumol/kg) did not markedly decrease the levels of radiotracers (oIV(1) and mIV(2)) in the rat brain. These results suggest that radioidinated m-iodovesamicol (mIV(2)) is suitable for use in presynaptic cholinergic neuron mapping.
Vesamicol is known to inhibit the transport of acetylcholine (ACh) into synaptic vesicles in vitro, but much less is known about its effects in the brain in vivo. To assess the effect of vesamicol in vivo, we examined cholinergic parameters, such as the subcellular distribution of ACh, activities of enzymes, uptake of choline, and muscarinic receptor binding in the striatum, hippocampus, and cerebral cortex of rats 30 and 60 min after intraperitoneal injection of vesamicol (3 mg/kg) or of vesamicol in combination with DDVP (5 mg/kg), which was administered 10 min before vasamicol. The levels of cytosolic ACh increased in all regions of the brain after injection of vesamicol, while those of vesicular ACh decreased in all regions except for the striatum. The increase in the levels of extracellular ACh and cytosolic ACh in the striatum induced by DDVP was generally enhanced after injection of vesamicol, Vesamicol did not reduce the level of vesicular ACh when DDVP had been injected previously. Vesamicol did not induce any significant changes in the activities of enzymes, choline uptake, or binding of [6H]quinuclidinyl benzilate to the muscarinic ACh receptors in the three regions. Changes in the cholinergic parameters caused by DDVP were not reversed by the combined administration of DDVP with vesamicol. The present results indicate that vesamicol can inhibit the transport of ACh into synaptic vesicles in the brain tissue in vivo, although it cannot reverse the effects of DDVP that has been injected prior to vesamicol.
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The relative configuration was determined for the title compound, C(26)H(34)O(6), which was prepared in a synthetic study on immunosuppressant FR65814. There is an intramolecular hydrogen bond between the hydroxy and epoxy groups.
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