Showing papers by "Ulrike Holzgrabe published in 2003"
TL;DR: The principles of muscarinicAllosteric interactions are illustrated, an overview of SARs in congeners of archetypal allosteric agents is given, and the topology of M(2) musCarinic allosterics interactions that are characterized by divergent binding modes are considered.
Abstract: Allosteric modulation of G protein-coupled receptors has been intensively studied at muscarinic acetylcholine receptors. Findings made with archetypal allosteric agents such as gallamine, alcuronium, and bis(ammonio)alkane-type agents revealed that binding of orthosteric ligands that attach to the acetylcholine site can be allosterically decreased or increased or left unaltered in a subtype-selective fashion. Analyses of structure/activity relationships (SARs) help to elucidate the molecular events underlying the allosteric action and they may pilot the development of new allosteric agents with improved properties and therapeutic perspectives. With a focus on SARs, this review illustrates the principles of muscarinic allosteric interactions, gives an overview of SARs in congeners of archetypal allosteric agents, and considers the topology of M(2) muscarinic allosteric interactions that are characterized by divergent binding modes.
41 citations
TL;DR: A series of structurally related, optimized candidates will be developed based on the promising characteristics of the novel acetylcholinesterase inhibitors presented, and a general binding mode for nearly all compounds could be identified.
Abstract: A novel series of acetylcholinesterase (AChE) inhibitors of the bispyridinium type was synthesized and the inhibitory activity against AChE and butyrylcholinesterase (BChE) measured. In essence, the substitution pattern influenced the inhibitory potency against AChE, where the most active bispyridiniumoxime (TMB-4) was bisbenzyl substituted followed by monobenzyl substituted, bismethyl substituted, and unsubstituted derivatives of TMB-4. Hence, the bisbenzyl ether of TMB-4 was further investigated. In order to obtain diverse lipophilic and electronic properties for these bisbenzyl bispyridinium derivatives (so-called DUO series), the lateral ring substitution was systematically varied. The lowest IC(50) value against AChE found thus far in the DUO series was 0.34 microM. Docking studies were carried out to elucidate the differences in biological activity. A general binding mode for nearly all compounds could be identified by these investigations. In this binding mode, the docked ligands span the narrow, deeply buried active-site gorge, interacting with Trp84 at the bottom of the gorge, Tyr334 or Phe331 halfway down the gorge, and Trp279 at the peripheral anionic site at the mouth of the gorge. For specific ligands, additional interactions were found which helped to explain their deviating activity. Based on the promising characteristics of the novel acetylcholinesterase inhibitors presented, a series of structurally related, optimized candidates will be developed.
38 citations
TL;DR: Derivatization with o‐phthaldialdehyde and thioglycolic acid is found to be appropriate for all antibiotics and has to be improved for amikacin and netilmicin.
Abstract: Aminoglycoside antibiotics are always a mixture of structurally related amino sugars, which do not have a chromophore or fluorophore. The aim of the study was to find one method for evaluation of the components and impurities of the antibiotics. Derivatization with o-phthaldialdehyde and thioglycolic acid is found to be appropriate for all antibiotics. The components of gentamicin (GM), sisomicin, netilmicin, kanamycin, amikacin, and tobramycin were tried to separate by means of micellar electrokinetic chromatography. The background electrolyte was composed of sodium tetraborate (100 mM, pH 10.0), sodium deoxycholate (20 mM), and beta-cyclodextrin (15 mM). This method is valid for evaluation of GM, kanamycin, and tobramycin. It has to be improved for amikacin and netilmicin. In addition, 46 bulk samples of GM of different manufacturer or pharmaceutical companies were investigated. Many samples were found to contain many minor products and different amounts. Beside different patterns of the main compounds GM C1, GM C1a, GM C2a, and GM C2, many lots were found consisting of a substantial number of minor products. The appearance of a high number of minor products is always associated with the existence of sisomicin, which is not found in "pure" samples. However, almost all samples met the requirements of the European Pharmacopoeia (EP) and United States Pharmacopoeia (USP).
35 citations
TL;DR: In this paper, the 1H and 13C NMR spectra of the free bases and corresponding sulfates were assigned using HMQC, HMBC and selective TOCSY experiments.
Abstract: The antibiotic agent gentamicin sulfate is a mixture of several structurally very similar aminoglycosides. The major components of gentamicin are gentamicin C1, C1a, C2 and C2a. These major components were separated by means of column chromatography. The 1H and 13C NMR spectra of the free bases and the corresponding sulfates were assigned using HMQC, HMBC and selective TOCSY experiments. Additionally, the 1H and 13C NMR spectra of the sulfates and hydrochlorides, respectively, of the minor components were assigned. The full assignment of all components of gentamicin is necessary for the quantitative analysis of batches of gentamicin. By means of coupled liquid chromatography–NMR, several different batches were studied, revealing different compositions of batches from various sources. Copyright © 2003 John Wiley & Sons, Ltd.
34 citations
TL;DR: Docking of HZ2 to the putative binding site model of the KOR revealed HZ1 to be tightly sitting in the binding pocket, and a formation of a hemiaminal bond between the keto carbonyl group of Hz2 and a lysine residue (Lys200) may explain the long duration of action.
Abstract: The 2,4-di-2-pyridyl-3,7-dimethyl-3,7-diazabicyclo[331]nonan-9-one 1,5-diester HZ2 was recently found to exhibit high affinity and selectivity to the κ-opioid receptor (KOR) in combination with an unusually long duration of action Docking of HZ2 to the putative binding site model of the KOR revealed HZ2 to be tightly sitting in the binding pocket Strong interactions, especially salts bridges between the protonated nitrogens of HZ2 and the glutamic acids 209 and 297, nicely explain the high affinity of HZ2 to the KOR A formation of a hemiaminal bond between the keto carbonyl group of HZ2 and a lysine residue (Lys200) may explain the long duration of action
33 citations
TL;DR: A series of symmetrical and nonsymmetrical compounds was synthesized in which the phthalimide residues were replaced by differently substituted imide moieties, finding that the gain in allosteric activity achieved by ring variation plus propyl chain methylation on one side of the molecule could not be augmented by symmetrical variations.
Abstract: Bis(ammonio)alkane compounds carrying lateral phthalimidopropyl substituents on the nitrogen atoms belong to the archetypal muscarinic allosteric agents. Herein, a series of symmetrical and nonsymmetrical compounds was synthesized in which the phthalimide residues were replaced by differently substituted imide moieties. The allosteric action was measured in porcine heart muscarinic M2 receptors using [3H]N-methylscopolamine (NMS) as a ligand for the orthosteric receptor site in equilibrium binding and dissociation experiments. 1,8-Naphthalimido residues conferred an up to 100-fold gain in affinity leading into the low nanomolar range, while the inhibition of NMS binding was maintained. Additional propyl chain methylation was accompanied by an allosteric elevation of orthosteric ligand binding. In general, the gain in allosteric activity achieved by ring variation plus propyl chain methylation on one side of the molecule could not be augmented by symmetrical variations. The elevation of the ligand binding ...
28 citations
Journal Article•
TL;DR: The results demonstrate that naphthylisoquinoline alkaloids constitute an interesting novel class of antitrypanosomal compounds worth further optimization.
Abstract: In view of the need to develop new drugs against human African trypanosomiasis, a series of naturally occurring naphthylisoquinoline alkaloids, axially chiral acetogenic products derived from tropical plants, have been investigated for their activity against Trypanosoma brucei brucei TC 221. Likewise compounds corresponding to the two molecular portions, the naphthalene and the isoquinoline parts were tested, as well as molecules related to the central biaryl core of the alkaloids. Among all compounds tested, the natural, genuine alkaloids themselves, in particular dioncophylline B with its biaryl system and a moderate number of free hydroxy functions, showed the highest activities. Our results demonstrate that naphthylisoquinoline alkaloids constitute an interesting novel class of antitrypanosomal compounds worth further optimization.
17 citations
TL;DR: In both experiments the formation of enantiomerically enriched HDMF could be demonstrated for the first time, whereas incubation experiments under neutral conditions resulted in the detection of racemic HDMF.
15 citations
TL;DR: A sensitive capillary electrophoretic method using low pH with direct UV detection with respect to quantification criteria is acceptable for routine control of reduced glutathione for pharmaceutical application.
Abstract: A sensitive capillary electrophoretic method using low pH with direct UV detection has been developed to evaluate the impurity profile of reduced glutathione obtained from its production and purification. The method is characterized by high detection sensitivity and selectivity. Validation has been performed with model mixtures consisting of the main known related substances—oxidized glutathione, glutamylcystein, cysteinylglycine and cysteine. The results from this study show that with respect to quantification criteria the method is acceptable for routine control of reduced glutathione for pharmaceutical application.
14 citations
TL;DR: In this paper, the piperidine ring, the benzodiazepine system, the phthalimide moiety and the chains connecting the ring systems were synthesized in a microwave assisted route.
14 citations
TL;DR: A capillary zone electrophoresis method is described for the enantioseparation of talinolol using heptakis(2,3‐diacetyl‐6‐sulfo)‐ β‐cyclodextrin (HDAS‐β‐CD) as a chiral selector and was found to be suitable in determination of tal inolol enantiomers in highly diluted samples obtained from in vitro experiments.
Abstract: A capillary zone electrophoresis method is described for the enantioseparation of talinolol using heptakis(2,3-diacetyl-6-sulfo)-beta-cyclodextrin (HDAS-beta-CD) as a chiral selector. After liquid-liquid extraction of talinolol from physiological solution, electrokinetic injection was employed to improve the sensitivity. The use of a coated capillary was necessary to achieve stable and reproducible enantioseparations. A baseline separation of the talinolol enantiomers was achieved in less than 10 min using 100 mM phosphate solution as background electrolyte and pH 3.5, at the presence of 3.0 mM HDAS-beta-CD and at 20 degrees C. In addition, this analytical condition proved to be useful for the enantioseparation of a number of other beta-blocking agents such as alprenolol, atenolol, bisoprolol, celiprolol, metipranolol, oxprenolol, and sotalol. For determining talinolol, the method could be validated in terms of precision, accuracy and linearity, and was found to be suitable in determination of talinolol enantiomers in highly diluted samples obtained from in vitro experiments.
TL;DR: It is shown that with the described capillary zone electrophoresis (CZE) method it is possible to handle small sample volumes of 60 microl, to detect clotrimazole concentrations of 0.3 microg ml(-1) (limit of detection), and to quantify clotrimzole down to concentrations of0.5 microgml(-1), the limit of quantification.
TL;DR: Bisquaternary dimers of strychnine and brucine were synthesized and their allosteric effect on muscarinic acetylcholine M(2) receptors was examined, which indicated ternary complex formation.
TL;DR: A simple electrophoretic method with UV detection has been developed for resolution of the enantiomers of 2,5-dimethyl-4-hydroxy-3(2H)-furanone, the key flavor compounds in strawberry fruit.
Abstract: A simple capillary electrophoretic method with UV detection has been developed for resolution of the enantiomers of 2,5-dimethyl-4-hydroxy-3(2H)-furanone, the key flavor compounds in strawberry fruit. The separation was performed in fused-silica capillaries (30/40.2 cm long×50μm i.d.) with running buffer consisting of 50mm ammonium acetate, pH 4.0, containing 20mm heptakis-(2,3-O-diacetyl-6-O-sulfato)-β-cyclodextrin (HDAS-β CD). The applied potential was 10 kV, the temperature 25°C, and detection was at 280 nm. The method was used to determine the enantiomer ratio of 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) isolated from strawberry fruits and from the yeastZygosaccharomyces rouxii. The formation of enantiomerically enriched(+)-DMHF byZ. rouxii was demonstrated for, the first time.
TL;DR: The findings are in line with the hypothesis that the phthalimido-moiety, but not the middle chain, is pivotal for the topology of interaction with the M2-receptor protein.
Abstract: Muscarinic M2-receptors allow for divergent modes of allosteric action, depending on the structure of the allosteric modulator. Phthalimido-substituted bis(ammonio)alkane-type modulators belong to the common mode allosteric agents, whereas a physicochemically closely related bispyridinium-oxime with dichlorobenzyl-substituents at both ends is an atypical agent. Here, we compared the actions of stepwise shortened compounds composed of the phthalimido moiety and middle chains of either the bispyridinium- or the bis(ammonio)alkane-type. Allosteric interactions were measured in pig M2 receptors with the orthosteric probe [3H]N-methylscopolamine ([3H]NMS) to label the acetylcholine binding site of the receptors. Dissociation and equilibrium binding experiments revealed parallel structure/activity-relationships in both series of compounds with regard to the cooperativity of interaction with [3H]NMS and to the underlying binding affinities in radioligand-occupied and free receptors. In conclusion, the findings are in line with the hypothesis that the phthalimido-moiety, but not the middle chain, is pivotal for the topology of interaction with the M2-receptor protein.
TL;DR: It was shown by molecular modelling that heterocyclic bicyclo[3.3.1]nonan-9-ones fit very well with the structure of ketazocine, a prototypic kappa-selective benzomorphan compound; when compared to the arylacetamide structure of U-69, a specific kappa1-receptor agonist, a similar geometry was found with a slightly different distribution of the charges.
Abstract: Previous pharmacological results have suggested that members of the heterocyclic bicyclo[3.3.1]nonan-9-one-like compounds are potent k-opioid receptor specific agonists. One lead molecule of this series, called compound 1 (dimethyl 7-methyl-2,4-di-2-pyridyl-3,7-diazabicyclo[3.3.1]nonan-9-one-1,5-dicarboxylate) exhibited high affinity for [3H]ethylketocyclazocine and [3H]U-69,593 binding sites in guinea pig cerebellar membranes which known to be a good source for k1 receptors. It was shown by molecular modelling that heterocyclic bicyclo[3.3.1]nonan-9-ones fit very well with the structure of ketazocine, a prototypic k-selective benzomorphan compound; when compared to the arylacetamide structure of U-69,593, a specific k1-receptor agonist, a similar geometry was found with a slightly different distribution of the charges. It is postulated, that the essential structural skeleton involved in the opioid activity is an aryl-propyl-amine element distributed along the N7-C6-C5-C4-aryl bonds.
TL;DR: By reaction of aromatic aldehydes with (-)-ephedrine aromatic 1,3-oxazolidines, the reaction was carried out either at conventional conditions or by microwave heating as discussed by the authors.
Abstract: By reaction of aromatic aldehydes with (-)-ephedrine aromatic 1,3-oxazolidines can be obtained. The reaction was carried out either at conventional conditions or by microwave heating. The different diastereomeric ratios were determined by means of 1H NMR spectroscopy.
TL;DR: In this article, a terphenyl-type allosteric modulator was designed using bis(triphenylphosphine)nickel(II) dichloride as a catalyst.
TL;DR: In this study, heptane‐bisammonio compounds were optimized with regard to the orthosteric antagonist NMS and stressed the importance of an aromatic moiety at both ends of the heptan‐bisAMmonio chain.
Abstract: Allosteric modulators are able to enhance or decrease the equilibrium binding of orthosteric agonists or antagonists. The treatment of Alzheimer's disease and the organophosphorus poisoning can take advantage of the enhancement of the ligand binding. Prerequisite is the formation of ternary complexes consisting of the receptor protein, the orthosteric ligand, e. g. N-methylscopolamine (NMS), and the alloster optimized for the corresponding orthoster. In this study, heptane-bisammonio compounds were optimized with regard to the orthosteric antagonist NMS. Comparing pairs of compounds characterized by phthalimides, cyclohexanedicarbonic acid imide and succinimides at both ends or a phthalimide at one end and either of the three imides at the other end stressed the importance of an aromatic moiety at both ends of the heptane-bisammonio chain.
TL;DR: In der nahen bzw. mittleren Zukunft ist die Zulassung weiterer Azole der 2. Generation sowie von weiteren Glucansynthase-Inhibitoren zu erwarten as discussed by the authors.
Abstract: In der nahen bzw. mittleren Zukunft ist die Zulassung weiterer Azole der 2. Generation sowie von weiteren Glucansynthase-Inhibitoren zu erwarten. Auch Inhibitoren der Chitinsynthese sind Gegenstand der aktuellen Antimykotikaentwicklung.
TL;DR: By reaction of aromatic aldehydes with (-)-ephedrine aromatic 1,3-oxazolidines, the reaction was carried out either at conventional conditions or by microwave heating as mentioned in this paper.
Abstract: By reaction of aromatic aldehydes with (-)-ephedrine aromatic 1,3-oxazolidines can be obtained. The reaction was carried out either at conventional conditions or by microwave heating. The different diastereomeric ratios were determined by means of 1H NMR spectroscopy.