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U Holzgrabe

Publications and source records attributed to U Holzgrabe.

64 records · Page 4Linked to original sources
PubMed1996

Comparison of structurally different allosteric modulators of muscarinic receptors by self-organizing neural networks.

Similarities in the molecular structure and surface properties of the allosteric modulators of muscarinic receptors, alcuronium, gallamine, tubocurarine, and the hexamethonium compound W84, a well-known pharmacological tool, are explored. The analysis of the molecular electrostatic potential (MEP) as well as of the shape of the molecular surface is performed by self-organizing neural networks. A distorted sandwich conformation of W84 is suggested to be the active form. The importance of the MEP for binding of these compounds could be established.

Alcuronium↗
PubMed1995

Variation of the oxime function of bispyridinium-type allosteric modulators of M2-cholinoceptors.

The bisbenzylether of the bispyridinium oxime, DUO 3-O (4,4'-Bis-[(2,6-dichlorobenzyloxyimino)-methyl]-1,1'-propane-1,3- diyl-bispyridinium dibromide), has been found to stabilize the antagonist binding to the M2-cholinoceptors which is indicative of an allosteric action. The oxygen of the oxime group was replaced with a nitrogen and a CH2-group leading to DUO 3-N and 3-C, respectively. The allosteric potency of the compounds was characterized by the concentrations which retarded the rate of dissociation of [3H]N-methyl-scopolamine from porcine cardiac cholinoceptors by a factor of 2 (EC50). The hydrazone derivative DUO 3-N was found to be the most active compound (ED50 = 2.7 microM) exceeding in activity DUO 3-O by a factor of 1.6 and DUO 3-C by a factor of 5. No correlation was found between the lipophilicity, determined as octanol/water partition coefficient, and the allosteric potency. The distribution of charges in the molecules was calculated by means of PEOE and displayed as Kohonen maps: The calculations exhibit a shift of the positive charge in the pyridinium ring from the nitrogen to the carbon atom in para-position when going from DUO 3-C to 3-O and 3-N. This shift parallels the rank order of the allosteric potency. From these results the conclusion has been drawn that the between distance the terminal ring-system and the positive charge is pivotal for the interaction of the allosteric modulators with the receptor protein.

Allosteric Regulation↗
PubMed1994

Search for the pharmacophore of bispyridinium-type allosteric modulators of muscarinic receptors.

The bis(dichlorobenzyl) ether of the bispyridinium oxime TMB 4 stabilizes antagonist binding to M2-cholinoceptors which is indicative of an allosteric action. More than 10 derivatives of the lead compound were synthesized to investigate structure-activity relationships. The allosteric potency of the compounds was indicated by the concentrations which retarded the rate of dissociation of [3H]N-methylscopolamine from porcine cardiac cholinoceptors by a factor of 2 (EC50). Compared with TMB 4, the bis(dichlorobenzyl) derivative 4a displayed a more than 200-fold higher potency (EC50 = 4.7 microM). One of the dichlorobenzyl groups could be replaced by a methyl group without loss of activity (EC50 = 4.5 microM). Further shortening of this end of the molecule was accompanied by a moderate decline in potency to a minimum of EC50 = 26 microM. The second quaternary nitrogen was not a prerequisite for an allosteric activity. It is concluded that one half of the lead compound is pivotal for an interaction with the allosteric site of the M2-cholinoceptor, whereas the opposite end of the molecule modulates the allosteric activity.

Allosteric Regulation↗
PubMed1994

Chiral discrimination of phenethylamines with beta-cyclodextrin and heptakis(2,3-di-O-acetyl)beta-cyclodextrin by capillary electrophoresis and NMR spectroscopy.

The resolution of nine sympathomimetic phenethylamine racemates by beta-cyclodextrin and heptakis(2,3-di-O-acetyl)beta-cyclodextrin has been investigated by capillary electrophoresis and 1H NMR spectroscopy. The NMR and capillary electrophoresis results showed that beta-cyclodextrin probably formed stronger complexes with the amines than did heptakis(2,3-di-O-acetyl)beta-cyclodextrin but was a poorer chiral discrimination agent in both techniques. The addition of heptakis(2,3-di-O-acetyl)beta-cyclodextrin to the capillary electrophoresis buffer gave baseline resolution of enantiomer peaks for seven of the compounds studied while beta-cyclodextrin resolved only three of the racemates.

Cyclodextrins↗
PubMed1994

A stable and highly potent hexamethonium derivative which modulates muscarinic receptors allosterically in guinea-pig hearts.

W84 (N,N,N',N'-tetramethyl-N,N'-bis-(3-phthalimidopropyl)-N,N'-hexane- 1,6- diyl-bis-ammonium dibromide) is a potent stabilizer of antagonist binding to muscarinic receptors; however, W84 hydrolyses in aqueous buffered medium. The synthesis of the stable derivative CHIN3/6 is presented containing a 2-phenyl-quinazolinone instead of the labile phthalimide substituent. This compound retarded [3H]N-methylscopolamine-dissociation in guinea-pig cardiac membranes with slightly higher potency than W84, the EC50 values amounting to 7.5 x 10(-7) and 13 x 10(-7) M, respectively. Molecular modelling revealed differences in the electron density of the substituents and in their molecular shape. It is suggested that the derivatives use partially different sites of attachment when occupying the allosteric binding site of the receptor protein.

Allosteric Regulation↗
PubMed1992

[Synthesis and stereochemistry of potentially powerful analgesics: 2,4-m-diaryl substituted 3,7-diazabicyclo(3,3,1)nonan-9-one-1,5-diesters].

The 2,4-di-2-pyridyl- substituted 7-methyl-3,7-diazabicyclo[3.3.1] nonan-9-one-1,5-diester shows a reasonable kappa-agonistic activity in the mouse vas deferens test. -To enhance the analgetic activity derivatives with m-Cl-, m-CH3-, m-OCH3-, m-OH-, and m-NO2 substituted phenyl residues at C-2/4 were synthesized: From the condensation of benzaldehydes, methylamine, and oxoglutarate isomeric mixtures of piperidones were obtained, containing cis-ketone and -enol and trans-enol; the isomerisation reactions of these piperidones were observed in CDCl3 and CD3OD. The bicyclus resulting from the reaction of the piperidones with HCHO and methylamine exhibits conformational rigidity because the free rotation of the 2,4-aryl groups is hindered. The rotational barrier around the C-2-aryl-bond was shown to be 18 kcal/mol by analysis of variable temp. 1H-NMR spectra.

Analgesics↗
PubMed1989

[Synthesis, stereochemistry and analgesic action of 3,7-diazabicyclo[3.3.1] nonan-9-ones and 1,3-diazaadamantan-6-ones].

The 1,3-diazaadamantan-6-ones 13-18 are synthesized from the 4-piperidones 1-3. Different conditions lead to stereoisomeric structures. The 3,7-diazabicyclo[3.3.1]nonan-9-ones 8 and 9 show similar geometrical isomerisms. The configuration is determined by means of 1H-NMR and 13C-NMR spectroscopic data. Whereas the diazabicyclo[3.3.1]nonanones 7 and 12 show opioid-like effects, the diazaadamantanone 13 is a peripheral analgesic.

Adamantane↗
PubMedDate not supplied

Conformational analysis, molecular shape comparison, and pharmacophore identification of different allosteric modulators of muscarinic receptors.

Structurally dissimilar compounds such as alcuronium and the newly synthesized substances derived from the bisbenzyl ether TMB4 and from hexamethonium stabilize antagonist binding to M2-cholinoceptors which is indicative of an allosteric action. In order to propose a hypothesis for the common pharmacophore and the corresponding active conformations, seven flexible compounds in a data set were individually aligned onto the most active and, additionally, rigid alcuronium molecule using a torsional angle flexible fit. An S-shape conformation was found to be a plausible general active conformation. In a subsequent molecular shape analysis the overlap and the nonoverlap steric volumes, RMS alignment as well as electrostatic field potentials were employed as possible structure--activity correlation descriptors. The corresponding 3D-QSAR formulation exhibits a correlation between allosteric modulation potency and the nonoverlap steric volume as well as the proton and oxygen anion probe electrostatic field potentials. Because of large structural diversity among the small number of compounds studied, the apparent 3D-QSAR is best thought of as a convenient representation of the common spatial pharmacophore hypothesis.

Alcuronium↗