Biomedical subjects

Tommy Liljefors

Publications and source records attributed to Tommy Liljefors.

35 records · Page 2Linked to original sources

PubMed2003

Rational design, synthesis, and pharmacological evaluation of 2-azanorbornane-3-exo,5-endo-dicarboxylic acid: a novel conformationally restricted glutamic acid analogue.

The design and synthesis of conformationally restricted analogues of alpha-amino acids is an often used strategy in medicinal chemistry research. Here we present the rational design, synthesis, and pharmacological evaluation of 2-azanorbornane-3-exo,5-endo-dicarboxylic acid (1), a novel conformationally restricted (S)-glutamic acid (Glu) analogue intended as a mimic of the folded Glu conformation. The synthesis of 1 was completed in its racemic form in eight steps from commercially available starting materials. As a key step, the first facially selective hydroboration of a 5-methylidene[2.2.1]bicyclic intermediate was investigated. In this transformation, the catalytic methodology of Wilkinson's/catechol borane proved superior to stoichiometric borane or dialkyl borane reagents, in terms of higher diastereomeric excess and chemical yield. To our surprise (+/-)-1 did not show affinity in binding studies on native 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) (IC(50) > 300 microM, [(3)H]AMPA) or kainic acid (IC(50) > 160 microM, [(3)H]kainic acid) receptors nor in binding studies on the cloned iGluR5,6 subtypes (IC(50) > 300 microM, [(3)H]kainic acid).

Aza Compounds↗

PubMed2003

Synthesis and structure-affinity relationship investigations of 5-heteroaryl-substituted analogues of the antipsychotic sertindole. A new class of highly selective alpha(1) adrenoceptor antagonists.

A new class of 5-heteroaryl-substituted 1-(4-fluorophenyl)-3-(4-piperidinyl)-1H-indoles as highly selective and potentially CNS-active alpha 1-adrenoceptor antagonists is described. The compounds are derived from the antipsychotic sertindole. The structure-affinity relationships of the 5-heteroaryl substituents, and the substituents on the piperidine nitrogen atom were optimized with respect to affinity for alpha 1 adrenoceptors and selectivity in respect to dopamine (D(1-4)) and serotonin (5-HT(1A-1B) and 5-HT(2A,2C)) receptors. The most selective compound obtained, 3-[4-[1-(4-fluorophenyl)-5-(1-methyl-1,2,4-triazol-3-yl)-1H-indol-3-yl]-1-piperidinyl]propionitrile (15c), has affinities of 0.99, 3.2, and 9.0 nM for the alpha(1a), alpha(1b), and alpha(1d) adrenoceptor subtypes, respectively, and a selectivity for adrenergic alpha(1a) receptors in respect to dopamine D2, D3, and D4 and serotonin 5-HT(2A) and 5-HT(2C) higher than 900, comparable to the selectivity of prazosin. In addition, the compound is more than 150-fold selective in respect to serotonin 5-HT(1A) and 5-HT(1B) receptors. A new basic pharmacophore for alpha 1-adrenoceptor antagonists based on a previously reported pharmacophore model for dopamine D2 antagonist is suggested.

Adrenergic alpha-Antagonists↗

PubMed2003

Competitive antagonism of AMPA receptors by ligands of different classes: crystal structure of ATPO bound to the GluR2 ligand-binding core, in comparison with DNQX.

Ionotropic glutamate receptors (iGluRs) constitute a family of ligand-gated ion channels that are essential for mediating fast synaptic transmission in the central nervous system. This study presents a high-resolution X-ray structure of the competitive antagonist (S)-2-amino-3-[5-tert-butyl-3-(phosphonomethoxy)-4-isoxazolyl]propionic acid (ATPO) in complex with the ligand-binding core of the receptor. Comparison with the only previous structure of the ligand-binding core in complex with an antagonist, 6,7-dinitro-2,3-quinoxalinedione (DNQX) (Armstrong, N.; Gouaux, E. Neuron 2000, 28, 165-181), reveals that ATPO and DNQX stabilize an open form of the ligand-binding core by different sets of interactions. Computational techniques are used to quantify the differences between these two ligands and to map the binding site. The isoxazole moiety of ATPO acts primarily as a spacer, and other scaffolds could potentially be used. Whereas agonists induce substantial domain closures compared to the apo structure, ATPO only induces minor conformational changes. These results are consistent with the hypothesis that domain closure is related to receptor activation. To facilitate the design of novel AMPA receptor antagonists, we present a modified model of the binding site that includes key residues involved in ligand recognition.

Binding Sites↗

PubMed2003

Design and synthesis of a new series of 4-alkylated 3-isoxazolol GABA A antagonists.

A number of analogues of the low-efficacy partial GABA(A) agonist 5-(4-piperidyl)-3-isoxazolol (4-PIOL), in which the 4-position of the 3-isoxazolol ring is substituted by different groups, were synthesized and tested as GABA(A) receptor ligands. While alkyl and benzyl substitution provided affinities and antagonist potencies comparable to those of 4-PIOL, diphenylalkyl and naphthylalkyl substitution resulted in marked increase in both affinity and potency. The 2-naphthylmethyl and the 3,3-diphenylpropyl analogues showed antagonist potencies comparable or markedly higher than that of the standard antagonist SR 95531. Molecular modeling studies exposed a large cavity in the vicinity of the 4-position of 4-PIOL, in which there seems to be additional sites for specific receptor interactions.

Alkylation↗

PubMed2003

Assessment of drug salt release from solutions, suspensions and in situ suspensions using a rotating dialysis cell.

A rotating dialysis cell consisting of a small (10 ml) and a large compartment (1000 ml) was used to study the release of drug salt (bupivacaine 9-anthracene carboxylate) from (i). solutions, (ii). suspensions and (iii). in situ formed suspensions. Initial release experiments from suspensions indicated that the release of drug salt in deionized water was predominantly limited by the diffusion across the membrane whereas it is essentially dissolution rate controlled in 0.05 M phosphate buffer (pH 7.40). Thus, the in vitro model appears to have a potential in formulation screening when phosphate buffer is used as release media. Generally, the initial release of the drug salt from in situ suspensions occurred faster as compared to conventional suspensions, probably due to incomplete precipitation of the drug salt, and hence formation of supersaturated solutions where the rate of release is predominantly determined by the concentration gradient. However, when an adequately concentrated solution of the drug salt was used to prepare the in situ suspension, the initial fast release was followed by a substantial sustained release indicating that the release had become dissolution rate limited.

Anesthetics, Local↗

PubMed2003

Alpha(1) adrenoceptor subtype selectivity. 3D-QSAR models for a new class of alpha(1) adrenoceptor antagonists derived from the novel antipsychotic sertindole.

Receptor-binding affinities for the alpha(1) adrenoceptor subtypes alpha(1a), alpha(1b) and alpha(1d) for a series of 39 alpha(1) adrenoceptor antagonists derived from the antipsychotic sertindole are reported. The SAR of the compounds with respect to affinity for the alpha(1a), alpha(1b) and alpha(1d) adrenoceptor subtypes as well as affinity obtained by an alpha(1) assay (rat brain membranes) were investigated using a 3D-QSAR approach based on the GRID/GOLPE methodology. Good statistics (r(2)=0.91-0.96; q(2)=0.65-0.73) were obtained with the combination of the water (OH2) and methyl (C3) probes. The combination of steric repulsion and electrostatic attractions explain the affinities of the included molecules. The adrenergic alpha(1a) receptor seems to be more tolerant to large substituents in the area between the indole 5- and 6-positions compared to the adrenergic alpha(1b) and alpha(1d) receptor subtypes. There seems to be minor differences in the position of areas in the alpha(1b) receptor compared to alpha(1a) and alpha(1d) receptors where electrostatic interaction between the molecules and the receptor (OH2 probe) contribute to increased affinity. These observations may be used in the design of new subtype selective compounds. In addition, the model based on biological data from an alpha(1) assay (rat brain membranes) resembles the model for the alpha(1b) adrenoceptor subtype.

Adrenergic alpha-1 Receptor Antagonists↗

PubMed2003

Pharmacophore and receptor models for neurokinin receptors.

Three neurokinin (NK) antagonist pharmacophore models (Models 1-3) accounting for hydrogen bonding groups in the 'head' and 'tail' of NK receptor ligands have been developed by use of a new procedure for treatment of hydrogen bonds during superimposition. Instead of modelling the hydrogen bond acceptor vector in the strict direction of the lone pair, an angle is allowed between the hydrogen bond acceptor direction and the ideal lone pair direction. This approach adds flexibility to hydrogen bond directions and produces more realistic RMS values. By using this approach, two novel pharmacophore models were derived (Models 2 and 3) and a hydrogen bond acceptor was added to a previously published NK2 pharmacophore model [Poulsen et al., J. Comput.-Aided Mol. Design, 16 (2002) 273] (Model 1). Model 2 as well as Model 3 are described by seven pharmacophore elements: three hydrophobic groups, three hydrogen bond acceptors and a hydrogen bond donor. Model 1 contains the same hydrophobic groups and hydrogen bond donor as Models 2 and 3, but only one hydrogen bond acceptor. The hydrogen bond acceptors and donor are represented as vectors. Two of the hydrophobic groups are always aromatic rings whereas the other hydrophobic group can be either aromatic or aliphatic. In Model 1 the antagonists bind in an extended conformation with two aromatic rings in a parallel displaced and tilted conformation. Model 2 has the same two aromatic rings in a parallel displaced conformation whereas Model 3 has the rings in an edge to face conformation. The pharmacophore models were evaluated using both a structure (NK receptor homology models) and a ligand based approach. By use of exhaustive conformational analysis (MMFFs force field and the GB/SA hydration model) and least-squares molecular superimposition studies, 21 non-peptide antagonists from several structurally diverse classes were fitted to the pharmacophore models. More antagonists could be fitted to Model 2 with a low RMS and a low conformational energy penalty than to Models 1 and 3. Pharmacophore Model 2 was also able to explain the NK1, NK2 and NK3 subtype selectivity of the compounds fitted to the model. Three NK 7TM receptor models were constructed, one for each receptor subtype. The location of the antagonist binding site in the three NK receptor models is identical. Compounds fitted to pharmacophore Model 2 could be docked into the NK1, NK2 and NK3 receptor models after adjustment of the conformation of the flexible linker connecting the head and tail. Models I and 3 are not compatible with the receptor models.

Amino Acid Sequence↗

PubMed2003

The selective activation of the glutamate receptor GluR5 by ATPA is controlled by serine 741.

Only a few agonists exhibit selectivity between the AMPA and the kainate subtypes of the glutamate receptor. The most commonly used kainate receptor preferring agonist, (S)-2-amino-3-(5-tert-butyl-3-hydroxy-4-isoxazolyl)propionic acid [(S)-ATPA], is an (R,S)-2-amino-3-(5-methyl-3-hydroxy-4-isoxazolyl)propionic acid (AMPA) derivative in which the methyl group at the 5-position of the isoxazole ring has been replaced by a tert-butyl group. When characterized by the two-electrode voltage clamp method in Xenopus laevis oocytes, ATPA exhibits at least 50-fold higher potency on the kainate receptor subtype, GluR5, compared with the AMPA receptors. Through mutagenesis studies of GluR5 and the AMPA receptor subtype, GluR1, we demonstrate that this pronounced selectivity for ATPA can be ascribed to Ser741 in GluR5 and Met722 in GluR1. Examination of other aliphatic substitutions at the 5-position of the isoxazole ring revealed that (R,S)-2-amino-3-(5-isopropyl-3-hydroxy-4-isoxazolyl)propionic acid (isopropyl-AMPA) displayed a 6-fold higher potency for GluR5 than for GluR1, whereas the analogs, propyl-AMPA and isobutyl-AMPA, did not exhibit significantly different potencies. Our study suggests that the GluR5 selectivity was a result not only of steric interference between the bulky tert-butyl group in ATPA and the methionine (Met722) in GluR1 but also a serine-dependent stabilization of the active conformation of GluR5 induced by ATPA. The stabilization was agonist-dependent and observed only for ATPA and isopropyl-AMPA, not for other AMPA analogs with bulky substitutions at the 5-position of the isoxazole ring.

Animals↗

PubMed2002

Activity of novel 4-PIOL analogues at human alpha 1 beta 2 gamma 2S GABA(A) receptors--correlation with hydrophobicity.

A series of novel 5-(4-piperidyl)-3-isoxazolol (4-PIOL) analogues where the 4-position of the 3-isoxazolol ring was substituted with groups of different size, flexibility, and lipophilicity have been characterised. Their activity as agonists and/or antagonists on human alpha(1)beta(2)gamma(2S) GABA(A) receptors expressed in Xenopus oocytes was studied using two-electrode voltage clamp electrophysiology. Methyl- and ethyl-substituted 4-PIOL analogues were characterised as partial agonists since weak agonist responses could be potentiated with lorazepam and inhibited by the competitive antagonist 2-(3-carboxypropyl)-3-amino-6-methoxyphenyl-pyradizinum bromide (SR95531). All larger substituents in the 4-position of the 3-isoxazolol ring of 4-PIOL converted the compounds into pure competitive antagonists. Additionally, for GABA, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), piperidine-4-sulphonic acid (P4S), and 5-(4-piperidyl)-3-isothiazolol (thio-4-PIOL), a negative linear correlation was found between the agonist efficacy of the compound and the ability of lorazepam to potentiate EC(95) responses. Furthermore, a positive linear correlation between the lipophilicity of the substituents in the 4-position of the 3-isoxazolol ring of 4-PIOL and the antagonist affinity was found. These data suggest that the GABA(A) receptor contains a hydrophobic binding pocket at the GABA recognition site and that the binding of the 4-PIOL analogues is largely determined by the transfer from the aqueous phase to the hydrophobic pocket.

Animals↗

PubMed2002

Refinement and evaluation of a pharmacophore model for flavone derivatives binding to the benzodiazepine site of the GABA(A) receptor.

To further develop and evaluate a pharmacophore model previously proposed by Cook and co-workers (Drug Des. Discovery 1995, 12, 193-248) for ligands binding to the benzodiazepine site of the GABA(A) receptor, 40 new flavone derivatives have been synthesized and their affinities for the benzodiazepine site have been determined. Two new regions of steric repulsive interactions between ligand and receptor have been characterized, and the receptor region in the vicinity of 6- and 3'-substituents has been mapped out. 2'-Hydroxy substitution is shown to give a significant increase in affinity, which is interpreted in terms of a novel hydrogen bond interaction with the previously proposed hydrogen bond-accepting site A2. On the basis of the results of these studies and the refined pharmacophore model, 5'-bromo-2'-hydroxy-6-methylflavone, the highest affinity flavone derivative reported so far (K(i) = 0.9 nM), was successfully designed. A comparison of the pharmacophore model with a recently proposed alternative model (Marder; et al. Bioorg. Med. Chem., 2001, 9, 323-335) has been made.

Animals↗

PubMed2002

Novel class of potent 4-arylalkyl substituted 3-isoxazolol GABA(A) antagonists: synthesis, pharmacology, and molecular modeling.

A number of analogues of the low-efficacy partial GABA(A) agonist 5-(4-piperidyl)-3-isoxazolol (4-PIOL, 5), in which the 4-position of the 3-isoxazolol ring was substituted by different groups, were synthesized and tested as GABA(A) receptor ligands. Substituents of different size and structural flexibility such as alkyl, phenylalkyl, diphenylalkyl, and naphthylalkyl were explored. Pharmacological characterization of the synthesized compounds was carried out using receptor binding assays and by electrophysiological experiments using whole-cell patch-clamp techniques. Whereas none of these compounds significantly affected GABA(B) receptor sites or GABA uptake, they did show affinity for the GABA(A) receptor site. While alkyl or benzyl substitution, compounds 7a-h, provided receptor affinities comparable with that of 5 (K(i) = 9.1 microM), diphenylalkyl and naphthylalkyl substitution, as in compounds 7m-t, resulted in a dramatic increase in affinity relative to 5. The 3,3-diphenylpropyl and the 2-naphthylmethyl analogues, compounds 7s and 7m, respectively, showed the highest affinities of the series (K(i) = 0.074 microM and K(i) = 0.049 microM). In whole-cell patch-clamp recordings from cultured cerebral cortical neurons, all of the tested compounds were able to inhibit the effect of the specific GABA(A) agonist isoguvacine (1), compounds 7m and 7s showing antagonist potency (IC(50) = 0.37 microM and IC(50) = 0.02 microM) comparable with or markedly higher than that of the standard GABA(A) antagonist 4 (IC(50) = 0.24 microM). Highly potent convulsant activity was demonstrated in mice with compounds 7m (ED(50) = 0.024 micromol/kg) and 7s (ED(50) = 0.21 micromol/kg) after intracerebroventricular administration, whereas no effects were found after subcutaneous administration. According to a previously proposed pharmacophore model for GABA(A) receptor agonists, a receptor cavity in the vicinity of the 4-position of the 3-isoxazolol ring in 4-PIOL exists. A molecular modeling study, based on compounds 7o,m,l,q,s, was performed to explore the dimensions and other properties of the receptor cavity. This study demonstrates the importance of the arylalkyl substituents in 7m and 7s and the considerable dimensions of this proposed receptor cavity.

Animals↗

PubMed2002

Correlation of aqueous solubility of salts of benzylamine with experimentally and theoretically derived parameters. A multivariate data analysis approach.

Twenty two salts of benzylamine and p-substituted benzoic acids were prepared and characterized. The p-substituent was varied with regard to electronic, hydrophobic, and steric effects as well as hydrogen bonding potential. A multivariate data analysis was used to describe the relationship between the aqueous solubility of the salts and experimentally determined physicochemical parameters and theoretically derived molecular descriptors. The model, based on all descriptors, gave R(2)=0.86 and Q(2)=0.72. The most significant descriptors exhibiting VIP (variance of importance) values above 1.0 were intrinsic dissolution rate, intrinsic solubility of the unionized acids (S(0)), Hansch's hydrophobic parameter, Charton's steric parameter and molecular weight (MW). Statistically good models for predicting solubility of a selected test set were obtained by using simple models consisting of a few descriptors only: (i) Charton, Hansch and MW (R(2)=0.73; Q(2)=0.70), and (ii) Charton and S(0) (R(2)=0.74; Q(2)=0.72).

Benzylamines↗

PubMed2002

Specific GABA(A) agonists and partial agonists.

The GABA(A) receptor system is implicated in a number of neurological and psychiatric diseases, making GABA(A) receptor ligands interesting as potential therapeutic agents. Only a few different classes of structures are currently known as ligands for the GABA recognition site on the hetero-pentameric GABA(A) receptor complex, reflecting the very strict structural requirements for GABA(A) receptor recognition and activation. Within the series of compounds showing agonist activity at the GABA(A) receptor site that have been developed, most of the ligands are structurally derived from the GABA(A) agonists muscimol, THIP, or isoguvacine, which we developed in the initial stages of the project. Using recombinant GABA(A) receptors, functional selectivity was demonstrated for a number of compounds, including THIP, showing highly subunit-dependent potency and maximal response. In light of the interest in partial GABA(A) receptor agonists as potential therapeutics, structure-activity studies of a number of analogs of 4-PIOL, a low-efficacy partial GABA(A) agonist derived from THIP, have been performed. In this connection, a series of GABA(A) ligands has been developed that exhibit pharmacological profiles from moderately potent low-efficacy partial GABA(A) agonist activity to potent and selective antagonist effects. Very little information is available on direct-acting GABA(A) receptor agonists in clinical studies. However, the results of clinical studies on the effect of the partial GABA(A) agonist THIP on human sleep patterns show that the functional consequences of a direct-acting agonist are different from those seen after the administration of GABA(A) receptor modulators, such as benzodiazepines and barbiturates.

Benzodiazepines↗

PubMed2002

Investigation of the metal binding site in methionine aminopeptidase by density functional theory.

All methionine aminopeptidases exhibit the same conserved metal binding site. The structure of this site with either Co2+ ions or Zn2+ ions was investigated using density functional theory. The calculations showed that the structure of the site was not influenced by the identity of the metal ions. This was the case for both of the systems studied; one based on the X-ray structure of the human methionine aminopeptidase type 2 (hMetAP-2) and the other based on the X-ray structure of the E. coli methionine aminopeptidase type I (eMetAP- 1). Another important structural issue is the identity of the bridging oxygen, which is part of either a water molecule or a hydroxide ion. Within the site of hMetAP-2 the results strongly indicate that a hydroxide ion bridges the metal ions. By contrast, the nature of the oxygen bridging the metal ions within the metal binding site of eMetAP-1 cannot be determined based on the results here, due to the similar structural results obtained with a bridging water molecule and a bridging hydroxide ion.

Aminopeptidases↗

PubMed2002

A pharmacophore model for NK2 antagonist comprising compounds from several structurally diverse classes.

A neurokinin 2 (NK2) antagonist pharmacophore model has been developed on the basis of five non-peptide antagonists from several structurally diverse classes. To evaluate the pharmacophore model, another 20 antagonists were fitted to the model. By use of exhaustive conformational analysis (MMFFs force field and the GB/SA hydration model) and least-squares molecular superimposition studies, 23 of the 25 antagonists were fitted to the model in a low energy conformation with a low RMS value. The pharmacophore model is described by four pharmacophore elements: Three hydrophobic groups and a hydrogen bond donor represented as a vector. The hydrophobic groups are generally aromatic rings, but this is not a requirement. The antagonists bind in an extended conformation with two aromatic rings in a parallel displaced and tilted conformation. The model was able to explain the enantioselectivity of SR48968 and GR159897.

Computer Simulation↗

PubMed2002

GABA(A) receptor ligands and their therapeutic potentials.

The GABA(A) receptor system is implicated in a number of neurological diseases, making GABA(A) receptor ligands interesting as potential therapeutic agents. Only a few different classes of structures are currently known as ligands for the GABA recognition site on the GABA(A) receptor complex, reflecting the very strict structural requirements for GABA(A) receptor recognition and activation. Within the series of compounds showing agonist activity at the GABA(A) receptor site that have been developed, most of the ligands are structurally derived from the GABA(A) agonists muscimol, THIP or isoguvacine. Using recombinant GABA(A) receptors, functional selectivity has been shown for a number of compounds such as the GABA(A)agonists imidazole-4-acetic acid and THIP, showing highly subunit-dependent potency and maximal response. In the light of the interest in partial GABA(A) receptor agonists as potential therapeutics, structure-activity studies of a number of analogues of 4-PIOL, a low-efficacy partial GABA(A) agonist, have been performed. In this connection, a series of GABA(A) ligands has been developed showing pharmacological profiles from moderately potent low-efficacy partial GABA(A) agonist activity to potent and selective antagonist effect. Only little information about direct acting GABA(A) receptor agonists in clinical studies is available. Results from clinical studies on the effect of the GABA(A) agonist THIP on human sleep pattern shows that the functional consequences of a direct acting agonist are different from those seen after administration of GABA(A) receptor modulators.

Animals↗

PubMedDate not supplied

Binding of alpha-hydroxy-beta-amino acid inhibitors to methionine aminopeptidase. The performance of two types of scoring functions.

The binding mode of a recently described set of alpha-hydroxy-beta-amino acid inhibitors of methionine aminopeptidase type 2 is suggested in the present work. The binding mode is supported by analysis of published structures of transition state analogues co-crystallised with E. coli methionine aminopeptidase and by a comparison of molecular interaction fields calculated using GRID for E. coli and human methionine aminopeptidase. Based on the suggested binding mode two types of scoring functions have been evaluated and compared. These are the commercially available consensus score, CScore, and scoring of the ligands employing energies calculated using the Merck Molecular Force Field (MMFF). Enriched subsets of ligands were obtained when using CScore, but these scores could not be used to assess the relative affinities of individual compounds. Although still not sufficiently accurate for reliable predictive purposes, an improved correlation was obtained between structure and affinity using a combined force field energy including contributions from solvation and conformational energy penalty for binding.

Algorithms↗