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Biomedical subjects

Tommy Liljefors

Publications and source records attributed to Tommy Liljefors.

At least 19 recordsLinked to original sources
PubMed2006

Identification of a putative binding site for 5-alkyl-benzothiadiazides in the AMPA receptor dimer interface.

Crystal structures of three different allosteric modulators co-crystallized with the iGluR2 ligand-binding domain are currently available. The modulators, cyclothiazide, aniracetam and CX614, bind at overlapping binding sites in the dimer interface between two iGluR2 subunits. However, pharmacological data indicate that there are one or more additional binding sites for this class of compounds. Based on differences in structure-activity relationship data we show that 5-alkyl-benzothiadiazide (5ABTD) modulators and a series of close analogs of cyclothiazide, despite having a common core structure, do not have the same binding site. In the present work, a new potential binding site for allosteric modulators has been identified in the dimer interface of the iGluR2 ligand-binding domain. By comparing different iGluR2 crystal structures including different co-crystallized agonists, this cavity is shown to be a structurally conserved part of the dimer interface. The cavity is characterized with respect to shape and potential favorable interactions with ligands and docking is used to find a reasonable binding mode for the core structure of the 5ABTDs. The extensive structure-activity data available for this series of compounds are in agreement with the proposed binding mode, supporting the conclusion that the identified cavity most likely is the binding site for the 5ABTDs.

Allosteric Site↗
PubMed2006

New ligands with affinity for the alpha4beta2 subtype of nicotinic acetylcholine receptors. Synthesis, receptor binding, and 3D-QSAR modeling.

A new series of piperazines, diazepanes, diazocanes, diazabicyclononanes, and diazabicyclodecanes with affinity for the alpha4beta2 subtype of nicotinic acetylcholine receptors were synthesized on the basis of results from a previous computational study. A predictive 3D-QSAR model was developed using the GRID/GOLPE approach (R2 = 0.94, Q2 = 0.83, SDEP = 0.34). The SAR was interpreted in terms of contour maps of the PLS coefficients and in terms of a homology model of the alpha4beta2 subtype of the nicotinic acetylcholine receptors. The results reveal that hydrogen bonding from both hydrogens on the protonated amine and from the pyridine nitrogen to a water molecule as well as van der Waals interactions between the substituent bearing the protonated amine and the receptor is of importance for ligand affinity. The combination of 3D-QSAR and homology modeling proved successful for the interpretation of structure-affinity relationships as well as the validation of the individual modeling approaches.

Animals↗
PubMed2006

4-quinolone derivatives: high-affinity ligands at the benzodiazepine site of brain GABA A receptors. synthesis, pharmacology, and pharmacophore modeling.

The 3-ethoxycarbonyl-4-quinolone compound 1 has previously been identified via a database search as an interesting lead compound for ligand binding at the benzodiazepine site of GABA(A) receptors (Kahnberg et al. J. Mol. Graphics Modelling 2004, 23, 253-261). Pharmacophore-guided optimization of this lead compound yielded a number of high-affinity ligands for the benzodiazepine site including compounds 20 and 23-25 displaying sub-nanomolar affinities. A few of the compounds have been tested on the alpha(1)beta(2)gamma(2S) and alpha(3)beta(2)gamma(2S) GABA(A) receptor subtypes, and two of the compounds (5 and 19) display selectivity for alpha(1)- versus alpha(3)-containing receptors by a factor of 22 and 27, respectively. This selectivity for alpha(1)beta(2)gamma(2S) is in the same range as that for the well-known alpha(1) subunit selective compound zolpidem.

4-Quinolones↗
PubMed2006

Potent 4-arylalkyl-substituted 3-isothiazolol GABA(A) competitive/noncompetitive antagonists: synthesis and pharmacology.

The GABA(A) agonists muscimol (1), 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP, gaboxadol, 3), and the partial GABA(A) agonist 5-(4-piperidyl)-3-isoxazolol (4-PIOL, 6a) and their respective 3-isothiazolol analogues thiomuscimol (2), thio-THIP (4), and thio-4-PIOL (7a) are ligands at the GABA(A) orthosteric (recognition) site. The structure-activity relationships (SARs) between these structures are key elements of a 3D-pharmacophore model for GABA(A) agonists and competitive antagonists [Frølund, B.; Jørgensen, A. T.; Tagmose, L.; Stensbøl, T. B.; Vestergaard, H. T.; Engblom, C.; Kristiansen, U.; Sanchez, C.; Krogsgaard-Larsen, P.; Liljefors, T. J. Med. Chem. 2002, 45, 2454-2468]. Prompted by this model, we now report the synthesis and SAR of a series of analogues of 7a, in which the 4-position of the 3-isothiazolol was substituted by alkyl or bulky aromatic groups such as naphthylmethyl and diphenylalkyl groups (7b-h). The compounds have been pharmacologically characterized using receptor binding assays and two-electrode voltage-clamped Xenopus oocytes expressing alpha1beta3gamma2S- and alpha4beta3delta-containing receptors. The compounds show SARs comparable with those of 6b-h but are generally 5-15 times more potent. The 2-naphthylmethyl, the 1-bromo-2-naphthylmethyl, and the 3,3-diphenylpropyl analogues, compounds 7e, 7f, and 7h, respectively, show affinity in the low-nanomolar range (K(i) 2-10 nM). Interestingly, 7e and 7h exhibited a mixed antagonist profile consisting of a noncompetitive component in the picomolar range and a competitive component at concentrations above 1 nM. This unique profile was shown not to be due to either use dependence or kinetic effects. This antagonist profile of 7e and 7h was particularly pronounced at alpha4beta3delta-containing GABA(A) receptors, which showed three- and 10-fold selectivity for 7h and 6h, respectively.

Animals↗
PubMed2006

Regioselectivity in lithiation of 1-methylpyrazole: experimental, density functional theory and multinuclear NMR study.

Reaction of 1-methylpyrazole with n-BuLi in THF followed by reaction with monodeuteromethanol (CH3OD) under kinetically controlled conditions leads to functionalisation at the methyl group, whereas reaction under thermodynamically controlled conditions leads to functionalisation at the pyrazole 5-position. The observed regioselectivity can be correctly predicted, at least qualitatively, using density functional B3LYP/6-31+G(d,p) calculations only when solvation effects (IEFPCM) are taken into account. The 1H,6Li HOESY and NOESY NMR spectra of the thermodynamic product 5-lithio-1-methylpyrazole (5-Li) in [D8]THF are consistent with an oligomeric structure.

Kinetics↗
PubMed2006

The structure of a mixed GluR2 ligand-binding core dimer in complex with (S)-glutamate and the antagonist (S)-NS1209.

Ionotropic glutamate receptors (iGluRs) mediate fast synaptic transmission between cells of the central nervous system and are involved in various aspects of normal brain function. iGluRs are implicated in several brain disorders, e.g. in the high-frequency discharge of impulses during an epileptic seizure. (RS)-NS1209 functions as a competitive antagonist at 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionate receptors, and shows robust preclinical anticonvulsant and neuroprotective effects. This study explores 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionate receptor binding and selectivity of this novel class of antagonists. We present here the first X-ray structure of a mixed GluR2 ligand-binding core dimer, with the high-affinity antagonist (S)-8-methyl-5-(4-(N,N-dimethylsulfamoyl)phenyl)-6,7,8,9,-tetrahydro-1H-pyrrolo[3,2-h]-isoquinoline-2,3-dione-3-O-(4-hydroxybutyrate-2-yl)oxime [(S)-NS1209] in one protomer and the endogenous ligand (S)-glutamate in the other. (S)-NS1209 stabilises an even more open conformation of the D1 and D2 domains of the ligand-binding core than that of the apo structure due to steric hindrance. This is the first time ligand-induced hyperextension of the binding domains has been observed. (S)-NS1209 adopts a novel binding mode, including hydrogen bonding to Tyr450 and Gly451 of D1. Parts of (S)-NS1209 occupy new areas of the GluR2 ligand-binding cleft, and bind near residues that are not conserved among receptor subtypes. The affinities of (RS)-NS1209 at the GluR2 ligand-binding core as well as at GluR1-6 and mutated GluR1 and GluR3 receptors have been measured. Two distinct binding affinities were observed at the GluR3 and GluR4 receptors. In a functional in vitro assay, no difference in potency was observed between GluR2(Q)(o) and GluR3(o) receptors. The thermodynamics of binding of the antagonists (S)-NS1209, DNQX and (S)-ATPO to the GluR2 ligand-binding core have been determined by displacement isothermal titration calorimetry. The displacement of (S)-glutamate by all antagonists was shown to be driven by enthalpy.

Animals↗
PubMed2005

Total synthesis of two novel subpicomolar sarco/endoplasmatic reticulum Ca2+-ATPase inhibitors designed by an analysis of the binding site of thapsigargin.

Analysis of molecular interaction fields based on the published crystal structure of thapsigargin bound to the sarco/endoplasmatic reticulum Ca(2+)-ATPase and analysis of the volume and shape of the ligand binding site and of the SERCA-thapsigargin interactions have enabled design of two new compounds inhibiting SERCA in the subpicomolar range. The two inhibitors were synthesized using (S)-carvone as starting material and found to be 3 and 10 times more potent than thapsigargin.

Azulenes↗
PubMed2005

Biflavones from Rhus species with affinity for the GABA(A)/benzodiazepine receptor.

In South Africa Rhus pyroides is traditionally used in the treatment of epilepsy. In the present study two biflavonoids with activity in the (3)H-Ro 15-1788 (flumazenil) binding assay were isolated by high pressure liquid chromatography (HPLC) fractionation of the ethanol extract of the leaves from Rhus pyroides. The structures of the two biflavonoids were elucidated by nuclear magnetic resonance spectroscopy (NMR) to be agathisflavone and amentoflavone. Agathisflavone and amentoflavone competitively inhibited the binding of (3)H-Ro 15-1788 with a K(i) of 28 and 37 nM, respectively. Extracts of Rhus dentata and Rhus pentheri were not as active as the extract from Rhus pyroides; both were found to contain apigenin and agathisflavone. The monomer apigenin, agathisflavone and amentoflavone were fitted into a pharmacophore model for ligands binding to the GABA(A) receptor benzodiazepine site. This reflected the affinities of the compounds in the [(3)H]-flumazenil binding assay.

Animals↗
PubMed2005

Potent 4-aryl- or 4-arylalkyl-substituted 3-isoxazolol GABA(A) antagonists: synthesis, pharmacology, and molecular modeling.

We have previously described a series of competitive GABA(A) antagonists derived from the low-efficacy partial agonist 5-(4-piperidyl)-3-isoxazolol (4-PIOL, 4). The 2-naphthylmethyl analogue, 4-(2-naphthylmethyl)-5-(4-piperidyl)-3-isoxazolol (5), provided affinity for the GABA(A) receptor site higher than that of the standard GABA(A) receptor antagonist, SR 95531 (3). Molecular modeling studies of these compounds exposed a cavity at the receptor recognition site capable of accommodating aromatic groups of substantial size in the 4-position in the 3-isoxazolol ring. Here we present a series of analogues of 5, with various substituents in different positions in the naphthyl ring system (6a-k), and compounds with aromatic substituents directly attached to the 4-position of the 3-isoxazolol ring (7l-n). The compounds have been pharmacologically characterized using receptor-binding assays and electrophysiological whole-cell patch-clamp techniques. All of the tested compounds show affinity for the GABA(A) receptor site. While the 5-, 7-, and 8-bromo analogues, 6b-d, showed receptor affinities (K(i) = 45, 109, and 80 nM, respectively) comparable with that of 5 (K(i) = 49 nM), the 1-bromo analogue, 6a, provided the highest receptor affinity of the series (K(i) = 10 nM). Introduction of a series of different substituents in the 1-position in the 2-naphthyl ring system led to compounds, 6e-k, with retained high affinity for the GABA(A) receptor (K(i) = 16-250 nM). Introduction of a phenyl ring directly into the 4-position on the 3-isoxazolol ring gave a 41-fold increase in affinity relative to that of 4-PIOL. 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, 6a showing antagonist potency (IC(50) = 42 nM) markedly higher than that of 3 (IC(50) = 240 nM). Molecular modeling studies, based on the compounds described, emphasized the importance of the distal ring in 5 for receptor affinity and the considerable dimensions of the proposed receptor cavity. Furthermore, the phenyl rings in 7l and in 6k were shown to represent highly favorable positions for an aromatic ring in previously unexplored receptor regions in terms of a pharmacophore model.

Animals↗
PubMed2005

Assessment of the combined approach of N-alkylation and salt formation to enhance aqueous solubility of tertiary amines using bupivacaine as a model drug.

Quaternary prodrug types of poorly water-soluble tertiary amines have been shown to exhibit significantly enhanced solubilities as compared to the parent amine. In the present study the combined effect of N-alkylation and salt formation to enhance aqueous solubility of tertiary amines have been investigated using bupivacaine as a model compound. X-ray structure analyses of selected salts were included to investigate the potential existence of correlations between salt solubility and crystal packing modes. Alkyl groups were methyl, ethyl, propyl, and butyl and the derivatives were isolated as their iodide salts. Chloride, mesylate, formate, acetate, glycolate, and tosylate salts were obtained by anion exchange of the N-methyl-bupivacaine derivative. N-Alkylation and salt formation afforded quaternary ammonium salts possessing pH-independent aqueous solubilities far exceeding that of the parent tertiary amine (up to a factor of 3200 at pH 8). A moderate reduction in solubility with increasing length of the alkyl chain was observed for the iodide salts of the N-alkylated bupivacaine derivatives. In case of the N-methyl-bupivacaine derivative variation of the counterion had a significant impact on the solubility with the iodide salt being 200 times less soluble than the chloride salt. X-ray analysis revealed that both the alkyl substituent and the anionic counterion influenced salt packing modes, however, in an unpredictable manner making establishment of quantitative correlations between crystal packing and solubility difficult even for a series of closely related derivatives.

Alkylation↗
PubMed2004

GABA(A) agonists and partial agonists: THIP (Gaboxadol) as a non-opioid analgesic and a novel type of hypnotic.

The GABA(A) receptor system is implicated in a number of central nervous system (CNS) disorders, 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. A large number of the compounds showing agonist activity at the GABA(A) receptor site are structurally derived from the GABA(A) agonists muscimol, THIP (Gaboxadol), or isoguvacine, which we developed at the initial stage of the project. Using recombinant GABA(A) receptors, functional selectivity has been shown for a number of compounds, including THIP, showing subunit-dependent potency and maximal response. The pharmacological and clinical activities of THIP probably reflect its potent effects at extrasynaptic GABA(A) receptors insensitive to benzodiazepines and containing alpha(4)beta(3)delta subunits. The results of ongoing clinical studies on the effect of the partial GABA(A) agonist THIP on human sleep pattern show that the functional consequences of a directly acting agonist are distinctly different from those seen after administration of GABA(A) receptor modulators, such as benzodiazepines. 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 derived from THIP, have been performed. In this connection, a series of GABA(A) ligands has been developed showing pharmacological profiles ranging from low-efficacy partial GABA(A) agonist activity to selective antagonist effect.

Analgesics, Non-Narcotic↗
PubMed2004

Aqueous solubility study of salts of benzylamine derivatives and p-substituted benzoic acid derivatives using X-ray crystallographic analysis.

Twenty two p-substituted benzoic acid derivates were used to prepare salts of N-methylbenzylamine (II) and N,N-dimethylbenzylamine (III), respectively. Only five salts of (II) and two salts of (III) were obtained in a crystalline state. The solubility of these salts was orders of magnitude higher than those reported for the corresponding salts of benzylamine (I). Thermal analysis indicated that the increased solubility was caused by reduced crystal lattice energy, which was most likely due to the reduced number of strong hydrogen bonds of the salt of (II) and (III). X-ray crystallographic analysis of p-hydroxybenzoic acid salt of (I), (II) and (III) suggested that the reduced number of hydrogen bonds caused the apparent higher solubility. Further analyses of seven salts of (I) were performed. It was not possible to identify any relationship between the number of hydrogen bonds and the corresponding solubility of the salts.

Benzoates↗
PubMed2004

The use of a pharmacophore model for identification of novel ligands for the benzodiazepine binding site of the GABAA receptor.

A Catalyst pharmacophore model has been developed for the benzodiazepine site within the GABA(A) receptor complex. The model is based on a pharmacophore model originally proposed by Cook and co-workers (Drug Des. Discovery 1995, 12, 193-248) and further developed by Kahnberg et al. (J. Med. Chem. 2002, 45, 4188-4201). The Catalyst pharmacophore model has been validated by using a series of flavonoids with varying affinities for the benzodiazepine receptor and has then been used as a search query in database searching with the aim of finding novel structures which have the possibility to be modified into novel lead compounds. Five of the hits from the database searching were purchased and their affinities for the benzodiazepine site of the GABA(A) receptor were determined. Two of the compounds displayed K(i) values below 10 microM. The substance showing highest potency in-vitro displayed an affinity of 121 nM making it an interesting compound for optimization. The false positive compounds (K(i) values >10 microM affinities) have been analysed in terms of conformational energy penalties and possibilities for hydrogen bond interactions. The analysis clearly demonstrates the need for post processing of Catalyst hits.

Animals↗
PubMed2003

A stereochemical anomaly: the cyclised (R)-AMPA analogue (R)-3-hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-5-carboxylic acid [(R)-5-HPCA] resembles (S)-AMPA at glutamate receptors.

(RS)-3-Hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-5-carboxylic acid (5-HPCA)(), which is a conformationally constrained cyclised analogue of AMPA has previously been described as causing glutamate receptor mediated excitations of spontaneously firing cat spinal interneurons in a similar fashion to AMPA. We have now prepared the enantiomers of through chiral chromatographic resolution of (RS)-3-(carboxymethoxy)-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-5-carboxylic acid () followed by a stereoconservative hydrolysis resulting in the enantiomers of with high enantiomeric excess (% ee [greater-than-or-equal] 99). The absolute configurations indicated by an X-ray analysis of (-)- monohydrate were confirmed by comparing observed and ab initio calculated electronic circular dichroism spectra and by stereoconservative synthesis of (S)- from (S)-AMPA, the pharmacologically active form of AMPA. The pharmacological effects at native and cloned (GluR1-4) AMPA receptors were shown to reside exclusively with (R)-(+)-, in striking contrast to the usual stereoselectivity trend among AMPA receptor agonists. The reasons for this anomalous behaviour became clear upon docking both enantiomers of to the agonist binding site of GluR2.

2-Amino-5-phosphonovalerate↗
PubMed2003

Design, synthesis, and pharmacology of a highly subtype-selective GluR1/2 agonist, (RS)-2-amino-3-(4-chloro-3-hydroxy-5-isoxazolyl)propionic acid (Cl-HIBO).

On the basis of structural studies, chloro-homoibotenic acid (Cl-HIBO) was designed and synthesized. Cl-HIBO was characterized in binding and electrophysiology experiments on native and cloned subtypes of GluRs. Electrophysiological selectivities ranged from 275 to 1600 for GluR1/2 over GluR3/4. The potent AMPA receptor activity was strongly desensitizing and the neurotoxicity similar to AMPA. Thus, Cl-HIBO is the most subtype selective agonist reported to date on GluR1/2, and offers a new standard for selectively studying subtypes of AMPA receptors.

Animals↗
PubMed2003

Synthesis and structure-affinity relationship investigations of 5-aminomethyl and 5-carbamoyl analogues of the antipsychotic sertindole. A new class of selective alpha1 adrenoceptor antagonists.

A new class of selective alpha(1) adrenoceptor antagonists derived from the antipsychotic drug sertindole is described. The most potent and selective compound 1-(2-(4-[5-aminomethyl-1-(4-fluorophenyl)-1H-indol-3-yl]-1-piperidinyl)ethyl)-2-imidazolidinone (11) binds with 0.50 nM affinity for alpha(1) adrenergic receptors and with more than 44 times lower affinity for dopamine D(2),D(3), D(4) and serotonin 5-HT(1A), 5-HT(1B), 5-HT(2A) and 5-HT(2C) receptors. The molecular features providing high affinity for adrenergic alpha(1) receptors and high selectivity towards dopamine D(2) and serotonin 5-HT(2A) and 5-HT(2C) receptors are discussed.

Adrenergic alpha-1 Receptor Agonists↗