Inositol monophosphatase--a putative target for Li+ in the treatment of bipolar disorder.

Attenuation of the phosphatidylinositol (PI) signal transduction pathway as a consequence of inhibition of inositol monophosphatase (IMPase) has been proposed as the mechanism for the efficacy of Li+ in the treatment of bipolar disorder. Nevertheless, Li+ also affects other aspects of PI signal transduction, and it is therefore not clear whether modulation of PI responses by Li+ can be attributed solely to inhibition of IMPase. However, inhibitors of IMPase mimic the effects of Li+ on some aspects of PI cell signalling, thus highlighting the potential of IMPase as a target for the treatment of bipolar disorder. The recent description of the three-dimensional structure of IMPase in conjunction with site-directed mutagenesis and kinetic studies has led to the elucidation of the enzyme mechanism. These structural and mechanistic data should prove useful in the development of novel inhibitors of IMPase that might ultimately prove useful clinically.

Molecular modeling.

The past year has seen a maturation of molecular modeling, with an increasing number of comparative studies between established methods becoming possible, together with an explosion of new work especially in the areas of combinatorial chemistry and molecular diversity. Traditionally 'difficult' areas such as modeling oligosaccharides look set to join the mainstream in the next few years.

Structure and mechanism of inositol monophosphatase.

Since lithium inhibits IMPase and modulates phosphatidylinositol (PtdIns) cell signalling at therapeutically relevant concentrations (0.5-1.0 mM), IMPase has attracted attention as a putative molecular target for lithium in the treatment of manic depression. IMPase is a homodimer, with each subunit organised in an alpha beta alpha beta alpha arrangement of alpha-helices and beta-sheets, and this type of structure seems crucial to the two-metal catalysed mechanism in which an activated water molecule serves as a nucleophile. Lithium appears to inhibit the enzyme following substrate hydrolysis by occupying the second metal binding site before the phosphate group can dissociate from its interaction with the site 1 metal. The understanding of IMPase structure and the mechanism of substrate hydrolysis and lithium inhibition should be useful in the development of novel inhibitors which may prove clinically useful in the treatment of manic depression.

N-Arylsulfonylindole derivatives as serotonin 5-HT(6) receptor ligands.

A series of N(1)-arylsulfonyltryptamines were found to be potent ligands of the human serotonin 5-HT(6) receptor with the 5-methoxy-1-benzenesulfonyl analogue (19) having the highest affinity. Additionally, it was discovered that a group such as 3-(3-methoxybenzyl)-1,2,4-oxadiazol-5-yl in the 2-position of the indole ring (43) can replace the arylsulfonyl substituent in the 1-position with no loss of affinity. This suggested that the binding conformation of the aminoethyl side chain at this receptor was toward the 4-position of the indole ring and was supported by the fact that the 4-(aminoethyl)indoles (45) also displayed high affinity, as did the conformationally rigid 1,3,4,5-tetrahydrobenz[c,d]indole (49). Molecular modeling showed that 19, 43, and 45 all had low-energy conformers that overlaid well onto 49. Both 19 and 49 had good selectivity over other serotonin receptors tested, with 49 also showing excellent selectivity over all dopamine receptors. In a functional adenylate cyclase stimulation assay, 19 and 49 had no agonist activity, whereas 45 behaved as a partial agonist. Finally, it was shown that 19 had good activity in the 5-HT(2A) centrally mediated mescaline-induced head twitch assay, which implies that it is brain-penetrant.

4-Heterocyclylpiperidines as selective high-affinity ligands at the human dopamine D4 receptor.

5-(4-Chlorophenyl)-3-(1-(4-chlorobenzyl)piperidin-4-yl)pyrazole (3) was identified from screening of the Merck sample collection as a human dopamine D4 (hD4) receptor ligand with moderate affinity (61 nM) and 4-fold selectivity over human D2 (hD2) receptors. Four separate parts of the molecule have been examined systematically to explore structure-activity relationships with respect to hD4 affinity and selectivity over other dopamine receptors. It was found that the 4-chlorophenyl group attached to the pyrazole is optimal, as is the 4-substituted piperidine. The lipophilic group on the basic nitrogen is more amenable to change, with the optimal group found to be a phenethyl. The aromatic heterocyle can be altered to a number of different groups, with isoxazoles and pyrimidines showing improved affinities. This heterocycle can also be advantageously alkylated, improving the selectivity of the compounds over D2 receptors. It is hypothesized that the conformation around the bond joining the aromatic heterocycle to the piperidine is important for D4 affinity, based on crystal structures of isoxazoles (29 and 30) and on a conformationally constrained compound (28). Putting all the favorable changes together led to the discovery that 5-(4-chlorophenyl)-4-methyl-3-(1-(2-phenylethyl)piperidin-4-yl)iso xazole (36) is a nanomolar antagonist at human dopamine D4 receptors with > 500-fold selectivity over hD2 and > 200-fold selectivity over hD3. Compound 36 is an antagonist of hD4 receptors with good oral bioavailability of 38%, a half life of 2 h, and brain levels 10-fold higher than plasma levels.

5-(Piperidin-2-yl)- and 5-(homopiperidin-2-yl)-1,4-benzodiazepines: high-affinity, basic ligands for the cholecystokinin-B receptor.

The design, synthesis, and biological activity of a series of high-affinity, basic ligands for the cholecystokinin-B receptor are described. The compounds, which incorporate a piperidin-2-yl or a homopiperidin-2-yl group attached to C5 of a benzodiazepine core structure, are substantially more basic (e.g., 9d, pKa = 9.48) than previously reported antagonists based on 5-amino-1,4-benzodiazepines (e.g., 5, pKa = 7.1) and have improved aqueous solubility. In view of their basicity, it would be tempting to speculate that the present series of compounds might be binding to the CCK-B receptor in their protonated form. Compounds such as 9d, e and 10d showed high affinity for this receptor (IC50 < 2.5 nM) and very good selectivity over CCK-A (CCK-A/CCK-B > 2000), even as the racemates. Additionally, a significantly improved in vivo half-life was observed for a selection of compounds compared to the clinical candidate L-365, -260 (1).

New selective cytotoxic diterpenylquinones and diterpenylhydroquinones.

A new series of diterpenylquinone/hydroquinones has been prepared by Diels-Alder cycloaddition between three labdanic diterpenoids (myrceocommunic acid, methyl myrceocommunate, and myrceocommunyl acetate) and p-benzoquinone or 1,4-naphthoquinone. Influences of the quinone/hydroquinone fragment and other structural features, such as the different functionalities in the terpenic core, are considered in relation to the cytotoxicity toward neoplastic cells and the selectivity of these diterpenylnaphthoquinones/hydroquinones and anthraquinones. Several compounds showed IC50 values under the micromolar level, and four of these derivatives were evaluated at the NCI screening panel. The results showed an important selectivity toward renal cancer lines, identifying these compounds as a very promising group of antineoplastics.

3-[3-(Piperidin-1-yl)propyl]indoles as highly selective h5-HT(1D) receptor agonists.

Several 5-HT(1D/1B) receptor agonists are now entering the marketplace as treatments for migraine. This paper describes the development of selective h5-HT(1D) receptor agonists as potential antimigraine agents which may produce fewer side effects. A series of 3-[3-(piperidin-1-yl)propyl]indoles has been synthesized which has led to the identification of 80 (L-772,405), a high-affinity h5-HT(1D) receptor full agonist having 170-fold selectivity for h5-HT(1D) receptors over h5-HT(1B) receptors. L-772,405 also shows very good selectivity over a range of other serotonin and nonserotonin receptors and has excellent bioavailability following subcutaneous administration in rats. It therefore constitutes a valuable tool to delineate the role of h5-HT(1D) receptors in migraine. Molecular modeling and physical properties have been utilized to postulate the binding conformation of these compounds in the receptor cavity.

Controlled modification of acidity in cholecystokinin B receptor antagonists: N-(1,4-benzodiazepin-3-yl)-N'-[3-(tetrazol-5-ylamino) phenyl]ureas.

The design, synthesis, and biological activity of a novel series of CCK-B receptor antagonists (1) which incorporate a tetrazol-5-ylamino functionality attached to the phenyl ring of the arylurea moiety of L-365,260 are described. In these compounds, the acidity of the tetrazole was gradually modified by utilization of simple conformational constraints, and X-ray crystallographic data were obtained to support the conformational depenence of the pK(a) of the aminotetrazoles. Compounds to emerge from the present work such as 1f and 2c,d are among the highest affinity and, in the case of 1f, most selective (CCK-A/CCK-B, 37 000) antagonists so far reported for this receptor. The C(5)-cyclohexyl compound 2c (L-736,380) dose-dependently inhibited gastric acid secretion in anesthetized rats (ID(50), 0.064 mg/kg) and ex vivo binding of [(125)I]CCK-8S in BKTO mice brain membranes (ED(50), 1.7 mg/kg) and is one of the most potent acidic CCK-B receptor antagonists yet described.

Development of peptide 3D structure mimetics: rational design of novel peptoid cholecystokinin receptor antagonists.

The two hormones cholecystokinin and gastrin share the same C-terminal sequence of amino acids, namely Gly(29)-Trp(30)-Met(31)-Asp(32)-Phe(33)-NH(2). Nevertheless, this congruence has not precluded using this structure to develop selective ligands for either CCK(1) or CCK(2) receptors. Manipulation of the hydrophobic residues at positions 31 and 33 gave a series of CCK(1) tripeptide antagonists, typified by N-t-BOC-Trp-2-Nal-Asp-2-(phenyl)ethylamide (pK(B) 6.8 +/- 0.3). Molecular modeling was used to identify the bioactive conformation of these CCK(1)-selective compounds and prompted the design of new peptoid structures. We aimed to maintain the conformation of the parent series by exploiting patterns of hydrogen-bonding and pi-stacking interactions present in the original molecule, rather than introducing additional covalent bonds. The prototype, N-(succinyl-D-Asp-2-phenylethylamido)-L-Trp-2-(2-naphthyl)ethylami de, was a potent and selective CCK(1) antagonist (pK(B) 7.2 +/- 0.3). Furthermore, the new series showed patterns of biological activity that mirrored those of the parent tripeptides. These compounds contain elements of both peptide primary and secondary structure and represent a novel approach to designing peptidomimetics. Interesting results were obtained from comparing models of a representative tripeptide CCK(1) antagonist with a conformation of CCK(30)(-)(33) that others have proposed to be responsible for its activity at the CCK(2) receptor. The results suggest that CCK(1) and CCK(2) receptors recognize enatiomeric dispositions of the Trp(30) indole, Asp(32) carboxylic acid, and C-terminal phenyl groups arrayed about a common backbone configuration. This "functional chirality" may underpin the mechanism by which these closely related receptor systems bind CCK(30)(-)(33) and explain patterns of selectivity observed with optical isomers of a number of peptoid and nonpeptide ligands.

Fluorination of 3-(3-(piperidin-1-yl)propyl)indoles and 3-(3-(piperazin-1-yl)propyl)indoles gives selective human 5-HT1D receptor ligands with improved pharmacokinetic profiles.

It has previously been reported that a 3-(3-(piperazin-1-yl)propyl)indole series of 5-HT1D receptor ligands have pharmacokinetic advantages over the corresponding 3-(3-(piperidin-1-yl)propyl)indole series and that the reduced pKa of the piperazines compared to the piperidines may be one possible explanation for these differences. To investigate this proposal we have developed versatile synthetic strategies for the incorporation of fluorine into these ligands, producing novel series of 4-fluoropiperidines, 3-fluoro-4-aminopiperidines, and both piperazine and piperidine derivatives with one or two fluorines in the propyl linker. Ligands were identified which maintained high affinity and selectivity for the 5-HT1D receptor and showed agonist efficacy in vitro. The incorporation of fluorine was found to significantly reduce the pKa of the compounds, and this reduction of basicity was shown to have a dramatic, beneficial influence on oral absorption, although the effect on oral bioavailability could not always be accurately predicted.

Structural studies on phospholamban and implications for regulation of the Ca(2+)-ATPase.

The cardiac sarcoplasmic reticulum (SR) protein phospholamban (PLB) is an endogenous inhibitor of the SR Ca(2+)-ATPase. Phosphorylation of PLB relieves this inhibition and up-regulates calcium transport. PLB has proved remarkably difficult to study by conventional solution-state nuclear magnetic resonance (NMR) methods, due primarily to the extreme hydrophobic nature of the protein and its propensity to form pentamers. That the C-terminal domain of PLB is helical and membrane spanning is now well established; the structure of the cytoplasmic domain is relatively ill defined. In order to discern the effect of phosphorylation on the structure of the cytoplasmic domain, we have characterized a variety of model peptides in several structure-inducing and/or lipid-mimicking environments using circular dichroism and solution-state NMR. The resolution of peptide structures obtained in aqueous trifluoroethanol was markedly improved by the incorporation of 15N labels into the peptide backbone, allowing a variety of isotope edited, filtered, and resolved techniques to be applied. Molecular dynamics simulations on the full-length protein were combined with an analysis of published data to suggest a revised model for the structure of PLB.

A method for including protein flexibility in protein-ligand docking: improving tools for database mining and virtual screening.

Second-generation methods for docking ligands into their biological receptors, such as FLOG, provide for flexibility of the ligand but not of the receptor. Molecular dynamics based methods, such as free energy perturbation, account for flexibility, solvent effects, etc., but are very time consuming. We combined the use of statistical analysis of conformational samples from short-run protein molecular dynamics with grid-based docking protocols and demonstrated improved performance in two test cases. Our statistical analysis explores the importance of the average strength of a potential interaction with the biological target and optionally applies a weighting depending on the variability in the strength of the interaction seen during dynamics simulation. Using these methods, we improved the num-top-ranked 10% of a database of drug-like molecules, in searches based on the three-dimensional structure of the protein. These methods are able to match the ability of manual docking to assess likely inactivity on steric grounds and indeed to rank order ligands from a homologous series of cyclooxygenase-2 inhibitors with good correlation to their true activity. Furthermore, these methods reduce the need for human intervention in setting up molecular docking experiments.

Social security benefits [continuing nursing education].

There is a wide range of benefits available for patients, clients and carers, and, in April this year two new benefits for disabled people were introduced together with new ways of claiming them. Is a knowledge of benefits necessary for a few nurse specialists only, or is it an integral part of professional practice for all?

Interventions at caesarean section for reducing the risk of aspiration pneumonitis.

BACKGROUND: Various interventions are used as prophylaxis for aspiration pneumonitis in obstetric anaesthesia. This review, based on a Cochrane systematic review currently being updated, examines whether interventions given before caesarean section reduce the risk of aspiration pneumonitis. METHODS: Twenty-two studies, involving 2658 women providing data in a usable format for meta-analysis were identified. RESULTS: Compared to no treatment or placebo, there was a significant reduction in the risk of intra-gastric pH <2.5 with antacids (risk ratio (RR) 0.17, 95% confidence interval (CI) 0.09-0.32), H2 antagonists (RR 0.09, 95% CI 0.05-0.18) and proton-pump antagonists (RR 0.26, 95% CI 0.14-0.46). H2 antagonists were associated with a reduced risk of intra-gastric pH <2.5 when compared with proton-pump antagonists (RR 0.39, 95% CI 0.16-0.97), but compared with antacids the findings were unclear. Combined use of antacids plus H2 antagonists was associated with a significant reduction in the risk of intra-gastric pH <2.5 when compared with placebo (RR 0.02, 95% CI 0.00-0.15) or compared with antacids alone (RR 0.12, 95% CI 0.02-0.92). CONCLUSION: The quality of evidence was weak and may not reflect a reduction in the risk of aspiration pneumonitis since none of the studies assessed substantive clinical outcomes or potential adverse effects. Further work is required to validate the suitability of surrogate markers of pH and gastric volume for clinical outcomes in the context of aspiration pneumonitis.