Synthesis, screening, and molecular modeling of new potent and selective antagonists at the alpha 1d adrenergic receptor.

In the present study, more than 75 compounds structurally related to BMY 7378 have been designed and synthesized. Structural variations of each part of the reference molecule have been introduced, obtaining highly selective ligands for the alpha(1d) adrenergic receptor. The molecular determinants for selectivity at this receptor are essentially held by the phenyl substituent in the phenylpiperazine moiety. The integration of an extensive SAR analysis with docking simulations using the rhodopsin-based models of the three alpha(1)-AR subtypes and of the 5-HT(1A) receptor provides significant insights into the characterization of the receptor binding sites as well as into the molecular determinants of ligand selectivity at the alpha(1d)-AR and the 5-HT(1A) receptors. The results of multiple copies simultaneous search (MCSS) on the substituted phenylpiperazines together with those of manual docking of compounds BMY 7378 and 69 into the putative binding sites of the alpha(1a)-AR, alpha(1b)-AR, alpha(1d)-AR, and the 5-HT(1A) receptors suggest that the phenylpiperazine moiety would dock into a site formed by amino acids in helices 3, 4, 5, 6 and extracellular loop 2 (E2), whereas the spirocyclic ring of the ligand docks into a site formed by amino acids of helices 1, 2, 3, and 7. This docking mode is consistent with the SAR data produced in this work. Furthermore, the binding site of the imide moiety does not allow for the simultaneous involvement of the two carbonyl oxygen atoms in H-bonding interactions, consistent with the SAR data, in particular with the results obtained with the lactam derivative 128. The results of docking simulations also suggest that the second and third extracellular loops may act as selectivity filters for the substituted phenylpiperazines. The most potent and selective compounds for alpha(1d) adrenergic receptor, i.e., 69 (Rec 26D/038) and 128 (Rec 26D/073), are characterized by the presence of the 2,5-dichlorophenylpiperazine moiety.

6-Chloropyridazin-3-yl derivatives active as nicotinic agents: synthesis, binding, and modeling studies.

3,8-Diazabicyclo[3.2.1]octane (1), 2,5-diazabicyclo[2.2.1]heptane (2), piperazine (3), and homopiperazine (4) derivatives, substituted at one nitrogen atom with the 6-chloro-3-pyridazinyl group while the other nitrogen atom was either unsubstituted or mono- or dimethylated, were synthesized and tested for their affinity toward the neuronal nicotinic acetylcholine receptors (nAChRs). All of the compounds had K(i) values in the nanomolar range. A molecular modeling study allowed location of their preferred conformations, the energies of which were recalculated in water with a continuum solvent model. Some of the compounds showed, in their populated conformations, only pharmacophoric distances longer than the values taken into consideration by the Sheridan model for nAChRs receptors. Thus, this SAR study gives support to the hypothesis that these longer distances are still compatible with affinity for alpha4beta2 receptors in the nanomolar range.

Central effects of 1,4-butanediol are mediated by GABA(B) receptors via its conversion into gamma-hydroxybutyric acid.

The aliphatic alcohol 1,4-butanediol in converted into gamma-hydroxybutyric acid (GHB) via two enzymatic steps: first, it is oxidised by alcohol dehydrogenase in gamma-hydroxybutyraldehyde; second, the latter is transformed, likely by aldehyde dehydrogenase, into GHB. Initially, the present study compared the sedative/hypnotic effect of GHB and 1,4-butanediol, measured as loss of righting reflex. 1,4-Butanediol was more potent than GHB, presumably because of a more rapid penetration of the blood brain barrier. Further alcohol dehydrogenase inhibitors, 4-methylpyrazole and ethanol, totally prevented the sedative/hypnotic effect of 1,4-butanediol; the aldehyde dehydrogenase inhibitor disulfiram partially blocked the sedative/hypnotic effect of 1,4-butanediol. Finally, the sedative/hypnotic effect of 1,4-butanediol was antagonised by the GABA(B) receptor antagonists, SCH 50911 [(2S)(+)-5,5-dimethyl-2-morpholineacetic acid] and CGP 46381 [(3-aminopropyl)(cyclohexylmethyl)phosphinic acid], but not by the putative GHB receptor antagonist NCS-382 (6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid), indicating that it is mediated by GABA(B) but not GHB receptors. Taken together, these results suggest that the sedative/hypnotic effect of 1,4-butanediol is mediated by its conversion in vivo into GHB which, in turn, binds to GABA(B) receptors. Accordingly 1,4-butanediol, unlike GHB, failed to displace [(3)H]GHB and [(3)H]baclofen in brain membranes.

Stereoselectivity of NCS-382 binding to gamma-hydroxybutyrate receptor in the rat brain.

gamma-Hydroxybutyric acid (GHB), a naturally occurring metabolite of gamma-aminobutyric acid (GABA), has been postulated to act both as a specific agonist of GHB receptors and as a weak GABA(B) receptor agonist. The racemic compound 6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (RS-NCS-382), the only available antagonist of GHB receptors, has been resolved in two enantiomers, R- and S-; the potency of the latter to displace 4-hydroxy [2-3-(3)H] butyric acid ([(3)H]GHB) and [(3)H]NCS-382 from GHB receptors, on one hand, and [(3)H]baclofen from GABA(B) receptors on the other was compared in rat brain homogenates. R-NCS-382 was found to be twice and 60 times more potent than the RS- and S-forms, respectively, in displacing [(3)H]GHB and 2 and 14 times, respectively, in displacing [(3)H]NCS-382 from GHB binding. Neither RS-NCS-382 nor its enantiomers inhibited [(3)H]baclofen binding up to a concentration of 1 mM. Our results demonstrate that R-NCS-382 is the enantiomer of RS-NCS-382 with higher affinity for GHB receptors.

Congo red analogues as potential anti-prion agents.

'Transmissible Spongiform Encephalopathies' (TSE) are a group of degenerative, progressive and fatal disorders of CNS which affect both humans and animals, characterised by a long incubation time. The pathogenetic mechanism in TSE is the conversion of normal prion protein (PrP(sen)) to an altered protease resistant isoform (PrP(res)) that accumulates in amyloid deposits into the brain; therefore, PrP(res) is the primary target for therapeutic strategies. The discovery that the sulphonated azo dye Congo red (CR) is able to inhibit the replications of TSE agents and the accumulation of PrP(res) in animals and in scrapie infected mouse neuroblastoma cells induced us to designe molecules structurally related to CR (1a-f, 2f,g). The compounds were tested in vitro to evaluate their interaction with 263K PrP(res). Six of the tested compounds were found to interact with PrP(res) molecules and to over-stabilise the PrP(res) aggregates, as CR does. However, none of them induced the reversion of PrP(res) to PrP(sen).

Synthesis, modelling, and antimitotic properties of tricyclic systems characterised by a 2-(5-Phenyl-1H-pyrrol-3-yl)-1,3,4-oxadiazole moiety.

Antitumour activity was observed in a series of tricyclic compounds characterised by a 2-(1H-pyrrol-3-yl)-1,3,4-oxadiazole moiety with various substitutions. Their synthesis and antiproliferative activity toward a panel of human tumour cell lines is described. The most interesting compounds 1 c and 4 c were selected for further evaluation to elucidate their possible mechanism of action.Interesting antitumour activity was observed in a series of tricyclic compounds characterised by the presence of a 2-(1H-pyrrol-3-yl)-1,3,4-oxadiazole moiety that is variously substituted. Their synthesis and antiproliferative activity toward a panel of human tumour cell lines is described. The two most interesting compounds were selected for further evaluation to elucidate their possible mechanism of action. Analysis of cell cycle, tubulin polymerisation, modulation of mitotic markers of the M phase, and apoptosis showed that antimitotic activity is the primary mechanism of the cytotoxic effects of these compounds. Experiments performed on isolated tubulin confirmed that the compounds act by inducing tubulin polymerisation, like taxanes. The binding model against tubulin was also examined by molecular modelling and docking. The results support the proposed binding model, which is able to explain the activity of the oxadiazole derivatives on the basis of their docking energy.

Synthesis of 3,6-diazabicyclo[3.1.1]heptanes as novel ligands for the opioid receptors.

In an effort to improve diazabicycloalkane-based opioid receptor ligands, N-3(6)-arylpropenyl-N-6(3)-propionyl-3,6-diazabicyclo[3.1.1]heptanes (3A,Ba-i) were synthesized and their affinity and selectivity towards mu-, delta- and kappa-receptors were evaluated. The results of the current study revealed a number of compounds (3Bb, 3Bg and 3Bh) having a high affinity for mu (Ki at mu-receptors ranging from 2.7 to 7.9 nM) versus delta (Ki at delta-receptors > 2000 nM) and versus kappa (Ki at kappa-receptors > 5000 nM) receptors. Molecular modelling carried out on the pair 3Aa/3Ba and on the 3Bh was consistent with the hypothesis that the two series of compounds 3A and 3B interact with the mu-receptor in very different ways.

Synthesis and cytotoxic activities of pyrrole[2,3-d]pyridazin-4-one derivatives.

1-Methyl-2-phenyl (1) and 1,3-dimethyl-2-phenyl (2)-substituted pyrrole[2,3-d]pyridazinones, as well as their tetracyclic analogues 3-6, were synthesized and evaluated in vitro by the National Cancer Institute against 60 human tumor cell lines derived from nine cancer cell types. Biological results showed that the antitumor activities of these compounds were related to the planarity of their ring systems with potency increasing in the order 2<4 congruent with 5<6<3. Among them, the most potent compound 3 showed significant cell line cytotoxicity, particularly against the renal cancer subpanel [GI(50) (microM) 5.07] and displayed significant potency [GI(50) (microM) 3.04-4.32] against MOLT-4, SR (leukemia), NCI-H460 (non-small cell lung), HCT-116 (colon), and SF-295 (CNS) cancer cells, respectively.

N-3(9)-arylpropenyl-N-9(3)-propionyl-3,9-diazabicyclo[3.3.1]nonanes as mu-opioid receptor agonists. Effects on mu-affinity of arylalkenyl chain modifications.

Two series of N-3-arylpropenyl-N-9-propionyl-3,9-diazabicyclo[3.3.1]nonanes (1b-j) and of the reverted N-3-propionyl-N-9-arylpropenyl isomers (2b-j) as analogues of the previously reported analgesic N-3(9)-cinnamyl-N-9(3)-propionyl-3,9-diazabicyclo[3.3.1]nonanes (DBN) (1a, 2a) were synthesised and their affinity and selectivity towards opioid mu-, delta- and kappa-receptors were evaluated. Several compounds (1e,i,j-2d,e,f,g,j) exhibited a mu-affinity in the low nanomolar range with moderate or negligible affinity towards delta- and kappa-receptors. The representative term N-9-(3,3-diphenylprop-2-enyl)-N-3-propionyl-DBN (2d) displayed in vivo (mouse) a potent analgesic effect (ED(50) 3.88 mg/kg ip) which favourably compared with that of morphine (ED(50) 5 mg/kg ip). In addition, 2d produced in mice tolerance after a period twice as long with morphine.

Selective gamma-hydroxybutyric acid receptor ligands increase extracellular glutamate in the hippocampus, but fail to activate G protein and to produce the sedative/hypnotic effect of gamma-hydroxybutyric acid.

Two gamma-hydroxybutyric acid (GHB) analogues, trans-gamma-hydroxycrotonic acid (t-HCA) and gamma-(p-methoxybenzyl)-gamma-hydroxybutyric acid (NCS-435) displaced [3H]GHB from GHB receptors with the same affinity as GHB but, unlike GHB, failed to displace [3H]baclofen from GABAB receptors. The effect of the GHB analogues, GHB and baclofen, on G protein activity and hippocampal extracellular glutamate levels was compared. While GHB and baclofen stimulated 5'-O-(3-[35S]thiotriphospate) [35S]GTPgammaS binding both in cortex homogenate and cortical slices, t-HCA and NCS-435 were ineffective up to 1 mm concentration. GHB and baclofen effect was suppressed by the GABAB antagonist CGP 35348 but not by the GHB receptor antagonist NCS-382. Perfused into rat hippocampus, 500 nm and 1 mm GHB increased and decreased extracellular glutamate levels, respectively. GHB stimulation was suppressed by NCS-382, while GHB inhibition by CGP 35348. t-HCA and NCS-435 (0.1-1000 microm) locally perfused into hippocampus increased extracellular glutamate; this effect was inhibited by NCS-382 (10 microm) but not by CGP 35348 (500 microm). The results indicate that GHB-induced G protein activation and reduction of glutamate levels are GABAB-mediated effects, while the increase of glutamate levels is a GHB-mediated effect. Neither t-HCA nor NCS-435 reproduced GHB sedative/hypnotic effect in mice, confirming that this effect is GABAB-mediated. The GHB analogues constitute important tools for understanding the physiological role of endogenous GHB and its receptor.

Synthesis of novel diazatricyclodecanes (DTDs). Effects of structural variation at the C3' allyl end and at the phenyl ring of the cinnamyl chain on mu-receptor affinity and opioid antinociception.

Two series of analogues of 9-propionyl-10-cinnamyl-9,10-diazatricyclo[4.2.1.1(2,5)]decane (1a) and 2-propionyl-7-cinnamyl-2,7-diazatricyclo[4.4.0.0(3,8)]decane (2a), in which the cinnamyl moiety was replaced by various aralkenyl chains, 1b-l and 2b-l, respectively, have been synthesized and evaluated for their ability to bind to the opioid mu-, delta- and kappa-receptors. The binding data indicated that compounds 1b,d,e,h and 2b,d,e,f,h,i showed a mu-affinity in the low nanomolar range with moderate or negligible affinity towards delta- and kappa-receptors. Selected DTDs, the pairs 1,2b, 1,2e and 1,2h, were also evaluated for analgesic effect. In the hot plate test, only 1b given ip was found to have similar opioid antinociception and chronic tolerance as morphine.