Monique Mathé-Allainmat

Effects of WAY 100635 and (−)-5-Me-8-OH-DPAT, a novel 5-HT1A receptor antagonist, on 8-OH-DPAT responses

The neurochemical profile at both post and presynaptic 5-HT1A receptors of a novel 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) analog, 5-methyl-8-hydroxy-2-(di-n-propylamino)tetralin ¿(+/-)-5-Me-8-OH-DPAT¿ and its stereoisomers was determined and compared to that of the highly selective 5-HT1A receptor antagonist, N-[4-(2-methoxyphenyl)-1-piperazinyl]-N-(2-pyridinyl) cyclo-hexanecarboxamide (WAY 100635). We evaluated their effects on 8-OH-DPAT-induced decrease in cAMP production, on 8-OH-DPAT-induced decrease in rat ventral hippocampal extracellular 5-hydroxytryptamine (5-HText) levels and in body temperature in mice. Both (+/-)- and (-)-5-Me-8-OH-DPAT blocked the 8-OH-DPAT-induced inhibition of forskolin-stimulated cAMP production. Moreover, while having no significant effect when injected alone, (+/-)-, (-)-5-Me-8-OH-DPAT and WAY 100635 antagonized the 8-OH-DPAT-induced decrease in 5-HText in rats and hypothermia in mice. By contrast, the (+) isomer inhibited the cAMP synthesis and did not modify the 8-OH-DPAT response on 5-HText in ventral hippocampus. These data suggest that (+/-)-5-Me-8-OH-DPAT acts selectively, its activity residing in the (-) enantiomer, this latter compound acting similarly to WAY 100635 as a full, selective and silent 5-HT1A antagonist.

Recent developments in melatonin receptor ligands

In recent years, many physiological properties of melatonin have been described resulting in much interest in the development of synthetic compounds possessing agonist or antagonist properties for melatonin receptors. These compounds have structural similarity to melatonin, being derivatives of either substituted tryptamines or of bioisosteric moieties of the indole ring such as benzothiophene, indene and naphthalene. Research to determine the structural parameters of the melatonergic pharmacophore led to the synthesis of potent constrained, polycyclic compounds. The important roles of substitutions on the 2 position of the indole ring and of the alkyl chain of the acyl group have been highlighted. The ethylamido chain seems to prefer the flexible conformation and a folded conformer has been shown to be the active conformation. Almost all of the compounds described have been patented. They have been claimed to be useful for the treatment of depression, sleep disorders and disturbances of circadian rhythm....

Serum Albumin-Catalyzed Trigger System by Using a Tandem Kemp Elimination/β-Elimination Reaction

The serum albumins are the most abundant proteins in blood serum and act as transport proteins for chemically diverse molecules, including long-chain fatty acids, amino acids, and steroids. The principal regions of ligand binding are located in hydrophobic cavities, which have been identified in some detail in recent crystal structures. 3] Human serum albumin (HSA) is also of pharmaceutical interest as a carrier for numerous drug molecules. Binding to HSA controls the free, active concentration of a drug, providing a reservoir for a long duration of action. In addition to its unique binding properties, several weak catalytic activities have been detected for bovine serum albumin (BSA) and HSA, such as esterase-like activity, Kemp elimination catalysis, 7] decomposition of a Meisenheimer complex, and, more recently, catalysis of S-nitrosothiol formation. Except for this last activity, the physiological significance of these catalytic properties has not been demonstrated. This albumin polyreactivity seems to be correlated to the basic active-site features of apolar pockets that can target several classes of hydrophobic substrates and act as a primitive active sites, thus allowing these promiscuous activities to take place. The IIA binding site of HSA consists of a hydrophobic pocket surrounding a reactive lysine. 2] This site has been shown to catalyze the so-called Kemp elimination reaction in which the substrate 5-nitrobenzisoxazole decomposes into a cyanophenol compound. 7] A lysine side chain, Lys222 in BSA and the homologous Lys199 in HSA, is thought to act as the catalytic base and trigger the reaction by abstracting the acid proton of the isoxazole cycle of the substrate. This “model” reaction was used to study the relative contribution of the medium effect due to the protein hydrophobic sites and general base catalysis in various proteins, including catalytic antibodies. However, the potential of the benzisoxazole system as a protecting group was only exploited once by the Kemp group. Here, we report the design of a new protective group that can be removed in vitro by using albumin as a natural catalyst. This approach is based on the catalysis of a reaction cascade that involves the opening of an isoxazole ring followed by a belimination reaction (Scheme 1). We show that this tandem reaction is efficiently catalyzed by BSA and HSA and could have a general applicability in a prodrug-activating strategy.

Structure-activity relationships for substrates and inhibitors of pineal 5-hydroxytryptamine-N-acetyltransferase: preliminary studies

Tryptamine, (1-naphthyl)ethylamine and phenethylamine derivatives were tested as substrates of ovine pineal serotonin-N-acetyl transferase (5-HT-NAT), a key enzyme involved in the synthesis of melatonin. Almost all of the indole derivatives possessed affinity similar to that of tryptamine (Km = 0.05 mM), while the substituted naphthalene and phenyl derivatives were less potent. However, the Km values seem be influenced by the steric hindrance and polar properties of the substituent. Vmax values for the naphthyl and phenyl derivatives were generally 10-20-fold higher than those of the indole derivatives and no clear structure-activity relationship was observed. Melatonin and several bioisosteric derivatives were shown to be inhibitors of 5-HT-N-acetyltransferase. Preliminary data suggested that over the 5-50-microM concentration range, melatonin was a competitive inhibitor (IC50 = 10 microM) with a concentration-dependent inhibitory effect on its own synthesis in the pineal gland. However, the bioisosteric naphthalene derivatives were characterized instead as mixed inhibitors. (1-Napthyl)ethylacetamido, a putative melatoninergic antagonist, was also shown to be an inhibitor of 5-HT-N-acetyltransferase (IC50 = 8 microM) and is a promising tool for the regulation of melatonin synthesis and the understanding of its role.

N-chloromethyl quinuclidinium derivatives : a new class of irreversible ligands for 5-HT3 receptors

Abstract The quinuclidine ring of potent 5-HT3 receptor antagonists such as zacopride and the 1,8-naphthalimide derivatives 3 reacts with methylene chloride at room temperature to produce the corresponding chloromethyl quaternary derivatives. The compounds derived from (S)-zacopride and (R)-3 are potent ligands for 5-HT3 receptor as evaluated in binding assays. Incubated with entorhinal cortex membranes, they produced a dose-dependent decrease in the Bmax value for [3H]-BRL-43694 which was inhibited by zacopride or GR 38032F. The quaternary derivative of (R)-3 is a promising tool for studying 5-HT3 receptors due to its high affinity and fluorescent properties.

Synthesis of new N-(arylcyclopropyl)acetamides and N-(arylvinyl)acetamides as conformationally-restricted ligands for melatonin receptors

N-(Arylcyclopropyl)acetamides and N-(arylvinyl)acetamides or methyl ureas have been prepared as constrained analogues of melatonin. The affinity of these new compounds for chicken brain melatonin receptors and recombinant human MT(1) and MT(2) receptors was evaluated using 2-[(125)I]-iodomelatonin as radioligand. Strict ethylenic or cyclopropyl analogues of the commercialized agonist agomelatine (Valdoxan®) were equipotent to agomelatine in binding bioassays. However, the ethylenic analogue was more effective than the cyclopropyl one in the melanophore aggregation bioassay, but was still less potent than the disubstituted 2,7-dimethoxy-naphtalenic compounds.

Imidacloprid and thiacloprid neonicotinoids bind more favourably to cockroach than to honeybee α6 nicotinic acetylcholine receptor: Insights from computational studies

The binding interactions of two neonicotinoids, imidacloprid (IMI) and thiacloprid (THI) with the extracellular domains of cockroach and honeybee α6 nicotinic acetylcholine receptor (nAChR) subunits in an homomeric receptor have been studied through docking and molecular dynamics (MD) simulations. The binding mode predicted for the two neonicotinoids is validated through the good agreement observed between the theoretical results with the crystal structures of the corresponding complexes with Ac-AChBP, the recognized structural surrogate for insects nAChR extracellular ligand binding domain. The binding site of the two insect α6 receptors differs by only one residue of loop D, a serine residue (Ser83) in cockroach being replaced by a lysine residue (Lys108) in honeybee. The docking results show very close interactions for the two neonicotinoids with both α6 nAChR models, in correspondence to the trends observed in the experimental neonicotinoid-Ac-AChBP complexes. However, the docking parameters (scores and energies) are not significantly different between the two insect α6 nAChRs to draw clear conclusions. The MD results bring distinct trends. The analysis of the average interaction energies in the two insects α6 nAChRs shows indeed better affinity of neonicotinoids bound to α6 cockroach compared to honeybee nAChR. This preference is explained by tighter contacts with aromatic residues (Trp and Tyr) of the binding pocket. Interestingly, the non-conserved residue Lys108 of loop D of α6 honeybee nAChR interacts through van der Waals contacts with neonicotinoids, which appear more favourable than the direct or water mediated hydrogen-bond interaction between the OH group of Ser83 of α6 cockroach nAChR and the electronegative terminal group of the two neonicotinoids (nitro in IMI and cyano in THI). Finally, in both insects nAChRs, THI is consistently found to bind more favourably than IMI.

Molecular recognition of thiaclopride by Aplysia californica AChBP: new insights from a computational investigation

The binding of thiaclopride (THI), a neonicotinoid insecticide, with Aplysia californica acetylcholine binding protein (Ac-AChBP), the surrogate of the extracellular domain of insects nicotinic acetylcholine receptors, has been studied with a QM/QM′ hybrid methodology using the ONIOM approach (M06-2X/6-311G(d):PM6). The contributions of Ac-AChBP key residues for THI binding are accurately quantified from a structural and energetic point of view. The importance of water mediated hydrogen-bond (H-bond) interactions involving two water molecules and Tyr55 and Ser189 residues in the vicinity of the THI nitrile group, is specially highlighted. A larger stabilization energy is obtained with the THI–Ac-AChBP complex compared to imidacloprid (IMI), the forerunner of neonicotinoid insecticides. Pairwise interaction energy calculations rationalize this result with, in particular, a significantly more important contribution of the pivotal aromatic residues Trp147 and Tyr188 with THI through CH···π/CH···O and π–π stacking interactions, respectively. These trends are confirmed through a complementary non-covalent interaction (NCI) analysis of selected THI–Ac-AChBP amino acid pairs.

Similar Comparative Low and High Doses of Deltamethrin and Acetamiprid Differently Impair the Retrieval of the Proboscis Extension Reflex in the Forager Honey Bee (Apis mellifera)

In the present study, the effects of low (10 ng/bee) and high (100 ng/bee) doses of acetamiprid and deltamethrin insecticides on multi-trial learning and retrieval were evaluated in the honey bee Apis mellifera. After oral application, acetamiprid and deltamethrin at the concentrations used were not able to impair learning sessions. When the retention tests were performed 1 h, 6 h, and 24 h after learning, we found a significant difference between bees after learning sessions when drugs were applied 24 h before learning. Deltamethrin-treated bees were found to be more sensitive at 10 ng/bee and 100 ng/bee doses compared to acetamiprid-treated bees, only with amounts of 100 ng/bee and at 6 h and 24 h delays. When insecticides were applied during learning sessions, none of the tested insecticides was able to impair learning performance at 10 ng/bee or 100 ng/bee but retention performance was altered 24 h after learning sessions. Acetamiprid was the only one to impair retrieval at 10 ng/bee, whereas at 100 ng/bee an impairment of retrieval was found with both insecticides. The present results therefore suggest that acetamiprid and deltamethrin are able to impair retrieval performance in the honey bee Apis mellifera.

(-)-5-methyl-8-hydroxy-(di-n-propylamino)tetralin a new 5-HT1A receptor antagonist

Abstract − (±)-5-Me-8-OH-DPAT 4 was synthesized by a new synthetic pathway recently described by us. The (+)- and (−)-enantiomers 4 were prepared from the primary amine 8 by crystallisation of the (+)- and (−)-mandelic acid salts. The enantiomers reacted with propyl iodide and were demethylated by 48% HBr to the (+)- and (−)- 4 compounds. These compounds had good affinity for 5-HT 1A receptors ( K i = 32.9 ± 0.8 and 45.6 ± 2 nM, respectively) but lacked enantioselectivity. In contrast to 8-OH-DPAT, but similar to WAY 100635 and (+)-WAY 100135, the addition of GTP-γS did not decrease the affinity of these compounds for 5-HT 1A receptors, suggesting a partial agonist or antagonist profile. Adenylyl cyclase assays with rat hippocampal membranes showed that (−)- 4 was totally inactive as an agonist over a wide concentration range in contrast to (+)- 4 which was a partial agonist. (−)- 4 (1 and 10 μM) shifted the concentration—effect curve for the inhibition by 8-OH-DPAT of forskolin-stimulated cyclic AMP production to the right (pA 2 = 7.6), demonstrating a competitive interaction between the two drugs.