Béatrice Brémont

Structural analysis by the comparative molecular field analysis method of the affinity of β-adrenoreceptor blocking agents for 5-HT1A and 5-HT1B receptors

The affinities of 17 beta-adrenoreceptor antagonists for 5-HT1A and 5-HT1B receptors were evaluated in binding assays. A large range of Ki values (2-10,000 nM) was observed and ortho or meta substitution of the aromatic ring carrying the amino chain was implicated in the high affinity Ki values, whereas para substitution elicited a dramatic drop in activity. These variations were analyzed with two molecular design tools: the active analogue approach (AAA) and the new 3D-QSAR (quantitative structure activity relationship) method, comparative molecular field analysis (CoMFA). The AAA method emphasized, by superimposition of selected conformations of the molecules, the favorable and unfavorable volumes implicated in the receptor recognition. CoMFA generated a linear expression between the biological data and the different values of electrostatic and steric fields surrounding the molecules. It predicted the values of selected molecules but also those of new molecules not included in the study. The excellent accuracy of the prediction revealed the potential of the method for the design of new compounds. CoMFA demonstrated the important contribution of steric parameters, evaluated at 92%, compared to the electrostatic field (evaluated at 8%) to explain the affinity for 5-HT1A and 5-HT1B receptors. This study emphasizes also the importance of the occupancy of a hydrophobic pocket in the receptor site located near the area interacting with the aromatic moiety, and subsequently its use for the design of new, potent, specific antagonists of 5-HT1A and 5-HT1B receptors.

Synthesis of quinazoline-2,4-dione and naphthalimide derivatives as new 5-HT3 receptor antagonists

Abstract New potent 5-HT 3 receptor antagonists have been designed from the naphthalimide moiety and a quinuclidine heterocycle and the structure-activity relationships are discussed here on the basis of the nature of the substituent on the aromatic system. The biological activity of the compounds was evaluated in binding assays with [ 3 H]BRL-43694 and by inhibition of the Bezold—Jarisch reflex. Compound 22 with a 4-amino substituent was equipotent to the reference compounds. In contrast to the benzamide derivatives, the activity resides essentially in the ( R ) enantiomer ( K i = 0.15 ± 0.05 nM, ID 50 = 1.6 μg/kg/iv) and it is demonstrated that the additional carbonyl group is involved in the inversion of the enantioselectivity of the receptor. Conformational studies of ( R )- 22 demonstrated the presence of a locked structure with 4 minimal energy conformers which were compared to those of ( S )-zacopride. The superimposition of the putative active conformers emphasized the presence of a second polar group in the binding site. The fluorescent properties of the compounds were studied and indicate that ( R )- 22 and its derivatives may be promising tools for the direct visualization of 5-HT 3 receptors.

Structural analysis of 5-HT3 receptor antagonists: synthesis and pharmacological activity of various aromatic esters or amides derived from tropane and 1,2,6-trisubstituted piperidine

Abstract Preliminary results of a structure-activity relationship in the field of 5-HT 3 receptor antagonists on the influence of the aromatic ring and steric hindrance around the basic nitrogen atom are reported. The favorable role of the naphthalene moiety substituted by a carbonyl function in position 1 was demonstrated by measuring the biological activity using the inhibition of the specific binding of [ 3 H]BRL 43694 and the inhibition of the Bezold-Jarisch reflex. Several esters and amides of 1,2,6-trisubstituted piperidine derivatives with a suitable fit with the antagonist reference compounds were synthesized. The lack of biological activity of these compounds emphasizes the importance of steric hindrance for binding with the anionic receptor site. These data confirm the major role of the tropane and quinuclidine frameworks in the potency of a number of 5-HT 3 antagonists.

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.

Serotoninergic properties of new conformationally restricted benzamides

Summary A new series of benzamides derived from metoclopramide have been synthesized, in which the vicinal carbon of the basic nitrogen atom of the ethyl chain is situated on the C3, C4, C5 and C6 rings. The diamino derivatives were prepared through Streckers reaction from the corresponding ketones except for the cyclopropyl derivatives where 1-ethoxy-1-trimethylsiloxy cyclopropane was used as the starting material. The benzamides were prepared using the mixed anhydride method. They were tested in binding assays for D2, 5-HT3 and 5-HT4 receptors. The results show a marked increase in the selectivity and potency of these derivatives for 5-HT3 receptors with regard to metoclopramide (compound 1d: 5-HT3 Ki = 9.03 nM; 5-HT4 Ki > 5000; D2 Ki > 5000). The influences of steric hindrance and hydrophobic properties on the affinity of benzamide derivatives for 5-HT3 receptors were also emphasized by these data. The X-ray crystal structure of compound 1d was compared with that of the minimal energy conformer of BRL 24682, a reference 5-HT3 receptor antagonist benzamide, determined using the Random Search program. Superimposition of the two structures showed a suitable fit between the pharmacophore groups previously determined to be important for 5-HT3 receptor antagonists. On the other hand, the hydrophobic parts of the basic moieties had different spatial occupancies.

Synthesis and pharmacological activity of a macrocyclic benzamide

Abstract a macrocyclic benzamide was synthesized and its affinities for 5-HT 3 , 5-HT 4 and D 2 receptors were evaluated in binding assays. It was compared to reference benzamldes possessing a piperidine ring with varlous orlentations of the N-substituent. It was clearly demonstrated that the orientation of the basic nitrogen atom lone pair is an essential structural parameter in the recognition of 5-HT 3 and 5-HT 4 receptors.

Derivatives of naphthalimide: new potent conformationally restricted antagonists of 5-HT3 receptors.

Abstract New potent 5-HT3 antagonists were synthesized from naphthalic anhydride and racemic or (R) and (S) 3-aminoquinuclidines. In contrast to zacopride, the activity resided essentially in the (R) enantiomer. Conformational studies demonstrated the presence of a locked structure. The reduction of one carbonyl function yielded equipotent compounds with a loss of enantioselectivity.

(-)-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.

Synthesis of new derivatives of 8-OH-DPAT: influence of substitution on the aromatic ring on the pharmacological profile

Abstract Several new derivatives of 8-OH-DPAT were prepared by a new synthetic route using the Curtius degradation of 2-tetralin carboxylic acid derivatives. Their affinity for 5-HT1A and 5-HT1B receptors was evaluated in binding assays with rat hippocampus and striatum respectively. The results emphasized the favorable effect of the substitution on the phenyl ring of a homocyclic ring fused in positions [6,7] or [6,5] to obtain specific ligands for the 5-HT1B receptor. Methyl substitution in position 5 gave a compound with good affinity for the 5-HT1A receptor and preliminary pharmacological assays an antagonist profile for this compound.