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New adenosine derivatives have been synthesized and tested as putative agonists of adenosine receptors. Compounds 2−6 derive from the introduction of several types of substituents (electron donating, electron withdrawing, and halogens) in the para-position of the phenyl ring of the parent compound 1, and compound 7 lacks the hydroxyl group of amino alcohol 1. In radioligand binding assays using recombinant human A1, A2A, A2B, and A3 receptors, all compounds showed very low or negligible affinity for A1 and A2B receptors but compounds 3, 5, and 7 displayed a remarkably potent affinity for the A2A receptor with Ki values of 1−5 nM. Bromo derivative 3 displayed a selectivity A1/A2A = 62 and A3/A2A = 16 whereas the presence of a hydroxyl group (compound 5) improved the selectivity of A1/A2A and A3/A2A to 120- and 28-fold, respectively. When the methoxy derivative 4 lacks the hydroxyl group on the side chain (compound 7), the binding affinity for A2A is increased to 1 nM, improving selectivity ratios to 356- and 100-fold against A1 and A3, respectively. In Chinese hamster ovary cells transfected with human A2A and A2B receptors, most compounds showed a remarkable activity for the A2A receptor, except chloro derivative 2, with EC50 values ranging from 1.4 to 8.8 nM. The compounds behaved as good A2A agonists, and all were more selective than 5‘-(N-ethylcarboxamino)adenosine (NECA), with A2B/A2A ratios of cAMP accumulation ranging from 48 for compound 2 to 666 for compound 7 while the corresponding A2B/A2A ratio for NECA was only 9. Compounds 1, 3, 5, and 7 also displayed higher selectivities than NECA up to 100-fold in isolated aortas of rat and guinea pig. In guinea pig tracheal rings precontracted by carbachol, compounds 2 and 4 were more potent than adenosine (100-fold) and NECA (10-fold), whereas compounds 1 and 7 displayed similar effects to NECA. Pretreatment of the tracheal rings with A2, A2A, and A2B receptor antagonists 3,7-dimethyl-l-propargylxanthine, 8-(3-chlorostyryl)caffeine, and alloxazine produced a marked inhibition of the tracheal relaxations induced by compounds 1, 2, and 4, but none of the compounds showed selectivity toward any of the adenosine receptors.

A series of 52 conformationally constrained butyrophenones have been synthesized and pharmacologically tested as antagonists at 5-HT2A, 5-HT2B, and 5-HT2C serotonin receptors, useful for dissecting the role of each 5-HT2 subtype in pathophysiology. These compounds were also a consistent set for the identification of structural features relevant to receptor recognition and subtype discrimination. Six compounds were found highly active (pKi > 8.76) and selective at the 5-HT2A receptor vs 5-HT2B and/or 5-HT2C receptors. Piperidine fragments confer high affinity at the 5-HT2A receptor subtype, with benzofuranone- and thiotetralonepiperidine as the most selective derivatives over 5-HT2C and 5-HT2B receptors, respectively; Ki 2A/2C and/or KB 2A/2B ratios greater than 100 were obtained. Compounds showing a more pronounced selectivity at 5-HT2A/5-HT2C than at 5-HT2A/5-HT2B bear 6-fluorobenzisoxazolyl- and p-fluorobenzoylpiperidine moieties containing one methylene bridging the basic piperidine to the alkanone moiety. An ethylene bridge between the alkanone and the amino moieties led to ligands with higher affinities for the 5-HT2B receptor. Significant selectivity at the 5-HT2B receptor vs 5-HT2C was observed with 1-1[(1-oxo-1,2,3,4-tetrahydro-3-naphthyl)methyl]-4-[3-(p-fluorobenzoyl)propyl]piperazine (more than 100-fold higher). Although piperidine fragments also confer higher affinity at 5-HT2C receptors, only piperazine-containing ligands were selective over 5-HT2A. Moderate selectivity was observed at 5-HT2C vs 5-HT2B (10-fold) with some compounds bearing a 4-[3-(6-fluorobenzisoxazolyl)]piperidine moiety in its structure. Molecular determinants for antagonists acting at 5-HT2A receptors were identified by 3D-QSAR (GRID-GOLPE) studies. Docking simulations at 5-HT2A and 5-HT2C receptors suggest a binding site for the studied type of antagonists (between transmembrane helices 2, 3, and 7) different to that of the natural agonist serotonin (between 3, 5, and 6).

A series of novel conformationally restricted butyrophenones (6-aminomethyl-4,5,6,7-tetrahydrobenzo[b]furan-4-ones bearing 4-(6-fluorobenzisoxazolyl)piperidine, 4-(p-fluorobenzoyl)piperidine, 4-(o-methoxyphenyl)piperazine, 4-(2-pyridyl)piperazine, 4-(2-pyrimidinyl)piperazine, or linear butyro(or valero)phenone fragments) were prepared and evaluated as antipsychotic agents by in vitro assays for affinity for dopamine receptors (D1, D2, D4) and serotonin receptors (5-HT2A, 5-HT2B, 5-HT2C), by neurochemical studies, and by in vivo assays for antipsychotic potential and the risk of inducing extrapyramidal side effects. Potency and selectivity depended mainly on the amine fragment connected to the cyclohexanone structure. Compounds 20b, with a benzoylpiperidine moiety, and 20c, with a benzisoxazolyl fragment, were selective for 5-HT2A receptors. The in vitro and in vivo pharmacological profiles of N-[(4-oxo-4,5,6,7-tetrahydrobenzo[b]furan-6-yl)methyl]-4-(p-fluorobenzoyl)piperidine (20b, QF1003B) and N-[(4-oxo-4,5,6,7-tetrahydrobenzo[b]furan-6-yl)methyl]-4-(6-fluorobenzisoxazol-3-yl)piperidine (20c, QF1004B) suggest that they may be effective as antipsychotic (neuroleptic) drugs.

A series of novel conformationally restricted butyrophenones (2-(aminoethyl)- and 3-(aminomethyl)thieno- or benzocycloalkanones bearing (6-fluorobenzisoxazolyl)piperidine, (p-fluorobenzoyl)piperidine, (o-methoxyphenyl)piperazine, or linear butyrophenone fragments) were prepared and evaluated as atypical antipsychotic agents by in vitro assays of affinity for dopamine receptors (D1, D2) and serotonin receptors (5-HT2A, 5-HT2C) and by in vivo assays of antipsychotic potential and the risk of inducing extrapyramidal side effects. Potency and selectivity depended mainly on the amine fragment connected to the cycloalkanone structure. As a group, compounds with a benzisoxazolyl fragment had the highest 5-HT2A activities, followed by the benzoylpiperidine derivatives; in general, α-substituted cycloalkanone derivatives were more active than the corresponding β-substituted congeners. CoMFA (comparative molecular field analysis) and docking studies showed electrostatic, steric, and lipophilic determinants of 5-HT2A and D2 affinities and 5-HT2A/D2 selectivity. The in vitro and in vivo pharmacological profiles of N-[(4-oxo-4H-5,6-dihydrocyclopenta[b]thiophene-5-yl)ethyl]-4-(6-fluorobenzisoxazol-3-yl)piperidine (23b, QF 0510B), N-[(4-oxo-4,5,6,7-tetrahydrobenzo[b]thiophene-5-yl)ethyl]-4-(6-fluorobenzisoxazol-3-yl)piperidine (24b, QF 0610B), and N-[(7-oxo-4,5,6,7-tetrahydrobenzo[b]thiophene-6-yl)ethyl]-4-(6-fluorobenzisoxazol-3-yl)piperidine (29b, QF 0902B) suggest that they may be effective antipsychotic drugs with low propensity to induce extrapyramidal side effects.