Dopamine/Serotonin Receptor Ligands. 13: Homologization of a Benzindoloazecine-Type Dopamine Receptor Antagonist Modulates the Affinities for Dopamine D₁−D₅ Receptors

Enlarging the 10-membered ring of 7-methyl-6,7,8,9,14,15-hexahydro-5H-indolo[3,2-f][3]benzazecine (1, LE 300) yielded two homologue antagonists. Their affinities and inhibitory activities at D1−D5 receptors were measured by radioligand binding experiments and a functional Ca2+ assay. Compared to 1, phenylpropyl homologue 3 was superior in selectivity and affinity for the D5 subtype (Ki = 0.6 nM), whereas the affinity of the indolylpropyl homologue 2 for all subtypes decreased. Compounds 2, 3, 10, 11, 17, and 18 are derivatives of novel heterocyclic ring systems

Dopamine/Serotonin Receptor Ligands. 9. Oxygen-Containing Midsized Heterocyclic Ring Systems and Nonrigidized Analogues. A Step toward Dopamine D₅ Receptor Selectivity

Eleven-membered heterocycles (dibenz[g,j]-1-oxa-4-azacycloundecenes) and open-chain analogues were synthesized and investigated for affinities to human dopamine receptor subtypes. The moderately rigidized rings displayed nanomolar and subnanomolar Ki values at D1-like receptors with a significant D1 to D2 and a slight D5 to D1 selectivity. The open-chain analogues showed lower affinities but significant D1 to D2 selectivities. Compound 3 (Ki(D5) = 0.57 nmol) showed antagonistic or inverse agonistic binding characteristics in a functional Ca assay

Dopamine/Serotonin Receptor Ligands. 9. Oxygen-Containing Midsized Heterocyclic Ring Systems and Nonrigidized Analogues. A Step toward Dopamine D₅ Receptor Selectivity

Eleven-membered heterocycles (dibenz[g,j]-1-oxa-4-azacycloundecenes) and open-chain analogues were synthesized and investigated for affinities to human dopamine receptor subtypes. The moderately rigidized rings displayed nanomolar and subnanomolar Ki values at D1-like receptors with a significant D1 to D2 and a slight D5 to D1 selectivity. The open-chain analogues showed lower affinities but significant D1 to D2 selectivities. Compound 3 (Ki(D5) = 0.57 nmol) showed antagonistic or inverse agonistic binding characteristics in a functional Ca assay

Dopamine/Serotonin Receptor Ligands. 12: SAR Studies on Hexahydro-dibenz[<i>d</i>,<i>g</i>]azecines Lead to 4-Chloro-7-methyl-5,6,7,8,9,14-hexahydrodibenz[<i>d,g</i>]azecin-3-ol, the First Picomolar D₅-Selective Dopamine-Receptor Antagonist

Hydroxylated, methoxylated, and/or chlorinated 7-methyl-5,6,7,8,9,14-hexahydrodibenz[d,g]azecines were generally synthesized out of substituted 2-phenylethylamines and isochromanones by Bischler−Napieralski cyclization of the resulting benzamides to dibenzoquinolizines and the quaternization and cleavage of the central C−N bond under Birch conditions. Chlorination of 2-phenylethylamines was useful for the site direction of cyclization, but chlorine atoms were removed under Birch conditions so that chlorination had to be repeated to get the respective chlorinated dibenz[d,g]azecines. The target compounds were tested for their affinity at the different human-cloned dopamine-receptor subtypes (D1 family, D2 family). Generally, hydroxylation and chlorination of the dibenz-azecines increased affinities significantly. 1-Chloro-2-hydroxy-hexahydro-dibenz[d,g]azecine was a subnanomolar antagonist at both subtype families. 4-Chloro-3-hydroxy-7-methyl-5,6,7,8,9,14-hexahydro-dibenz[d,g]azecine was identified as the most potent and selective dopamine D5 receptor ligand described to date with Ki(D1) = 0.83, Ki(D2L) = 4.0, Ki(D3) = 24.6, Ki(D4) = 5.2 nM, and Ki(D5) = 57 pM (radioligand binding experiments), respectively

Dopamine/Serotonin Receptor Ligands. 12: SAR Studies on Hexahydro-dibenz[<i>d</i>,<i>g</i>]azecines Lead to 4-Chloro-7-methyl-5,6,7,8,9,14-hexahydrodibenz[<i>d,g</i>]azecin-3-ol, the First Picomolar D₅-Selective Dopamine-Receptor Antagonist

Hydroxylated, methoxylated, and/or chlorinated 7-methyl-5,6,7,8,9,14-hexahydrodibenz[d,g]azecines were generally synthesized out of substituted 2-phenylethylamines and isochromanones by Bischler−Napieralski cyclization of the resulting benzamides to dibenzoquinolizines and the quaternization and cleavage of the central C−N bond under Birch conditions. Chlorination of 2-phenylethylamines was useful for the site direction of cyclization, but chlorine atoms were removed under Birch conditions so that chlorination had to be repeated to get the respective chlorinated dibenz[d,g]azecines. The target compounds were tested for their affinity at the different human-cloned dopamine-receptor subtypes (D1 family, D2 family). Generally, hydroxylation and chlorination of the dibenz-azecines increased affinities significantly. 1-Chloro-2-hydroxy-hexahydro-dibenz[d,g]azecine was a subnanomolar antagonist at both subtype families. 4-Chloro-3-hydroxy-7-methyl-5,6,7,8,9,14-hexahydro-dibenz[d,g]azecine was identified as the most potent and selective dopamine D5 receptor ligand described to date with Ki(D1) = 0.83, Ki(D2L) = 4.0, Ki(D3) = 24.6, Ki(D4) = 5.2 nM, and Ki(D5) = 57 pM (radioligand binding experiments), respectively

Dopamine/Serotonin Receptor Ligands. 16. Expanding Dibenz[<i>d,g</i>]azecines to 11- and 12-Membered Homologues. Interaction with Dopamine D₁−D₅ Receptors

Oxygenated 7-methyl-5,6,7,8,9,14-hexahydrodibenz[d,g]azecines are potent dopamine receptor antagonists, preferentially at D1/D5. We synthesized the hydroxylated, methoxylated, and chlorinated 11-membered and 12-membered homologues of these 10-membered heterocycles. Their affinities for the human cloned D1−D5 receptors (radioligand binding) and functionalities (calcium assay) were measured. Enlarging the dibenzazecines to the corresponding dibenzazacycloundecenes and dibenzazacyclododecenes generally maintains the high antagonistic affinity for D1/D5 but also leads to a compound with a clozapine-like binding profile due to additional affinity for D4

Dopamine Receptor Ligands. Part 18: Modification of the Structural Skeleton of Indolobenzazecine-Type Dopamine Receptor Antagonists

On the basis of the D1/5-selective dopamine antagonist LE 300 (1), an indolo[3,2-f]benzazecine derivative, we changed the annulation pattern of the heterocycles. The target compounds represent novel heterocyclic ring systems. The most constrained indolo[4,3a,3-ef]benzazecine 2 was inactive, but the indolo[4,3a,3-fg]benzazacycloundecene 3 showed antagonistic properties (functional Ca2+ assay) with nanomolar affinities (radioligand binding) for all dopamine receptor subtypes, whereas the indolo[2,3-f]benzazecine 4 displayed a selectivity profile similar to 3 but with decreased affinities

Tacrine–Ferulic Acid–Nitric Oxide (NO) Donor Trihybrids as Potent, Multifunctional Acetyl- and Butyrylcholinesterase Inhibitors

In search of multifunctional cholinesterase inhibitors as potential anti-Alzheimer drug candidates, tacrine–ferulic acid–NO donor trihybrids were synthesized and tested for their cholinesterase inhibitory activities, release of nitric oxide, vasodilator properties, cognition improving potency, and hepatotoxicity. All of the novel target compounds show higher in vitro cholinesterase inhibitory activity than tacrine. Three selected compounds (3a, 3f, and 3k) produce moderate vasorelaxation in vitro, which correlates with the release of nitric oxide. Compared to its non-nitrate dihybrid analogue (3u), the trihybrid 3f exhibits better performance in improving the scopolamine-induced cognition impairment (mice) and, furthermore, less hepatotoxicity than tacrine

Bivalent β-Carbolines as Potential Multitarget Anti-Alzheimer Agents

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder with multifactorial causes that requires multitargeted treatment. Inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) improve cholinergic signaling in the central nervous system and thus AChE inhibitors are well established in the therapy of AD to improve memory disturbances and other cognitive symptoms. On the other hand, AD patients benefit from reduction of pathologic glutamate-induced, Ca2+-mediated excitotoxicity by the N-methyl-d-aspartate receptor (NR) antagonist memantine. New drugs that simultaneously affect both cholinergic transmission and glutamate-induced excitotoxicity may further improve AD treatment. While connecting β-carboline units by alkylene spacers in two different series of compounds and subsequent evaluation of their AChE/BChE-inhibitory potential, we found that several of these bivalent β-carbolines were potent NR blockers. The most promising compound was a N9-homobivalent β-carboline with a nonylene spacer, which displayed IC50 values of 0.5 nM for AChE, 5.7 nM for BChE, and 1.4 μM for NR, respectively

NO-Donating Tacrine Hybrid Compounds Improve Scopolamine-Induced Cognition Impairment and Show Less Hepatotoxicity

A series of tacrine−NO donor hybrid compounds are synthesized and evaluated for cholinesterase inhibitory activity, cognition improving activity, and hepatotoxicity. The pharmacological results indicate that hybrid compounds 1, 2, and 3a potently inhibit cholinesterase in vitro and significantly improve the scopolamine-induced cognition impairment, whereas an analogue (3h) of 2 without the NO donor moiety does not. Compared to tacrine, 1 and 2 show much less hepatotoxicity. Molecular modeling studies suggest that 2 may interact with the catalytic and the peripheral anionic site of acetylcholinesterase