The synthesis of cyclic and acyclic long‐chain arylpiperazine derivatives of salicylamide as serotonin receptor ligands

Radioligand and computational insight in structure - Activity relationship of saccharin derivatives being ipsapirone and revospirone analogues

Schizophrenia and depression are diseases that significantly impede human functioning in society. Current antidepressant drugs are not fully effective. According to literature data, the effect on D₂R or 5-HT_1AR can effectively reduce the symptoms of depression or schizophrenia. Recent research hypothetized that the synergism of both of these receptors can improve the effectiveness of therapy. Ipsapirone, a representative of long-chain arylpiperazines, is a known 5-HT_1AR ligand that has antidepressant effect. This compound has no affinity for the D₂R. Bearing in mind, we decided to design ligands with improved affinity to D₂R and confirmed that in some cases elongation of the carbon linker or arylpiperazine exchange may have beneficial influence on the binding to D2R and 5-HT1AR. Four groups of ligands being ipsapirone analogues with butyl, pentyl, hexyl and stiffened xylene chains were designed. All compounds were obtained in solvent-free reactions supported by a microwave irradiation with an efficiency mainly above 60%. All ligands containing 1-(2-pyrimidinyl)piperazine exhibited high affinity to 5-HT_1AR. In this case, chemical modifications within the chain did not affect the affinity to D₂R. In the case of ligands containing 1-phenylpiperazine, 1-(3-trifluoromethylphenyl)piperazine, 1-(1-naphthyl)piperazine, and 1-(4-chlorophenyl)piperazine, elongation of carbon linker increases of affinity to D₂R. For ligands containing 1- (2-pyridyl) piperazine, and 1-(2,3-dichlorophenyl)piperazine, we observed an opposite effect. For ligands containing 1-phenylpiperazine, 1-(2-methoxyphenyl)piperazine and 1-(2-pyridyl)piperazine, chain elongation had no effect on 5-HT_1AR binding. In turn of ligands containing 1-(3-trifluoromethylphenyl)piperazine and 1- (2,3-dichlorophenyl)piperazine, we observed that elongation of carbon linker has a positive influence to 5-HT_1AR. Molecular modelling was used to support the SAR study.

Solvates of New Arylpiperazine Salicylamide Derivative-a Multi-Technique Approach to the Description of 5 HTR Ligand Structure and Interactions

A new ligand for 5-HT1A and 5-HT7 receptors, an arylpiperazine salicylamide derivative with an inflexible spacer, is investigated to identify preferred fragments capable of creating essential intermolecular interactions in different solvates. To fully identify and characterize the obtained crystalline materials, various methods including powder and single-crystal X-ray diffraction, solid-state NMR, and thermal analysis were employed, supplemented by periodic ab initio calculations. The molecular conformation in different solvates, types, and hierarchy of intermolecular interactions as well as the crystal packing were investigated to provide data for future research focused on studying protein–ligand interactions. Based on various methods of crystal structure analysis, including the interaction energy calculation and programs using an artificial neural network, a salicylamide fragment was found to be crucial for intermolecular contacts, mostly of dispersion and electrostatic character. A supramolecular 2D kite-type layer of {4,4} topology was found to form in crystals. The closed voids between layers contain disordered solvents, very weakly interacting with the molecule and the layer. It has been postulated that the separation of the layers might be influenced by an increase in temperature or the size of the solvent; hence, only methanol and ethanol hemi-solvates could be obtained from a series of various alcohols.

The Effect of Carboxamide/Sulfonamide Replacement in Arylpiperazinylalkyl Derivatives on Activity to Serotonin and Dopamine Receptors

A series of carboxamide and sulfonamide alkyl (p-xylyl and benzyl) 1-(2-methoxyphenyl)piperazine (o-OMe-PhP) and 1-(2,3-dichlorophenyl)piperazine (2,3-DCPP) analogs were prepared and tested for their affinity to bind to serotonin 5-HT_1A /5-HT₆ /5-HT₇ and dopamine D₂ receptors. This chemical modification let us explore the impact of the replacement of the carboxamide by the sulfonamide group on the affinity changes. In both the o-OMe-PhP and 2,3-DCPP series, the relative activities of the carboxamides versus sulfonamides toward the 5-HT_1A /5-HT₆ /5-HT₇ and D₂ receptors show similar trends. Varied or similar activities for particular receptors were found for the carboxamides/sulfonamides with p-xylyl spacer, while of the two classes of carboxamides and sulfonamides examined, benzyl derivatives of the sulfonamides displayed the highest serotoninergic affinity, in particular to the 5-HT₇ receptors (K_i 8-85 nM). The K_i values revealed that, irrespective of the carboxamide/sulfonamide zone, both p-xylyl and benzyl derivatives had the highest affinity for the dopamine D₂ receptor (i.e., 16 out of 24 compounds investigated have an affinity below 100 nM). A molecular modeling study of carboxamide 9a and sulfonamide 9b showed that their binding effects to each of 5-HT_1A R and D₂ R created binding modes interaction with different conserved receptors residues. Structural similarities of carboxamide 9a in complexes with a 5-HT_1A R (9aI) and D₂ R (9aII) are over 83%, while the respective similarities of sulfonamide 9b structures (9bI/9bII) are only about 40%.

New arylpiperazines with flexible versus partly constrained linker as serotonin 5-HT(1A)/5-HT(7) receptor ligands

A series of new long-chain arylpiperazine (LCAP) derivatives with flexible and partly constrained alkyl linker were synthesized and investigated in vitro as potential serotonin 5-HT(1A) and 5-HT(7) receptor ligands. The compounds were prepared by a two-step procedure using naphthalimide and 2H-1,3-benzoxazine-2,4(3H)-dione as imides, and 1-(2-methoxyphenyl)piperazine (o-OMe-PhP) and 1,2,3,4-tetrahydroisoquinoline (THIQ) as amine pharmacophores. Modifications of the spacer structure included introduction of flexible penta- and hexamethylene chains as well as partly constrained m- and p-xylyl moieties. In general, the new compounds were more active at the 5-HT(1A) than at the 5-HT(7) receptor, and the o-OMe-PhP derivatives displayed higher affinities than their respective THIQ analogs. The spacer modifications had little effect on the observed in vitro activities. Within the o-OMe-PhP series, except for a small binding reduction for ligands containing the m-xylyl moiety, there was no substantial change in the compounds' potency at both receptors, while for the THIQ derivatives a clear structure-activity relationship was visible only for the interaction of the compounds with the 5-HT(7) receptor, which strongly favored flexible analogs.