1-Sulfonylindazoles as potent and selective 5-HT6 ligands

Multifunctional arylsulfonamide derivatives with 5-HT6/5-HT7 receptor antagonistic activity: a structural study

Nowadays, a search for antagonists co-acting on serotonin receptor subtypes 6 and 7 (5-HT₆R and 5-HT₇R, respectively) is of great interest due to the increasing number of patients suffering from dementia and related behavioural and psychological symptoms. The X-ray crystal structures of four promising multifunctional ligands in the hydrochloride forms were determined, namely 4-(6-fluoro-1,2-benzoxazol-3-yl)-1-[3-(3-methylbenzenesulfonamido)propyl]piperidin-1-ium chloride, C₂₂H₂₇FN₃O₃S⁺·Cl^-, (I), 4-(6-fluoro-1,2-benzoxazol-3-yl)-1-[4-(5-fluoro-3-methylbenzo[b]thiophene-2-sulfonamido)butyl]piperidin-1-ium chloride, C₂₅H₂₈F₂N₃O₃S₂⁺·Cl^-, (II), 4-(6-fluoro-1,2-benzoxazol-3-yl)-1-[4-(6-fluorobenzo[b]thiophene-2-sulfonamido)butyl]piperidin-1-ium chloride, C₂₄H₂₆ClFN₃O₃S₂⁺·Cl^-, (III), and 4-(6-fluoro-1,2-benzoxazol-3-yl)-1-[3-(3-chloro-4-fluorobenzenesulfonamido)propyl]piperidin-1-ium chloride, C₂₁H₂₂ClF₂N₃O₃S₂⁺·Cl^-, (IV). Two pharmacologically important functional groups, i.e. arylsulfonamide and piperidinyl-fluorobenzisoxazole, are linked by three- and four-membered aliphatic chains. These compounds crystallize as hydrochloride salts in monoclinic space groups, i.e. C2/c for (I), P2₁/c for (II) and (III), and P2₁/n for (IV). In the asymmetric unit, a charge-assisted hydrogen bond is observed between the cation located at the piperidine N atom and the chloride anion. The protonated piperidine N atom is critical to the pharmacological activity for the compounds, allowing for a strong interaction with monoaminergic receptors in the central nervous system. The sulfonyl group plays the role of a hydrogen-bond acceptor in the pharmacophore model and is involved in several C-H...O interactions. Two aromatic fragments of the presented structures are involved in C-H...π contacts, which were studied by Hirshfeld structure analysis. The distances between the mentioned functional groups are in agreement with pharmacophore models given in the literature. The studied interactions observed in the crystal structure indicate the main forces responsible for ligand-receptor recognition and binding.

The effect of the intramolecular C–H⋯O interactions on the conformational preferences of bis-arylsulfones – 5-HT6 receptor antagonists and beyond

The development of compounds with enhanced activity and selectivity by a conserved spatial orientation of the pharmacophore elements has a long history in medicinal chemistry. Rigidified compounds are an example of this concept. However, the intramolecular interactions were seldom used as a basis for conformational restraints. Here, we show the weak intramolecular interactions that contribute to the relatively well-conserved geometry of N1-arylsulfonyl indole derivatives. The structure analysis along with quantum mechanics calculations revealed a crucial impact of the sulfonyl group on the compound geometry. The weak intramolecular C–H⋯O interaction stabilizes the mutual "facing" orientation of two aromatic fragments. These findings extend the pharmacological interpretation of the sulfonyl group role from the double hydrogen bond acceptor to the conformational scaffold based on intramolecular forces. This feature has, to date, been omitted in in silico drug discovery. Our results should increase the awareness of researchers to consider the conformational preference when designing new compounds or improving computational methods.

The impact of weak intramolecular C–H⋯O interactions on the conformational stability of bis-arylsulfones is discussed, suggesting different role of sulfonyl group in the ligand – 5HT₆ receptor interaction.

Synthesis and Antibacterial Activity of Benzo[4,5]isothiazolo[2,3-a]pyrazine-6,6-dioxide Derivatives

Using a routine procedure, a number of derivatives of the benzo[4,5]isothiazolo[2,3-a]pyrazine-6,6-dioxide ring system have been synthesized from readily available starting materials. A series of chalcones were synthesized, which were subsequently reacted with chlorosulfonic acid to generate chalcone sulfonyl chlorides. The chalcone sulfonyl chlorides were then treated with bromine to generate dibromo chalcone sulfonyl chlorides. These were subsequently reacted with 1,2-diaminopropane and 2-methyl-1,2-diaminopropane in boiling ethanol resulting in compounds 2-10 and 11-19 respectively, in 12-80% yields. The products were characterized by spectral analysis and the definitive structure of compound 11 was determined by X-ray crystallography. The synthesized compounds were screened for potential antibacterial properties against Bacillus subtilis, Escherichia coli, Proteus vulgaris and Staphylococcus aureus.

Bioisosteric matrices for ligands of serotonin receptors

The concept of bioisosteric replacement matrices is applied to explore the chemical space of serotonin receptor ligands, aiming to determine the most efficient ways of manipulating the affinity for all 5-HT receptor subtypes. Analysis of a collection of over 1 million bioisosteres of compounds with measured activity towards serotonin receptors revealed that an average of 31 % of the ligands for each target are mutual bioisosteres. In addition, the collected dataset allowed the development of bioisosteric matrices—qualitative and quantitative descriptions of the biological effects of each predefined type of bioisosteric substitution, providing favored paths of modifying the compounds. The concept exemplified here for serotonin receptor ligands can likely be more broadly applied to other target classes, thus representing a useful guide for medicinal chemists designing novel ligands.

Design and synthesis of novel series of 5-HT6 receptor ligands having indole, a central aromatic core and 1-amino-4 methyl piperazine as a positive ionizable group

The exclusive distribution of 5-HT6 receptor in the brain regions and high affinity for antipsychotic and antidepressant drugs makes 5-HT6 receptor a promising target in treatment of CNS diseases. Based on a pharmacophore model reported in the literature, we designed and synthesized a novel series of 5-HT6 receptor ligands having indole as a central aromatic core and 1-amino-4-methyl piperazine as positive ionizable group. Out of 32 compounds we have successfully identified 10 new compounds as 5-HT6 receptor antagonists. The structure-activity relationship (SAR) studies have been carried out by mapping the compounds with the 3D QSAR model.

Role of serotonin in Alzheimer's disease: a new therapeutic target?

Mounting evidence accumulated over the past few years indicates that the neurotransmitter serotonin plays a significant role in cognition. As a drug target, serotonin receptors have received notable attention due in particular to the role of several serotonin-receptor subclasses in cognition and memory. The intimate anatomical and neurochemical association of the serotonergic system with brain areas that regulate memory and learning has directed current drug discovery programmes to focus on this system as a major therapeutic drug target. Thus far, none of these programmes has yielded unambiguous data that suggest that any of the new drug entities possesses disease-modifying properties, and significantly more research in this promising area of investigation is required. Compounds are currently being investigated for activity against serotonin 5-HT(1), 5-HT(4) and 5-HT(6) receptors. This review concludes that most work done in the development of selective serotonin receptor ligands is in the pre-clinical or early clinical phase. Also, while many of these compounds will likely find application as adjuvant therapy in the symptomatic treatment of Alzheimer's disease, there are currently only a few drug entities with activity against serotonin receptors that may offer the potential to alter the progression of the disease.

Investigation of the structure requirement for 5-HT₆ binding affinity of arylsulfonyl derivatives: a computational study

5-HT₆ receptor has been implicated in a series of diseases including anxiety, depression, schizophrenia and cognitive dysfunctions. 5-HT₆ ligands have been reported to play a significant role in the treatment for central nervous system (CNS) diseases. Presently, a large series of 223 5-HT₆ ligands were studied using a combinational method by 3D-QSAR, molecular docking and molecular dynamics calculations for further improvement of potency. The optimal 3D models exhibit satisfying statistical results with r²_ncv, q² values of 0.85 and 0.50 for CoMFA, 0.81 and 0.53 for CoMSIA, respectively. Their predictive powers were validated by external test set, showing r²_pred of 0.71 and 0.76. The contour maps also provide a visual representation of contributions of steric, electrostatic, hydrophobic and hydrogen bond fields as well as the prospective binding models. In addition, the agreement between 3D-QSAR, molecular docking and molecular dynamics simulation proves the rationality of the developed models. These results, we hope, may be helpful in designing novel and potential 5-HT₆ ligands.

Identification of 3-sulfonylindazole derivatives as potent and selective 5-HT(6) antagonists

As part of our efforts to develop agents for cognitive enhancement, we have been focused on the 5-HT(6) receptor in order to identify potent and selective ligands for this purpose. Herein we report the identification of a novel series of 3-sulfonylindazole derivatives with acyclic amino side chains as potent and selective 5-HT(6) antagonists. The synthesis and detailed SAR of this class of compounds are reported.