Benzimidazolone-based serotonin 5-HT1A or 5-HT7R ligands: Synthesis and biological evaluation

Insights into the development of 99mTc-radioligands for serotonergic receptors imaging: Synthesis, labeling, In vitro, and In vivo studies

Serotonergic (5-hydroxytryptamine; 5-HT) receptors play critical roles in neurological and psychological disorders such as schizophrenia, anxiety, depression, and Alzheimer's diseases. Therefore, it is particularly important to develop novel radioligands or modify the existing ones to identify the serotonergic receptors involved in psychiatric disorders. Among the 16 subtypes of serotonergic systems, only technetium-99m based radiopharmaceuticals have been evaluated for serotonin-1A (5-HT1A), serotonin-2A (5-HT2A), 5-HT1A/7 heterodimers and serotonin receptor neurotransmitter (SERT). This review focuses on recent efforts in the design, synthesis and evaluation of 99mTc-radioligands used for single photon emission computerized tomography (SPECT) imaging of serotonergic (5-HT) receptors. Additionally, the discussion will cover aspects such as chemical structure, in vitro/vivo stability, affinity toward serotonin receptors, blood-brain barrier permeation (BBB), and biodistribution study.

Towards selective CNS PET imaging of the 5-HT7 receptor system: Past, present and future

Since its discovery in 1993, the serotonin receptor subtype 7 (5-HT₇) has attracted significant attention as a potential drug target; due to its elucidated roles in conditions such as insomnia, schizophrenia, and more. Therefore, it is unsurprising that there has been relatively early efforts undertaken to develop a positron emission tomography (PET) imaging agent for said receptor system. PET can be clinically used to probe receptor systems in vivo, permitting information such as a drug's occupancy against this system to be investigated. This review focuses on the efforts towards the development of a 5-HT₇R selective PET CNS tracer over the last 20 years, critically reflecting on applied strategies and commonly employed chemical frameworks and suggests future considerations that are needed to successfully develop a PET tracer for this clinically relevant target. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Proton transfer in the benzimidazolone and benzimidazolthione tautomerism process catalyzed by polar protic solvents

The tautomeric equilibrium of benzimidazolone and benzimidazolthione have been studied by the density functional theory method using the CAM-B3LYP functional together with the 6-311G(d,p) basis set. Two separate mechanisms have been investigated: a direct intramolecular transfer using the polarizable continuum model and an indirect proton transfer assisted by a molecule of solvent (C6H12, H2O, CH3OH, and H2O2). In both cases, the results obtained indicate that ketone and thione are the most stable forms. However, the enhanced height of the activation barrier for the four-center mechanisms describing the tautomerism reaction as a direct intramolecular transfer implicates a relatively disadvantaged process. The participation of a polar protic solvent molecule allows the lowering of the activation energy barrier. Potential energy profiles of keto-enol and thio-enol tautomerism assisted by methanol and water are very different. The former one describes a concerted mechanism but the latter does not because it is associated with asynchronous processes that take place during the thio-enol tautomerism.

Towards new 5-HT7 antagonists among arylsulfonamide derivatives of (aryloxy)ethyl-alkyl amines: Multiobjective based design, synthesis, and antidepressant and anxiolytic properties

A series of 39 arylsulfonamide/amide derivatives of (aryloxy)ethyl alkyl amines, was designed with the support of the Virtual Combinatorial Library-Virtual Screening protocol, and synthesized using solid-phase methodologies. Representative compounds were biologically evaluated for their affinity for 5-HT7Rs and for their selectivity over related 5-HTRs (5-HT1ARs, 5-HT2ARs, 5-HT6Rs), dopamine D2Rs and adrenergic α1Rs. The study identified the derivatives 27 (3-fluoro-N-{1-[2-(2-cyclopentylphenoxy)ethyl]piperidin-4-yl}-benzenesulfonamide; PZ-1417) and 35 (4-fluoro-N-(1-{2-[(propan-2-yl)phenoxy]ethyl}-8-azabicyclo[3.2.1]octan-3-yl)-benzenesulfonamide; PZ-1150) as being potent 5-HT7R antagonists with antidepressant and anxiolytic properties in the forced swim test (0.625-5 mg/kg and 0.625 mg/kg, respectively), the tail suspension test (0.625 mg/kg and 0.625 mg/kg, respectively), and in four plate test (0.625 mg/kg and 1.25-2.5 mg/kg, respectively) in mice. It has to be stressed that new compounds displayed higher activity than that of SB-269970, a reference 5-HT7R antagonist. Finally, the study provided valuable insight into the development of potential therapeutic agents for the treatment of CNS disorders.

Synthesis and antibacterial activities of 1-alkyl-3-methacryloyl (acryloyl) of benzimidazolone (thione) derivatives

A series of (28) 1-alkyl-3-methacryloyl (acryloyl)-benzimidazolone (thione) deriv-atives were synthesized. The structures of the new derivatives were confirmed by ¹H-NMR, ¹³C-NMR and ESI-MS spectral analysis. The antibacterial activities of these compounds against several strains of bacteria, such as Bacillus cereus, Bacillus subtilis, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, were evaluated by methods of paper disc-diffusion and broth mciro-dilution. Methacryloyl derivatives displayed higher antibacterial activities against tested bacterial strains than those of acryloyl derivatives in in vitro tests. A structure-activity relationship (SAR) study revealed that the presences of the methacryloyl moieties is essential to the antibacterial activities of the compounds.

Synthesis and Properties of Polymers Containing 2H-Benzimidazol-2-one Moieties: Polymerization via N-C Coupling Reactions

Novel homopolymers and copolymers containing 2H-benzimidazol-2-one units have been synthesized by N-C coupling reactions of 1H-benzo[d]imidazol-2(3H)-one and activated aromatic dihalides under conditions similar to those for the synthesis of poly(aryl ether)s and poly(benzimidazole sulfone)s. 1H-Benzo[d]imidazol-2(3H)-one behaved like a bisphenol in the polymerization reaction to afford, quantitatively, high molecular weight linear polymers with inherent viscosities (η_inh) ranging from 0.57 to 1.31 dL/g. The polymers were soluble in various organic solvents, and transparent, flexible, and creasable films were cast from its dichloromethane-solution. The homopolymer had a remarkably high glass transition temperature (T_g 348 °C) and good thermal stability. Only 30 mol % (8.9 wt %) of the 2H-benzimidazol-2-one unit for the copolymer with 4,4'-biphenol was required to raise the T_g of commercial poly(aryl ether), Radel R-5000 from 220 to 269 °C.

5-Nitro-1-nonyl-1H-benzimidazol-2(3H)-one

In the title mol­ecule, C₁₆H₂₃N₃O₃, the dihedral angle between the benzimidazole and nitro group planes is 5.34 (9)° and the dihedral angle between the benzimidazole and aliphatic chain mean planes is 73.23 (5)°. The C—C—C—C torsion angles (about 176°) of the nonyl group indicate an all-anti­periplanar conformation. In the crystal, adjacent mol­ecules are linked by pairs of N—H⋯O hydrogen bonds into inversion dimers. These mol­ecules are further connected through C—H⋯O inter­actions, building tapes parallel to (22).

Synthesis of 1-acyl-3-isopropenylbenzimidazolone derivatives and their activity against Botrytis cinerea

A series of 1-acyl-3-isopropenylbenzimidazolone derivatives were synthesized, and their structures were characterized by (1)H and (13)C NMR and elemental analysis. Their fungicidal activities against Botrytis cinerea were also evaluated by spore germination assay. The acrylic acid, methacrylic acid, 4-chlorophenyl acetic acid, and 2-chlorobenzoic acid derivatives exhibited strong fungicidal activity. This implied that benzimidazolones might be potential fungicide leading compounds.