NMR-based investigations of acyl-functionalized piperazines concerning their conformational behavior in solution

Overcoming NMR line broadening of nitrogen containing compounds: A simple solution

This study presents a straightforward solution to the challenge of elucidating the structures of nitrogen containing compounds undergoing isomerization. When spectral line broadening occurs related to isomerization, be it prototropic tautomerism or bond rotations, this poses a significant obstacle to structural elucidation. By adding acids, we demonstrate a simple approach to overcome this issue and effectively sharpen NMR signals for acid stable prototropic tautomers as well as the conformational isomers containing a morpholine or piperazine ring.

Copper-Mediated N-Trifluoromethylation of O-Benzoylhydroxylamines

The use of trifluoromethyl containing compounds is well established within medicinal chemistry, with a range of approved drugs containing C-CF3 and O-CF3 moieties. However, the utilisation of the N-CF3 functional group remains relatively unexplored. This may be attributed to the challenging synthesis of this unit, with many current methods employing harsh conditions or less accessible reagents. A robust methodology for the N-trifluoromethylation of secondary amines has been developed, which employs an umpolung strategy in the form of a copper-catalysed electrophilic amination. The method is operationally simple, uses mild, inexpensive reagents, and has been used to synthesise a range of novel, structurally complex N-CF3 containing compounds.

Tripodal Organic Cages with Unconventional CH···O Interactions for Perchlorate Remediation in Water

Perchlorate anions used in industry are harmful pollutants in groundwater. Therefore, selectively binding perchlorate provides solutions for environmental remediation. Here, we synthesized a series of tripodal organic cages with highly preorganized Csp3-H bonds that exhibit selectively binding to perchlorate in organic solvents and water. These cages demonstrated binding affinities to perchlorate of 105-106 M-1 at room temperature, along with high selectivity over competing anions, such as iodide and nitrate. Through single crystal structure analysis and density functional theory calculations, we identified unconventional Csp3-H···O interactions as the primary driving force for perchlorate binding. Additionally, we successfully incorporated this cage into a 3D-printable polymer network, showcasing its efficacy in removing perchlorate from water.

Building Up a Piperazine Ring from a Primary Amino Group via Catalytic Reductive Cyclization of Dioximes

Piperazine is one of the most frequently found scaffolds in small-molecule FDA-approved drugs. In this study, a general approach to the synthesis of piperazines bearing substituents at carbon and nitrogen atoms utilizing primary amines and nitrosoalkenes as synthons was developed. The method relies on sequential double Michael addition of nitrosoalkenes to amines to give bis(oximinoalkyl)amines, followed by stereoselective catalytic reductive cyclization of the oxime groups. The method that we developed allows a straightforward structural modification of bioactive molecules (e.g., α-amino acids) by the conversion of a primary amino group into a piperazine ring.

Syntheses, crystal structures and Hirshfeld surface analysis of three salts of 1-(4-nitro-phenyl)-piperazine

The structures and Hirshfeld surface analysis of three salts of 1-(4-nitro-phenyl)-piperazine are discussed. In 4-(4-nitro-phen-yl)piperazin-1-ium salicylate (C₁₀H₁₄N₃O₂ ⁺·C₇H₅O₃ ^-), there are strong hydrogen bonds between cation and anion and the 4-nitro-phenyl substituent occupies an equatorial position in the piperazinium ring. The cation and anion are linked together by supra-molecular inter-actions [graph-set notation of hydrogen bonding (6) propagating in the a-axis direction]. Additionally, there is π-π stacking involving the salicylate anion and the piperazinium cation in adjacent asymmetric units as well as a C-H⋯π inter-action between a hydrogen atom on the piperazine ring and the phenyl ring within the salicyclate anion. In bis-[4-(4-nitro-phen-yl)piperazin-1-ium] bis-(4-fluoro-benzoate) trihydrate (2C₁₀H₁₄N₃O₂ ⁺·2C₇H₄FO₂ ^-·3H₂O), there are two cations, two anions, and three water mol-ecules of solvation in the asymmetric unit, all linked by hydrogen bonds [graph-set notation of hydrogen bonding R ² ₂(20) between adjacent cations and R ³ ₃(9) between a cation and its adjacent anion]. In the anion, the 4-nitro-phenyl ring occupies an axial substitution position in the piperazinium ring, which is relatively rare. Within the asymmetric unit, the phenyl groups in the cations show an offset π-π inter-action. Additionally, there is a C-H⋯π inter-action between a hydrogen atom on the phenyl ring within a cation and the phenyl ring within an anion. In 4-(4-nitro-phen-yl)piperazin-1-ium 3,5-di-nitro-benzoate (C₁₀H₁₄N₃O₂ ⁺·C₇H₄N₂O₆ ^-), there is a strong N-H⋯O hydrogen bond linking the cation and anion and the 4-nitro-phenyl ring occupies an axial substitution position in the piperazinium ring, as seen in the previous structure. In the crystal, the cation and the anion form a complex three-dimensional hydrogen-bonded array involving R ² ₂(8), R ⁴ ₄(12) and R ⁴ ₄(20) rings propogating in the a-axis direction. The nitro-phenyl group is disordered with occupancies of 0.806 (10) and 0.194 (10).

Syntheses and crystal structures of four 4-(4-nitro-phen-yl)piperazinium salts with hydrogen succinate, 4-amino-benzoate, 2-(4-chloro-phen-yl)acetate and 2,3,4,5,6-penta-fluoro-benzoate anions

The syntheses and crystal structures are presented for four organic salts of the 4-(4-nitro-phen-yl)piperazinium cation, namely, 4-(4-nitro-phen-yl)piperazinium hydrogen succinate, C₁₀H₁₄N₃O₂ ⁺·C₄H₅O₄ ^- (I), 4-(4-nitro-phen-yl)piperazinium 4-amino-benzoate monohydrate, C₁₀H₁₄N₃O₂ ⁺·C₇H₆NO₂ ^-·H₂O (II), 4-(4-nitro-phen-yl)piperazinium 2-(4-chloro-phen-yl)acetate, C₁₀H₁₄N₃O₂ ⁺·C₈H₆ClO₂ ^- (III) and 4-(4-nitro-phen-yl)piperazinium 2,3,4,5,6-penta-fluoro-benzoate, C₁₀H₁₄N₃O₂ ⁺·C₇F₅O₂ ^- (IV). The salts form from mixtures of N-(4-nitro-phen-yl)piperazine and the corresponding acid [succinic acid (I), 4-amino-benzoic acid (II), 2-(4-chloro-phen-yl)acetic acid (III) and 2,3,4,5,6-penta-fluoro-benzoic acid (IV)] in mixed solvents of methanol and ethyl acetate. Salts I, III, and IV are anhydrous, whereas II is a monohydrate. In each structure, the overall conformation of the cation is determined by the disposition of the exocyclic N-C bond of the piperazine ring (either axial or equatorial) and twists about the N-C bond between the piperazine ring and its attached 4-nitro-phenyl ring. The packing motifs in each structure are quite different, though all are dominated by strong N-H⋯O hydrogen bonds, which are augmented in I and II by O-H⋯O hydrogen bonds, and in III by a π-π stacking inter-action between inversion-related 4-nitro-phenyl groups.

Bioevaluation of quinoline-4-carbonyl derivatives of piperazinyl-benzothiazinones as promising antimycobacterial agents

The quinoline moiety remains a privileged antitubercular (anti-TB) pharmacophore, whereas 8-nitrobenzothiazinones are emerging potent antimycobacterial agents with two investigational candidates in the clinical pipeline. Herein, we report the synthesis and bioevaluation of 30 piperazinyl-benzothiazinone-based quinoline hybrids as prospective anti-TB agents. Preliminary evaluation revealed 24/30 compounds exhibiting substantial activity (minimum inhibitory concentration [MIC] = 0.06-1 µg/ml) against Mycobacterium tuberculosis (Mtb) H37Rv. Cytotoxicity analysis against Vero cells found these to be devoid of any significant toxicity, with the majority displaying a selectivity index of >80. Furthermore, potent nontoxic compounds, when screened against clinical isolates of drug-resistant Mtb strains, demonstrated equipotent inhibition with MIC values of 0.03-0.25 µg/ml. A time-kill study identified a lead compound exhibiting concentration-dependent bactericidal activity, with 10× MIC completely eliminating Mtb bacilli within 7 days. Along with acceptable aqueous solubility and microsomal stability, the optimum active compounds of the series manifested all desirable traits of a promising antimycobacterial candidate.

Structural elucidation of two novel degradants of lurasidone and their formation mechanisms under free radical-mediated oxidative and photolytic conditions via liquid chromatography-photodiode array/ultraviolet-tandem mass spectrometry and one-dimensional/two-dimensional nuclear magnetic resonance spectroscopy

Lurasidone is an antipsychotic drug clinically used for the treatment of schizophrenia and bipolar disorder. During a mechanism-based forced degradation study of lurasidone, two novel degradation products were observed under free radical-mediated oxidative (via AIBN) and solution photolytic conditions. The structures of the two novel degradants were identified through an approach combining HPLC, LC-MSⁿ (n = 1, 2), preparative HPLC purification and NMR spectroscopy. The degradant formed under the free radical-mediated condition is an oxidative degradant with half of the piperazine ring cleaved to form two formamides; a mechanism is proposed for the formation of the novel N,N'-diformyl degradant, which should be readily applicable to other drugs that contain a piperazine moiety that is widely present in drug molecules. The degradant observed under the solution photolytic condition is identified as the photo-induced isomer of lurasidone with the benzisothiazole ring altered into a benzothiazole ring.

Crystal structures of six 4-(4-nitrophenyl)piperazin-1-ium salts

Six piperazinium salts are reported, five of them are hydrated and two crystallized as 2:2 salts. They exhibit asymmetric units of a common 4-nitro­phenyl­piperazine cation and different p-substituent benzoate anions. Their crystal structures mainly pack as chains stabilized by strong N—H⋯O and O—H⋯O hydrogen bonds and other weak inter­actions such as C—H⋯O and C—H⋯π.

Six piperazinium salts, namely 4-(4-nitro­phenyl)­piperazin-1-ium 4-bromo­ben­zo­ate dihydrate, C₁₀H₁₄N₃O₂⁺·C₇H₄BrO₂⁻·2H₂O, (I), 4-(4-nitro­phenyl)­pi­per­a­zin-1-ium 4-iodo­benzoate dihydrate, C₁₀H₁₄N₃O₂⁺·C₇H₄IO₂⁻·2H₂O, (II), 4-(4-nitro­phenyl)­piperazin-1-ium 4-hy­droxy­benzoate monohydrate, C₁₀H₁₄N₃O₂⁺·C₇H₅O₃⁻·H₂O, (III), 4-(4-nitro­phenyl)­piperazin-1-ium 4-methyl­benzoate monohydrate, C₁₀H₁₄N₃O₂⁺·C₈H₇O₂⁻·H₂O, (IV), 4-(4-nitro­phenyl)­piperazin-1-ium 4-meth­oxy­benzoate hemihydrate, 2C₁₀H₁₄N₃O₂⁺·2C₈H₇O₃⁻·H₂O, (V), and 4-(4-nitro­phenyl)­piperazin-1-ium 4-eth­oxy­benzoate, 2C₁₀H₁₄N₃O₂⁺·2C₉H₉O₃⁻, (VI), have been synthesized and their crystal structures solved by single-crystal X-ray diffraction, revealing that all of them crystallize in the triclinic space group P except for (V), which crystallizes in the monoclinic space group P2₁/c and has a disordered nitro group. Compounds (I) and (II) are isostructural. The crystal packing of (I)–(V) is constructed from organic chains formed by a combination of hydrogen bonds of type N—H⋯O and/or O—H⋯O and other weak inter­actions of type C—H⋯O and/or C—H⋯π, forming sheets, whereas (VI) shows a cationic and anionic-based layer structure.

Piperazine-1,4-diol (PipzDiol): synthesis, stereodynamics and assembly of supramolecular hydrogen-bonded 2D networks

The manuscript describes a novel small building block, 1,4-piperazinediol (PipzDiol), which has an extended H-bond donor structure compared to piperazine.

Synthesis, in vitro evaluation and molecular docking of a new class of indolylpropyl benzamidopiperazines as dual AChE and SERT ligands for Alzheimer's disease

During the last decade, the one drug-one target strategy has resulted to be inefficient in facing diseases with complex ethiology like Alzheimer's disease and many others. In this context, the multitarget paradigm has emerged as a promising strategy. Based on this consideration, we aim to develop novel molecules as promiscuous ligands acting in two or more targets at the same time. For such purpose, a new series of indolylpropyl-piperazinyl oxoethyl-benzamido piperazines were synthesized and evaluated as multitarget-directed drugs for the serotonin transporter (SERT) and acetylcholinesterase (AChE). The ability to decrease β-amyloid levels as well as cell toxicity of all compounds were also measured. In vitro results showed that at least four compounds displayed promising activity against SERT and AChE. Compounds 18 and 19 (IC₅₀ = 3.4 and 3.6 μM respectively) exhibited AChE inhibition profile in the same order of magnitude as donepezil (DPZ, IC₅₀ = 2.17 μM), also displaying nanomolar affinity in SERT. Moreover, compounds 17 and 24 displayed high SERT affinities (IC₅₀ = 9.2 and 1.9 nM respectively) similar to the antidepressant citalopram, and significant micromolar AChE activity at the same time. All the bioactive compounds showed a low toxicity profile in the range of concentrations studied. Molecular docking allowed us to rationalize the binding mode of the synthesized compounds in both targets. In addition, we also show that compounds 11 and 25 exhibit significant β-amyloid lowering activity in a cell-based assay, 11 (50% inhibition, 10 μM) and 25 (35% inhibition, 10 μM). These results suggest that indolylpropyl benzamidopiperazines based compounds constitute promising leads for a multitargeted approach for Alzheimer's disease.