Piperazine Linker Research Articles

New Type of Ferrocene‐Betulonic Acid Hybrids. Bioactivity, Synthesis, Structure, IR and CD versus DFT Calculations

AbstractFerrocene‐modified natural compounds are of interest for the development of new pharmaceuticals due to improved bioavailability, increased bioactivity, and also as redox markers or vectors. Betulin is a natural plant‐derived product with a wide range of pharmacological properties. However, it is limited in its bioavailability and efficacy. In order to enhance its pharmacological profile, the ferrocene modification of betulin was used in this study. A hybrid of the betulin core (up to 30 % betulin in birch bark) with a ferrocene moiety combined through a piperazine linker (compound 12) was prepared in good yield from readily available ferrocene carboxylic acid and betulonic acid, a natural betulin derivative, via coupling reactions. Spectroscopic techniques, including 1H and 13C NMR, IR and UV‐vis spectroscopy, as well as circular dichroism (CD), were applied to characterize the physicochemical and chiroptical properties. The cytotoxicity of the synthesized hybrid 12 and its ferrocene precursor 13 on MCF‐7 human cancer cell lines were in vitro evaluated by the MTT assay. The IC50 cytotoxicity index of 12 was found to be 26 μM. The theoretically calculated energies of the HOMO‐LUMO orbitals and electronic characteristics of betulin 10, betulonic acid 11, hybrid 12 and ferrocenyl piperazine 13 were determined by the DFT method with hybrid functionals ωB97XD, LC‐ωPBE and B3LYP‐D3 and pure M06 L functionals, with a 6‐311+G(d), 6‐31G(d) or TZV basis set.

Synthesis and agricultural antimicrobial evaluation of new quinazoline derivatives containing both a piperazine linker and the N-acetyl moiety.

To discover more efficient agricultural antimicrobial agents, a series of new quinazoline derivatives containing both a piperazine linker and the N-acetyl moiety were prepared and assessed for their antibacterial and antifungal activities. All the target compounds were characterized by 1H and 13C NMR as well as high-resolution mass spectrometry (HRMS), and the chemical structure of the most potent compound E19 incorporating a 4-trifluoromethoxy substituent was clearly confirmed via single crystal X-ray diffraction measurements. The bioassay results indicated that some compounds possessed notable inhibitory effects in vitro against the bacterium Xanthomonas oryzae pv. oryzicola (Xoc). For example, compound E19 had an EC50 (effective concentration for 50% activity) value of 7.1 μg/mL towards this pathogen, approximately 15- and 10-fold more effective than the commercial bactericides thiodiazole copper and bismerthiazol (EC50 = 110.2 and 72.4 μg/mL, respectively). Subsequently, the mechanistic studies showed that compound E19 likely exerted its antibacterial efficacies by altering the cell morphology, increasing the permeability of bacterial cytoplasmic membrane, suppressing the production of bacterial extracellular polysaccharides and the extracellular enzyme activities (amylase and cellulase), and blocking the swimming motility of Xoc. Moreover, the proteomic analysis revealed that compound E19 could reduce the bacterial flagellar biosynthesis and decrease the flagellar motility by down-regulating the expression of the related differential proteins. Compound E19 exhibited good potential for further development as a bactericide candidate for control of Xoc. © 2024 Society of Chemical Industry.

Novel hybrid benzoisothiazole-1,2,3-triazole-4-carboxamides with sub-micromolar toxicity towards human breast carcinoma cells and high affinity to DNA

A pharmacophore hybridization strategy to combine biologically active scaffolds was implemented for design and synthesis of benzoisothiazole-1,2,3-triazole-4-carboxamide conjugates via piperazine linker. In vitro screening led to identification of the compounds 5h and 5j, with para-chlorine- or fluorine- substitution on the phenyl ring, and isopropyl or cyclopropyl substituents in position 5 of 1,2,3-triazole cycle as potent anticancer agents. These compounds demonstrated toxicity towards human breast adenocarcinoma cells of the MCF-7 line in sub-micromolar concentrations with IC50 = 0.76 ± 0.04 μM and 0.90 ± 0.02 μM, respectively, while showing no toxicity in normal cells (IC50 > 100 μM). Colony formation and proliferation of carcinoma MCF-7 cells were effectively inhibited by the derivatives 5h and 5j. These derivatives caused DNA fragmentation of the MCF-7 cells. We suggest that the DNA-damaging action of the compounds 5h and 5j may be related to their high capability of intercalating into DNA molecule that is comparable to such ability of known anticancer agent – the doxorubicin. High affinity of the compounds 5h and 5j for the DNA was confirmed using computational molecular docking in silico.

Design, synthesis and application of dual-channel fluorescent probes for ratiometric detection of HClO and H2S based on phenothiazine coumarins

The ubiquity of diverse material entities in environmental matrices renders the deployment of unifunctional fluorescent indicators inadequate. Consequently, this study introduces a ratiometric dual-emission fluorescent sensor (Probe CP), synthesized by conjugating phenothiazine coumarin to hydroxycoumarin through a piperazine linker for concurrent detection of HClO and H2S. Upon interaction with HClO, the phenothiazine unit's sulfur atom undergoes oxidation to sulfoxide, facilitating a shift from red to green fluorescence in a ratiometric manner. Concurrently, at the opposite terminus of Probe CP, 2,4-dinitroanisole serves as the reactive moiety for H2S recognition; it restores the blue emission characteristic of 7-hydroxycoumarin while maintaining the red fluorescence emanating from phenothiazine coumarin as an internal standard for ratio-based assessment. Exhibiting elevated specificity and sensitivity coupled with minimal detection thresholds (0.0506 μM for HClO and 1.7292 μM for H2S) alongside rapid equilibration periods (3 min for HClO and half an hour for H2S), this sensor was efficaciously employed in cellular environments and within zebrafish models as well as imaging applications pertaining to alcohol-induced hepatic injury in murine subjects.

Immobilized nickel nanoparticles on modified magnetic titanium dioxide: A proficient and eco-friendly nanocatalyst for the green A3-coupling synthesis of propargylamines

In this research, a novel and highly efficient magnetic catalyst was synthesized by surface modification of Fe3O4/TiO2 with epibromohydrine and N-(2-aminoethyl)piperazine linkers and then by immobilization of Ni nanoparticles onto the surface of magnetic titanium dioxide. The synthesized Fe3O4/TiO2-EP-NAEP/Ni nanocomposite was identified by FT-IR, PXRD, TEM, FE-SEM, ICP, EDX, TGA, and VSM techniques, and its catalytic performance was investigated in an A3 coupling reaction of amines, various aldehyde, and terminal alkynes in solvent-free conditions and propargylamine derivatives was gained with excellent yields. Also, the catalyst has high recyclability and can be reused at least six times in the synthesis of propargylamine derivatives with good yields.

Screening of efficient salicylaldoxime reactivators for DFP and paraoxon-inhibited acetylcholinesterase.

Previously we reported two salicylaldoxime conjugates (L7R3 and L7R5) showing equal or even higher reactivating efficiency for both organophosphorus nerve agent and pesticide inhibited acetylcholinesterase in comparison to obidoxime and HI-6. In this study, L7R3 and L7R5 were selected as lead compounds and refined by employing a fragment-based drug design strategy, and a total of 32 novel salicylaldoxime conjugates were constructed and screened for DFP and paraoxon inhibited acetylcholinesterase. The findings demonstrate that the conjugate L73R3, which contains a 4-nitrophenyl group, exhibited a higher reactivation efficacy against paraoxon-inhibited acetylcholinesterase compared to obidoxime and HI-6. It was confirmed that the combination of a 4-pyridinyl or 4-nitrophenyl peripheral site ligand, a piperazine linker and a methyl or chloro-substituted salicylaldoxime could construct efficient nonquaternary oxime reactivators. The results hold promise for developing a new generation of highly effective antidotes for organophosphate poisoning.

A Piperazine Linked Rhodamine-BODIPY FRET-based Fluorescent Sensor for Highly Selective Pd2+ and Biothiol Detection.

A class of rhodamine-based fluorescent sensors for the selective and sensitive detection of Pd2+ metal ions in aqueous media has been developed. A rhodamine-based sensor PMS and a rhodamine-BODIPY Förster resonance energy transfer (FRET)-pair sensor PRS have been incorporated with a piperazine linker and an O-N-S-N podand ligand for specific recognition of Pd2+ ion. Both probes displayed colorimetric and fluorescent ratiometric changes when exposed to Pd2+, due to their spirolactam rings opening and restoring rhodamine conjugation. PRS is highly selective to Pd2+ over 22 other metal ions, showing a 0.6-fold ratiometric difference at I600nm/I515nm. Additionally, the lactam ring in Pd2+ coordinated PRS-Pd could be switched back to the closed form in the presence of various thiols, providing a "red-green traffic light" detection mechanism between red and green emission. Furthermore, PRS showed excellent cell viability and was successfully employed to image Pd2+ and the PRS-Pd complex ensemble could interchangeably detect biothiols including glutathione (GSH) in A549 human lung cancer cells.

Evaluation of Astatine-211-Labeled Fibroblast Activation Protein Inhibitor (FAPI): Comparison of Different Linkers with Polyethylene Glycol and Piperazine.

Fibroblast activation proteins (FAP) are overexpressed in the tumor stroma and have received attention as target molecules for radionuclide therapy. The FAP inhibitor (FAPI) is used as a probe to deliver nuclides to cancer tissues. In this study, we designed and synthesized four novel 211At-FAPI(s) possessing polyethylene glycol (PEG) linkers between the FAP-targeting and 211At-attaching moieties. 211At-FAPI(s) and piperazine (PIP) linker FAPI exhibited distinct FAP selectivity and uptake in FAPII-overexpressing HEK293 cells and the lung cancer cell line A549. The complexity of the PEG linker did not significantly affect selectivity. The efficiencies of both linkers were almost the same. Comparing the two nuclides, 211At was superior to 131I in tumor accumulation. In the mouse model, the antitumor effects of the PEG and PIP linkers were almost the same. Most of the currently synthesized FAPI(s) contain PIP linkers; however, in our study, we found that PEG linkers exhibit equivalent performance. If the PIP linker is inconvenient, a PEG linker is expected to be an alternative.

Antibiotic resistance and drug modification: Synthesis, characterization and bioactivity of newly modified potent pleuromutilin derivatives with a substituted piperazine moiety

Antibiotic-resistant bacteria pose a major global public health concern, owing to the lack of effective antibacterial drugs. Consequently, the discovery and development of innovative antibacterial drug classes with unique mechanisms of action are urgently needed. In this study, we designed, synthesised, and tested a series of novel pleuromutilin derivatives with piperazine linker substituted by amino acids moieties to determine their antibacterial properties. Most synthesized compounds exhibited potent activities against Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), and methicillin-resistant Staphylococcus epidermidis. Compound 6l, the most potent antibacterial agent created in this study, displayed a rapid bactericidal activity against MRSA, Klebsiella pneumoniae and S. aureus cfr N12. Moreover, pharmacokinetics study of compound 6l exhibited good PK performance with a low in vivo clearance (CL = 1965 mL/h/kg) and a suitable half-life (T1/2 = 11.614 ± 5.123 h). Molecular docking experiments revealed the binding model of compound 6l to the unmethylated A2503 of peptidyl transferase centre of 23S rRNA. Interaction pattern of 6l with cfr-mediated ribosomes revealed by molecular dynamics. Moreover in vivo mouse systemic infection experiments with compound 6l revealed its effectiveness against MRSA and S. aureus cfr N12 with the ED50 of 11.08 mg/kg and 14.63 mg/kg body weight, respectively.

Structural Modifications and Biological Evaluations of Rift Valley Fever Virus Inhibitors Identified from Chemical Library Screening.

The Rift Valley fever virus (RVFV) is an emerging high-priority pathogen endemic in Africa with pandemic potential. There is no specific treatment or approved antiviral drugs for the RVFV. We previously developed a cell-based high-throughput assay to screen small molecules targeting the RVFV and identified a potential effective antiviral compound (1-N-(2-(biphenyl-4-yloxy)ethyl)propane-1,3-diamine) as a lead compound. Here, we investigated how structural modifications of the lead compound affected the biological properties and the antiviral effect against the RVFV. We found that the length of the 2-(3-aminopropylamino)ethyl chain of the compound was important for the compound to retain its antiviral activity. The antiviral activity was similar when the 2-(3-aminopropylamino)ethyl chain was replaced with a butyl piperazine chain. However, we could improve the cytotoxicity profile of the lead compound by changing the phenyl piperazine linker from the para-position (compound 9a) to the meta-position (compound 13a). Results from time-of-addition studies suggested that compound 13a might be active during virus post-entry and/or the replication phase of the virus life cycle and seemed to affect the K+ channel. The modifications improved the properties of our lead compound, and our data suggest that 13a is a promising candidate to evaluate further as a therapeutic agent for RVFV infection.

Highly bioresistant, hydrophilic and rigidly linked trityl-nitroxide biradicals for cellular high-field dynamic nuclear polarization.

Cellular dynamic nuclear polarization (DNP) has been an effective means of overcoming the intrinsic sensitivity limitations of solid-state nuclear magnetic resonance (ssNMR) spectroscopy, thus enabling atomic-level biomolecular characterization in native environments. Achieving DNP signal enhancement relies on doping biological preparations with biradical polarizing agents (PAs). Unfortunately, PA performance within cells is often limited by their sensitivity to the reductive nature of the cellular lumen. Herein, we report the synthesis and characterization of a highly bioresistant and hydrophilic PA (StaPol-1) comprising the trityl radical OX063 ligated to a gem-diethyl pyrroline nitroxide via a rigid piperazine linker. EPR experiments in the presence of reducing agents such as ascorbate and in HeLa cell lysates demonstrate the reduction resistance of StaPol-1. High DNP enhancements seen in small molecules, proteins and cell lysates at 18.8 T confirm that StaPol-1 is an excellent PA for DNP ssNMR investigations of biomolecular systems at high magnetic fields in reductive environments.

A mitochondria-targeting and polarity-sensitive fluorescent probe for cancer diagnosis

Polarity is a significant microenvironment-related parameter in living systems. It has been reported that the mitochondrial polarity level in cancer cells is remarkably lower than that in normal cells, demonstrating the potential of being a potential marker for the accurate diagnosis of cancers. Hence, in this work, a mitochondria-targeting fluorescent probe (NCT) with polarity-sensitive property was developed for cancer diagnosis based on the distinct mitochondrial polarity difference between cancerous cells and normal cells. For the design of the probe, we rationally combined two common ICT-based fluorophores (naphthalimide and coumarin) via a piperazine linker to endow the probe with more robust polarity-sensitive properties. The spectra results showed that all the fluorescence emission properties (emission intensity, quantum yield and lifetime) of probe were changed with the surrounding polarity, confirming the excellent polarity-sensitive merits of probe in solution. Subsequently, we explored the potential of this polarity-sensitive probe for the diagnosis of cancer. The imaging results demonstrated that NCT could emit strong fluorescence in the cancer cells, tissues and solid tumors (low-polarity environment), while almost no fluorescence was observed in normal cells, tissues and organs (high-polarity environment). In other words, NCT could differentiate cancer cells from normal cells in living systems based on the mitochondrial polarity difference of them. Consequently, we believe that this polarity-sensitive fluorescent probe could not only provide insight into the relationship between mitochondrial polarity and cancer, but also emerged as a potential tool for the diagnosis of tumors.

Synthesis and antifungal activity of new hybrids thiazolo[4,5-d]pyrimidines with (1H-1,2,4)triazole

Synthesis and antifungal activity of hybrids of thiazolo[4,5-d]pyrimidines with (1H-1,2,4)triazoles are presented. The solubility and lipophilicity of compounds was assessed and it was discovered that compounds with piperazine linker exhibited significant antifungal activity against filamentous and yeast fungi.

A rainbow of acridinium chemiluminescence.

Multicolor chemiluminescent acridinium derivatives were synthesized by attaching various common fluorophores to the N10 -acridinium position through a piperazine linker. Triggering of each acridinium derivative using alkaline hydrogen peroxide resulted in a chemiluminescence spectrum dominated by a strong emission (>95%) from the attached fluorophore. The highly quenched emission from the triggered acridinium, acting as a donor, points to a highly efficient intramolecular energy transfer in acridinium-based chemiluminophore-fluorophore tandems. A variable, and in many cases minimal, spectral overlap between the donor emission and the acceptor absorption may indicate that in such tandems the energy transfer follows the Dexter electron exchange mechanism. Moreover, fluorophores affixed through the acridinium 9-position produce a typical acridinium emission profile, demonstrating the need for close distances and favorable intramolecular orientation of the donor and acceptor moieties for the energy transfer to occur. A family of red-shifted chemiluminescent labels, all sharing a uniform triggering method, will find immediate application in multicolor ligand-receptor assays. Along with the multiplexing capabilities, the red-shifted chemiluminescent detection offers a higher tolerance to green-colored biological interferences and will therefore benefit many screening and diagnostic clinical tests.

Discovery of novel tetrahydrobenzo[b]thiophene-3-carbonitriles as histone deacetylase inhibitors

The discovery and development of isoform-selective histone deacetylase (HDAC) inhibitor is a challenging task because of the sequence homology among HDAC enzymes. In the present work, novel tetrahydro benzo[b]thiophene-3-carbonitrile based benzamides were designed, synthesized, and evaluated as HDAC inhibitors. Pharmacophore modeling was our main design strategy, and two novel series of tetrahydro benzo[b]thiophene-3-carbonitrile derivatives with piperidine linker (series 1) and piperazine linker (series 2) were identified as HDAC inhibitors. Among all the synthesised compounds, 9h with 4-(aminomethyl) piperidine linker and 14n with piperazine linker demonstrated good activity against human HDAC1 and HDAC6, respectively. Both the compounds also exhibited good antiproliferative activity against several human cancer cell lines. Both these compounds (9h and 14n) also induced cell cycle arrest and apoptosis in U937 and MDA-MB-231 cancer cells. Overall, for the first time, this research discovered potent isoform-selective HDAC inhibitors using cyclic linker instead of the aliphatic chain and aromatic ring system, which were reported in known HDAC inhibitors.

Synthesis ofN‐HeterocyclicCarbine Silver(I) and Palladium(II) Complexes with Acylated Piperazine Linker and Catalytic Activity in Three Types of C—C Coupling Reactions

Main observation and conclusionTwo bis‐imidazolium salts LH2·Cl2and LH2·(PF6)2with acylated piperazine linker and twoN‐heterocyclic carbene (NHC) silver(I) and palladium(II) complexes [L2Ag2](PF6)2(1) and [L2Pd2Cl4] (2) were prepared. The crystal structures of LH2·Cl2and 1 were confirmed by X‐ray analysis. In 1, one 26‐membered macrometallocycle was generated through two silver(I) ions and two bidentate ligands L. The catalytic activity of 2 was investigated in Sonogashira, Heck‐Mizoroki and Suzuki‐Miyaura reactions. The results displayed that these C—C coupling reactions can be smoothly carried out under the catalysis of 2.

Coal-Tar Dye-based Coordination Cages and Helicates.

A strategy to implement four members of the classic coal‐tar dye family, Michler's ketone, methylene blue, rhodamine B, and crystal violet, into [Pd2L4] self‐assemblies is introduced. Chromophores were incorporated into bis‐monodentate ligands using piperazine linkers that allow to retain the auxochromic dialkyl amine functionalities required for intense colors deep in the visible spectrum. Upon palladium coordination, ligands with pyridine donors form lantern‐shaped dinuclear cages while quinoline donors lead to strongly twisted [Pd2L4] helicates in solution. In one case, single crystal X‐ray diffraction revealed rearrangement to a [Pd3L6] ring structure in the solid state. For nine examined derivatives, showing colors from yellow to deep violet, CD spectroscopy discloses different degrees of chiral induction by an enantiomerically pure guest. Ion mobility mass spectrometry allows to distinguish two binding modes. Self‐assemblies based on this new ligand class promise application in chiroptical recognition, photo‐redox catalysis and optical materials.

Combining hydrophilic and hydrophobic environment sensitive dyes to detect a wide range of cellular polarity.

Intracellular polarity is an important parameter of pathological and biological phenomena of cells; abnormal polarities are associated with diabetes, neurological diseases, and cancer. However, previously reported polarity probes have issues with quantitatively detecting intracellular polarities, can measure only a limited range of polarities, and can only detect specific intracellular regions. Here, we developed a novel two-dye system, RPS-1, that contains a new "turn-on" polarity probe (Dye1) based on a spiropyran intramolecular ring closing-opening system activated in polar protic solvents, and a benzothiadiazole containing dye (Dye3), which emits only in non-polar solvents with a large stoke shift. Individually, Dye1 and Dye3 selectively localized to lysosome and lipid droplets, respectively; however, combining these dyes, which have completely different characteristics, via a piperazine linker resulted in the staining of various intracellular organelles. Therefore, as Dye1 and Dye3 have the same absorption but different emissions, combining them resulted in a ratiometric polarity probe that could quantitatively measure a wider polarity range inside the cell using a single excitation source. In addition, ratiometric imaging using our RPS-1 probe to quantitatively detect the distribution of polarity in different cell lines indicated that lysosomes were the most polar organelles in the cell.

A 18β-glycyrrhetinic acid conjugate with Vorinostat degrades HDAC3 and HDAC6 with improved antitumor effects

Semisynthetic 18β-glycyrrhetinic acid (GA) analogues bearing 1-en-2-cyano-3-oxo substitution on ring A have enhanced antitumor effects with reduced levels of HDAC3 and HDAC6 proteins. Aiming to inhibit both HDAC protein and activity, we developed a hybrid molecule by tethering active GA analogue methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate (CDODA-Me) and Vorinostat (SAHA). We tested the proper hybrid approaches of GA with hydroxamic acid and turned out that GA conjugated with SAHA by a piperazine linker was the best. The conjugate (15) of CDODA-Me and SAHA linked through a piperazine group was a potent cytotoxic agent against cancer cells with apoptosis induction. Compound 15 was more effective than the simple combination of CDODA-Me and SAHA to induce apoptosis. Mechanistic studies revealed that 15 was less effective than SAHA to inhibit HDAC activity, but was more effective than CDODA-Me to decrease the levels of HDAC3 and HDAC6 proteins with upregulated levels of acetylated H3 and acetylated α-tubulin. Compound 15 represents a new HDAC3 and HDAC6 inhibitor by reducing protein levels.

Design, Synthesis, and Evaluation of Lipopeptide Conjugates of Mercaptoundecahydrododecaborate for Boron Neutron Capture Therapy.

We developed new 10 B carriers for boron neutron capture therapy (BNCT) that can effectively transport and accumulate boron clusters into cells. These carriers consist of a lipopeptide, mercaptoundecahydrododecaborate (BSH), and a disulfide linker. The carriers were conceived according to the structure of pepducin, a membrane-penetrating lipopeptide targeting protease-activated receptor 1 (PAR1). To improve the membrane permeability of BSH, the structure was optimized using various lipopeptides possessing different peptides and lipid moieties. These synthesized lipopeptides were conjugated with BSH and evaluated for intracellular uptake using T98G glioblastoma cells. Among them, the most effectively incorporated and accumulated in the cells was compound 5 a, which contains a peptide of 13 residues derived from the intracellular third loop of PAR1 and a palmitoyl group. For further improvement of 10 B accumulation in cells, the introduction of an amine linker was investigated; intracellular uptake similar to that of 5 a was observed for compound 14, which has a piperazine linker. Both compounds 5 a and 14 showed a stronger radiosensitizing effect than BSH along on T98G cells under mixed-neutron beam irradiation. The results demonstrate that lipopeptide conjugation is effective for enhancing intracellular delivery and accumulation of BSH and improving the cytotoxic effect of BNCT.