Ligands 1a Research Articles

Pharmacological explorations of eco-friendly amide substituted (Z)-β-enaminones as anti-breast cancer drugs.

Amide substituted (Z)-β-enaminones were synthesized by green chemistry and stereo-specific synthetic pathway as novel phosphoinositide 3-kinase (PI3K) inhibitors and breast cancer drugs. PI3K inhibition was measured by competitive ELISA. A panel of cancer cell lines including MCF-7 (breast cancer), G-361 (skin cancer), and HCT 116 (colon cancer) were used to assess the anticancer potentials. In the PI3K assay, 2c and 2f were indolent for the proposed inhibitory action, which was recognized from the obtained IC50 (>1.0 μM). Excellent activity potential of 2a, 2b, and 2d was recognized from the IC50 range (<0.05 μM) whereas an intermediate action potential was observed for compounds 2e and 2i (IC50 0.1 and 0.25, respectively). The docking results exclusively proposed that the hydrophobic interactions in the PI3K binding pocket were overwhelmed by the binding affinity of the most potent ligands (2a, 2b, and 2d: inhibitory constant Ki = 18.16, 84.87, and 56.14 nM). MTT assay results revealed the antiproliferative activity domination of selected compounds (2a, 2b, and 2d) toward MCF-7. The relative activities of 2a, 2b, and 2d of 84.56, 80.87, and 90.12%, respectively, were comparable to that of the standard, doxorubicin (82.16%). SAR studies demonstrated amide substituted (Z)-β-enaminones as precise PI3K inhibitors to treat breast cancer.

Novel 5-(quinuclidin-3-ylmethyl)-1,2,4-oxadiazoles to investigate the activation of the α7 nicotinic acetylcholine receptor subtype: Synthesis and electrophysiological evaluation

α7 nicotinic acetylcholine receptors (nAChRs) are relevant therapeutic targets for a variety of disorders including neurodegeneration, cognitive impairment, and inflammation. Although traditionally identified as an ionotropic receptor, the α7 subtype showed metabotropic-like functions, mainly linked to the modulation of immune responses. In the present work, we investigated the structure-activity relationships in a set of novel α7 ligands incorporating the 5-(quinuclidin-3-ylmethyl)-1,2,4-oxadiazole scaffold, i.e. derivatives 21a-34a and 21b-34b, aiming to identify the structural requirements able to preferentially trigger one of the two activation modes of this receptor subtype. The new compounds were characterized as partial and silent α7 nAChR agonists in electrophysiological assays, which allowed to assess the contribution of the different groups towards the final pharmacological profile. Overall, modifications of the selected structural backbone mainly afforded partial agonists, among them tertiary bases 27a-33a, whereas additional hydrogen-bond acceptor groups in permanently charged ligands, such as 29b and 31b, favored a silent desensitizing profile at the α7 nAChR.

Inhibition of adherence of the yeast Candida albicans to buccal epithelial cells by synthetic aromatic glycoconjugates

The yeast Candida albicans is an opportunistic fungal pathogen which induces superficial and systemic infections in immunocompromised patients. Adherence to host tissue is critical to its ability to colonise and infect the host. The work presented here describes the synthesis of a small library of aromatic glycoconjugates (AGCs) and their evaluation as inhibitors of C. albicans adherence to exfoliated buccal epithelial cells (BECs). We identified a divalent galactoside, ligand 2a, capable of displacing over 50% of yeast cells already attached to the BECs. Fluorescence imaging indicates that 2a may bind to structural components of the fungal cell wall.

Radiosynthesis and in vivo evaluation of a fluorine-18 labeled pyrazine based radioligand for PET imaging of the adenosine A2B receptor

On the basis of a pyrazine core structure, three new adenosine A2B receptor ligands (7a–c) were synthesized containing a 2-fluoropyridine moiety suitable for 18F-labeling. Compound 7a was docked into a homology model of the A2B receptor based on X-ray structures of the related A2A receptor, and its interactions with the adenosine binding site were rationalized. Binding affinity data were determined at the four human adenosine receptor subtypes. Despite a rather low selectivity regarding the A1 receptor, 7a was radiolabeled as the most suitable candidate (Ki(A2B) = 4.24 nM) in order to perform in vivo studies in mice with the aim to estimate fundamental pharmacokinetic characteristics of the compound class. Organ distribution studies and a single PET study demonstrated brain uptake of [18F]7a with a standardized uptake value (SUV) of ≈1 at 5 min post injection followed by a fast wash out. Metabolism studies of [18F]7a in mice revealed the formation of a blood–brain barrier penetrable radiometabolite, which could be structurally identified. The results of this study provide an important basis for the design of new derivatives with improved binding properties and metabolic stability in vivo.

Anticancer Activity and Catalytic Potential of Ruthenium(II)-Arene Complexes with N,O-Donor Ligands.

The special ability of organometallic complexes to catalyze various transformations might offer new effective mechanisms for the treatment of cancer. Studies that report both the biological properties and the ability of metallic complexes to promote therapeutically relevant catalytic reactions are limited. Herein, we report the anticancer activity and catalytic potential of some ruthenium(II)-arene complexes bearing bidentate Schiff base ligands (2a and 2b) and their reduced analogues (5a and 5b, respectively). In comparison to their Schiff base counterparts 2a and 2b, we demonstrate that amine complexes 5a and 5b display (i) a higher in vitro antiproliferative activity on different human cancer cell lines, (ii) a lower rate of hydrolysis, and (iii) an improved initial catalytic rate for the reduction of NAD+ to NADH. In contrast to their imine analogues 2a and 2b, we also show that amine complexes 5a and 5b induce the generation of intracellular reactive oxygen species (ROS) in MCF-7 breast cancer cells. Our results highlight the impact that a simple ligand modification such as the reduction of an imine moiety can have on both the catalytic and biological activities of metal complexes. Moreover, the ruthenium complexes reported here display some antiproliferative activity against T47D breast cancer cells, known for their cis-platin resistance.

New (arene)ruthenium(II) complexes of 4‑aryl‑4H‑naphthopyrans with anticancer and anti-vascular activities

A series of four 2‑amino‑3‑cyano‑4‑(3/4‑pyridyl)‑4H‑benzo[h]chromenes 2a–d and their dichlorido(p‑cymene)ruthenium(II) complexes 3a–d were tested for antiproliferative, vascular-disruptive, anti-angiogenic and DNA-binding activity. The coordination of the 4‑pyridyl‑4H‑naphthopyrans 2 to ruthenium led to complexes with pleiotropic effects. Unlike the free ligands 2a–d, their ruthenium complexes 3a–d showed a significant affinity for DNA as demonstrated by electrophoretic mobility shift assays (EMSA) and ethidium bromide assays. Binding of 3a–d to calf thymus DNA proceeded about 10-times faster compared with cisplatin. Treatment of HT-29 colon carcinoma, 518A2 melanoma and MCF-7Topo breast cancer cells with 3a and 3b caused an accumulation of cells in the G2/M phase and an increase of the fraction of mitotic cells in the case of HT-29, due to alterations of the microtubule cytoskeleton as shown by immunofluorescence staining. Complexes 3b–c showed a dual effect on the vascular system. They suppressed angiogenesis in zebrafish embryos and they destroyed the vasculature of the chorioallantoic membrane (CAM) in fertilized chicken eggs. They also inhibited the vasculogenic mimicry, typical of U-87 glioblastoma cells in tube formation assays.

Structural Characterization of a Fluorido‐Amide of Niobium, and Facile CO2 Incorporation Affording a Fluorido‐Carbamate

We have prepared the first niobium(V) compounds bearing fluorido and monodentate amido ligands (1a–c), which are tetranuclear cations, by the reaction between NbF5 and Me3SiNMe2 in the presence of a chloride (or bromide) source. The fluorido/carbamato derivative NbF2(O2CNMe2)3 (2) was obtained in good yield from the reaction of NbF5 and Me3SiNMe2 in the presence of carbon dioxide at 1 atm pressure and ambient temperature. All the products were characterized by analytical and spectroscopic (IR, multinuclear NMR) methods, and by X‐ray diffraction in the cases of 1b,c. DFT calculations were useful for elucidating the structures of the products and also for providing an insight into the reaction pathways.

Fluorescent chemosensor based on urea/thiourea moiety for sensing of Hg(II) ions in an aqueous medium with high sensitivity and selectivity: A comparative account on effect of molecular architecture on chemosensing

Mercury is a well-known heavy metal ion which is extremely poisonous to health but is still employed in the form of mercury salts and organomercury compounds in various industrial, anthropological and agricultural activities. Henceforth, its sensing in aqueous medium is an area of great interest in order to avoid its hazardous effect. In the present manuscript, urea/thiourea linkage bearing four organic ligands (1a, 1b, 2a and 2b) are synthesized by a three-step synthetic approach. The organic ligands were then employed to develop organic nanoparticles by re-precipitation method which was further probed for their selective recognition behavior in an aqueous medium using fluorescence spectroscopy. The fluorescence emission profile of the ONPs is used as a tool for the tracking of sensing behavior. The ONPs of 1b has shown selective recognition towards Hg(II) in aqueous medium evidenced by enhancement of fluorescence emission intensity after complexation of 1b ONP with Hg(II), among several alkali, alkaline earth and transition metal ions with a detection limit of the order of 0.84 μM. The ability of the proposed sensor to sense Hg(II) ions with high selectivity and sensitivity could be accounted to photo-induced electron transfer (PET) “OFF” mechanism at λem = 390 nm. This study reveals the application of the proposed thiourea-based sensor for the selective recognition of the Hg(II) ions in an aqueous medium.

Cyclometalated N-heterocyclic carbene iridium(iii) complexes with naphthalimide chromophores: a novel class of phosphorescent heteroleptic compounds.

A series of cyclometalated N-heterocyclic carbene complexes of the general formula [Ir(C^N)2(C^C:)] has been prepared. Two sets of compounds were designed, those where (C^C:) represents a bidentate naphthalimide-substituted imidazolylidene ligand and (C^N) = ppy (3a), F2ppy (4a), bzq (5a) and those where (C^C:) represents a naphthalimide-substituted benzimidazolylidene ligand and (C^N) = ppy (3b), F2ppy (4b), bzq (5b). The naphthalimide-imidazole and naphthalimide-benzimidazole ligands 1a,b and the related imidazolium and benzimidazolium salts 2a,b were also prepared and fully characterized. The N-heterocyclic carbene Ir(iii) complexes have been characterized by NMR spectroscopy, cyclic voltammetry and elemental analysis. Moreover, the molecular structures of one imidazolium salt and four Ir(iii) complexes were determined by single-crystal X-ray diffraction. The structures provide us with valuable information, most notably the orientation of the naphthalimide chromophore with respect to the N-heterocyclic carbene moiety. All compounds are luminescent at room temperature and in a frozen solvent at 77 K, exhibiting a broad emission band that extends beyond 700 nm. The presence of the naphthalimide moiety changes the character of the lowest excited state from 3MLCT to 3LC, as corroborated by DFT and TD-DFT calculations. Remarkably, replacing imidazole with a benzimidazole unit improves the quantum yields of these compounds by decreasing the knr values which is an important feature for optimized emission performance. These studies provide valuable insights about a novel class of N-heterocyclic carbene-based luminescent complexes containing organic chromophores and affording metal complexes emitting across the red-NIR range.

A convenient transesterification method for synthesis of AT2 receptor ligands with improved stability in human liver microsomes

A series of AT2R ligands have been synthesized applying a quick, simple, and safe transesterification-type reaction whereby the sulfonyl carbamate alkyl tail of the selective AT2R antagonist C38 was varied. Furthermore, a limited number of compounds where acyl sulfonamides and sulfonyl ureas served as carboxylic acid bioisosteres were synthesized and evaluated. By reducing the size of the alkyl chain of the sulfonyl carbamates, ligands 7a and 7b were identified with significantly improved in vitro metabolic stability in both human and mouse liver microsomes as compared to C38 while retaining the AT2R binding affinity and AT2R/AT1R selectivity. Eight of the compounds synthesized exhibit an improved stability in human microsomes as compared to C38.

Cobalt (II) complexes bearing N , N , S tridentate ligands as precatalysts for 1,3-butadiene polymerization

Abstract A series of cobalt(II) complexes supported by 8-(methylthio)-2-(R-pyrazolyl)quinoline (R = H, CH3, and Ph) ligands (3a–3e) were synthesized and characterized by elemental, FT-IR, and UV–visible analyses. X-ray diffraction analysis revealed that complexes 3b and 3c adopted distorted square pyramidal geometry and trigonal bipyramidal geometry, respectively. Activated by methylaluminoxane (MAO) and ethylaluminum sesquichloride (EASC), the polymerization of 1,3-butadiene with these complexes afforded polymers with high cis-1,4 regularity (ca. 95%) in high yields. The substituent structure on the ligand influenced the catalytic behaviors. Complex 3a without substituent exhibited higher activity than its methyl-substituted counterparts 3b and 3c, while the phenyl-substituted complexes gave polymers in quantitative yields. In particular, even at a high temperature of 100 °C MAO- and EASC- based systems gave polymers in relatively high yields, indicating high thermal stability of the generated active species.

A pronounced ligand effect on platinum‐catalyzed Hydrosilylation of terminal alkynes

The use of ligands to tune the reactivity and regioselectivity of transition metal‐based catalyst for silicon‐mediated organic synthesis (SiMOS) is an important topic and challenge in organosilicon chemistry and synthetic organic chemitstry. In this manuscript, the dual ligand platinum catalyst system was developed for the hydrosilylation of alkynes. It was found that regioselectivity enhancement was determined with combinational use of phosphine ligand (6a) and multifunctional Py‐BINMOL ligand (4a). The corresponding vinylsilanes were obtained in high yields and high regioselectivities.

Bifunctional role of ephrin A1-Eph system in stimulating cell proliferation and protecting cells from cell death through the attenuation of ER stress and inflammatory responses in bovine mammary epithelial cells.

Structural and functional development of the mammary gland is constant in the mammary gland life cycle. Eph receptors and their ligands, ephrins, control events through cell-to-cell interactions during embryonic development, and adult tissue homeostasis; however, little information on participation of ephrin A1, a representative ligand of the Eph receptor, in the development and function of normal mammary glands is known. In this study, we demonstrated functional effects of the ephrin A1-Eph system and mechanisms of its action on bovine mammary epithelial (MAC-T) cells. The in vitro cultured MAC-T cells expressed the ephrin A1 ligand and EphA1, A2, A4, A7, and A8 among the eight members of the Eph A family. Our results revealed that ephrin A1 induced MAC-T cell cycle progression and stimulated cell proliferation with abundant expression of nucleic PCNA and cyclin D1 proteins. Additionally, ephrin A1 induced activation of intracellular signaling molecules involved in PI3 K/AKT and MAPK signaling, and the proliferation-stimulating effect of ephrin A1 was mediated by activation of these pathways. Furthermore, ephrin A1 influenced expression and activation of various ER stress-related proteins and protected MAC-T cells from stress-induced cell death. Finally, ephrin A1 alleviated LPS-induced cell death through down-regulation of inflammatory cytokines. In conclusion, the results of this study suggest that the Eph A-ephrin A1 system is a positive factor in the increase and maintenance of epithelial cells in mammary glands of cows; the signaling system contributes to development, remodeling, and functionality of normal mammary glands and could overcome mastitis in cows and other mammals.

Highly Active ansa-(Fluorenyl)(amido)titanium-Based Catalysts with Low Load of Methylaluminoxane for Syndiotactic-Specific Living Polymerization of Propylene

ansa-Dimethylsilylene(fluorenyl)(amido)titanium complexes bearing various electron-donating substituents are synthesized and applied to propylene polymerization by the use of MMAO/2,6-di-tert-butyl-4-methylphenol as a cocatalyst. The complexes containing adamantylamido ligands (1a,b) show unexpectedly high activity (31150 kg of polymer (mol of Ti)−1 h–1) with a low Al:Ti ratio of 20. The catalysts also promote syndiotactic-specific living polymerization to produce propylene-ethylene block copolymers.

Synthesis of meta-substituted monodentate phosphinite ligands and implication in hydroformylation $$^\dagger $$ †

Synthesis of meta-substituted phosphinite ligands 3,3 $$'$$ -(methoxyphosphanediyl)bis(N,N- diethylaniline) (4a) and methoxybis(3-methoxyphenyl)phosphane (4b), in high yields, has been demonstrated. Typical phosphorus chemical shift between 110–120 ppm, appearance of methoxy protons and corresponding carbon, as well as ESI-MS spectra unambiguously confirmed the existence of phosphinite ligands 4a and 4b. To demonstrate the synthetic usefulness of 4a and 4b, these ligands were tested in the rhodium catalyzed hydroformylation of 1-octene. The diethylamine substituted ligand 4a was found to be highly active, whereas 4b was less reactive but revealed slightly better regioselectivity of 62% under optimized conditions. Additionally, 4a and 4b were found to catalyze the hydroformylation of styrene, 1-undecenol and 1,1-disubstituted functional olefin, methyl methacrylate. Both the ligands displayed excellent conversion of styrene, and 4b revealed an excellent branch selectivity of 75%. Although 1-undecenol proved to be amenable to hydroformylation (85–90% conversion to aldehyde), both the ligands failed to discriminate between the linear and branched products. Substrate methyl methacrylate proved to be highly challenging and reduced conversion (between 33–42%) was observed under optimized conditions. Ligand 4a was found to be highly selective towards linear aldehyde (81% linear selectivity). Synopsis Two step synthetic protocol to access meta-substituted monodentate phosphinite ligands 3,3 $$'$$ -(methoxyphosphanediyl)bis(N,N-diethylaniline) (4a) and methoxybis(3-methoxyphenyl)phosphane (4b) has been developed and the ligands have been fully characterized. Apart from catalyzing the hydroformylation of benchmark substrates 1-octene and styrene, 4a and 4b were found to catalyze the hydroformylation of 1-undecenol, a functional olefin and a highly challenging 1,1-disubstituted functional olefin methyl methacrylate.

Incorporation of dihydroartemisinin into memantine through a propriate spacer to make hybrid with enhanced effects to protect PC12 cells from corticosterone-caused impairments

Ten memantine(Mema)-dihydroartemisinin(DHA) ligands were designed and synthesized. Three types of isomers including α, β, and a defined γ isomer were found in each intermediates(1a—1e). Type γ isomer was firstly reported here and confirmed as a less stable eclipsed conformation. The bonding of Mema with DHA through different carbon chains generally makes the new entities more cytotoxic than either Mema or artemisinin(Arte). The β Mema/DHA ligands are a little bit more cytotoxic than α ligands. By applying corticosterone(Cort)-impaired PC12 cells models, it was found that Mema and those ligands with more than 3 carbon chains showed weak or no neuro-protective activities against the insults. However, two ligands, 2a(β) and 2b(β) showed better effects than either Arte or their combination(Mema/Arte in 1:1 molar ratio) at a dose of 5 µmol/L. Furthermore, ligands 2a(β), 2b(β) and 2c(β) were confirmed as mild N-methyl-D-aspartate(NMDA) antagonists, and their corresponding α isomers are weak NMDA antagonists. All the data indicate that the bonding of Mema/DHA in compacted β conformation mode results in enhanced effects against Cort-induced insults in PC12 cells and might reverse memantine as an anti-depression NMDA antagonist.

Synthesis, Structural Characterization and Catalytic Evaluation of Anionic Phosphinoferrocene Amidosulfonate Ligands

Triethylammonium salts of phosphinoferrocene amidosulfonates with electron-rich dialkyphosphino substituents, R2PfcCONHCH2SO3(HNEt3) (4a–c), where fc = ferrocene-1,1′-diyl, and R = i-Pr (a), cyclohexyl (Cy; b), and t-butyl (c), were synthesized from the corresponding phosphinocarboxylic acids-borane adducts, R2PfcCO2H·BH3 (1a–c), via esters R2PfcCO2C6F5·BH3 (2a–c) and adducts R2PfcCONHCH2SO3(HNEt3)·BH3 (3a–c). Compound 4b was shown to react with [Pd(μ-Cl)(η-C3H5)]2 and AgClO4 to afford the zwitterionic complex [Pd(η3-C3H5)(Cy2PfcCONHCH2SO3-κ2O,P)] (5b), in which the amidosulfonate ligand coordinates as a chelating donor making use of its phosphine moiety and amide oxygen. The structures of 3b·CH2Cl2, 4b and 5b·CH2Cl2 were determined by single-crystal X-ray diffraction analysis. Compounds 4a–c and their known diphenylphosphino analogue, Ph2PfcCONHCH2SO3(HNEt3) (4d), were studied as supporting ligands in Pd-catalyzed cyanation of aryl bromides with K4[Fe(CN)6] and in Suzuki–Miyaura biaryl cross-coupling performed in aqueous reaction media under mild reaction conditions. In the former reaction, the best results were achieved with a catalyst generated from [PdCl2(cod)] (cod = η2:η2-cycloocta-1,5-diene) and 2 equiv. of the least electron-rich ligand 4d in dioxane–water as a solvent. In contrast, the biaryl coupling was advantageously performed with a catalyst resulting from palladium(II) acetate and ligand 4a (1 equiv.) in the same solvent.

Antibacterial activities of sulfamethoxazolyl-azo-phenols and their Cu(II) complexes along with molecular docking properties.

Sulfamethoxazolyl-azo-phenols [SMX-N=N-C6H2(R)(R/)-OH] (1a, 2a) and their Cu(II) complexes, [Cu(SMX-N=N-C6H2(R)(R/)-O)2] (1b, 2b) (R=p-OMe, R/=H, 1a/1b; R=p-Cl, R/=m-CH3, 2a/2b) show antibacterial sensitivity against Gram-positive bacteria, B. subtillis; IC50: 281.47±1.84μM (1a), 126.39±1.66μM (1b), and 279.94±3.15μM (2a), 123.62±1.27μM(2b), and Gram-negative bacteria, E. coli; IC50: 204.66±3.31μM (1a) and 89.05±1.48μM (1b), 223.13±2.71μM (2a), and 98.26±1.59μM (2b). Interaction of DNA with free ligand (1a and 2a) is insignificant, while the complexes (1b and 2b) interact strongly and the binding constants are K b, 8.413×104 M-1 (1b) and 6.56×105 M-1 (2b). Optimized structures of the compounds are docked with protein structure of DHPS (E. coli) to propose the most favoured binding mode of the drugs in the active site. The in silico test of the compound helps to understand drug metabolism, drug-protein interactions, and toxicity (ADMET).

Living polymerization of 1,3-butadiene catalyzed by half-titanocene complex bearing dibenzhydryl-substituted aryloxide ligand

Half-titanocene complexes bearing dibenzhydryl-substituted aryloxide ligands (2a−2d) were prepared. Among them, 2c adopted a three-legged distorted tetrahedral geometry evidenced by X-ray crystallography. The poly-1,3-butadiene with high molecular weight and narrow molecular weight distribution was obtained by using these complexes as the catalysts activated with methylaluminoxane (MAO). The catalytic activities of the complexes depended on their structures. The Ti―O―C bond in the complexes with large angle afforded them with higher activity, while Cp*-based complexes exhibited lower activities than the Cp-based analogues. The activity of complex increased with increasing the polymerization temperature while the selectivity remained no change, indicating the high thermal stability. Furthermore, the polymerization of 1,3-butadiene catalyzed by 2a/MAO at 0 °C has been found in a living fashion.

Facile synthesis of new divergent imidazole-containing ligands for a 1-D cobalt(II) coordination polymer

A new divergent ligand (3a) containing a triaryl core and two imidazole side-arms has been designed and synthesized. The synthetic procedure utilizes a two-step strategy, i.e. the Kröhnke condensation, followed by a Cu-catalyzed Ullman-type coupling. This synthetic strategy allows the facile introduction of various substituents on the 4-position of the central pyridine in the ligands, which was proved by the synthesis of a ligand analog (3b). The new ligands were well characterized by spectroscopic methods and X-ray structural analysis was carried out for 3a. Reaction of 3a with Co(NCS)2 by a layering method afforded single crystals of a coordination polymer 5, which was structurally characterized by X-ray diffraction. 5 is composed of two ligands and one Co(NCS)2 in its asymmetric unit and features a 1-D coordination polymer with nano-scale metallomacrocyles. The structure of 5 is found to be quite different from all known coordination networks composed of Co(NCS)2 and closely related divergent ligands.