Macrocyclic Bis Research Articles

Synthesis, Characterization, and Computational Studies on Gallium(III) and Iron(III) Complexes with a Pentadentate Macrocyclic bis-Phosphinate Chelator and Their Investigation As Molecular Scaffolds for 18F Binding.

With the aim of obtaining improved molecular scaffolds for 18F binding to use in PET imaging, gallium(III) and iron(III) complexes with a macrocyclic bis-phosphinate chelator have been synthesized and their properties, including their fluoride binding ability, investigated. Reaction of Bn-tacn (1-benzyl-1,4,7-triazacyclononane) with paraformaldehyde and PhP(OR)2 (R = Me or Et) in refluxing THF, followed by acid hydrolysis, yields the macrocyclic bis(phosphinic acid) derivative, H2(Bn-NODP) (1-benzyl-4,7-phenylphosphinic acid-1,4,7-triazacyclononane), which is isolated as its protonated form, H2(Bn-NODP)·2HCl·4H2O, at low pH (HClaq), its disodium salt, Na2(Bn-NODP)·5H2O at pH 12 (NaOHaq), or the neutral H2(Bn-NODP) under mildly basic conditions (Et3N). A crystal structure of H2(Bn-NODP)·2HCl·H2O confirmed the ligand's identity. The mononuclear [GaCl(Bn-NODP)] complex was prepared by treatment of either the HCl or sodium salt with Ga(NO3)3·9H2O or GaCl3, while treatment of H2(Bn-NODP)·2HCl·4H2O with FeCl3 in aqueous HCl gives [FeCl(Bn-NODP)]. The addition of 1 mol. equiv of aqueous KF to these chloro complexes readily forms the [MF(Bn-NODP)] analogues. Spectroscopic analysis on these complexes confirms pentadentate coordination of the doubly deprotonated (bis-phosphinate) macrocycle via its N3O2 donor set, with the halide ligand completing a distorted octahedral geometry; this is further confirmed through a crystal structure analysis on [GaF(Bn-NODP)]·4H2O. The complex adopts the geometric isomer in which the phosphinate arms are coordinated unsymmetrically (isomer 1) and with the stereochemistry of the three N atoms of the tacn ring in the RRS configuration, denoted (N)RRS, and the phosphinate groups in the RR stereochemistry, denoted (P)RR, (isomer 1/RR), together with its (N)SSR (P)SS enantiomer. The greater thermodynamic stability of isomer 1/RR over the other possible isomers is also indicated by density functional theory (DFT) calculations. Radiofluorination experiments on the [MCl(Bn-NODP)] complexes in partially aqueous MeCN/NaOAcaq (Ga) or EtOH (Ga or Fe; i.e. without buffer) with 18F- target water at 80 °C/10 min lead to high radiochemical incorporation (radiochemical yields 60-80% at 1 mg/mL, or ∼1.5 μM, concentration of the precursor). While the [Fe18F(n-NODP)] is unstable (loss of 18F-) in both H2O/EtOH and PBS/EtOH (PBS = phosphate buffered saline), the [Ga18F(Bn-NODP)] radioproduct shows excellent stability, RCP = 99% at t = 4 h (RCP = radiochemical purity) when formulated in 90%:10% H2O/EtOH and ca. 95% RCP over 4 h when formulated in 90%:10% PBS/EtOH. This indicates that the new "GaIII(Bn-NODP)" moiety is a considerably superior fluoride binding scaffold than the previously reported [Ga18F(Bn-NODA)] (Bn-NODA = 1-benzyl-4,7-dicarboxylate-1,4,7-triazacyclononane), which undergoes rapid and complete hydrolysis in PBS/EtOH (refer to Chem. Eur. J. 2015, 21, 4688-4694).

Switch in Selectivities by Dinuclear Nickel Catalysis: 1,4-Hydroarylation of 1,3-Dienes to Z-Olefins.

One of the most challenging tasks in organic synthesis is to control selectivities, especially switching the well-known selectivity to obtain new isomers that were previously inaccessible. Inspired by biological catalysis involving multiple metal centers, catalysis enabled by binuclear metal complexes offers the potential to induce reactivity and selectivity that might not be available to mononuclear catalysts. Herein, we describe that using a macrocyclic bis pyridyl diimine dinickel complex as the catalyst, the commonly observed 4,3-regioselectivity of hydroarylation of 1,3-dienes is switched to 1,4-hydroarylation with thermodynamically less stable Z-stereoselectivity, offering challenging synthetic target Z-olefins. DFT calculations show that the activation of 1,3-diene proceeds through dinuclear Ni-diolefin coordination, and the synergistic effects of two Ni nuclei enable reactivity and selectivity of this binuclear catalysis substantially different from those of mononuclear nickel complexes in the current reaction.

Hydrodehalogenation of aryl halides by the mixture of palladium(II) and a newly synthesized chiral macrocyclic bis(N-heterocyclic carbene) ligand

A novel macrocyclic bis(N-heterocyclic carbene) precursor was designed and prepared, which manifested high catalytic efficiency when combining Pd(OAc)2 in hydrodehalogenation of aryl halides. The generation of a little amount of the intermediate product chlorobenzene is closely related with the synergistic effect of two imidazoline protons lying on the two opposite sides of the macrocycle.

Synthesis and the Antimicrobial Activity of Salt Carbenoid Compounds

Aim. To synthesize aliphatic and aromatic derivatives of salt carbenoid compounds of the series of imidazole, benzimidazole, pyridine, pyrimidine and 1,3,4-oxadiazole containing fluorophenyl, cetyl or adamantyl substituents, and study their antimicrobial (antibacterial and antifungal) activities.Results and discussion. New derivatives of heterocyclic carbenoid salts and zwitterions based on the imidazole, benzimidazole, pyridine, pyrimidine and 1,3,4-oxadiazole heterocyclic systems containing fluorophenyl, cetyl or adamantyl substituents were synthesized. For this purpose, reactions of cyclization of the corresponding diimines with ethoxymethyl chloride (imidazolium salts), quaternization of the corresponding azoles with cetyl bromide or 1-adamantyl bromide in organic solvents (benzimidazolium, pyridinium and 1,3,4-oxadiazolium salts), cyclization of di(1-adamantylamino)alkanes hydrobromides with the orthoformic ester (4,5-dihydroimidazolium and tetrahydropyridinium salts) were used. Zwitterionic compounds were obtained by the reaction of the corresponding azolium salts with phenyl isothiocyanate in the presence of potassium carbonate. Some macrocyclic and adamantyl substituted heterocyclic compounds showed antifungal and antibacterial activities.Experimental part. The structure of the compounds synthesized was proven by 1H and 13C NMR spectroscopy methods. The antimicrobial activity was studied out by the agar diffusion method to determine diameters of the growth inhibition zones of microorganisms (bacteria and fungi) and by the method of serial dilutions to determine the minimum inhibitory concentration and minimum bactericidal and fungicidal concentrations.Conclusions. The synthesis of new heterocyclic carbenoid salts and zwitterions based on the imidazole, benzimidazole, pyridine, pyrimidine and 1,3,4-oxadiazole heterocyclic systems containing fluorophenyl, cetyl or adamantyl substituents has been performed. Compounds of macrocyclic and adamantyl heterocyclic series with antifungal and antibacterial activities have been found. 1,3-Dicetylimidazolium bromide, macrocyclic bis(decylenebenzimidazolium) bromides, azolium-N-phenylthiocarboximides have been proven to be the most active.

Anti-Tumour Activities from Secondary Metabolites and Their Derivatives in Bryophytes: A Brief Review

Bryophytes are a poorly studied group of land plants that have been used in traditional medicine as a multipurpose remedy for centuries. Due to their peculiar morphology and physiology, bryophytes synthesise a multitude of secondary metabolites with a wide range of nutraceutical and pharmaceutical activities. Research has highlighted that secondary metabolites in bryophytes can also act as antitumour agents. Several studies have shown that bryophyte extracts and pure metabolites are cytotoxic against many cancer cell lines. Interestingly, some of these molecules and their derivatives are capable of acting on a specific target in cancer cells. Some macrocyclic(bis)bibenzyls from bryophytes can inhibit P-glycoprotein, reverting multidrug resistant cancer cell phenotypes, induce depolymerization of tubulin, stimulate apoptotic pathways, and inhibit angiogenesis. This brief review aims to collect recent knowledge on secondary metabolites of bryophytes and their derivatives, which have demonstrated an interaction with different molecular processes in cancer cells.

Intramolecular Arene Bonds of Complexes Featuring Terphenyl Bis(carbene) Macrocyclic Ligands

A series of macrocyclic bis(carbene) ligands were synthesized by linking 2,2″-bis(imidazole)terphenyl with a methylene, ethylene, propylene, or borate unit. Coordination complexes of iron were synt...

Synthesis Efforts of Acyclic Bis(monoalkylamino)maleonitriles and Macrocyclic Bis(dialkylamino)maleonitriles as Fluorescent Probes for Cations and a New Colorimetric Copper(II) Chemodosimeter

AbstractIn this article, we report on the synthesis of acyclic bis(monoalkylamino)maleonitriles and on the intended synthesis of macrocyclic bis(dialkylamino)maleonitriles to get fluorescent probes for cations. During our efforts to synthesize macrocyclic bis(dialkylamino)maleonitriles, we were only able to isolate macrocyclic bis(dialkylamino)‐fumaronitriles. The synthesis of macrocyclic bis(dialkylamino)maleonitriles is challenging, due to the fact that bis‐(dialkylamino)fumaronitriles are thermodynamically more stable than the corresponding bis(dialkylamino)‐maleonitriles. Further, it turned out that the acyclic bis(monoalkylamino)maleonitriles and macrocyclic bis‐(dialkylamino)fumaronitriles are no suitable tools to detect cations by a strong fluorescence enhancement. Further, only the bis(monoalkylamino)maleonitriles, which are bearing a 2‐pyridyl unit as an additional complexing unit, are able to selectively recognize copper(II) by a color change from yellow to red.

Synthesis and Ethylene Reactivity of Dinuclear Iron and Cobalt Complexes Supported by Macrocyclic Bis(pyridine-diimine) Ligands Containing o-Terphenyl Linkers

The synthesis and ethylene reactivity of a new family of dinuclear Co2Br4 and Fe2Br4 complexes supported by binucleating macrocyclic bis(pyridine-diimine) (PDI) ligands that contain 4,4″-R2-3,3″-o-terphenyl linkers (1, R = H; 2, R = Me; 3, R = iPr) are described. In the solid state, (1–3)M2Br4 (M = Zn, Fe, Co) adopt Cs-skew-syn structures in which the (PDI)M planes are skewed 49–82° relative to each other and both middle rings of the o-terphenyl bridges are on the same side of the molecule. The metal–metal distances range between 5.7600(8) and 6.232(1) Å. In solution, (1)M2Br4 (M = Zn, Co, Fe) undergo a fluxional process that permutes the two inequivalent (PDI)M units, while (2)M2Br4 and (3)M2Br4 are static and adopt Cs-symmetric structures similar to those observed in the solid state. Activation of (2)Fe2Br4 and (3)Fe2Br4 with MMAO-12 or triisobutylaluminum (TIBA) in the presence of ethylene generates catalysts that produce solid polyethylene (Mw = 4500–280000 Da), which contrasts with the reported production of α-olefins by analogous mononuclear (PDI)FeCl2 catalysts. (3)Fe2Br4/TIBA and (3)Fe2Br4/MMAO-12 produce polyethylenes with broad molecular weight distributions (MWDs) due to chain transfer to Al. (3)Co2Br4/1000 TIBA and (3)Co2Br4/1000 MMAO-12 also produce polyethylenes with broad MWDs. However, in these cases chain transfer to Al is not operative and the broad MWDs result from multisite behavior.

Template-Free Synthesis of a Macrocyclic Bis(pyridine-dienamine) Proligand and Metal Complexes of Its Bis(pyridine-diimine) and Bis(pyridine-dienamido) Forms.

We describe the template-free synthesis of the bis(pyridine-dienamine) proligand [4,5-(m-xylylenediamine)NH-C═(CH)(9-butyl-octahydroacridine)]2 (2'), a variant of Burrows's macrocyclic bis(pyridine-diimine) (bis-PDI) ligand [2,6-(m-xylylenediamine)N═C(py)]2 (A), using octahydroacridine as the ligand backbone. The octahydroacridine backbone favors macrocyclization by constraining the PDI units in the (s-cis)2 conformation. The template-free synthesis of 2' enables facile access to a wide array of bis-PDI and bis(pyridine-dienamido) (bis-PDE) metal complexes. Five-coordinate binuclear bis-PDI (2)M2Cl4 complexes {2 = [4,5-(m-xylylenediamine)N═C(9-butyl-octahydroacridine)]2; M = Zn, Co, or Fe} and a four-coordinate bis-PDI [(2)Pd2Br2][B(3,5-(CF3)2-Ph)4]2 complex were synthesized and characterized. (2)Zn2Cl4 undergoes macrocyclic ring inversion on the nuclear magnetic resonance (NMR) time scale with a free energy barrier ΔG⧧ of 15.5(3) kcal/mol at 295 K. In contrast, (2)Fe2Cl4 and (2)Co2Cl4 undergo slow ring inversion on the NMR chemical shift time scale at 295 K. The amine elimination reaction of 2' with Zr(NMe2)4 yields the bis-PDE complex (2'-4H)Zr2(NMe2)4, which was alkylated with AlMe3 and Al(CH2SiMe3)3 to generate (2'-4H)Zr2Me4 and (2'-4H)Zr2(CH2SiMe3)2(NMe2)2, respectively.

Design, Synthesis and Structure-activity Relationship Study of a Series of Bis(bibenzyl)-type Natural Products, Riccardin C Derivatives, as Candidate Anti-MRSA Agents

We previously showed that a naturally occurring macrocyclic bis(bibenzyl) derivative, riccardin C (RC), exhibits antibacterial activity towards methicillin-resistant Staphylococcus aureus (MRSA), with a potency comparable to that of the clinically used drug vancomycin. Here, we synthesized a series of RC derivatives to explore the structure-activity relationships (SAR). The SAR results clearly indicated that the number and positions of the phenolic hydroxyl groups are primary determinants of the anti-MRSA activity. Pharmacological characterization of the macrocyclic bis(bibenzyl) derivatives, together with fragment compounds and their dimers, indicated that the macrocycles and the fragment compounds elicit anti-MRSA activity with different mechanism(s) of action. The macrocyclic bis(bibenzyl)s are bactericidal, while the fragment compounds are bacteriostatic, showing only weak bactericidal activity. Treatment with a macrocyclic bis(bibenzyl) derivative significantly changed the intracellular Na+ and K+ concentrations of Staphylococcus aureus, and transmission electron microscopy revealed that treated cells developed intracellular lamellar mesosomal-like structures. These results indicated that the macrocyclic compound directly damages the gram-positive bacterial membrane, resulting in increased permeability.

Exploring the Conversion of Macrocyclic 2,2′-Biaryl Bis(thioureas) into Cyclic Monothioureas: An Experimental and Computational Investigation

Macrocyclic bis(thioureas) derived from 2,2'-biphenyl and binaphthyl skeletons have been synthesized by reaction of 2,2'-diaminobiaryl and 2,2'-bis(isothiocyanato)biaryl derivatives. The splitting of these bis(thioureas) into two units of the respective cyclic monothioureas has been monitored by NMR, shedding some light on the factors that control these processes. Additionally, a computational study revealed up to three mechanistic paths for the conversion of the 2,2'-biphenyl-derived bis(thiourea) into the corresponding monothiourea. The proposed mechanisms account for the participation of a molecule of water as an efficient proton-switch as well as for different classes of putative intermediates. The computational study also supports the ability of the thiourea group to participate in a plethora of processes, such as prototropic equilibria, sigmatropic shifts, heteroene and retro-heteroene reactions, and cis ⇆ trans isomerizations.

Access to the Enantiopure Axially Chiral Cyclophane Isoplagiochin D through Atropo-diastereoselective Heck Coupling.

Macrocyclization is typically the key step in the syntheses of cyclophane-type natural products. Considering cyclophanes with axially chiral biaryl moieties, the control of atroposelectivity is essential with biological activity and is synthetically challenging. We report an atroposelective approach involving Heck cyclization, which for the first time enables the total synthesis of an enantiopure macrocyclic bis(bibenzyl), namely isoplagiochin D. An enantiopure sulfinyl auxiliary in the ortho position of a biaryl axis (still flexible) was used to induce an atropo-diastereoselective Heck coupling (up to 98 % de). The traceless character of the sulfinyl auxiliary enables the introduction of a hydroxy group to give the target molecule with 98 % ee as well.

Fullerene bisadduct regioisomers containing an asymmetric diamide tether

Four macrocyclic bis(pyrrolidino)fullerene regioisomers with e-edge, e-face, trans-4 and cis-2 addition patterns were synthesized from the corresponding monoadduct by Prato's cycloaddition in a yield of 50%, and fully characterized by spectroscopic techniques. Bisadduct regioisomers were isolated easily in a pure form using dry-flash column chromatography. The relative ratio of the isolated regioisomers e-edge/e-face/trans-4/cis-2 was 1.0:1.9:1.5:4.9. Morphology of self-assembled structures of the four bisadduct regioisomers in solution was characterized using scanning electron microscopy.

Transcriptome Analysis of Marchantin Biosynthesis from the Liverwort Marchantia polymorpha

Marchantin A, the first characterized macrocyclic bis(bibenzyls) found in the liverwort Marchantia polymorpha shows interesting biological activities such as antifungal, antimicrobial, cytotoxic, antioxidant and muscle relaxing activity. Previously, Zenk et al. reported the phenylpropane/polymalonate pathway in the biosynthesis of the marchantins in M. polymorpha. To clear this pathway, transcriptome sequencing and digital gene expression analyses of M. polymorpha were carried out by using Illumina RNA-seq system.

Minimum structural requirements for cell membrane leakage-mediated anti-MRSA activity of macrocyclic bis(bibenzyl)s

Macrocyclic bis(bibenzyl)-type phenolic natural products, found exclusively in bryophytes, exhibit potent antibacterial activity towards methicillin-resistant Staphylococcus aureus (anti-MRSA activity). Here, in order to identify the minimum essential structure for cell membrane leakage-mediated anti-MRSA activity of these compounds, we synthesized acyclic fragment structures and evaluated their anti-MRSA activity. The activities of all of the acyclic fragments tested exhibited similar characteristics to those of the macrocycles, i.e., anti-MRSA bactericidal activity, an enhancing effect on influx and efflux of ethidium bromide (EtBr: fluorescent DNA-binder) in Staphylococcus aureus cells, and bactericidal activity towards a Staphylococcus aureus strain resistant to 2-phenoxyphenol (4). The latter result suggests that they have a different mechanism of action from 4, which is a FabI inhibitor previously proposed to be the minimum active fragment of riccardin-type macrocycles. Thus, cyclic structure is not a necessary condition for cell membrane leakage-mediated anti-MRSA activity of macrocyclic bis(bibenzyl)s.

Towards the enantioselective synthesis of axially chiral cyclic bis(bibenzyls) through sulfoxide-controlled diastereoselective Suzuki coupling

Natural macrocyclic bis(bibenzyls) exhibiting configurationally stable axially chiral biaryls are of high interest from a structural as well as from a synthetic point of view. An enantiopure sulfinyl auxiliary controlling an atropo-diastereoselective biaryl Suzuki coupling reaction has been investigated and promising results for the preparation of the biaryl moiety of cyclic bis(bibenzyls) like isoplagiochins C or D have been obtained. Furthermore, models explaining the stereoselectivity during transition state, and substitution effects including double stereo-differentiation, were discussed.

Reactivity of a Nickel(II) Bis(amidate) Complex with meta-Chloroperbenzoic Acid: Formation of a Potent Oxidizing Species.

Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped following reaction of a Ni(II) precursor bearing a macrocyclic bis(amidate) ligand with meta-chloroperbenzoic acid (HmCPBA). This compound is only detectable at temperatures below 250 K and is much more reactive toward organic substrates (i.e., C-H bonds, C=C bonds, and sulfides) than previously reported well-defined nickel-oxygen species. Remarkably, this species is formed by heterolytic O-O bond cleavage of a Ni-HmCPBA precursor, which is concluded from experimental and computational data. On the basis of spectroscopy and DFT calculations, this reactive species is proposed to be a Ni(III) -oxyl compound.

Riccardin C derivatives cause cell leakage in Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major problem in clinical settings, and because it is resistant to most antimicrobial agents, MRSA infections are difficult to treat. We previously reported that synthetic macrocyclic bis(bibenzyl) derivatives, which were originally discovered in liverworts, had anti-MRSA activity. However, the action mechanism responsible was unclear. In the present study, we elucidated the action mechanism of macrocyclic bis(bibenzyl) RC-112 and its partial structure, IDPO-9 (2-phenoxyphenol). Survival experiments demonstrated that RC-112 had a bactericidal effect on MRSA, whereas IDPO-9 had bacteriostatic effects. IDPO-9-resistant mutants exhibited cross-resistance to triclosan, but not to RC-112. The mutation was identified in the fabI, enoyl-acyl carrier protein reductase gene, a target of triclosan. We have not yet isolated the RC-112-resistant mutant. On the other hand, the addition of RC-112, unlike IDPO-9, caused the inflow of ethidium and propidium into S. aureus cells. RC-112-dependent ethidium outflow was observed in ethidium-loaded S. aureus cells. Transmission electron microscopy also revealed that S. aureus cells treated with RC-112 had intracellular lamellar mesosomal-like structures. Intracellular Na+ and K+ concentrations were significantly changed by the RC-112 treatment. These results indicated that RC-112 increased membrane permeability to ethidium, propidium, Na+, and K+, and also that the action mechanism of IDPO-9 was different from those of the other compounds.

Anti-MRSA activity of isoplagiochin-type macrocyclic bis(bibenzyl)s is mediated through cell membrane damage

We synthesized three geometrical isomers of a macrocyclic bis(bibenzyl) based on isoplagiochin, a natural product isolated from bryophytes, and evaluated their antibacterial activity towards methicillin-resistant Staphylococcus aureus (anti-MRSA activity). The isomer containing a 1,4-linked ring (5) showed only weak activity, whereas the isomers containing a 1,3-linked (6) or 1,2-linked (7) C ring showed potent anti-MRSA activity. Molecular dynamics calculations indicated that these differences are probably due to differences in the conformational flexibility of the macrocyclic ring; the active compounds 6 and 7 were more rigid than 5.In order to understand the action mechanism of anti-MRSA activity, we investigated the cellular flux of a fluorescent DNA-binder, ethidium bromide (EtBr), in the presence and absence of these macrocycles. The active compound 6 increased the levels of EtBr inflow and outflow in S. aureus cells, as did our potent anti-MRSA riccardin derivative (4), indicating that these compounds increased the permeability of the cytoplasmic membrane. Inactive 5 had no effect on EtBr inflow or outflow. Furthermore, compound 6 abrogated the normal intracellular concentration gradients of Na+ and K+ in S. aureus cells, increasing the intracellular Na+ concentration and decreasing the K+ concentration, while 5 had no such effect. These results indicate that anti-MRSA-active macrocyclic bis(bibenzyl) derivatives directly damage the gram-positive bacterial membrane, resulting in increased permeability.

Macrocyclic bis(ureas) as ligands for anion complexation.

Two macrocyclic bis(ureas) 1 and 2, both based on diphenylurea, have been synthesized. Compound 1 represents the smaller ring with two ethynylene groups as linkers and 2 the larger ring with two butadiynylene groups. On thermal treatment to 130 °C molecule 1 splits up into two dihydroindoloquinolinone (3) molecules. Both compounds 1 and 2 form adducts with polar molecules such as dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) and act as complexing agents towards a series of anions (Cl−, Br−, I−, NO3−, HSO4−). The crystal structures of 3, 2·2DMSO, 2·2DMF, and of the complex NEt4[Br·2] have been determined. Quantitative investigations of the complexation equilibria were performed via 1H NMR titrations. While 1 is a rather weak complexing agent, the large ring of 2 binds anions with association constants up to log K = 7.93 for chloride ions.