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PubMed2005

Structural analysis of chiral complexes of palladium(0) with 15-membered triolefinic macrocyclic ligands.

The complete structural analysis of the palladium complexes of the triolefinic macrocycles (E,E,E)-1,6,11-tris(arylsulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-trienes, which featured from three identical to three different aryl groups, was achieved by performing X-ray diffraction studies, NMR spectroscopy, and other calculations. The stereochemical complexity is determined by the different isomers formed through complexation of the metal to one or other face of each of the three olefins involved. The palladacyclopropane formulation of the palladium-olefin interaction offers a clear picture of the stereogenicity of the olefin carbon atoms that are complexed to the metal. The energetically favorable isomers were identified in the solid-state and in solution by performing X-ray diffraction and NMR spectroscopic analysis, respectively.

Journal Article↗
PubMed2006

Encapsulation of cyanometalates by a tris-macrocyclic ligand tricopper(II) complex: syntheses, structural variation, and magnetic exchange coupling pathways.

The reaction of [M(CN)(6)](3-) (M = Cr(3+), Mn(3+), Fe(3+), Co(3+)) and [M(CN)(8)](4-/3-) (M = Mo(4+/5+), W(4+/5+)) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu(3)(L)](6+)) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu(3)(L)](6+) forms the isostructural host-guest complexes [[[Cu(3)(L)(OH(2))(2)][M(CN)(6)](2)][M(CN)(6)]][M(CN)(6)]30 H(2)O with one bridging, two partially encapsulated, and one isolated [M(CN)(6)](3-) unit. The octacyanometalates of Mo(4+/5+) and W(4+/5+) are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)(8)](4-) were obtained. The Mo(4+) and W(4+) complexes were crystallized in two different structural forms: [[Cu(3)(L)(OH(2))](2)[Mo(CN)(8)]](NO(3))(8)15 H(2)O with a structural motif that involves isolated spherical [[Cu(3)(L)(OH(2))](2)[M(CN)(8)]](8+) ions and a "string-of-pearls" type of structure [[[Cu(3)(L)](2)[M(CN)(8)]][M(CN)(8)]](NO(3))(4) 20 H(2)O, with [M(CN)(8)](4-) ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the CuCu pairs in the [Cu(3)(L)](6+) "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr(3+), exchange coupling of Mn(3+) and Fe(3+) is very small, and the octacoordinate Mo(4+) and W(4+) systems have a closed-shell ground state.

Journal Article↗
PubMed2005

Synthesis of nitrogen- and oxygen-containing macrocycles--derivatives of lithocholic Acid.

Palladium-catalyzed amination of 3,24-bis(3-bromophenoxy)cholane (4) with various polyamines and polyoxadiamines 5 taken in 1:1 ratio was used for the synthesis of the macrocycles 6, which contain steroidal and polyamine moieties and were obtained in 38-65 % yields. The same reaction with excess polyamine (2.2-3 equiv) provided bis(polyamino) derivatives of 3,24-diphenoxycholane 7 in excellent yields, whereas the diarylation of polyamines with two equivalents of 3,24-bis(3-bromophenoxy)cholane afforded their bis(steroidal) derivatives 8. Compounds 7 and 8 were employed in the syntheses of cyclodimers 9, which possess two steroidal and two polyamine fragments; the efficiency of two methods was compared.

Lithocholic Acid↗
PubMed2006

New macrocycles with planar chirality-synthesis and determination of absolute configurations.

A versatile system for preparing macrocyclic compounds with planar chirality is presented. In this system chiral diazacoronands are synthesized readily from lariat-type diesters 13 and 14 and unsymmetrical diamines 7, 8, 12, 15, and 16 under non-high-dilution conditions. The title compounds were subjected to structural analysis by X-ray crystallography and circular dichroism spectroscopy, and absolute configurations for two representative examples (compounds 2 and 3) were assigned by molecular modeling. The correctness of the theoretical approach was verified by the crystallographic results obtained experimentally.

Journal Article↗
PubMed2002

Survey of factors determining the circularly polarised luminescence of macrocyclic lanthanide complexes in solution.

The development of emissive lanthanide complexes as structural or reactive probes to signal changes in their local chiral or ionic environment has been inhibited by the lack of understanding of correlating structural and electronic spectral information. The definition of relatively rigid enantiopure macrocyclic lanthanide complexes, whose inter- and intramolecular exchange dynamics have been defined, offers scope for remedying this situation. Chiral axially symmetric lanthanide complexes in solution give rise to large emission dissymmetry values (g(em)) in CPL spectra. The sign and magnitude of g(em) are determined by the degree of twist about the principal axis, which is predicted to be a maximum at +/-22.5 degrees, and by the site symmetry and local ligand field. In particular, the polarisability of the ligand donor atoms, especially for any axial donor, is very important. Examples of each case are discussed for structurally related cationic Eu(III) complexes.

Chemistry↗
PubMed2004

Chiral analysis of butaclamol enantiomers in human plasma by HPLC using a macrocyclic antibiotic (vancomycin) chiral stationary phase and solid phase extraction.

An enantioseparation of the antipsychotic drug butaclamol in human plasma by high-performance liquid chromatography (HPLC) with solid phase extraction is presented. The separation was achieved on the vancomycin macrocyclic antibiotic chiral stationary phase (CSP) Chirobiotic V with a polar ionic mobile phase (PIM) consisting of methanol : glacial acetic acid : triethylamine (100:0.2:0.05, v/v/v) at a flow rate of 0.5 ml/min. The detection wavelength was 262 nm. Bond Elut C18 solid phase extraction cartridges were used in the sample preparation of butaclamol samples from plasma. The method was validated over the range of 100-3,000 ng/ml for each enantiomer concentration (R(2) > 0.999). Recoveries for (+)- and (-)-butaclamol were in the range of 94-104% at the 300-2,500 ng/ml level. The method proved to be precise (within-run precision ranged from 1.1-2.6% and between-run precision ranged from 1.9-3.2%) and accurate (within-run accuracies ranged from 1.5-5.8% and between-run accuracies ranged from 2.7-7.7%). The limit of quantitation (LOQ) and limit of detection (LOD) for each enantiomer in human plasma were 100 ng/ml and 50 ng/ml, respectively.

Anti-Bacterial Agents↗
PubMed1994

Evaluation of the macrocyclic antibiotic vancomycin as a chiral selector for capillary electrophoresis.

Vancomycin is one of a family of related macrocyclic glycopeptide antibiotics that were discovered by scientists at the Eli Lilly Company in the 1950s. It has been used to treat severe staphylococcal infections, particularly when bacterial resistance to other antibiotics has developed. Vancomycin is a naturally occurring chiral compound and has a number of stereogenic centers. Furthermore, it contains a variety of functionalities that are known to be useful for enantioselective interactions (e.g., hydrogen bonding groups, hydrophobic pockets, aromatic groups, amide linkages, etc.). The physiochemical properties of vancomycin, including its stability in solution, are discussed as they pertain to capillary electrophoresis. Over 100 racemates were resolved including many nonsteroidal antiinflammatory drugs, antineoplastic compounds and N-derivatized amino acids. Many of these compounds had very high resolution factors. Optimization and the effect of different experimental parameters on the enantioselective separations are discussed.

Amino Acid Sequence↗
PubMed1997

Capillary electrophoretic enantioseparations using macrocyclic antibiotics as chiral selectors.

Macrocyclic antibiotics are the newest class of chiral selector used in capillary electrophoresis (CE) enantioseparations. Two basic types of compounds have proven to produce useful enantioseparations. They are the ansa compounds and the glycopeptides. The ansa compounds best resolve basic or cationic racemates while the glycopeptides best resolve acidic or anionic analytes. The structure and use of these chiral selectors are discussed. The factors affecting separation and the separation mechanism are considered as well.

Anti-Bacterial Agents↗
PubMed2003

Study of the fragmentation mechanism of novel functionalized macrocycles by Fourier transform ion cyclotron resonance mass spectrometry.

Liquid secondary ion mass spectrometry (L-SIMS) of six new functionalized macrocycles was investigated. All six compounds yielded abundant fragment ions and protonation molecular ions [M + H](+) under L-SIMS conditions. The proposed fragmentation mechanisms were supported by high-resolution accurate mass data from Fourier transform ion cyclotron resonance mass spectrometric and MS(n) experiments on using sustained off-resonance irradiation collision-induced dissociation.

Cyclotrons↗
PubMed2004

Electrospray mass and tandem mass spectrometry of homologous and isomeric singly, doubly, triply and quadruply charged cationic ruthenated meso-(phenyl)m-(meta- and para-pyridyl)n (m + n = 4) macrocyclic porphyrin complexes.

Ten homologous or isomeric singly, doubly, triply and quadruply charged cationic macrocyclic complexes I-Va, bn+ (n = 1-4) formed by the coordination of [Ru(bipy)2Cl]+ to the pyridyl N-atoms of a series of meso-(phenyl)m-(meta or para-pyridyl)n-porphyrins (m + n = 4) were transferred to the gas phase and structurally characterized by electrospray ionization (ESI) mass (MS) and tandem mass (MS/MS) spectrometry. Previously known to be stable in solution and in the solid state, I-Va, bn+ are found to constitute also a new class of stable, long-lived multiply charged gas-phase ions with spatially separated charge sites. Increasing intramolecular electrostatic repulsion from Ia, b+ to IVa, b3+ facilitates in-source and tandem collision-induced dissociation (CID). However, for the quadruply charged ions Va, b4+, electrostatic repulsion is alleviated mainly by ion pairing with the CF3SO3- counterion forming the salt clusters [Va,b/CF3SO3]3+ and [Va,b/(CF3SO3)2]2+ with reduced charge states. Ion-pairing that yields [IVa,b/CF3SO3]2+ is also observed as a minor ESI process for the triply charged ions IVa, b3+. The gaseous ions I-Va, bn+ (n = 2, 3 or 4) dissociate by sequential 'charge partitioning' with the formation of two cationic fragments by the release of [Ru(bipy)2Cl]+. The meta (a) and para (b) isomers and the positional isomers II2+ and III2+ display nearly identical ESI-MS and ESI-MS/MS spectra. ESI-MS/MS of I-Va, bn+ shows that the Ru-py(P) is, intrinsically, the weakest bond since this bond breaks preferentially upon CID.

Cations↗
PubMed1986

Magnetic field dependence of solvent proton relaxation rates induced by Gd3+ and Mn2+ complexes of various polyaza macrocyclic ligands: implications for NMR imaging.

The magnetic field dependence of the solvent water proton longitudinal relaxation rate 1/T1 (the NMRD profile) has been measured for solutions of chelates of Gd3+ and Mn2+ ions with two different polyaza macrocyclic ligands: 1,4,7-triazacyclononane-N,N',N",-triacetic acid (NOTA) and 1,4,7,10-tetraazacyclododecane-N,N',N",N'"-tetraacetic acid (DOTA). Studies were carried out mainly near physiological pH, but the pH dependence was also examined in some cases. The results are compared with published data for complexes of Gd3+ and Mn2+ ions with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). Competition experiments for the NOTA and DOTA chelates with EDTA and DTPA were also performed. It is found that, over the field range in which NMR imaging is currently being done, different symmetries of otherwise similar chemical ligands can alter 1/T1 of solvent protons by factors of up to three. The ligand environment can influence the relaxation times of the electronic spin moments of the ions, as well as their coordination number, thereby changing both the inner and outer sphere contributions to the relaxivities of the complexes. The relevance of these results to questions of efficiency and toxicity of these chelates as agents for enhancement of contrast in NMR images is discussed.

Animals↗
PubMed1995

The design of macrocyclic ligands for monitoring magnesium in tissue by 31P NMR.

A series of ligands based upon 1,4,7-triazacyclononane, containing variable numbers of acetate vs methylenephosphonate ester or methylenephosphonate sidechains, has been synthesized and characterized as possible 31P NMR probes for monitoring [Mg2+]free. The diacetate monophosphonate and diacetate monophosphonate ester mixed ligands proved to have conditional (dissociation) constants at pH 7.4 in an appropriate range for measuring typical levels of intracellular [Mg2+]free, and binding selectivities for Mg2+ over Ca2+ that ranged from 1.4 to 6.8. The 31P resonances of these ligands were well downfield of typical tissue phosphate metabolite resonances, and addition of Mg2+ to any one of these ligands resulted in well-resolved resonances for HL and MgL (where L = ligand), in slow chemical exchange. The chemical shift differences between the HL and MgL species varied from 2.1 to 2.6 ppm for three different ligands. The conditional Mg(2+)-L binding constants were sensitive to pH in the physiological range, due to protonation of a single macrocyclic nitrogen at high pH (log K1 values ranged from 10 to 12). However, given conditions that allow an independent assessment of pH (i.e., from the 31P chemical shift of Pi), we show that accurate KD values can be estimated from the known thermodynamic stability constants (KMgL) and ligand protonation constants (Ki). This makes these ligands potentially useful for monitoring [Mg2+]free by 31P NMR over a variety of solution conditions, even during conditions when the pH may be changing.

Chelating Agents↗
PubMed2001

Development of an analytical system for the simultaneous determination of anabolic macrocyclic lactones in aquatic environmental samples.

An analytical procedure that enables routine analysis for trace determination of six anabolic macrocyclic lactones (zearalenone, alpha- and beta-zearalenol, zearalanone, zeranol, and taleranol) in sewage treatment plant (STP) samples has been developed. The method uses solid-phase extraction, followed by high-performance liquid chromatography with on-line tandem mass spectrometry using atmospheric pressure chemical ionization (LC/APCI-MS/MS). The extraction of these compounds from filtered water samples was performed off-line with C(18) solid-phase cartridges. The detection was achieved by isocratic reversed-phase high-performance liquid chromatography coupled with an heated nebulizer (HN) APCI interface operating in negative ion mode. Mean recovery of the analytes in STP effluent samples generally exceeded 81%. This method was used to determine the occurrence of target analytes in the aquatic environment. In the selected STP effluent samples, zearalenone and alpha-zearalenol were detected in the ng/L range.

Chromatography, High Pressure Liquid↗
PubMed1996

Analysis of the disulfide linkage pattern in circulin A and B, HIV-inhibitory macrocyclic peptides.

Circulin A and B are members of a family of macrocyclic peptides, originally isolated from the tropical tree Chassalia parvifolia, that have been shown to display anti-HIV activity. Complete structural elucidation of these highly constrained peptides was difficult due to their cyclic amide backbone and the presence of six disulfide-linked cysteines. In the present study, the disulfide pairing motif of circulin A and circulin B was determined. Since the circulins were resistant to enzymatic proteolysis, cysteine residue pairings were identified by analysis of the complex mixture of cleavage products that resulted from partial acid hydrolysis of the native peptides. Combined utilization of HPLC, fast atom bombardment mass spectrometry and peptide recognition software ("F-MASS" and "F-LINK" programs) were employed to identify the cleavage products. Thus, we were able to unambiguously identify the disulfide linkage pattern in circulin A and circulin B as Cys1-Cys4, Cys2-Cys5 and Cys3-Cys6, where the numbers on the cystine residues refer to their respective order in the peptides.

Amino Acid Sequence↗
PubMed1999

A radicicol-related macrocyclic nonaketide compound, antibiotic LL-Z1640-2, inhibits the JNK/p38 pathways in signal-specific manner.

Macrocyclic nonaketide compounds, radicicol and its two analogues, 87-250904-F1 and LL-Z1640-2, have various biological activities. Here we show that these compounds inhibit signal-dependent transcriptional activation with different specificity with distinct mechanism. Although all three compounds inhibited PMA-induced AP-1 transcriptional activity in cell-based reporter assay, these compounds exhibited differential effects in separate transcriptional reporter assays for NF-kappaB and glucocorticoid receptor. Next we found that one of these compounds, LL-Z1640-2, was a signal-specific inhibitor of the JNK/p38 pathways. In contrast to LL-Z1640-2, radicicol and 87-250904-F1 did not inhibit JNK/p38 activation. Recently, radicicol was reported as an inhibitor of activated-Ras-induced ERK activation. These results indicated that radicicol and LL-Z1640-2 showed distinct specificity to various MAP kinase pathways despite their structural similarity. Furthermore, LL-Z-1640-2 inhibited anisomycin-induced but not TNF-induced JNK/p38 activation, indicating that the inhibition mechanism is signal-specific.

3T3 Cells↗
PubMed1999

Solution structure by NMR of circulin A: a macrocyclic knotted peptide having anti-HIV activity.

The three-dimensional solution structure of circulin A, a 30 residue polypeptide from the African plant Chassalia parvifolia, has been determined using two-dimensional 1H-NMR spectroscopy. Circulin A was originally identified based upon its inhibition of the cytopathic effects and replication of the human immunodeficiency virus. Structural restraints consisting of 369 interproton distances inferred from nuclear Overhauser effects, and 21 backbone dihedral and nine chi1 angle restraints from spin-spin coupling constants were used as input for simulated annealing calculations and energy minimisation in the program X-PLOR. The final set of 12 structures had mean pairwise rms differences over the whole molecule of 0.91 A for the backbone atom, and 1.68 A for all heavy atoms. For the well-defined region encompassing residues 2-12 and 18-27, the corresponding values were 0.71 and 1.66 A, respectively. Circulin A adopts a compact structure consisting of beta-turns and a distorted segment of triple-stranded beta-sheet. Fluorescence spectroscopy provided additional evidence for a solvent-exposed Trp residue. The molecule is stabilised by three disulfide bonds, two of which form an embedded loop completed by the backbone fragments connecting the cysteine residues. A third disulfide bond threads through the centre of this loop to form a "cystine-knot" motif. This motif is present in a range of other biologically active proteins, including omega-contoxin GVIA and Cucurbita maxima trypsin inhibitor. Circulin A belongs to a novel class of macrocyclic peptides which have been isolated from plants in the Rubiaceae family. The global fold of circulin A is similar to kalata B1, the only member of this class for which a structure has previously been determined.

Amino Acid Sequence↗
PubMed1996

Purification, spectroscopic analysis and biological activity of the macrocyclic dihydroxamate siderophore alcaligin produced by Bordetella pertussis and Bordetella bronchiseptica.

Hydroxamate siderophores of virulent Bordetella pertussis and Bordetella bronchiseptica strains were purified using a simple large-scale isolation procedure, and identified by various spectroscopic techniques as the macrocyclic dihydroxamate siderophore trivially known as alcaligin, 1,8(S),11,18(S)- tetrahydroxy-1,6,11,16-tetraazacycloeicosane-2,5,12,15-tetrone+ ++, which was previously isolated from the taxonomically-related bacterial species Alcaligenes denitrificans subsp. xylosoxydans. Alcaligin purified from iron-depleted cultures of B. pertussis and B. bronchiseptica exhibited specific growth-promoting activity under iron-restricted conditions for Bordetella indicator strains, and ere active in [55Fe]ferric alcaligin transport assays. Evidence suggests that several C2-symmetric conformations of alcaligin exist simultaneously in both methanolic and aqueous solution.

Alcaligenes↗