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PubMedDate not supplied

Molecular similarity analysis on biologically active macrocyclic bis(bibenzyls).

Conformational analysis of marchantin A (1), a bis(diarylether) type, and riccardin A (2), a diarylether-biphenyl type macrocyclic bis(bibenzyl) was carried out by systematic unbounded multiple minimum search (SUMM). Mobility of the macrocyclic rings was analysed by variable temperature 1H-NMR study. Molecular similarity analysis was performed on the minimum energy conformers of 1 and 2 comparing their steric, electrostatic and hydrophobic properties. Correlation between complexation properties and calmodulin inhibitor activity was established. Differences in steric and electrostatic profiles may be responsible for the reduced Ca2+ affinity and activity of 2.

Bibenzyls↗
PubMed1998

Evaluation of the macrocyclic antibiotic avoparcin as a new chiral selector for HPLC.

Avoparcin is a macrocyclic glycopeptide antibiotic structurally related to vancomycin, teicoplanin, and ristocetin A. When attached to 5-microns spherical silica gel, the avoparcin proved to be an effective chiral stationary phase (CSP) that could be used in the reversed-phase, normal-phase, and polar-organic modes. The avoparcin CSP was complimentary to the other macrocyclic glycopeptide CSPs in that it could resolve some racemates that the others could not, and vice versa. Some important compounds resolved on the avoparcin CSP include verapamil, thyroxine, mephenytoin, and 2-imidazolidone-4-carboxylic acid. The use of this CSP and the optimization of separations on it are discussed. Avoparcin appears to be a useful addition to this family of CSPs.

Anti-Bacterial Agents↗
PubMed1999

Evaluation of the macrocyclic antibiotic LY333328 as a chiral selector when used as a mobile phase additive in narrow bore HPLC.

The macrocyclic antibiotic LY333328 has been evaluated as a chiral selector for the enantioseparation of nine dansylated amino acids. This macrocyclic glycopeptide was used as a chiral mobile phase additive (CMPA) in conjunction with narrow bore high-performance liquid chromatography (HPLC). The key mobile phase parameters of LY333328 concentration and buffer pH were varied, along with variations in stationary phases consisting of C8, phenyl, cyano, and silica. After observing and plotting changes in retention and resolution based on corresponding variation in these parameters, a better understanding of the behavior of this chiral selector was obtained. The pKa values of the dansyl amino acid analytes and LY333328 were measured and used to gain a better understanding of the microenvironment in which these enantioseparations occur. Optimized conditions resulted in the baseline separation of eight of nine dansyl amino acids.

Amino Acids↗
PubMed2000

Membrane properties of archaeal macrocyclic diether phospholipids.

Several biophysical properties of four synthetic archaeal phospholipids [one polyprenyl macrocyclic lipid A and three polyprenyl double-chain lipids (B, C, D) bearing zero, one or four double bonds in each chain] were studied using differential scanning calorimetry, electron and optical microscopies, stopped-flow/light scattering and solid-state 2H-NMR techniques. These phospholipids gave a variety of self-organized structures in water, in particular vesicles and tubules. These assemblies change in response to simple thermal convection. Some specific membrane properties of these archaeal phospholipids were observed: They are in a liquid-crystalline state over a wide temperature range; the dynamics of their polyprenyl chains is higher than that of n-acyl chains; the water permeability of the membranes is lower than that of n-acyl phospholipid membranes. It was also found that macrocyclization remarkably improves the barrier properties to water and the membrane stability. This may be related to the adaptation of Methanococcus jannaschii to the extreme conditions of the deep-sea hydrothermal vents.

Cryoelectron Microscopy↗
PubMed1999

Gold(I) and Gold(0) Complexes of Phosphinine-Based Macrocycles.

A "CO-like matrix", showing coordination analogous to that of carbonyl groups, is provided by silacalix[4]phosphinine macrocycles. Reaction with Au(I) leads to the first gold(I) complexes of macrocycles, which can be reduced with sodium or potassium to the paramagnetic gold(0) complexes (an example is shown), as evidenced by cyclic voltammetry and EPR spectroscopy.

Journal Article↗
PubMed1999

Avoparcin, a new macrocyclic antibiotic chiral run buffer additive for capillary electrophoresis.

Avoparcin, like vancomycin, teicoplanin, and ristocetin A, belongs to the family of macrocyclic glycopeptide antibiotics. These antibiotics have all been used as effective chiral selectors for capillary electrophoresis (CE), thin-layer chromatography (TLC), and high performance liquid chromatography (HPLC). The present work focuses on avoparcin, which has been shown to be an excellent chiral selector for the CE enantioseparation of many N-blocked amino acids, as well as several anti-inflammatory drugs of pharmaceutical importance. The use of avoparcin as a chiral run buffer additive in CE is discussed, as well as the effects of changing experimental parameters, like avoparcin concentration, pH, organic modifiers, etc. Comparisons of enantioseparations of some N-3,5-dinitrobenzoyl-derivatized amino acids, using either avoparcin, ristocetin A, teicoplanin, or vancomycin in the run buffer, are also made. In general, vancomycin had the longest migration times, and ristocetin A the shortest, while avoparcin was intermediate. Generally, at least one of the four chiral selectors produced an excellent separation, while a different macrocyclic antibiotic produced a poor separation. Currently, we see no way to predict which chiral run buffer additive will be best or worst for an individual solute.

Anti-Bacterial Agents↗
PubMed2000

The influence of macrocyclic polyether constitution upon ammonium ion/crown ether recognition processes

Secondary dialkylammonium (R2NH2+) ions are bound readily by dibenzo[24]crown-8 (DB24C8) to form threaded complexes, namely [2]pseudo-rotaxanes. The effect of replacing one or both of the catechol rings in DB24C8 with resorcinol rings upon the crown ether's ability to bind R2NH2+ ions has now been investigated. When only one aromatic ring is changed from catechol to resorcinol, a crown ether with a [25]crown-8 constitution is created-namely benzometaphenylene[25]crown-8 (BMP25C8). A [2]pseudorotaxane is formed in the solid state when BMP25C8 is co-crystallized with dibenzylammonium hexafluorophosphate, as evidenced by its X-ray crystal structure. Furthermore, this crown ether has been shown to bind R2NH2+ ions in solution, an observation which has been exploited in the synthesis of the first BMP25C8-containing [2]rotaxane. The methodology employed to generate this [2]rotaxane--the reaction of an amine with an isocyanate to form a urea--was tested initially on a system incorporating DB24C8 and was shown to work efficiently. Both [2]rotaxanes have been fully characterized by 1H and 13C NMR spectroscopies, FAB mass spectrometry and X-ray crystallography. Interestingly, the unsymmetrical nature of the dumbbell-shaped component in each of the two [2]rotaxanes renders each face of the encircling macrocyclic polyether diastereotopic, a feature that is apparent upon inspection of their 1H NMR spectra. The resonances associated with the diastereotopic protons on each face of the macrorings are well enough resolved to enable the faces of the crown ethers to be readily identified with respect to their protons by 1H NMR spectroscopy. Unambiguous assignments can be made as a result of the fact that the protons on each face of the macrocyclic polyether experience a unique set of through-space interactions, as evidenced by T-ROESY experiments. Additionally, the two-dimensional NMR analyses are in agreement with the X-ray crystallographic studies performed on these [2]rotaxanes, indicating that the crown ethers are located intimately around the NH2+ centers as expected. Replacement of both catechol rings in the DB24C8 constitution with resorcinol rings results in a crown ether with a [26]crown-8 constitution--namely bismetaphenylene[26]crown-8 (BMP26CS). All the evidence to date points to the fact that this further change in constitution results in a crown ether that does not bind R2NH2+ ions in either the solution or solid states.

Journal Article↗
PubMed2000

Giant vesicles from 72-membered macrocyclic archaeal phospholipid analogues: initiation of vesicle formation by molecular recognition between membrane components

Stereochemically pure archeal acyclic bola-amphiphilic diphosphates 4 and 5, with the basic structure of the phospholipids found in Sulfolobus, have been synthesized for the first time. The self-assembly properties have been compared with those of the nearly identical 72-membered macrocyclic tetraether phosphates 3a and 3b, analogues of the major phospholipid components of Sulfolobus, Thermoplasma, and methanogenic Archea, which were also synthesized. Phase contrast and fluorescence microscopies have shown that the dipolar lipids 1 and 2 spontaneously formed vesicles. Whereas the macrocyclic dipolar phosphates 3 spontaneously formed vesicles (phase contrast and fluorescence microscopies), the bolaform phosphate 4 gave only a lamellar structure (synchrotron diffraction pattern: repeat distance of about 4.25 nm but with only a few layers). However, upon addition of the unphosphorylated precursors phytanol, phytol, or geranylgeraniol to the acyclic lipids 4 and 5, giant vesicles were rapidly formed. Addition of n-hexadecanol or cholesterol did not lead to vesicle formation. Therefore it was concluded that this vesicle formation occurs only when the added molecule is closely compatible with the constituents of the lipid layer and can be inserted into the double layer. A slight mismatch (cholesterol or n-hexadecanol/polyprenyl chains) is therefore enough to block the insertion process presumably required for vesicle formation.

Journal Article↗
PubMed2001

Self-assembly and dynamics of [2]- and [3]rotaxanes with a dinuclear macrocycle containing reversible Os-N coordinate bonds.

With a dinuclear macrocycle 2 that contains weak reversible OsVI-N coordinate bonds, self-assembly and equilibrium dynamics of [2]- and [3]rotaxanes have been investigated. When the macrocycle 2 was mixed together with threads 4a-e, which all contain an adipamide station but different sizes of end groups, [2]pseudorotaxane- and rotaxane-like complexes were immediately formed with large association constants of >7 x 103M(-1) in CDCl3 at 298 K. Exchange dynamics, explored by 2D-EXSY experiments, suggest that assembly and disassembly of complexes occur through two distinct pathways, slipping or clipping, and this depends on the size of the end groups. The slipping pathway is predominant with smaller end groups that give pseudorotaxane-like complexes, while the clipping pathway is observed with larger end groups that yield rotaxane-like complexes. Under the same conditions, exchange barriers (deltaG++) were 14.3 kcalmol(-1) for 4a and 16.7 kcalmol(-1) for 4d, and indicate that the slipping process is at least one order of magnitude faster than the clipping process. Using threads 13a and 13b that contain two adipamide groups, more complicated systems have been investigated in which [2]rotaxane, [3]rotaxane, and free components are in equilibrium. Concentration- and temperature-dependent 1H NMR spectroscopic studies allowed the identification of all possible elements and the determination of their relative distributions in solution. For example, the relative distribution of the free components, [2]rotaxane, and [3]rotaxane are 30, 45, and 25 %, respectively, in a mixture of 2 (2mM) and 13a (2mM) in CDCl3 at 10 degrees C. However, [3]rotaxane exists nearly quantitatively in a mixture of 2 (4 mM) and 13 a (2 mM) in CDCl3 at a low temperature - 10 degrees C.

Journal Article↗
PubMed2002

Alternating right- and left-handed helical loops in a self-assembled polymer: direct observation of ring-opening polymerization of a macrocyclic gold complex.

Reaction of the ligand NN'-bis(pyridin-3-yl)-1,3-benzenedicarboxamide (1) with the diphosphanedigold(I) complex [(mu-PP)(AuO2CCF3)2] occurred by displacement of the trifluoroacetate ligands by the pyridyl groups of 1, and crystallization gave the macrocyclic complex [Au2(mu-PP)(mu-1)](CF3CO2)2 (2b), when PP = trans-[Ph2PCH=CHPPh2] but the polymer [(Au2(mu-PP)(mu-1)]x](CF3CO2)2x (3), when PP= Ph2PCH2CH2PPh2. The polymer 3 contains a series of helical turns connected by linear chain sections. and the helices have alternating right- and left-handed conformations. The polymer 3 dissolves to give an equilibrium mixture of the macrocyclic ring complex [Au2(mu-PP)(mu-1)](CF3CO2)2 (2a), and ring-opened oligomers, thus giving insight into the mechanism of the ring-opening polymerization reaction.

Journal Article↗
PubMed2002

How to synthesize macrocycles efficiently by using virtual combinatorial libraries.

The selection of different diimines 4 a-c by alkaline earth ions from a virtual combinatorial library (VCL) is described. The products were stabilized by reduction to the diamines 6 a-c; this allowed easy analysis. The library can be directed toward different target molecules 6 a-c upon addition of alkaline earth ions with different radii. Competition experiments show the possibility of synthesizing the macrocycles 6 a, 6 b, and 6 c simultaneously when using Mg(2+), Ca(2+), and Ba(2+) as template ions. The scope of this thermodynamically controlled, reversible approach for macrocycle syntheses is illustrated.

Combinatorial Chemistry Techniques↗
PubMed2002

Completely spirocyclopropanated macrocyclic oligodiacetylenes and their permethylated analogues: preparation and properties.

The acyclic dehydrotrimer (12) and -hexamer (28) of 1,1-diethynyl-2,2,3,3-tetramethylcyclopropane were prepared from 1-chloro-1-(trimethylsilylethynyl)-2,2,3,3-tetramethylcyclopropane (4) in six and nine steps, respectively, in 36 and 8 % overall yield, respectively, using Cadiot-Chodkiewicz or Hay coupling procedures as key steps. Mono-tert-butyldimethylsilyl (TBDMS) protection of the acyclic dehydrotrimer (20) and -hexamer (23) of 1,1-diethynylcyclopropane followed by Hay coupling and protiodesilylation furnished the acyclic dehydrohexamer (23) and -dodecamer (29) in 35 and 56 % overall yield, respectively. Subsequent cyclizing oxidative dimerization of 12 or cyclization of 28 using a modified Glaser protocol produced the first completely permethylspirocyclopropanated macrocyclic oligodiacetylene, compound 30 in 49 and 21 % yield, respectively. The cyclic dehydrohexa- (31) and dehydrododecamer (32) have been prepared from 23 and 29 in 49 and 7 % yield by applying the same protocol. The macrocycle 32 is particularly interesting in that it contains 60 carbon atoms in the inner ring, and indeed a decomposition mode consecutively cleaving off ethylene units from it as well as from 31 and tetramethylethylene from the permethylated exp-[6]rotane 30 has been proved by differential scanning calorimetry with evolved gas analysis. The thermal decomposition of these "exploding" [6]rotanes 31 and 30 set on at 100 and 135 degrees C, respectively, and release energies of 478 and 285 kcal. mol(-1), respectively, significantly more than the energy release of the explosive hexogen with 143 kcal mol(-1).

Journal Article↗
PubMed2002

Nucleoside monophosphates recognition using macrocyclic polyamine bonded phase in capillary electrochromatography.

An open-tubular wall-coated macrocyclic polyamine capillary column (70 cm x 75 microm ID) with 50 cm effective length for the separation of nucleoside monophosphates is described. Some parameters with respect to concentration, pH, composition of the buffer, and voltage in order to optimize the separation were studied. The coated capillary showed reversed electroosmotic flow (EOF), allowing anions to be separated in the co-EOF mode. Baseline separations were achieved for the eight nucleotides in less than 26 min using a background electrolyte consisting of H(3)PO(4)-NaH(2)PO(4) (30 mM, pH 3.10), an applied voltage of -15 kV, and detection at 254 nm. The macrocyclic polyamine on the capillary wall introduced anion coordination for the interaction with the analytes, the strength of which could be moderated by the type and concentration of the competing ion used in the background electrolyte (BGE). With a low concentration of the competing ion (phosphate ion), the migration behavior followed that obtained in the electrophoretic system. Increasing the concentration of the competing ion resulted in a faster migration and more complete elution of the analyte. The method established was also employed for the analysis of nucleotides in mushrooms. Aqueous extracts of mushrooms from different species and various extraction methods were injected directly for the analysis. Uridine 5'-monophosphate, guanosine 5'-monophosphate, adenosine 5'-monophosphate, and cytidine 5'-monophosphate, were found in the sample tested.

Agaricales↗
PubMed1996

Brazilian Baccharis toxins: livestock poisoning and the isolation of macrocyclic trichothecene glucosides.

Samples of the toxic Brazilian plant, Baccharis coridifolia, which is responsible for numerous cases of livestock poisoning in southern Brazil and Argentina, were collected during the growing season, and the toxicities in calves of the plant materials were correlated with the levels of macrocyclic trichothecenes present. Female plants in flower were considerably more toxic than male plants or plants not in flower. Plants not in flower were of intermediate toxicity. The female plants in flower typically contained 5-10 times the levels of toxins as were found in the male plants. In addition, six new glucosides of the macrocyclic trichothecenes were isolated and characterized. The most prominent glucosides, those of roridins A and E, were found in high levels in the female plants.

Acetylation↗
PubMed2003

Recent methods for the synthesis of (E)-alkene units in macrocyclic natural products.

(E)-Alkene units are frequently found in macrocyclic natural products. Among the reactions that form the double bond during the cyclization, the classical Horner-Emmons coupling is still frequently used with success. During the last decade, ring-closing metathesis has emerged as a very powerful tool for the synthesis of large rings, but the E/Z selectivity, which is rarely predictable, depends on many factors which will be discussed in this review. The best solution might be a two-step procedure involving ring-closing alkyne metathesis (RCAM) followed by stereoselective reduction of the macrocyclic alkyne unit to the corresponding E double bond.

Alkenes↗
PubMed2003

Application of the empirical force field to macrocyclic ion carriers, siderophores, and biomimetic analogs.

The empirical force field (EFF), developed by Prof. Lifson, was applied to the study of macrocyclic alkali ion carriers and to di- and tripodal and open chain siderophores and synthetic biomimetic molecules binding transition metals. The highly symmetric nature of these structures facilitated a favorable coordination geometry of the ligating groups about the metal, which helped organize the entire molecule into a fairly rigid structure. In our combined experimental-theoretical approach, EFF calculations were used to help predict likely candidates to synthesize, and provided a wealth of structural data to complement what we learned from the spectroscopic measurements, while feedback from these measurements allowed us to continue improving the EFF itself. The simple, highly modular design of the biomimetic analogs allowed rapid synthesis and systematic examination of a large number of related structures, as well as facilitating an efficient, piecewise conformational scanning for the theoretical calculations. In the early years, we focused on macrocyclic polylactones and lactams binding monovalent alkali ions, particularly the natural products enniatin and valinomycin, including inside a crystal lattice. Later we switched to bi- and tridentate siderophores, natural microbial iron carriers, and synthetic biomimetic analogs-in particular, of enterobactin, ferrichrome, and ferrioxamine B. Over the years a large number of biomimetic siderophores have been prepared, some active in a broad range of microorganisms while others are highly species specific. The results of this work have broad applications in many areas, including the design of novel drugs and antimicrobial agents, helical polymeric structures, and polynuclear metal complexes.

Ion Transport↗
PubMed1989

Mass spectral investigations on trichothecene mycotoxins. VIII--Thermospray ionization and collisionally activated dissociation of macrocyclic trichothecenes.

Several structurally similar, biologically active macrocyclic trichothecenes were ionized under thermospray conditions followed by collisionally activated dissociation of the ammonium adducts. Most of the observed daughter ions were formed by bond cleavage at the exocyclic ester bridges. Compounds with similar ester bridges formed several common daughter ions and underwent similar neutral losses. Fragmentation pathways proposed for the dissociation of the adducts were confirmed from the corresponding neutral loss spectra. Simple experiments designed for the sequential monitoring of the characteristic daughter ions were used for the rapid, direct and accurate analysis of macrocyclic trichothecenes in real samples. The primary drawback of the method is its inability to distinguish between isomers.

Chemical Phenomena↗
PubMed2004

14-Methylpentadecano-15-lactone (muscolide): a new macrocyclic lactone from the oil of Angelica archangelica L.

The chemical composition of seed and root oils from Angelica archangelica L. was investigated. Analyses were performed by GC/MS and GC using two columns of different polarities (polyethylene glycol (DB-Wax) and 5% phenyl/95% polydimethylsiloxane (HP-5)), for the separation of several co-eluting components. A total of 58 compounds were identified, accounting for 96.3% (seed) and 93.5% (root) of the oils, respectively. A high content of beta-phellandrene (74.7%) was found in Angelica seed oil. Root oil contained a larger amount of macrocyclic lactones (1.3%) in comparison to the seed oil (0.4%). Different harvest dates produced only slight changes in the root-oil composition. In root oil harvested in summer, the beta-phellandrene content increased by ca. 36%, but no significant changes in the relative compositions of other components were observed. Fresh root oils were collected in five fractions (constant time intervals) during steam distillation (see Table). The highest-boiling fraction contained 9.3% of macrocyclic lactones such as tridecano-13-lactone (5.0%), 12-methyltridecano-13-lactone (0.4%), tetradecano-14-lactone (0.1%), pentadecano-15-lactone (3.5%), 14-methylpentadecano-15-lactone (1; trace), hexadecano-16-lactone (trace), and heptadecano-17-lactone (0.2%). This is the first report of the occurrence of 14-methylpentadecano-15-lactone (muscolide; 1) in a natural product.

Angelica archangelica↗