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PubMed2005

Solid-supported reagents and catalysts for the preparation of large ring compounds.

Parallel combinatorial synthesis in solution using immobilized reagents, catalysts, and scavengers has emerged as a powerful technique for the preparation of diverse libraries of compounds. This technique has only recently been applied to the synthesis of large-ring compounds. In this comprehensive review several strategies are presented and discussed, including Pd-catalyzed allylic alkylation, Stille-coupling, macrolactonization and macrolactamization using solid supported reagents and catalysts. In several cases site isolation has allowed operation, of these macrocyclization reactions in concentrated solution (pseudo-dilution effect).

Catalysis↗

PubMed1997

Synthesis and Structural Characterization of Nonplanar Tetraphenylporphyrins and Their Metal Complexes with Graded Degrees of beta-Ethyl Substitution.

Different porphyrin conformations are believed to play a role in controlling the cofactor properties in natural tetrapyrrole-protein complexes. In order to study the correlation between macrocycle nonplanarity and physicochemical properties in detail, a series of six porphyrins with graded degrees of macrocycle distortion were synthesized via mixed condensation of pyrrole, diethylpyrrole, and benzaldehyde. The formal introduction of successively more beta-ethyl groups into the tetraphenylporphyrin parent macrocycle gave access to diethyltetraphenylporphyrin (H(2)DETPP), two regioisomers of tetraethyltetraphenylporphyrin (H(2)tTETPP, H(2)cTETPP), and hexaethyltetraphenylporphyrin (H(2)HETPP). These conformationally designed compounds bridge the gap between the well-known tetraphenylporphyrin (H(2)TPP) and the very nonplanar octaethyltetraphenylporphyrin (H(2)OETPP), which are also formed during the reaction. Crystallographic studies showed that the macrocycle distortion in the solid state increases gradually in the order TPP < DETPP < tTETPP < cTETPP < HETPP < OETPP, i.e. with increasing degree of beta-ethyl substitution and the number and localization of potential beta-ethyl meso-phenyl interactions. This correlates well with increasing bathochromic shifts of the absorption bands in solution. Depending on the substituent pattern, different saddle-shaped macrocycle conformations were observed. While the conformation of tTETPP was symmetric, DETPP, cTETPP, and HETPP showed asymmetric distortion modes with individual beta-pyrrole displacements reaching those described for dodecasubstituted porphyrins. Overall, higher displacements from planarity were found close to beta-ethyl-meso-phenyl groups whereas smaller displacements were observed in parts of the molecules bearing beta-hydrogen atoms. Nevertheless, a certain amount of redistribution of steric strain occurs as evidenced by significant displacements for pyrrole carbon atoms with beta-hydrogens. Synthesis and structural investigation of the respective metal complexes with M = Cu(II), Ni(II), and Zn(II) showed similar correlations between beta-ethyl substitution, bathochromic shift of absorption bands and nonplanarity as described for the free bases. The only exception was found for Ni(II)tTETPP, which exhibited a highly nonplanar ruffled conformation. Additionally, the metal complexes allowed a study of the conformational effects of different metals at each level of macrocycle distortion. As observed for symmetric, nonplanar porphyrins larger metals led to a decrease in conformational distortion with associated changes in bond lengths and bond angles.

Journal Article↗

PubMed2006

Electrochemistry and spectroelectrochemistry of meso-substituted free-base corroles in nonaqueous media: reactions of (Cor)H3, [(Cor)H4]+, and [(Cor)H2]-.

Eleven free-base corroles with different electron-donating or electron-withdrawing meso substituents were characterized as to their electrochemistry and UV-visible spectroscopy in benzonitrile (PhCN) or pyridine containing tetra-n-butylammonium perchlorate (0.1 M). Six forms of the compounds with different numbers of protons and/or oxidation states were spectroscopically identified and are represented as (Cor)H3, (.Cor)H2, [(Cor)H2]-, [(.Cor)H2]2-, [(Cor)H4]+, and [(.Cor)H4]2+, where Cor is a trianionic corrole macrocycle. The electrochemistry and UV-visible properties are a function of corrole basicity, solvent basicity, and types or sizes of the meso substituents, and the compounds could be subdivided into one of two different groups, one of which comprises sterically hindered corroles and another that does not. The electroactive species in PhCN is (Cor)H3, whereas in pyridine, one inner proton dissociates, generating a mixture of (Cor)H3, [(Cor)H2]-, and pyH+. The addition of one electron to [(Cor)H2]- reversibly gives the [(.Cor)H2]2- pi-anion radical, whereas a reversible oxidation of the same species gives the neutral radical (.Cor)H2. The first one-electron reduction of (Cor)H3 occurs at the macrocycle in PhCN, but the initial product rapidly converts to [(Cor)H2]-, which undergoes additional reversible redox reactions at the conjugated pi-ring system. The first oxidation of (Cor)H3 in PhCN leads to a mixture of (.Cor)H2 and [(Cor)H4]+, both of which could be further oxidized or reduced. The UV-visible spectra of [(Cor)H4]+ were measured in PhCN after titrations with trifluoroacetic acid, after which selected samples were examined as to their electrochemistry. The HOMO-LUMO gaps of [(Cor)H2]-, (Cor)H3, and [(Cor)H4]+ were also determined.

Journal Article↗

PubMed1988

Intercalation of tetracationic metalloporphyrins and related compounds into DNA.

Electron paramagnetic resonance (e.p.r.) studies of thin DNA-chelate films indicate that both the water soluble planar macrocyclic chelates, cobalt (II) tetra (2,3-N-methylpyridinium) porphyrazine (cobalt (II) TMTPPA), and vanadyl (II) 5,10,15,20-tetra-(4-methylpyridinium) porphyrin (Vo (II) TMTPyP) can bind to calf thymus DNA intercalatively. The intercalation of cobalt (II) porphyrazine is in contrast to the binding of cobalt (II) porphyrin, which is known to bind nonintercalatively. Five-coordinate cobalt (II) porphyrazine is sufficiently slim, even with its single out-of-plane ligand, to permit significant intercalative binding. Vanadyl (II) porphyrin intercalates into calf thymus DNA, but not as readily as cobalt (II) porphyrazine.

Animals↗

PubMed1995

Quantitative structural activity relationship study of bis-tetraazacyclic compounds. A novel series of HIV-1 and HIV-2 inhibitors.

This work describes a study of quantitative structural activity relationships (QSAR) of bis-tetraazamacrocyclic compounds. These compounds represent a novel class of very potent and selective anti-HIV inhibitors, with a new mode of action. The QSAR study correlates structural features of the compounds with anti-HIV activity, resulting in a model which has a high predictive capacity (predictive r2 = 0.79). This predictive model will be of major importance for the design of new anti-HIV inhibitors of this class. Use is made of partial least-squares (PLS) analysis, with the novelty being that structural features derived by inclusion of all sterically allowed conformations for each molecule are included in the analysis. PLS analysis was made of descriptors, including structural parameters, macrocyclic ring size, metal chelating ability, etc., and those features necessary for the observed antiviral activities of these compounds were deduced from the models. Since all sterically allowed conformations are included in the analysis, the flexibility of the molecules is also taken into account. In addition, a correlation is found (indicated by a predictive r2 value of 0.61) between inhibition of HIV-1 (HIV-2) and syncytium formation inhibition in the presence of bis-cyclam analogues, leading to the suggestion of a common target, namely, gp120, being involved in both inhibition of virus replication and syncytium formation.

Antiviral Agents↗

PubMed2003

Templated synthesis of a rotaxane with a [Ru(diimine)3]2+ core.

A rotaxane containing a ruthenium bisphenanthroline complex, acting as an axis, and a macrocycle incorporating a 2,2'-bipyridine (bpy) unit, threaded by the axis, has been synthesized. The bisphenanthroline ligand is such that its ruthenium(II) complexes possess a clearly identified axis, making such compounds ideal components of rotaxanes constructed around an octahedral ruthenium(II) center, which serves as a template. The ring is threaded by the axial ruthenium(II) precursor complex, to afford the corresponding pseudorotaxane in moderate yield. The X-ray structure analysis of this compound reveals the threaded nature of the complex. The length of the threaded ring (35 atoms in the periphery) is too short to allow easy threading of the axis through the macrocycle. As a consequence, an isomer is also obtained for which the axial ruthenium complex is attached in an exo fashion. (1)H NMR studies have been carried out, which reveal various conformational equilibria for the pseudorotaxane. Light-induced decoordination of the bpy-containing cyclic fragment was shown to be quantitative and to lead to the free ring and the axial ruthenium(II) complex, regardless of the starting compound (pseudorotaxane or exo isomer). Finally, the real rotaxane could be prepared, although it could not be separated from its exo isomer.

Journal Article↗

PubMed2000

Electrospray ionisation Fourier-transform ion cyclotron resonance mass spectrometry of dynamic combinatorial libraries.

The use of electrospray ionisation Fourier-transform ion cyclotron resonance tandem mass spectrometry (ESI-FTICR-MS/MS) for the analysis of dynamic combinatorial libraries (DCLs) of pseudo-peptide macrocyclic hydrazone oligomers is presented. The design of library building blocks results in mixtures of compounds with greater diversity than libraries generated by conventional combinatorial chemistry and so presents increased demands for analysis. The extended capabilities of the FTICR technique, specifically selective ion trapping, sensitivity, high resolution and mass accuracy over a broad mass range, are compatible with these increased demands and, most importantly, without the need for chromatography. Preliminary studies on the sequencing of cyclic oligomers and confirmation of the presence of sequence isomers are presented. These studies highlight the potential of FTICR-MS as a superior technique for the analysis of combinatorially generated compounds.

Aldehydes↗

PubMedDate not supplied

Effects of macrocyclic trichothecene mycotoxins on the murine immune system.

Macrocyclic trichothecenes are a class of mycotoxins, some of which exhibit substantial antileukemic properties. These compounds vary in their toxicity by approximately 100 fold and are suspected immunotoxins. We studied 11 of these mycotoxins: roritoxin B, myrotoxin B, roridin A, verrucarin A, 16-hydroxyverrucarin A, verrucarin J, baccharinoid B12, roridin D, roridin E, baccharinoid B4 and baccharinoid B5 for their immunotoxicity in CD-1 mice. An equitoxic dose was prepared in 1% DMSO in saline and administered i.p. at half the LD50. Organ weights, WBC, RBC, differentials of blood cell counts, blastogenesis of splenic lymphocytes in response to concanavalin A (Con A), lipopolysaccharide (LPS), phytohemagglutinin (PHA) and pokeweed mitogen (PWM), and mixed lymphocyte reaction (MLR) were studied on day 4 after administration of each mycotoxin. Organ weights showed significant differences between the controls and the baccharinoids with a decrease in spleen weight in baccharinoid B12 and an increased liver weight in B4 and B5 treated animals. Administration of myrotoxin B, roridin A, verrucarin J and roridin E had total WBC counts statistically different from controls, while mice administered myrotoxin B shoed a decrease in numbers of RBC. Differentials of WBC were unremarkable regardless of the mycotoxin. Roritoxin B and baccharinoid B5 increased Con A stimulation of splenic lymphocytes. Roridin A and baccharinoid B12 increased LPS stimulation of splenic lymphocytes while baccharinoid B5 decreased the LPS response. Stimulation of splenic lymphocytes with PHA was significantly increased by roridin A and baccharinoid B5. Stimulation of splenic lymphocytes with PWM was not altered significantly by any mycotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2001

Synthesis and antifungal activities of novel 1,3-beta-D-glucan synthase inhibitors. Part 2.

Highly potent 1,3-beta-D-glucan synthase inhibitors, 7b, 10a, 10b and 12, have been identified by the chemical modification of the ornithine residue of a fungicidal macrocyclic lipopeptidolactone, RO-09-3655 (1), isolated from the cultured broth of Deuteromycotinia spp. These compounds showed stronger antifungal activity against systemic candidiasis as well as pulmonary aspergillosis in mice, and less hepatotoxicity as compared with 1.

Animals↗

PubMed1995

Effect of micelles and mixed micelles on efficiency and selectivity of antibiotic-based capillary electrophoretic enantioseparations.

Vancomycin (an oligophenolic, glycopeptide, macrocyclic antibiotic) has been shown to be a superb chiral selector for anionic and neutral compounds. It was found that adding sodium dodecyl sulfate to the run buffer increased efficiency by over 1 order of magnitude, decreased analysis times, and reversed the elution order of the enantiomers. This allows for control of the retention order as well as the resolution of enantiomers in complex mixtures in a single run. A mechanism is proposed which explains all of the observed effects and is verified experimentally. Since vancomycin is present in both the micelle and in free solution, previously proposed micelle-selector models are, at best, limiting cases. A general equation is derived which can be used to describe all possible interactions, including those with the capillary wall, if needed. Also, it is shown that electrophoretic mobilities and not migration times must be used to calculate binding constants of a solute to the micelle, the chiral selector, or both. Furthermore, it is shown that a neutral marker molecule cannot be used to accurately correct mobilities that have been altered due to changes in solution viscosity. While this work utilizes the practical vancomycin-micelle system, the general conclusions and theory apply to most other analogous CE systems as well.

Anti-Bacterial Agents↗

PubMed2004

Structure of two azide salts of a copper(II) macrocycle and magnetic properties of Cu(14ane)Cu(N3)4.

Synthesis of azide complexes with the copper(II) macrocycle complex Cu(14ane)(2+) (where 14ane = 1,4,8,11-tetraazacyclothetradecane) has yielded two compounds. Cu(14ane)Cu(N(3))(4) contains micro(1,3)-azido bridged chains of Cu(14ane)(2+) cations and Cu(N(3))(4)(2)(-) anions. Magnetic studies reveal the presence of ferromagnetic interactions within the chains with J/k = 0.635(4) K. [Cu(14ane)N(3)]BF(4) contains [Cu(14ane)N(3)]+ cations with elongated square pyramidal geometry. The BF(4)(-) anions are weakly coordinated in the sixth coordination site of the cations.

Journal Article↗

PubMed2002

Synthesis of mayolene-16 and mayolene-18: larval defensive lipids from the European cabbage butterfly.

A tandem Wittig approach has been employed for the synthesis of both (11S,9Z,12Z,15Z)- and (11R,9Z,12Z,15Z)-hydroxyoctadeca-9,12,15-trienoic acid (11-hydroxylinolenic acid, 11-HLA) from (R)-glyceraldehyde acetonide. From (11R)-HLA we have prepared the corresponding palmitic acid and stearic acid esters, mayolene-16 (1) and mayolene-18 (2), insect defensive compounds recently identified from Pieris rapae larvae. In addition, we describe the synthesis of three macrocyclic oligomers (24-26) derived from (11R)-HLA.

Animals↗

PubMed2002

Synthesis of novel phthalocyanine-tetrathiafulvalene hybrids; intramolecular fluorescence quenching related to molecular geometry.

A number of silicon phthalocyanine bis-esters have been synthesized and characterized, with axial ligands containing one or more tetrathiafulvalene groups. Variations in the substitution positions around a central aromatic "hinge" within the ligands lead to different molecular geometries, and the fluorescence of the macrocyclic core is subsequently quenched to varying degrees by the electron-rich tetrathiafulvalene moiety, the magnitude of this effect being dependent upon both the relative separation of the two units and the flexibility of the linking group. Pc derivative 24, with a highly flexible linker group, and pc derivative 28, with a dendritic axial ligand, have the intensity of the macrocycle emission reduced by 99% and 96%, respectively, relative to a similar silicon pc reference compound lacking the TTF moieties. Molecular modeling studies of a series of such hybrids allow the degree of this fluorescence quenching to be related to the intramolecular spacing. Additionally, the potential for rapid electrochemical switching of the phthalocyanine fluorescence by oxidation of the appended tetrathiafulvalene units is explored.

Journal Article↗

PubMed2000

Wittig reactions on photoprotoporphyrin IX: new synthetic models for the special pair of the photosynthetic reaction center.

A first example of spirochlorin-chlorin dimer with fixed distances and orientations as potential model for the "special pair" of the photosynthetic reaction center is discussed. For the preparation of such a novel structure, the Wittig reagent of the desired "spacer" 5 was reacted with photoprotoporphyrin IX dimethyl ester 3 to produce the intermediate dimer 6, which on intramolecular [4 + 2] Diels-Alder cycloaddition gave an unexpected spirochlorin-chlorin dimer 9. Dehydration of dimer 6 under acid-catalyzed conditions generated the corresponding spirochlorin-porphyrin dimer 16 in quantitative yield. The asymmetry in dimer 6 caused by the biphenyl-type anisotropic effect was confirmed by NMR and model studies. The formation of dihydrobenzoporphyrin 14 by reacting chlorin 3 with the phosphonium salt of p-methylbenzylbromide 10 and isolation of 8-phenanthrenevinylporphyrin 19 from chlorin 7 further confirmed our proposed mechanism for the formation of a spirochlorin-chlorin dimer 9. Following a similar approach, chlorin 3 on reacting with bis-phosphonium salt of 4, 4'-bischloromethylbiphenyl produced conjugated chlorin dimer 25. The spectroscopic data obtained from these dimers suggest that, in these compounds, the individual chromophores are not behaving as an individual molecule, but as a single macrocycle. To examine whether the pi-pi interaction exhibited by dimer 9 resembles the structural arrangement of bacteriochlorophylls in reaction center (RC), we investigated the geometrical parameters used to characterize the pi-pi interactions in tetrapyrrolic macrocycles. Starting from the crystallographic coordinates of 9, the molecular mechanics energy minimization was performed to obtain the model dimer structure. The geometrical parameters that measure the single pyrrole ring overlap were used to compare the model structure with the crystallographic coordinates of the special pair in photosynthetic reaction center. The results indicated that the ring A of spirochlorin and the ring C of chlorin in our model dimer 9 mimic the ring A-ring A interaction found in the crystallographic special pairs, which are strategically placed by the surrounding photosynthetic reaction center protein matrix.

Dimerization↗

PubMed2000

Synthesis of the ring system of phomactin D using a Suzuki macrocyclization.

[reaction: see text]The ring system of phomactin D was synthesized in racemic form in an efficient manner from 2,3-dimethylcyclohexanone. Notable transformations include (1) an alkylation of the enolate of a vinylogous thiolester to install a quaternary stereocenter, (2) a conjugate addition of cyanide to an alpha,beta-unsaturated aldehyde, (3) the formation of a Weinreb amide directly from a cyanohydrin, and (4) an intramolecular Pd-mediated Suzuki coupling of a B-alkyl-9-BBN derivative and a vinyl iodide to form the macrocyclic ring.

Cyclization↗

PubMed2005

Marine natural products as anticancer drugs.

The chemical and biological diversity of the marine environment is immeasurable and therefore is an extraordinary resource for the discovery of new anticancer drugs. Recent technological and methodologic advances in structure elucidation, organic synthesis, and biological assay have resulted in the isolation and clinical evaluation of various novel anticancer agents. These compounds range in structural class from simple linear peptides, such as dolastatin 10, to complex macrocyclic polyethers, such as halichondrin B; equally as diverse are the molecular modes of action by which these molecules impart their biological activity. This review highlights several marine natural products and their synthetic derivatives that are currently undergoing clinical evaluation as anticancer drugs.

Animals↗

PubMed1998

Differential selectivity of ligands for the C1a and C1b phorbol ester binding domains of protein kinase Cdelta: possible correlation with tumor-promoting activity.

Protein kinase C (PKC) represents the major, high-affinity receptor for the phorbol esters as well as for a series of structurally diverse natural products. The phorbol esters function by binding to the tandem C1a and C1b domains in PKC, leading to enzyme activation. Although the typical phorbol esters represent the paradigm for tumor promoters in mouse skin, it is now clear that different high affinity ligands for PKC have distinct biological effects. Thus, the daphnane analogue mezerein is a second-stage promoter, the macrolide bryostatin 1 is a partial antagonist, and certain 12-deoxyphorbol 13-monoesters also function as partial antagonists but with a different pattern of activity. The biochemical basis for these differences is an area of active investigation. In this report, we have examined the relative interaction of ligands differing in structure and pattern of biological response with the C1a and C1b domains of PKCdelta. We mutated either or both of the C1 domains of PKCdelta, expressed the constructs in NIH 3T3 cells, and monitored the interaction of the ligands by their ability to induce translocation of the mutated PKCdelta from the cytosol to the particulate fraction. We found that different ligands showed different dependence on the C1a and C1b domains for translocation. Whereas phorbol 12-myristate 13-acetate and the indole alkaloids indolactam and octylindolactam were selectively dependent on the C1b domain, selectivity was not observed for mezerein, for the 12-deoxyphorbol 13-monoesters prostratin or 12-deoxyphorbol 13-phenylacetate, or for the macrocyclic lactone bryostatin 1. Provocatively, the pattern of response corresponds with the activity of the compounds as complete tumor promoters.

3T3 Cells↗

PubMed2002

Involvement of protein tyrosine phosphorylation and reduction of cellular sulfhydryl groups in cell death induced by 1' -acetoxychavicol acetate in Ehrlich ascites tumor cells.

Elucidation of the mechanisms underlying potential anticancer drugs continues and unraveling these mechanisms would not only provide a conceptual framework for drug design but also promote use of natural products for chemotherapy. To further evaluate the efficacy of the anticancer activity of 1'-acetoxychavicol acetate (ACA), this study investigates the underlying mechanisms by which ACA induces death of Ehrlich ascites tumor cells. ACA treatment induced loss of cell viability, and Western blotting analysis revealed that the compound stimulated tyrosine phosphorylation of several proteins with 27 and 70 kDa proteins being regulated in both dose- and time-dependent manner prior to loss of viability. Protein tyrosine kinase inhibitor herbimycin A moderately protected cells from ACA-induced toxicity. In addition, cellular glutathione and protein sulfydryl groups were also significantly reduced both dose- and time-dependently during evidence of cell death. Replenishing thiol levels by antioxidant, N-acetylcysteine (NAC), an excellent supplier of glutathione and precursor of glutathione, substantially recovered the viability loss, but the recovery being time-dependent, as late addition of NAC (at least 30 min after ACA addition to cultures) was, however, ineffective. Addition of NAC to ACA treated cultures also abolished tyrosine phosphorylation of the 27 kDa protein. These results, at least partly, identify cellular sulfhydryl groups and protein tyrosine phosphorylation as targets of ACA cytotoxicity in tumor cells.

Animals↗