Abstract: As part of a program aimed at introducing functionality onto the Trager’s base framework post-synthesis, we investigated the formylation reaction of Trager’s base analogues with Vilsmeier reagents. We found that rather than the anticipated reaction at the aryl rings, these compounds react with Vilsmeier reagents to afford compounds with a modified strap, whereby the apical methylene group is replaced by a methylene strap bearing an N,N-disubstituted amine. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
Abstract: The nonlinear optical (NLO) properties of a series of anilines and N,N-dimethylanilines are studied with second-order Moller-Plesset perturbation theory (MP2). The effect of solvents on the calculated NLO properties is investigated by considering a wide range of solvent systems within the polarizable continuum model. In order to identify systems with high first-order hyperpolarizability, the effects of four basic variations to the molecules on the calculated NLO properties are studied. The modifications comprise changes to the donor strength (NH(2) to N(CH(3))(2)), changes to the acceptor strength (NO(2), CN and CHO), variation of additional substituents (H, CH(3), Br, OCH(3)), and changes in the conjugation length. It is found that the first-order hyperpolarizability increases when the compounds have N,N-dimethyl as donor, vinyl nitro group as acceptor at the 4-position, and a methoxy group as substituent at the 2-position. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.
Abstract: A series of proflavine derivatives for use to further image A beta amyloid deposits were synthesized and characterized. Aged 3xTg-AD (23 months old) mice hippocampus sections incubated with these derivatives revealed preferential labeling of amyloid plaques. Furthermore an in vitro binding study showed an inhibitory effect, although moderate, of these compounds on A beta(40) fibril formation. This study highlights the potential of proflavine as a molecular scaffold for designing new A beta imaging agents, its native fluorescence allowing in vitro neuropathological staining in AD damaged brain sections. (C) 2011 Elsevier Ltd. All rights reserved.
Abstract: Troger’s base analogues were prepared bearing methoxy groups in the 1,7-, 2,8-, 3,9- or 4,10-positions. These compounds were converted to their dihydroxy analogues in excellent yields upon treatment with boron tribromide and the 4,10-dihydroxy analogue could be prepared by directly from 4-hydroxyaniline. The synthetic utility of the dihydroxy-functionalised compounds as building blocks was demonstrated by the synthesis of a dialkoxy and a diester Troger’s base analogue. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
Abstract: The yields of ester-functionalised Troger’s base analogues are dramatically improved by incorporating an electron-donating group on the aromatic ring and/or enhancing solubil-ity of the aniline unit. In addition to 2,8-diester compounds, 1,7-, 3,9- and 4,10-diester-functionalised Trager’s base analogues have been prepared for the first time.
Abstract: The reaction of four Troger’s base analogues with NBS and NCS to afford mono and / or dihalogenated products is described. They constitute the first examples of introducing a halogen onto the aryl rings of a Troger’s base framework bearing pre-existing substituents and offer access to non-symmetric (hybrid) compounds
Abstract: In the molecule of the title compound, C(21)H(22)N(2)O(4), the 1,7-diethyl ester analogue of Troger’s base, the dihedral angle between the two benzene rings is 93.16 (3)degrees; the molecule is C(2) symmetric.
Abstract: A protocol for the introduction of spiro[4.5] lactone straps onto the Troger’s base scaffold has been developed. The conversion was found to be most efficient when an appropriate carboxylic acid derivative reacted with 5,6,11,12-tetrahydrodibenzo[b,f][1,5]diazocines. Whilst phthaloyl dichloride was the main strap-forming precursor used, other 1,2-unsaturated dicarboxylic acids could be used in the presence of N,N-dicyclohexylcarbodiimide.
Abstract: The synthesis of six new examples of 2,8-dinitro-substituted Troger’s base analogues are reported, together with the first examples of 1,7-, 3,9- and 4,10-dinitro Troger’s base analogues and the first example of a tetranitro Troger’s base compound. Several of these dinitro compounds lack substituents at the 2- and 8-positions and therefore provide further examples of Troger’s base analogues derived from anilines lacking a para substituent. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Abstract: The one-step synthesis of a series of hybrid dibenzo Troger’s base analogues bearing at least one halogen atom is described. The strategy involves a reaction between two different anilines and affords hybrid compounds in yields as high as 46%, together with the symmetric Troger’s base products. This straightforward approach requires only one chromatographic step and has the potential to replace multistep approaches to hybrid Troger’s base compounds. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Abstract: Troger’s base analogues are of interest in areas such as host-guest chemistry, synthetic receptor design and asymmetric catalysis. We foresee that access to diverse functionality attached to the bridge of Troger’s base compounds will be beneficial for the development of these applications. As a starting point, we report a facile and general methodology to prepare a range of diversely functionalised 5,6,11,12-tetrahydrodibenzo[b,f][1,5]diazocines, compounds that may be viewed as “strap-clipped†Troger’s bases. As a demonstration of their reactivity, these compounds were reacted with benzaldehyde to introduce phenyl substituted straps onto a Troger’s base framework.
Abstract: In the molecule of the title compound, C16H14Cl2N2, the ethano-strapped 2,8-dichloro analogue of Troger’s base, the dihedral angle between the two benzene rings is 87.01 (3)degrees.
Abstract: The asymmetric unit of the title compound, C21H22N2O4, a Troger’s base analogue derived from methyl 4-aminophenylacetate, contains two crystallographically independent molecules with dihedral angles of 88.44 (5) and 88.68 (6)degrees between the two benzene rings.
Abstract: The title compound, C(15)H(10)Br(2)Cl(2)N(2), a 2,8-dibromo-4,10-dichloro Troger’s base analogue derived from 4-bromo-2-chloroaniline, has a dihedral angle of 110.9 (10)degrees between the two aryl rings, the largest yet measured for a simple dibenzo analogue.
Abstract: In the molecule of the title compound, C16H14N2O2, an N,N’-dimethyldianthranilide, the two methyl groups are disordered over two positions; site occupation factors were kept fixed as 0.75:0.25 and 0.65:0.35. The dihedral angle between the two benzene rings is 75.57 (3)degrees.
Abstract: In the title compound, C17H16Br2N2, the 1,7-dibromo-2,8-dimethyl analogue of Troger’s base, the aryl rings are offset with respect to one another. The dihedral angle between the two benzene rings is 97.47 (5)degrees; the molecule is C-2-symmetric.
Abstract: In the title compound, C17H16Br2N2, the 3,9-dibromo-2,8-dimethyl analogue of Troger’s base, the diazocine bridge imparts a twist such that the aryl rings are offset with respect to one another. The dihedral angle between the two benzene rings is 97.10 (7)degrees.
Abstract: The crystal structure of the title compound, C20H20N2O4, contains two molecules in the asymmetric unit. The crystal packing involves pi-pi, C-(HO)-O-... and C-(HN)-N-... interactions.
Abstract: In the molecule of the title compound, C17H16Br2N2, the 4,10-bromo- 2,8-dimethyl analogue of Troger’s base, the two aryl rings are offset with respect to one another by virtue of the diazocine bridge. There are two crystallographically independent molecules in the unit cell and both of these have a dihedral angle of 95.4 (1)degrees between the two aryl rings.
Abstract: In the molecule of the title compound, C17H16N4O4, the 2,8-dimethyl-1,9-dinitro analogue of Troger’s base, the diazocine bridge imparts a twist such that the two aryl rings are offset with respect to one another. The dihedral angle between the two benzene rings is 94.75(4)degrees.
Abstract: The title compound, C25H27N3, possesses an essentially planar, fused tricyclic platform, from which two p-tolyl rings project on the same face to create a hydrophobic pocket.
Abstract: In the molecule of the title compound, C15H14N2, the unsubstituted analogue of Troger’s base, the two aromatic rings are offset with respect to one another. The dihedral angle between the two benzene rings is 95.42 (4)degrees.
Abstract: In the title compound, C21H18N2 center dot CH4O, the two naphthyl ring systems are arranged almost orthogonal to one another, with a dihedral angle of 89.8 (1)degrees.
Abstract: In the molecule of the title compound, C(19)H(18)N(6)O(10), the 2,8-dimethoxy- 4,10-dimethyl-1,3,7,9-tetranitro analogue of Troger’s base, the diazocine bridge imparts a twist such that the two aryl rings are offset with respect to one another. The hinge angle of the molecule, measured as the dihedral angle between the two benzene rings, is 103.64 ( 5)degrees.
Abstract: The synthesis and redox properties of a series of free-base and metal(II) quinoxalino[2,3-b’]porphyrins and their use in an investigation of the substituent effects on the degree of communication between the porphyrin and its beta,beta’-fused quinoxalino component are reported. ESR, thin-layer spectroelectrochemistry, and quantum chemical calculations of the resultant radical anions from one-electron reduction indicate that localization of the unpaired electron across both the porphyrin and the fused quinoxalino group can be controlled, the system as a whole behaving as a highly polarizable pi-expanded porphyrin radical anion. ESR studies on the radical anions of zinc(II) quinoxalino[2,3-b’]porphyrin derivatives indicate that nitrogen-atom spin distribution changes as a function of chemical substitution: 27% quinoxaline character when the porphyrin ring bears a 7-nitro substituent, 34% quinoxaline character in the unsubstituted parent, and 51-61% nitroquinoxaline character when the quinoxalino unit has one or more nitro groups. Close analogies are found between the calculated and observed nitrogen-atom spin distributions, indicating that the calculations embody the key chemical effects. The calculations also indicate that the nitrogen-atom spin distributions closely parallel the important total porphyrin, quinoxaline, and nitro spin distributions, indicating that the observed quantities realistically depict the change in the nature of the delocalization of the radical anion as a function of chemical substitution. The profound effects observed indicate long-range communication of the type that is essential in molecular electronics applications.
Abstract: The first synthesis of Troger’s base analogues bearing three and four atoms in the apical strap is reported, leading to a dramatic change in the shape of the aromatic scaffold with respect to the Troger’s base framework. (C) 2007 Elsevier Ltd. All rights reserved.
Abstract: In the molecule of the title compound, C19H18N2O4, the 2,8-dimethyl ester analogue of Troger’s base, the diazocine bridge imparts a twist such that the two aryl rings are offset with respect to one another. The dihedral angle between the two benzene rings is 96.51 (5)degrees.
Abstract: In the molecule of the title compound, C15H10Br4N2, the 2,4,8,10-tetrabromo analogue of Troger’s base, the two aryl rings are offset with respect to one another by virtue of the diazocine bridge. The dihedral angle of 108.44 (4)degrees between the two benzene rings is the largest yet measured for a dibenzo system.
Abstract: In the molecule of the title compound, C15H12Br2N2, the 2,8-dibromo analogue of Troger’s base, the two aryl rings are offset with respect to one another by virtue of the diazocine bridge. The dihedral angle between the two benzene rings is 94.45 (4)degrees.
Abstract: In the molecule of the title compound, C21H20Br2N2O4, the 4,10-dibromo-2,8-diethyl ester analogue of Troger’s base, the diazocine bridge imparts a twist such that the two aryl rings are offset with respect to one another. A twofold rotation axis passes through the bridgehead C atom. The asymmetric unit contains only one-half molecule and the dihedral angle between the two symmetry-related benzene rings is 98.24 (4)degrees.
Abstract: Monomeric and polymeric 5-nitroquinoxaline derivatives disubstituted in the 2 and 3 positions with 2-pyrrolyl (A), 2-furyl (B) and 2-thienyl (C) groups were prepared and characterized. The substituted 5-nitroquinoxalines were used as active components in poly(vinyl chloride)-membrane and electropolymerized electrodes that were then tested as possible sensors for various cationic species. In contrast to the difurylnitroquinoxaline-based systems, the monomeric and polymeric dipyrrolyl- and dithienylquinoxaline electrodes displayed a good selectivity for Ag+ ions, providing a near-Nernstian response in the 10(-5) to 10(-2) mol L-1 concentration range. The similar potentiometric behavior displayed by the monomeric and polymeric forms of systems A and C supports the contention that the main binding modes displayed by the monomeric forms are retained in the corresponding polymeric structures.
Notes: European Conference on Analytical Chemistry (Euroanalysis 12), DORTMUND, GERMANY, SEP 08-13, 2002
Abstract: FT Raman spectroscopy was used to characterize a set of five newly synthesized 5-nitroquinoxaline derivatives 2,3-disubstituted with 2-pyrrolyl, 2-furyl, 2-thienyl, phenyl and 2-pyridyl groups. Afterwards the 5-nitroquinoxalines were electrochemically reduced to 5-aminoquinoxalines and electropolymerized as films on the Pt electrode coated with porous Au. Comparing the SERS spectra of polymers with the Raman spectra of monomers, a mechanism of polymerization has been suggested. Specific spectral and electrochemical properties of films based on pyrrole substituted 5-aminoquinoxaline were verified by electropolymeriration of 2,3-dipyrrol-2 ‘ -yl-5-nitroquinoxaline without a reduction step. (C) 2001 Elsevier Science B.V. All rights reserved.
Notes: XXVth European Congress on Molecular Spectroscopy, COIMBRA, PORTUGAL, AUG 27-SEP 01, 2000
Abstract: The synthesis of optically pure functionalized cleft molecules derived from dibenzobicyclo[bf][3.3.1]nona-5a,6a-diene-6,12-dione is reported. These clefts are reminiscent of Troger’s base but contain clefts with different dimensions and additional carbonyl (or alcohol) groups that may be utilized in molecular recognition studies. The 2,8-dimethyl and 2,8-dibromo derivatives were synthesized via an intramolecular Friedel-Crafts acylation and were resolved by chiral HPLC. The 2,8-dinitro derivative was prepared by regiospecific nitration of dibenzobicyclo[bf][3.3.1]nona-5a,6a-diene- 6,12-dione. The dibromo and dinitro derivatives allow direct access to a range of functionalized molecular clefts. Palladium-catalyzed coupling of the dibromo derivative afforded the disubstituted phenyl, anisole, and acetylene derivatives, while reduction of the dinitro derivative and acetylation provided amino-dione and amide-hydroxyl derivatives. X-ray crystal structures of the dimethyl 12, dibromo 13, di(p-methoxyphenyl) 16, dinitro 18, and dimethyl dinitro 22 derivatives show cleft angles between the planes between the aromatic rings of 84-104 degrees. The synthetic route, structural features, and potential for molecular recognition studies of this class of clefts are compared with those of the more widely studied Troger’s base cleft molecules.
Abstract: The use of the 3,4-difluoro-1H-pyrrole as a building block for the preparation of octamethyloctafluorocalix[4]pyrrole and 2,3-di(3’,4’-difluoropyrrol-2’yl)quinoxaline is described. These latter two entities act as neutral anion receptors and were found to bind anions such as fluoride, chloride, or dihydrogen phosphate with an enhanced affinity compared to their non-fluorinated congeners as judged from H-1 NMR, F-19 NMR, and fluorescence emission spectroscopic analyses. The increase in affinity was especially high in case of chloride and dihydrogen phosphate anion, with the 2,3-di(3’,4’-difluoropyrrol-2’-yl)quinoxaoline system, in particular, displaying an affinity for H2PO4- that was improved by 3 orders of magnitude as compared to its nun-fluorinated congener. This improvement in the affinity for the dihydrogen phosphate is accompanied by change of color from pale yellow to orange, thus allowing the use of such compounds as naked-eye sensors for phosphate anion. In the case of the octafluorocalix[4]pyrrole system X-ray diffraction analyses revealed the presence of four different macrocyclic conformations in the solid state, as well as close intermolecular contacts mediated by apparent CF- -HN hydrogen bonds.
Abstract: A number of aromatic and nonaromatic expanded porphyrins have been prepared in the authors’ laboratories. These are allowing a number of important themes to be explored, including the construction of novel cation- and anion-complexing agents and the generation of drug candidates with considerable therapeutic potential. In this paper, the use of gadolinium(III) and lutetium(III) texaphyrin derivatives as, respectively, adjuvants for X-ray radiation cancer therapy and photosensitizers for use in photodynamic treatments of cancer, atheromatous plaque, and age-related macular degeneration will be reviewed. Also discussed are the use of water soluble sapphyrins as potential fluorescent phosphate sensors and organic soluble 2,3-dipyrrylquinoxaline derivatives as possible fluoride anion signaling agents. Recent synthetic work, designed to produce expanded porphyrins with new shapes and novel topologies, is also summarized.
Notes: 4th International Symposium on Functional Dyes - Science and Technology of Functional pi-Electron Systems, OSAKA, JAPAN, MAY 31-JUN 04, 1999
Abstract: Addition of a dinaphtho-crown ether to the components of a chiral metallomacrocycle affords a [2]catenane as the exclusive thermodynamic product; the reversible assembly process is driven by a combination of zinc(II)-bipyridyl ligation and pi-donor/pi-acceptor interactions between the electronically complementary aromatic components.
Abstract: In this paper we demonstrate the use of F-19-labelled ligands in the study of the therapeutically important vancomycin group of antibiotics. The substantial simplification of spectra that occurs when such labelled ligands are employed is used to study the anticooperativity between ligand binding and dimerisation of ristocetin A. The general utility of F-19-labelled ligands is demonstrated, with the caveat that the positioning of the label has to be carefully considered. With the growing therapeutic importance of the vancomycin group of glycopeptide antibiotics, such a tool may prove valuable in the detailed study of their mode of action.
Abstract: The synthesis and resolution of two chiral carbocyclic cleft molecules containing carbonyl groups on the periphery of the cavity are reported. These compounds are reminiscent of Troger’s base but contain a smaller cleft and additional carbonyl (or alcohol) groups. X-ray crystal structures of the dibromo and dimethyl derivatives show that the dihedral angle between the two aromatic rings is 79 degrees and 85 degrees respectively. The dibromo derivative provides entry into new supramolecular hosts, via introduction of additional recognition groups into the cleft molecules. (C) 1998 Elsevier Science Ltd. All rights reserved.
Abstract: Background: The emergence of bacteria that are resistant to vancomycin, the drug of choice against methicillin-resistant Staphylococcus aureus, has made the study of the binding characteristics of glycopeptides to biologically relevant depsipeptides important. These depsipeptides, terminating in -D-alanyl-D-lactate, mimic the cell-wall precursors of resistant bacteria. Results: The use of F-19-labelled ligands in the study of the therapeutically important vancomycin series of antibiotics is demonstrated. The substantial simplification of spectra that occurs when such labelled ligands are employed is used in the measurement of binding affinities of depsipeptides to chloroeremomycin (CE), Large enhancements of binding affinities are found at a model bacterial cell-wall surface (constituted from depsipetides that are anchored into vesicles) relative to those measured in free solution. Conclusions: Surface-enhanced binding, previously shown for strongly dimerising glycopeptide antibiotics to normal -D-alanyl-D-alanine-terminating cell-wall precursors, is now demonstrated for CE to the surface of models of VanA- and VanB-resistant bacteria. The effect of depsipeptide chain length is shown to be critically important in producing and maximising this enhancement.
Abstract: Methods for the formation of supported lipid monolayers on top of a hydrophobic self assembled monolayer in a surface plasmon resonance instrument are described. Small unilamellar vesicles absorb spontaneously to the surface of the hydrophobic self-assembled monolayer to form a surface which resembles the surface of a cellular membrane, Lipophilic ligands, such as small acylated peptides or glycosylphosphatidylinositol-anchored proteins, were inserted into the absorbed lipid and binding of analytes to these ligands was analysed by surface plasmon resonance. Conditions for the formation of lipid monolayers have been optimised with respect to lipid type, chemical and buffer compatibility, ligand stability and reproducibility. (C) 1998 Elsevier Science B.V. All rights reserved.
Abstract: The dizinc(II) bis-porphyrin Troger’s base analogue 3 can be resolved on a moderate scale by chromatography over a mixed silica-L-histidine benzyl ester medium. (C) 1997 Elsevier Science Ltd.
Abstract: In this paper we demonstrate the importance of binding geometry and dimerisation at the surface of model cell membranes in the mode of action of the clinically important glycopeptide antibiotics. This has been achieved through the use of model cell membranes (micelles and vesicles) to which cell wall analogues are anchored via a hydrophobic decanoyl chain. rh number of -D-Ala-terminating cell wall analogues, ranging from two to six residues in length, have been used. Dipeptide, pentapeptide and hexapeptide display enhanced binding to the antibiotic at the model cell surface, but tripeptide and tetrapeptide do not. The possible implications of the observed binding geometries for bacterial systems are discussed.
Abstract: The mode of action of a semisynthetic glycopeptide active against vancomycin-resistant bacteria has been investigated. It is shown that the antibiotic, biphenylchloroeremomycin or LY307599, dimerizes strongly and anchors to membranes. It is hypothesized that these two locating devices, previously identified by us when acting separately, might combine to give enhanced binding at a cell surface. This hypothesis is tested experimentally by showing that glycopeptides can bind cell-wall precursor analogues from resistant bacteria (terminating in D–lactate) in a similar manner to those from susceptible bacteria (terminating in D–alanine) and by using model cell surfaces where the benefits of dimerization can be expressed and studied. These model systems use vesicles to represent the cell. membrane, to which cell wall analogues are anchored via a docosanoyl chain, so mimicking the arrangement encountered at the cell surface. Using H-1 NMR spectroscopy, we demonstrate enhanced binding due to dimerization and propose that this enhancement will act cooperatively with membrane anchoring in biphenylchloroeremomycin.
Abstract: Background: Recent work has indicated that dimerization is important in the mode of action of the vancomycin group of glycopeptide antibiotics. NMR studies have shown that one member of this group, ristocetin A, forms an asymmetric dimer with two physically different binding sites for cell wall peptides. Ligand binding by ristocetin A and dimerization are slightly anti-cooperative. In contrast, for the other glycopeptide antibiotics of the vancomycin group that have been examined so far, binding of cell wall peptides and dimerization are cooperative. Results: Here we show that the two halves of the asymmetric homodimer formed by ristocetin A have different affinities for ligand binding, One of these sites is preferentially filled before the other, and binding to this site is cooperative with dimerization. Ligand binding to the other, less favored half of the dimer, is anti-cooperative with dimerization. Conclusions: In dimer complexes, anti-cooperativity of dimerization upon ligand binding can be a result of asymmetry, in which two binding sites have different affinities for ligands, Such a system, in which one binding site is filled preferentially, may be a mechanism by which the cooperativity between ligand binding and dimerization is fine tuned and may thus have relevance to the control of signal transduction in biological systems.
Abstract: The H-1 NMR chemical shift of amide protons in the binding pocket of glycopeptide antibiotics has been used to monitor the interaction of these amide protons with the carboxylate group of cell wall analogues and related ligands. A good correlation is observed between overall ligand binding energy (Delta G degrees) and amide NH chemical shift. We conclude that the strength of the electrostatic interaction of the carboxylate group, which is crucial to recognition and binding by the antibiotics, is cooperatively enhanced by adjacent functional groups on the same ligand template. Hydrogen bonding and burial of hydrocarbon in adjacent sites produce an enhancement of electrostatic binding of the carboxylate group. The data provide experimental evidence for an enthalpic contribution to the chelate effect that is distinct from, and works in addition to, the classic entropic chelate effect. The correlation between amide NH chemical shift and overall binding energy has been used to show binding affinity for eremomycin and chloroeremomycin by di-N-Ac-Lys-D-Ala-D-Lac (Lac = lactate), which is a cell wall analogue of bacteria which exhibit vancomycin resistance. Binding constants for this ligand have also been determined by UV difference spectrophotometry (70 dm(3) mol(-1) and 240 dm(3) mol(-1) respectively).
Abstract: Glycopeptide antibiotics bind to bacterial cell wall peptide analogues terminating in -L-Lys-D-Ala-D-Lac in a similar manner to that of cell-wall analogues terminating in -L-Lys-D-Ala-D-Ala.
Abstract: The synthesis of 4 and 9, in which two porphyrins are joined by a biquinoxalinyl bridge and by a quinoxaline Troger’s base, respectively, provide systems which have interporphyrin centre-centre and edge-edge distances that very closely match those between the primary donor - primary acceptor tetrapyrrolic pair in bacterial photosynthetic reaction centres. Copyright (C) 1996 Elsevier Science Ltd
Abstract: A novel peptide, XR586, has been isolated from fermentations of Acremonium persicinum (Xenova culture collection number X21488). The structure of XR586 has been elucidated by means of NMR spectroscopy, electrospray and fast-atom bombardment MS, derivatization and enzymic digestion. It has been shown to be helical by CD measurements. XR586 shows many structural and conformational features in common with peptaibols, particularly the zervamicins. Peptaibol antibiotics are peptides, typically of 15-20 residues, containing a large proportion of alpha-aminoisobutyric acid (Aib) residues. These peptides adopt a helical conformation in solution and display anti-bacterial and toxic properties due to their ability to form pores in membranes. However, while XR586 contains several Aib residues, it lacks a terminal phenylalaninol and terminates in the sequence Phe-Gly. The lack of reduction of the penultimate residue at the C-terminus may indicate that this step is normally at the end of the biosynthetic pathway of peptaibols and occurs with cleavage of Gly. The H-1 chemical shift assignments of XR586 are reported in Supplementary Publication SUP 50179 (3 pages), which has been deposited at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J.(1996) 313, 9 (’Deposition of data’).
Abstract: Resolution of the bisporphyrin Troger’s base analogue 1 affords homochiral clefts that tightly bind histidine esters in 80-86% e.e. and lysine benzyl ester in 48% e.e.; the histidine esters are bound in fixed conformations that can be readily detected by H-1 NMR spectroscopy as a result of the large dispersion of proton resonances by the ring currents of the two porphyrins.
Abstract: 2-Amino-5,10,15,20-tetraarylporphyrins react with formaldehyde to give good yields of the corresponding octaaryl derivatives of the Troger’s base analogue in which two porphyrins are covalently linked by a diazocine bridge; the X-ray crystal structure of the bis(tetraphenylporphyrinato)dipaliadium(II) derivative 6 reveals a concave chiral cavity with two metal ion binding sites suitable for ditopic interactions with guest molecules.
