bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthetic Glycopeptides for the Development of Antitumour Vaccines
Authors: Dziadek Sebastian , Espínola Carmen G. , Kunz Horst
Published: August 2003

Glycoproteins of tumour cells often are aberrantly glycosylated. In its tumour-associated form, the epithelial mucin MUC1 carries short saccharide structures such as TN, T, sialyl-TN, and sialyl-T antigens. Due to the incomplete saccharide components, peptide epitopes of the backbone become accessible to the immune system. For the construction of synthetic antitumour vaccines, glycopeptides have been synthesized which contain tumour-associated saccharide antigens and peptide sequences from the tandem repeat portion of MUC1. In the synthesis of these glycopeptides, preformed glycosyl–amino acid building blocks are applied in solution- or solid-phase strategies. Examples are given for the use of N-Fmoc-protected TN, T, sialyl-TN, and sialyl-T antigen–serine and –threonine conjugates in syntheses of glycopeptides from the tandem repeat region from MUC1 and the N-terminal portion of leukosialin (CD43). In solid-phase syntheses allylic linkers (cleavable under neutral conditions), acid-sensitive linkers, and the novel 2-phenyl-2-trimethylsilyl-ethyl ester linker (detachable with fluoride under neutral conditions) have successfully been applied. The synthetic tumour-associated glycopeptide antigens, identical to nature, often exhibit low immunogenicity. Therefore, their conjugation to carrier proteins is demanded. To this aim, glycopeptide antigens have been equipped with biotin labels or conjugated with T-cell peptide epitopes. Some of these synthetic glycopeptide antigens induce proliferation of T-cells and a cytotoxic T-cell response.
A Total Synthesis of the Styryllactone (+)-Goniodiol from Naphthalene
Authors: Banwell Martin G. , Coster Mark J. , Edwards Alison J. , Karunaratne Ochitha P. , Smith Jason A. , Welling Lee L. , Willis Anthony C.
Published: August 2003

The cytotoxic natural product (+)-goniodiol (1) has been prepared in twelve steps from the enantiomerically pure cis-dihydrocatechol (2), which is readily obtained by microbial oxidation of naphthalene. Elaboration of compound (2) involves an initial oxidative cleavage to dialdehyde (7) followed by reduction to give diol (12). Conversion of compound (12) into acetal (17) required, inter alia, selective oxidation of the benzylic alcohol moiety followed by a metal-catalyzed decarbonylation of the resulting aldehyde. Allylation of compound (17) with allyltributylstannane in the presence of lithium perchlorate gave a ca. 2.7 : 1 mixture of alcohols (18) and (19), each of which was converted into the corresponding acrylate under standard conditions. Subjection of these ester derivatives to a ring-closing metathesis (RCM) reaction with Grubbs' first-generation catalyst gave the anticipated lactones (22) and (23). Acid-catalyzed removal of the acetonide protecting group within compound (22) then afforded (+)-goniodiol (1), while analogous deprotection of congener (23) afforded 6-epi-(+)-goniodiol (24).
CP-225,917 and CP-263,114 Synthesis Support Studies: Testing a Radical Cyclization Strategy for Installation of the Side-Chains
Authors: Banwell Martin G. , Coster Mark J. , Edwards Alison J. , Vögtle Markus
Published: August 2003

The selenocarbonate (18) has been prepared and shown to react with hexabutyldistannane hydride/allyltributyl-stannane to give, via a radical cyclization/allylation sequence, the lactone (21) embodying vicinal and trans-related functionality likely to be appropriate for elaboration to the side-chains associated with the title compounds (1) and (2) (phomoidrides A and B).
Kinetic Isotope and Collision Energy Effects in the Dissociation of Chloride and Bromide Adducts of Aliphatic Alcohols, Benzaldehyde, and 2,4-Pentanedione
Authors: Augusti Rodinei , Zheng Xubin , Turowski M. , Cooks R. Graham
Published: August 2003

A tandem-in-space triple quadrupole mass spectrometer was used to measure kinetic isotopic effects (KIEs) for the dissociation of chloride and bromide adducts of several compounds that bind halide anions via either hydrogen bonds or by nucleophilic attachment. Two isotopomers of each adduct were simultaneously mass-selected in the first quadrupole and dissociated by collision with argon in the second quadrupole. The KIEs were measured by comparing the extents of dissociation of the lighter versus the heavier isotopomeric adducts. In most cases, lower collision energies and multiple collision conditions favoured larger KIE values, an expected feature of easily dissociated cluster ions considering zero-point energies (ZPEs). The larger chloride adduct of cyclohexanol gave greater KIEs compared with the smaller alcohols, a consequence of slower dissociation due to the larger number of degrees of freedom. Dissociation of the chloride adducts gave greater KIEs than the corresponding bromide adducts, a result that is also consistent with expectations based on ZPEs. Both the chloride and bromide adducts of 2,4-pentanedione, when dissociated at 6 eV collision energy under single-collision conditions, displayed normal KIEs (1.0460 ± 0.0012 and 1.0092 ± 0.0035 respectively). These and the alcohol results were correctly predicted by the ZPEs calculated using commonly applied ab initio Hartree–Fock (HF) and B3LYP density functional theory (DFT) methods with large basis sets (6–311 containing both polarization and diffuse functions). Geometry optimization calculations for the 2,4-pentanedione chloride adduct using either the Restricted Hartree–Fock (RHF) method with a 6–31G* basis set or using the more accurate 6–31++G** method showed that, in the most stable form, the chloride is bonded at multiple sites by a molecule of 2,4-pentanedione. In this structure, chloride binds weakly to both the methylene and the methyl hydrogen atoms. Collision-induced dissociation furnishes chloride and 2,4-pentanedione anion ([M – H]–) as competitive negatively charged products, which is consistent with the proposed structure. It is interesting that the intermolecular KIEs in this study tend to be normal, while intramolecular isotope effects in halides, notably of the type M1Cl+M2 are inverse, as a consequence of the lower ZPEs associated with the heavier isotopomers. The difference in the two systems is that the stronger bonds are found in the products in the case of M1Cl+M2 dissociation but in the reactants in the case of MCl– dissociation.
Isomers of 1,4,8,11-Tetraazacyclotetradecane-6,13-dicarboxylate Characterized as Cobalt(III) Complexes
Authors: Bernhardt Paul V. , Hambley Trevor W. , Lawrance Geoffrey A. , Maeder Marcel , Wilkes Eric N.
Published: August 2003

The major trans (1) and minor cis (2) isomers of 1,4,8,11-tetraazacyclotetradecane-6,13-dicarboxylate have been characterized as the complexes [Co(1)](ClO4) and [Co(H2)(OH2)]Cl(ClO4)·H2O. The former crystallized in the C2/c space group and the latter in the P21/c space group, with cell parameters a 16.258(7), b 9.050(3), c 15.413(6) Å, β133.29(3)°, and a 9.694(4), b 16.135(1), c 12.973(5) Å, β 93.00(2)°, respectively. Their characterization completes identification of the respective trans and cis isomers for the series of c-pendant macrocycles also including 1,4,8,11-tetraazacyclotetradecane-6-amine-13-carboxylate ((3), (4)) and 1,4,8,11-tetraazacyclotetradecane-6,13-diamine ((5), (6)). The complexes show limited distortion from octahedral geometry with the strain in the presence of the coordinated c-pendant carboxylate significantly reduced compared with that for the c-pendant amine in analogues, a consequence mainly of six-membered as opposed to five-membered chelate rings involving the pendant donor. A comparison of the physical properties for the trans isomers of the octahedral complexes of (1), (3), and (5), which reflect progressively increasing strain, is presented.
Retention Characteristics of Lanthanide Ions on a Mixed Phosphonic Acid - Carboxylic Acid Cation Exchanger
Authors: Shaw Matthew J. , Nesterenko Pavel N. , Dicinoski Greg W. , Haddad Paul R.
Published: August 2003

The chromatographic behaviour of lanthanide ions on a dual phosphonate- and carboxylate-functionalized ion-exchange resin (Dionex IonPac CS12A and CG12A) was studied using various mobile phase compositions. By suppressing ion-exchange interactions through increasing the ionic strength of the eluent, the column selectivity changed to that of a chelation mechanism via the phosphonate functional groups. Retention was based on the varying conditional stability constants of the lanthanide ions with the phosphonate groups. Eluent pH was additionally found to exert a strong influence on analyte retention, but no further changes to the column selectivity occurred. The inclusion of small concentrations of organic solvents could also be used to manipulate retention to a more minor extent, as could altering the column temperature. Examples of separations are given, especially the separation of gadolinium and europium, which are often co-eluted when using nitrogen–oxygen-chelating groups such as iminodiacetic acid.
Regulation of Toxicants in the Australian Environment
Authors: Batley Graeme E.
Published: August 2003

The chemical behaviour of toxicants in the environment is a critical control on their impacts on human and ecological health. The current status of regulations for air, soils, groundwater, surface waters, and sediments in Australia are discussed, with particular focus on metals. It is now recognized that speciation and bioavailability are important in assessing potential effects, yet only now are environmental guidelines addressing these. Recent chemical and ecotoxicological studies of metal bioavailability in waters and sediments investigate robust methods for speciation measurement and report improved models to describe metal uptake and predict toxicity. The way forward with respect to toxicant regulation is a departure from single-number guidelines, to site-specific risk-based assessments, such as those adopted in the new ANZECC/ARMCANZ water quality guidelines.
Superexchange-Mediated Charge Separation and Charge Recombination in Covalently Linked Donor - Bridge - Acceptor Systems
Authors: Paddon-Row Michael N.
Published: August 2003

Evidence is presented in support of the concept that electron transfer (ET) between a pair of chromophores may take place efficiently over large distances (>10 Å) by the mediation of an intervening saturated hydrocarbon medium. For example, ET is found to take place on a sub-nanosecond timescale through saturated norbornylogous bridges greater than 13 Å in length, by a superexchange (through-bond coupling) mechanism. The dependence of the ET dynamics on the bridge length and configuration are consistent with the operation of a superexchange mechanism. The distinction between molecular wire behaviour and superexchange-mediated ET is made. The distance dependence of ET dynamics through different types of bridges—saturated and unsaturated hydrocarbon bridges, proteins, and duplex DNA—is discussed and explained. Strategies for prolonging the lifetimes of charge-separated states are explored and discussed. In general, long-lived charge-separated species have been generated using giant multichromophoric systems in which the charges are separated by large distances, often exceeding 20 Å. In contrast, it is shown that very long-lived charge-separated states, possessing the triplet multiplicity, may be generated using short ‘dwarf’ dyads, in which the charges are less than 6 Å apart. Charge recombination in these species is slowed by the difference in electron spin multiplicity between the charge-separated state and the ground state.
New Multidentate Pyrazolyl - Pyridine Ligands—Synthesis and Structures
Authors: Bell Zöe R. , McCleverty Jon A. , Ward Michael D.
Published: August 2003

Five new multidentate ligands have been prepared containing N,N-bidentate pyrazolyl–pyridine units linked to a central aromatic spacer unit. The ligands 3,3′-bis(3-{pyridin-2-yl}-pyrazol-1-yl-methyl)-p-terphenyl (1), 4,4′-bis(3-{pyridin-2-yl}-pyrazol-1-yl)biphenyl (2), and 1,8-bis(3-{pyridin-2-yl}-pyrazol-1-yl-methyl)naphthalene (3) have two bidentate arms and are therefore potentially tetradentate; 2,6-bis(3-{pyridin-2-yl}-pyrazol-1-yl-methyl)pyridine (4) has two bidentate arms with an additional nitrogen-donor in the aromatic spacer unit (a pyridyl group) and is therefore potentially pentadentate; and 1,3,5-trimethyl-2,4,6-tris(3-{pyridin-2-yl}-pyrazol-1-yl-methyl)benzene (5) has three bidentate arms and is therefore potentially hexadentate. The X-ray crystal structures of all of these ligands have been determined.
Metal-Assisted Reactions. Part XXX. Control of Rates of Heterogeneously Catalyzed Transfer Hydrogenolysis through Changes in Solvent Composition
Authors: Alves José A. C. , Brigas Amadeu F. , Johnstone Robert A. W.
Published: August 2003

Adsorption isotherms in the liquid phase can be used to determine the relative strengths of adsorption of reactants and solvent at a catalyst surface. Such isotherms can then be used to indicate which type of solvent would be most suitable for a heterogeneously catalyzed reaction in the liquid-phase. Solubility in any chosen solvent is also important. As examples, rates of heterogeneously catalyzed liquid-phase transfer hydrogenolyzes of aryl tetrazolyl ethers (1) have been shown to be highly dependent on both the nature of the solvent and on the solution concentrations of the reactants. The rate of reaction can be varied from zero to a maximum and then back to zero simply by adjusting the solubility of the reductant through changes in the proportion of water in a mixed-solvent system.
The Synthesis of 5-Hydroxy-3-methylnaphtho[2,3-c]furan-4,9-dione and 5,8-Dihydroxy-1-methylnaphtho[2,3-c]furan-4,9-dione
Authors: Piggott Matthew J. , Wege Dieter
Published: August 2003

5-Hydroxy-3-methylnaphtho[2,3-c]furan-4,9-dione (1), a metabolite isolated from Aloe ferox and Bulbine capitata, has been synthesized by a sequence involving an annulation reaction between the anion of 4-methoxy-3-oxo-1,3-dihydroisobenzofuran-1-carbonitrile (8) and (E)-pent-3-en-2-one, followed by subsequent construction of the furan ring through allylic bromination, hydrolysis, and dehydration as the key steps. The formation of several unusual products observed in annulation reactions between (8) and O-protected derivatives of (E)-5-hydroxypent-3-en-2-one (9) can be rationalized by invoking the intermediacy of a reactive o-quinone methide. 5,8-Dihydroxy-1-methylnaphtho[2,3-c]furan-4,9-dione (2), another naturally occurring naphtho[2,3-c]furan-4,9-dione, has been prepared by a Friedel–Crafts acylation of 1,4-dimethoxybenzene with 2-methylfuran-3,4-dicarbonyl dichloride. Arguments are presented that 5,8-dihydroxynaphtho[2,3-c]furan-4,9-dione is a better structural representation than the alternative 4,9-dihydroxynaphtho[2,3-c]furan-5,8-dione tautomer in such systems, as the latter would contain a reactive isobenzofuran moiety.
Chemistry of Carbon Nanotubes
Authors: Lin Tong , Bajpai Vardhan , Ji Tao , Dai Liming
Published: August 2003

Judicious application of site-selective reactions to non-aligned and aligned carbon nanotubes has opened a rich field of carbon nanotube chemistry. In order to meet specific requirements demanded by particular applications (e.g. biocompatibility for nanotube biosensors and interfacial strength for blending with polymers), chemical modification of carbon nanotubes is essential. The tips of carbon nanotubes are more reactive than their sidewalls, allowing a variety of chemical reagents to be attached at the nanotube tips. Recently, some interesting reactions have also been devised for chemical modification of both the inner and outer nanotube walls, though the seamless arrangement of hexagon rings renders the sidewalls relatively unreactive. This review provides a brief summary of very recent progress in the research on chemistry of carbon nanotubes.
Homoanomeric Effect in the 1,2-Dimethoxyethyl Radical
Authors: Henry David J. , Beckwith Athelstan L. J. , Radom Leo
Published: August 2003

A homoanomeric effect is found to stabilize the 1,2-dimethoxyethyl radical (CH3O–ĊH–CH2OCH3) in a conformation in which the singly-occupied orbital at the radical centre is approximately coplanar with the p-type lone pair on the α-oxygen and with the β-C–O bond. The magnitude of this stabilization is predicted to be ~10–12 kJ mol−1 at the G3(MP2)-RAD and CBS-RAD levels of theory.
Incorporation of Cyano Transition Metal Complexes in KCl Crystals—Experimental and Computational Studies
Authors: Carter Damien J. , Ogden Mark I. , Rohl Andrew L.
Published: August 2003

Experimental and computational studies of the incorporation of hexacyanoferrate(II), hexacyanocobaltate(III), and hexacyanoferrate(III) into potassium chloride crystals are described. The experimental results showed that the extent of incorporation follows the trend hexacyanoferrate(II) » hexacyanoferrate(III) > hexacyanocobaltate(III). Computational modelling produced replacement energies that match the experimental trend. The calculated geometry of the incorporated complexes was also found to match well with previous experimental results.
An Investigation of Gaseous α-Halogenated Carbocations and Isomeric Halonium, Halenium, and Allylhalonium Ions
Authors: Holman Robert W. , Davis Jennifer , Walstrom Amy , McCombs Michelle , Jackson Gina , Sullivan Shannon , Gross Michael L.
Published: August 2003

We investigated with tandem mass spectrometric methods (MS/MS) the nature and extent of stabilization of gas-phase alkyl, vinyl and 2-allyl carbenium ions caused by halogen participation of neighboring chlorine and bromine atoms. The extent of halogen atom stabilization is greatest for alkyl ions, followed closely by that for vinyl ions, and is significantly less for the 2-halosubstituted allyl ions. The data is consistent with bridged halonium ion formation in alkyl systems and bridged halenium ion formation in vinyl systems. Our results for the 2-chloro allyl system are in accord with an earlier NMR interpretation rather than with recent theory, indicating that a bridged allyl halonium ion species is involved.
Unimolecular Rearrangements of Transient Carboxy Radicals and Cations
Authors: Schröder Detlef , Soldi-Lose Héloïse , Schwarz Helmut
Published: August 2003

Charge reversal (CR) and neutralization–reionization (NR) mass spectra of aliphatic carboxylate ions RCOO– provide insight into the behaviour of the transient neutral carboxy radicals RCOO• as well as the short-lived RCOO+ cations. For the neutral radicals, a novel hydrogen rearrangement is proposed, which might explain the sometimes only modest yields in the Hunsdiecker reaction of carboxylic acids in the condensed phase.
Magnetic Resonance Studies of β-Amyloid Peptides
Authors: Lau Tong-Lay , Barnham Kevin J. , Curtain Cyril C. , Masters Colin L. , Separovic Frances
Published: August 2003

The deposition of senile plaques is a characteristic event in the progression of Alzheimer's disease (AD). Associated with the progression of the disease, the main component of the deposited material, the β-amyloid peptide (Aβ), undergoes a structural transition and a toxic gain of function. For this reason, extensive structural studies of Aβ and Aβ fragments have been carried out in order to determine the relationship between neurotoxicity and conformational changes of the peptide that lead to fibril formation. NMR studies in aqueous solution and in membrane-mimicking environments are reviewed, and include the effects of temperature, pH, and metal ions on Aβ structure. In addition, electron paramagnetic resonance (EPR) studies of Aβ in model membranes and the effect of metals of Aβ are discussed and demonstrate the pleiomorphic nature of the peptide. The contradictory results obtained from the various experiments are a result of studying different fragments of Aβ and illustrate the importance of studying the full-length peptide.
Unimolecular Rearrangements and Fragmentations in the Gas Phase: [1,3] Sigmatropic Isomerizations and [2 + 2] Cycloreversions
Authors: Ahmad Mohammad R. , Kass Steven R.
Published: August 2003

Trimethylsilyl ethers of 3-buten-2-ol, 1-vinylcyclopropanol, 1-vinylcyclobutanol, and cyclobutanol were treated with fluoride over a wide temperature range (–40 to 300°C) in a variable-temperature flowing afterglow–triple quadrupole device. The structures of the resulting alkoxides and enolates were probed by ion–molecule reactions and their collision-induced dissociation (CID) spectra. Activation energies were obtained for several anion-accelerated [1,3] sigmatropic rearrangements and [2 + 2] cycloreversions. The mechanisms for these isomerizations and fragmentations (stepwise versus concerted) and their synthetic potential are discussed.
Enclathrating Benzene in a Neutral Dicopper(II) Coordination Framework
Authors: Liu Hong-Bo , Yu Shu-Yan , Huang Hui , Zhang Zhong-Xing
Published: August 2003

Two infinite complexes {[Cu2(O2CCH3)4](3-tpt)(CH3OH)2}∞ (1) and {[Cu2(O2CPh)4](3-tpt)(C6H6)1.5}∞ (2) were obtained by reactions of 2,4,6-tris(3′-pyridyl)-1,3,5-triazine (3-tpt) with Cu2(O2CCH3)4 and Cu2(O2CPh)4, respectively, which have been structurally established by single-crystal X-ray diffraction. Complex (1) consists of one-dimensional zig-zag chains in its solid state, which can encapsulate methanol molecules; complex (2) consists of one-dimensional helical chains in its solid state, providing large channels which can selectively enclathrate benzene molecules. (1) crystallizes in the monoclinic space group P21/c with a 8.2892(4), b 22.8479(8), c 16.9258(10) Å, β 99.1480(10)°, V 3164.8(3) Å3, and Z 4; (2) crystallizes in the triclinic space group P1 with a 10.7641(8), b 12.0908(8), c 18.9039(12) Å, α 82.514(3)°, β 85.268(2)°, γ 79.746(4)°, V 2395.9(3) Å3, and Z 2. The inclusion selectivity toward aromatic molecules was discussed.
Deep Space Organometallic Chemistry
Authors: Petrie Simon
Published: August 2003

Interstellar clouds, characterized by extremely low temperatures and very low particle densities, host a variety of commonplace and exotic metal-containing molecules; quantum chemical calculations are ideally suited to their characterization. Such calculations have proven invaluable in unravelling the chemical secrets of cold, gaseous extraterrestrial environments in which metal-based chemistry is beginning to be seen as an active and fruitful field of exploration. By probing the formation of minimalistic metal compounds such as MgNC, we hope to obtain valuable new clues to the distribution of the chemical elements within star- and planet-forming regions.
Arylpropanolamines Incorporating an Antioxidant Function as Neuroprotective Agents
Authors: Joubran Lida , Jackson W. Roy , Campi Eva M. , Robinson Andrea J. , Wells Bradley A. , Godfrey Peter D. , Callaway Jennifer K. , Jarrott Bevyn
Published: August 2003

A series of arylpropanolamines containing dipyrrolidinylpyrimidines as an antioxidant function have been synthesized and evaluated as dual function neuroprotective agents. Their in vitro efficacy as sodium channel blocking agents and antioxidants has been evaluated and compared with those of the ethanolamine derivative (1), which has been shown to be neuroprotective in a rat model of stroke. The ability of the present compounds to displace 3H-BTX toxin from sodium-ion channels in a rat brain membrane fraction was shown to be largely independent of the substituents on the aryl ring, which suggests that this activity may be mainly associated with the aminopyrimidine moiety. Structure–activity relationships for antioxidant efficacy were less clear, but the unsymmetrical pyrimidines were consistently more active than their symmetrical isomers. A brief theoretical investigation of this observation is reported.
Ultraviolet Laser Irradiation of Low Concentration Liquid Microjets: Solute Evaporation and Solvent Initiated Reactivity
Authors: Holstein Wendy L. , Dobeck Laura M. , Otten Dale E. , Metha Gregory F. , Buntine Mark A.
Published: August 2003

Resonance-enhanced 266 nm 1 + 1 multiphoton ionization has been used in conjunction with a liquid microjet time-of-flight mass spectrometer to explore the photochemistry of a 10–3 M solution of anisole in ethanol. Only ions generated in the condensed phase originating from the three-photon non-resonant ionization of the ethanol solvent are liberated into the vacuum. No solute ions generated in solution are observed unless the concentration is increased to 1 M. Under high concentration conditions, solute pairing or aggregation at the liquid surface is a necessary precursor towards liberating solute photoions into the vacuum via a Coulombic explosion. At a solution concentration of 10–3 M, a decreased solute ion density at the liquid surface is insufficient to initiate a Coulombic explosion into the vacuum. Rather, non-resonantly generated solvent ions on the liquid surface dominate the ion ejection process. Related studies on 10–3 M solutions of 4-methoxyphenol in both ethanol and water show that at this concentration solute ionization is most likely to be observed following thermal evaporation from the surface of a liquid beam.
Nitrogen versus Oxygen Group Protection in Hydroxypropylbenzimidazoles
Authors: Indusegaram Sutharsiny , Katsifis Andrew G. , Ridley Damon D. , Vonwiller Simone C.
Published: August 2003

In order to convert 1′H-benzimidazol-2′-ylpropanols into aryl ethers using Mitsunobu coupling, it was necessary to protect the benzimidazole nitrogen in the starting alcohols. Selective protection at nitrogen was achieved through N-benzyl derivatives, but attempts to protect the nitrogen directly through tert-butoxycarbonyl, acetyl, trityl, or tetrahydropyranyl derivatives were complicated either by selective reactions at oxygen or by the formation of bis-protected compounds. Transformations of some oxygen-protected derivatives are discussed, and in particular the conversion of the acetates of 1′H-benzimidazol-2′-ylpropanols to N-tetrahydropyranyl derivatives is described. Mitsunobu coupling involving the N-benzyl and N-tetrahydropyranyl derivatives and methyl 4-hydroxybenzoate were achieved, and thus afforded synthetic routes to the desired propylbenzimidazole aryl ethers.
Equine Metabolites of Norethandrolone: Synthesis of a Series of 19-Nor-17α-pregnanediols and 19-Nor-17α-pregnanetriols
Authors: McKinney Andrew R. , Ridley Damon D. , Turner Peter
Published: August 2003

A range of 19-nor-17α-pregnanediols and 19-nor-17α-pregnanetriols have been synthesized and used to confirm the structures of major equine urinary metabolites of the synthetic anabolic steroid norethandrolone (1). 19-Nor-5α,17α-pregnane-3α,17β-diol (2), 19-nor-5α,17α-pregnane-3β,17β-diol (4), 19-nor-5β,17α-pregnane-3α,17β-diol (6), and 19-nor-5β,17α-pregnane-3β,17β-diol (7) were prepared by stereoselective reduction of the 3-ene-4-one of norethandrolone. The 19-nor-5α,17α-pregnane-3β,16α,17β-triol (8) and 19-nor-5α,17α-pregnane-3β,16β,17β-triol (9) were prepared from 19-nortestosterone (11) by multistep processes in which the critical step involved Grignard additions to 16-acetoxy-17-ones. The triols (20R)-19-nor-5α,17α-pregnane-3β,17β,20-triol (22) and (20S)-19-nor-5α,17α-pregnane-3β,17β,20-triol (23) were prepared from norethindrone (24) by initial selective A-ring reduction, then subsequent modification of the 17-ethynyl group. By comparison of these compounds with post-administration equine urine samples it was possible to establish A-ring reduction with 3β,5α stereochemistry as well as non-stereospecific 16-hydroxylation and 20-hydroxylation as significant metabolic pathways affecting norethandrolone in the horse.
Ruthenium(II) Complexes of Multidentate Ligands Derived from Di(2-pyridyl)methane
Authors: D'Alessandro Deanna M. , Keene F. Richard , Steel Peter J. , Sumby Christopher J.
Published: August 2003

Bis(2,2′-bipyridyl)ruthenium complexes of the model ligand di(2-pyridyl)methane (1) and its multidentate derivatives 1,1,2,2-tetra(2-pyridyl)ethane (2), tetra(2-pyridyl)ethene (3), and hexa(2-pyridyl)[3]radialene (4) have been prepared and characterized by NMR, visible absorption spectroscopy, electrochemical measurements, and, in two cases, by X-ray crystallography. Complexes of (2) and (3) exist as conformationally rigid species with lower than expected symmetry. Ligands (2) and (3) proved surprisingly resistant to forming dinuclear ruthenium complexes. The two diastereoisomeric dinuclear complexes of (4), Δ Λ/Λ Δ and Δ Δ/Λ Λ (rac), are shown to be locked in conformations of C1 and C2 point-group symmetry, respectively. This represents a rare example where the Δ Λ/Λ Δ-dinuclear complex of a achiral, symmetrically bridging ligand is not a meso compound.
The Synthesis and in Vitro Cytotoxicity of Two trans-Platinum Complexes of Heterocyclic Amines
Authors: Giannikopoulos Georgina , Teo Chih-Lynne , Hall Matthew D. , Fenton Ronald R. , Hambley Trevor W.
Published: August 2003

The syntheses and crystal structures of the platinum(II) complexes trans-[PtCl2(DMSO)(C4H9NO)] and trans-[PtCl2(DMSO)(dmdze)] are described and the mechanisms leading to their formation are discussed. The complex trans-[PtCl2(DMSO)(C4H9NO)] crystallizes in the triclinic space group P1, a 8.1432(8), b 8.5224(8), c 9.0801(9) Å, α 111.780(1), β 91.074(2), γ 98.349(2)°, Z 2, and its structure was refined to an R value of 0.019 on 2470 F. The cytotoxicity of this complex was determined and was found to be lower than that of cisplatin. The complex trans-[PtCl2(DMSO)(dmdze)] crystallizes in the monoclinic space group C2/c, a 23.498(5), b 8.048(2), c 17.859(6) Å, β 120.88(2), Z 8, and its structure was refined to an R value of 0.034 on 2712 F.
Structural Definition of the Low-Temperature Phase Transition of Tris(ethane-1,2-diamine)zinc(II) Dinitrate
Authors: Bernhardt Paul V. , Riley Mark J.
Published: August 2003

The 93 K X-ray crystal structure of tris(ethane-1,2-diamine)zinc(II) dinitrate is reported. As predicted by the spectroscopic studies of other workers, there is a reversible phase transition of the structure at low temperature. We have determined this temperature to be 143 K. The structure at this temperature and below resembles that of the room temperature structure, except the crystallographic D3 symmetry of the complex cation (296 K) is lowered to C2 (below 144 K) by subtle changes in cation–anion hydrogen bonding. No change in the conformation of the cation or its bond lengths and angles was found.
Total Synthesis of (+)-Crocacin A
Authors: Feutrill John T. , Rizzacasa Mark A.
Published: August 2003

The first asymmetric total synthesis of the electron-transport inhibitor crocacin A (1) is described. The key step involved acylation of the anion derived from dienecarbamate (6) with the acid chloride (5) to afford the enamide (14). Desilylation, oxidation, and N-deprotection gave acid (17), which was coupled with glycine methyl ester to afford (1).
Regioselectivity in the Syntheses of Enantiopure 2-Benzopyrans through Intramolecular Cyclization of Tethered Lactaldehydes. Conformations of the Products
Authors: Aggarwal Rachna , Birkbeck Anthony A. , Giles Robin G. F. , Green Ivan R. , Gruchlik Yolanta , Oosthuizen Francois J.
Published: August 2003

Using titanium tetraisopropoxide, the enantiopure tethered lactaldehyde (α′ S,2S)-2-(3′-hydroxy-α′-methyl-benzyloxy)propanal (6) is cyclized with complete regio- and diastereoselectivity ortho to the phenolic hydroxyl group to give (1S,3S,4R)-3,4-dihydro-1,3-dimethyl-2-benzopyran-4,5-diol (7). Similar cyclization of the epimeric (α′ R,2S)-lactaldehyde (25) yields solely the corresponding (1R,3S,4R)-4,5-diol (34). The 4,5-diacetate (26), but not (35), undergoes conformational inversion of the heterocyclic ring through significant 4,5-peri interactions between the adjacent acetoxy substituents. Spontaneous cyclizations of the corresponding phenoxide ions of the lactalde-hydes (6) and (25), generated by fluoride from their silyl ethers, led to the related 4,7-diols with high regioselectivity through ring-closure para to the aromatic oxygen.
Intracellular Protein Unfolding and Aggregation: The Role of Small Heat-Shock Chaperone Proteins
Authors: Treweek Teresa M. , Morris Amie M. , Carver John A.
Published: August 2003

Molecular chaperones are a diverse group of proteins that interact with partially folded protein states to stabilize and prevent their mutual (illicit) association. Proteins require involvement with molecular chaperones throughout their lifespan: from their synthesis and folding through intracellular transport, membrane translocation, and to their ultimate degradation. Small heat-shock proteins (sHsps) are a ubiquitous family of molecular chaperones that are found in all organisms. Unlike many of the well-characterized chaperones, for example from the Hsp60 and Hsp70 families, sHsps are not involved in regulating protein folding. Instead, under conditions of cellular stress, such as elevated temperatures, they interact and stabilize partially folded target proteins to prevent their aggregation and precipitation. Because of this ability, their expression is elevated in many protein diseases that are characterized by protein aggregation and precipitation, including Alzheimer's, Creutzfeldt–Jakob, and Parkinson's diseases. The principal lens protein, α-crystallin, is a sHsp. Its chaperone ability is important in preventing lens protein precipitation and hence in maintaining lens transparency. This review summarizes the salient structural features of sHsps that enable them to act as highly efficient chaperones to prevent protein precipitation under stress conditions. The mechanism of chaperone action and the state of the target protein when interacting with sHsps are also discussed. Finally, diseases in which sHsp expression is elevated are discussed including the potential roles of sHsps and their therapeutic uses in the treatment of these diseases.
Sphaeropsidin F, a New Pimarane Diterpene Produced in Vitro by the Cypress Pathogen Sphaeropsis sapinea f. sp. Cupressi
Authors: Evidente Antonio , Sparapano Lorenzo , Andolfi Anna , Bruno Giovanni , Motta Andrea
Published: August 2003

A new pimarane diterpene was isolated from liquid cultures of Sphaeropsis sapinea f. sp. cupressi, a plant pathogenic fungus causing a form of canker disease of Italian cypress (Cupressus sempervirens L.). The metabolite, characterized by spectroscopic methods, was named sphaeropsidin F. When assayed on test plants sphaeropsidin F caused less severe symptoms that those of sphaeropsidin A, which is the main toxin produced by this fungus. A solution of sphaeropsidin F (0.1 mg mL–1) tested on severed cypress twigs caused yellowing of the apical leaves of C. sempervirens twigs, whereas C. macrocarpa and C. arizonica were not affected. This shows that the three cypress species had a different grade of sensitivity to the action of the toxin. As already demonstrated for rings B and C, the modification of the A ring strongly reduced the biological activity of the molecule.
High-Resolution Electrospray-Ionization Fourier-Transform Ion Cyclotron Resonance and Gas Chromatography - Mass Spectrometry of Macadamia Nut Oil
Authors: Fard Ahmad Mokhtari , Turner Athol G. , Willett Gary D.
Published: August 2003

An oil sample from macadamia nuts is examined using electrospray-ionization (ESI) Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) and gas chromatography–mass spectrometry (GC-MS). The neat oil, the methanol extract of the oil, the esterified oil, and the esterified methanol extract of the oil are examined using these two techniques. Various acylglycerols and fatty acids are identified using the high-resolution exact mass and elemental analysis routines. High performance liquid chromatography is also used for separation and collection of oil-extract fractions, prior to the mass spectrometry studies, to identify various molecular isomers of compounds in the nut oil. A comparison of the results from GC-MS experiments on the esterified oil and methanol extract of the oil with those from the FTICR-MS experiments reveals that the latter technique provides more detailed information on the composition of the macadamia oil including a relative concentration profile for the free fatty acids present in the oil. We observe the presence of fatty acids and acylglycerides containing one or more additional oxygen atoms, which may be in the form of peroxy, hydroperoxy, oxo (ketone or aldehyde functionalities), hydroxy, and/or epoxy substituents as well as a number of unusual free fatty acids and mono- and di-acylglycerides containing an odd number of carbon atoms. The simplicity of the sample preparation when combined with the results from the high resolution, high mass accuracy ESI-FTICR-MS experiments on the macadamia nut oil indicate that this method is a powerful tool that can be used for the analysis of trace compounds in animal and plant oils.
Fragmentations of Deprotonated Alkyl Hydroperoxides (ROO− Upon Collisional Activation: A Combined Experimental and Computational Study
Authors: Blanksby Stephen J. , Kato Shuji , Bierbaum Veronica , Ellison G. Barney
Published: August 2003

The collision-induced dissociation (CID) mass spectra of the [M − H]– anions of methyl, ethyl, and tert-butyl hydroperoxides have been measured over a range of collision energies in a flowing afterglow–selected ion flow tube (FA-SIFT) mass spectrometer. Activation of the CH3OO– anion is found to give predominantly HO– fragment anions whilst CH3CH2OO− and (CH3)3COO– produce HOO– as the major ionic fragment. These results, and other minor fragmentation pathways, can be rationalized in terms of unimolecular rearrangement of the activated anions with subsequent decomposition. The rearrangement reactions occur via initial abstraction of a proton from the α-carbon in the case of CH3OO– or the β-carbon for CH3CH2OO– and (CH3)3COO–. Electronic structure calculations suggest that for the CH3CH2OO– anion, which can theoretically undergo both α- and β-proton abstraction, the latter pathway, resulting in HOO– + CH2CH2, is energetically preferred.
Reactions Catalyzed by Bacterial Cytochromes P450
Authors: Cryle Max J. , Stok Jeanette E. , De Voss James J.
Published: August 2003

The cytochromes P450 are a large family of oxidative haemoproteins that are responsible for a wide variety of oxidative transformations in a variety of organisms. This review focuses upon the reactions catalyzed specifically by bacterial enzymes, which includes aliphatic hydroxylation, alkene epoxidation, aromatic hydroxylation, oxidative phenolic coupling, heteroatom oxidation and dealkylation, and multiple oxidations including C–C bond cleavage. The potential for the practical application of the oxidizing power of these enzymes is briefly discussed.
Evaluating the Effect of Termination by Chain - Chain Coupling in Living Free-Radical Polymerizations
Authors: Pyun Jeffrey , Rees Ian , Fréchet Jean M. J. , Hawker Craig J.
Published: August 2003

A novel approach based on the reaction of multifunctional star polymers with chromophore-labelled linear polymers is presented for evaluating the extent of termination by chain–chain coupling during living free-radical polymerizations. A mixed initiating system consisting of an unlabelled, multifunctional initiator and an excess of a monofunctional alkoxyamine initiator containing a chromophore, such as pyrene, is used to initiate the living polymerization of vinyl monomers leading to a mixture of star and linear polymers. The occurrence of chain–chain coupling is readily identified and quantified by isolating the star polymer that is obtained and elucidating the level of incorporation of pyrene units by UV/vis spectroscopy. This allows the level of chain–chain coupling to be determined since the inclusion of pyrene into the star structure is a direct result of termination by radical coupling.
Preparation of the First Isobenzofuran Containing Two Ring Nitrogens: A New Diels - Alder Diene for the Synthesis of Molecular Scaffolds Containing One or More End-Fused 3,6-Di(2-pyridyl)pyridazine Ligands
Authors: Warrener Ronald N. , Butler Douglas N. , Margetic Davor
Published: August 2003

Preparation of a stable, crystalline isobenzofuran containing two ring-nitrogen atoms, 4,7-di(2-pyridyl)-5,6-diazaisobenzofuran (diaza-IBF) (12), is reported here for the first time. Diaza-IBF was prepared using the s-tetrazine-induced fragmentation of 1,4-di(2-pyridyl)-5,8-epoxy-5,8-dihydrophthalazine (9), for which a synthesis is provided. Diaza-IBF was also prepared by flash vacuum pyrolysis (FVP) of the isomeric N-methyl-1,4-di(2-pyridyl)-5,8-epoxy-5,6,7,8-tetrahydrophthalazine-6,7-dicarboximides (18) and (19), formed in three steps from furan, N-methyl maleimide, and 3,6-di(2-pyridyl)-s-tetrazine. Diaza-IBF was employed in cycloaddition protocols with alkenes to form scaffold mono- or bis-3,6-di-(2-pyridyl)-pyridazine ligands having novel molecular architectures.
Conversion of Gibberellic Acid into the B-Ring seco-Kaurenoid, Longirabdolactone
Authors: Adamson George , Mander Lewis N.
Published: August 2003

The base-catalyzed rearrangement of an α-hydroxy aldehyde derived from the gibberellin GA15 results in ring-expansion of the five-membered B-ring of the gibberellin molecule and transformation into an ent-kaurene derivative. Further manipulation affords 19,7-acetals and access to the highly functionalized B-ring seco-kaurenoid bioactive secondary metabolites that have been isolated from the genus Rabdosia. The methodology is illustrated by the synthesis of longirabdolactone from gibberellic acid. Unanticipated and unobserved epimerization at C5 led initially to the 5-epimer of the synthetic target by a series of ketol rearrangements, but the isomerization could be avoided through the use of milder reaction conditions.
The Dissociation Energy of the Benzene - Argon van der Waals Complex Determined by Velocity Map Imaging
Authors: Sampson Rebecca K. , Lawrance Warren D.
Published: August 2003

The technique of velocity map imaging has been used to determine the dissociation energy of the C6H6+–Ar van der Waals complex. From the change in the ionization energy between the complex and free benzene and the spectroscopic shift of the S1←S0 transition, the dissociation energies in the S0 and S1 states of the neutral complex were determined, being 314 ± 7 and 335 ± 7 cm−1 for the S0 and S1 states of the neutral complex, respectively, and 486 ± 5 cm−1 for the cation ground (D0) state.
Unimolecular Gas-Phase Reactions of Diethyl Phthalate, Isophthalate, and Terephthalate upon Electron Ionization
Authors: Tajima Susumu , Mamada Masashi , Nakajima Satoshi , Takahashi Yutaka , Nibbering Nico M. M.
Published: August 2003

Unimolecular gas-phase reactions of diethyl phthalate (1), isophthalate (2), and terephthalate (3), upon electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and deuterium labelling. The metastable molecular ions (1)+ decompose to give exclusively the ions m/z 176 ([M – CH3CH2OH]+) and not the ions by the loss of CH3CH2O as proposed earlier in the literature. The metastable molecular ions (2)+ and (3)+ fragment differently from (1)+ and lead not only to the formation of the major fragment ions m/z 194 ([M − CH2CH2]+) via a McLafferty rearrangement but also to minor fragment ions m/z 193 ([M – CH2CH3]+).Yet, molecular ions decomposing in the ion source all show as primary fragmentation channel the loss of CH3CH2O to give the ions at m/z 177, which further dissociate to give the ions at m/z 149 through the loss of C2H4 or CO, indicating the resulting ions are +COC6H4COOH and +C6H4COOCH2CH3. The +COC6H4COOH ions decompose into the m/z 121, 93, and 65 ions by the consecutive losses of three carbon monoxide molecules, respectively. Prior to the second CO loss, a migration of the OH group to the benzene ring occurs. During the metastable fragmentation of the +C6H4COOCH2CH3 ions no ethoxy migration occurs, in contrast to the methoxy migration taking place in the metastable decomposition of the lower homologue +C6H4COOCH3 ions.
John Hamilton Bowie: An Appreciation
Authors: O'Hair Richard A. J.
Published: August 2003

This special issue of the Australian Journal of Chemistry is dedicated to Professor John Bowie on the occasion of his sixty-fifth birthday on July 16, 2003. Through this collection of papers, John's students, collaborators, colleagues, and friends gratefully acknowledge his diverse and important contributions to organic chemistry. This introduction is divided into two parts: firstly a summary of John's research career[1] and secondly an 'interview' with John[2] to provide insights into his career and his thoughts on a variety of issues.
Structural Diversity in Silver(I) Complexes of 3,6-Di(2-pyridyl)pyridazines
Authors: Constable Edwin C. , Housecroft Catherine E. , Kariuki Benson M. , Neuburger Markus , Smith Christopher B.
Published: August 2003

Silver(I) complexes of 3,6-di(2-pyridyl)pyridazines have been prepared and characterized. In the solid state, complexes with 1 : 2 and 2 : 2 M : L stoichiometries have been characterized. In no case have we obtained evidence for higher nuclearity gridlike structures.
The Total Synthesis of ( - )-Tetrahydrolipstatin
Authors: Bodkin Jennifer A. , Humphries Edward J. , McLeod Malcolm D.
Published: August 2003

Careful control during the bromolactonization of β,γ;-unsaturated acid (4) was required to regioselectively afford the trans-β-lactone (3) as the major diastereomer. Radical debromination of (3) followed by a three-step sequence of reactions afforded the lipase inhibitor (–)-tetrahydrolipstatin (1).
Should we manage soil organic carbon in Vertosols in the northern grains region of Australia?
Authors: Farquharson R. J. , Schwenke G. D. , Mullen J. D.
Published: August 2003

Two issues prompted this paper. The first was the measured soil organic carbon decline in fertile northern Australian soils under continual cropping using traditional management practices. We wanted to see whether it was theoretically possible to maintain or improve soil organic carbon concentrations with modern management recommendations. The second was the debate about use of sustainability indicators for on-farm management, so we looked at soil organic carbon as a potential indicator of soil health and investigated whether it was useful in making on-farm crop decisions. The analytical results indicated first that theoretically the observed decline in soil organic carbon concentrations in some northern cracking clay soils can be halted and reversed under continuous cropping sequences by using best practice management. Second, the results and associated discussion give some support to the use of soil organic carbon as a sustainability indicator for soil health. There was a consistent correlation between crop input decisions (fertilisation, stubble management, tillage), outputs (yield and profits) and outcomes (change in soil organic carbon content) in the short and longer term. And this relationship depended to some extent on whether the existing soil organic carbon status was low, medium or high. A stock dynamics relationship is one where the change in a stock (such as soil organic carbon) through time is related not only to the management decisions made and other random influences (such as climatic effects), but also to the concentration or level of the stock itself in a previous time period. Against such a requirement, soil organic carbon was found to be a reasonable measure. However, the inaccuracy in measuring soil organic carbon in the paddock mitigates the potential benefit shown in this analysis of using soil organic carbon as a sustainability indicator.These results are based on a simulation model (APSIM) calibrated for a cracking clay (Vertosol) soil typical of much of the intensively-cropped slopes and plains region of northern New South Wales and southern Queensland, and need to be interpreted in this light. There are large areas of such soils in north-western New South Wales; however, many of these experience lower rainfalls and plant-available soil water capacities than in this case, and the importance of these characteristics must also be considered.