bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanistic Insight Gained into the Ligand Substitution Reactions of Bis(o‐benzosemiquinonediiminato)(triphenylphosphane)cobalt(III) − Kinetic, Solvent, and Volume Profile Studies
Authors: Alzoubi Basam M. , Hamza Mohamed S. A. , Dücker‐Benfer Carlos , van Eldik Rudi
Published: August 2003

The ligand substitution reactions of bis(o‐benzosemiquinonediiminato)(triphenylphosphane)cobalt(III), [CoIII(s‐BQDI)2(Ph3P)]+, were studied with imidazole (Imid) and 4‐dimethylaminopyridine (4‐Me2Npy) as entering nucleophiles in MeOH and CH3CN as solvents (S). The complex [CoIII(s‐BQDI)2(Ph3P)S]+ undergoes dissociation of the solvent to form a five‐coordinate intermediate, [CoIII(s‐BQDI)2(Ph3P)]+, which binds the entering nucleophile in a rate‐determining step through a six‐coordinate transition state, [CoIII(s‐BQDI)2(Ph3P)L]+, followed by the release of triphenylphosphane to form [CoIII(s‐BQDI)2L]+. From the temperature and pressure dependence of the substitution of triphenylphosphane by imidazole, the activation parameters for the forward and reverse reactions of [CoIII(s‐BQDI)2(Ph3P)]+ with imidazole in MeOH were found to be ΔH‡ = 58±2 and 43.4±0.5 kJ·mol−1, ΔS‡ = −116±6 and −73±2 J·K−1·mol−1, and ΔV‡ = −10.6±0.1 and −8.7±0.3 cm3·mol−1, respectively. In CH3CN, however, ΔH‡, ΔS‡, and ΔV‡ for the forward reaction were found to be 50±3 kJ·mol−1, −111±9 J·mol−1·K−1, and −12.9±0.3 cm3·mol−1, respectively. The activation parameters for the reaction between [CoIII(s‐BQDI)2(Ph3P)]+ and 4‐dimethylaminopyridine in MeOH for the forward and reverse reactions were found to be ΔH‡ = 76±2 and 47.9±0.4 kJ·mol−1, ΔS‡ = −51±7 and −64±2 J·K−1·mol−1, and ΔV‡ = −10.5±0.3 and −11.1±0.2 cm3·mol−1, respectively. From these reported rate and activation parameters, the substitution of triphenylphosphane by imidazole and 4‐dimethylaminopyridine follows an associative mechanism. The ligand substitution reactions of [CoIII(s‐BQDI)2(Ph3P)]+ in CH3CN were found to be faster than those in MeOH, which is attributed to the potential for hydrogen bond formation with the entering nucleophile in the case of MeOH as solvent. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Potential MRI Contrast Agents Based on Micellar Incorporation of Amphiphilic Bis(alkylamide) Derivatives of [(Gd−DTPA)(H2O)]2−
Authors: Kimpe Kristof , Parac‐Vogt Tatjana N. , Laurent Sophie , Piérart Corinne , Elst Luce Vander , Muller Robert N. , Binnemans Koen
Published: August 2003

DTPA‐bisamide derivatives with alkyl chains containing 14, 16 and 18 carbon atoms were synthesized and complexes of various trivalent lanthanide ions (Ln = Gd, La, Pr, Eu) were formed. Variable temperature proton NMR spectroscopy of paramagnetic praseodymium(III) and europium(III) complexes revealed that long aliphatic substituents considerably increase the energy barrier for the intramolecular rearrangement around the lanthanide ion. The gadolinium(III) complexes were incorporated into mixed micelles, and photon correlation spectroscopy showed that the mean sizes of all the micelles were within the same range. The NMRD curves of all three DTPA‐bisamide‐gadolinium complexes incorporated in mixed micelles display higher relaxivity values than the commercially available Gd−DTPA contrast agent. The higher relaxivity obtained for the micellar DTPA‐bisamide‐gadolinium complexes with C14 and C16 chains relative to the micellar DTPA‐bisamide‐GdIII C18 chain complex could be attributable to the fact that the alkyl chain containing 18 carbon atoms is longer than the alkyl chain of the major component of the micelles, DPPC, in which it is inserted. This would allow increased mobility of the polar head and hence a lower relaxivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Study of Inorganic Systems by NMR Spectroscopy in Conjunction with Parahydrogen‐Induced Polarisation
Authors: Duckett Simon B. , Blazina Damir
Published: August 2003

The study of reaction mechanisms by NMR spectroscopy normally suffers from limitations in sensitivity that result in substantial difficulties in the detection and characterisation of reaction intermediates. One technique that can circumvent this problem is the use of para‐enriched hydrogen. Here, an overview of the developments in the study of chemical reactions using parahydrogen‐assisted NMR spectroscopy is presented, with the characterisation of a number of new hydride complexes of iridium, rhodium, ruthenium and tantalum being described. A number of studies involving transition metal clusters and catalytic applications are also considered. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
HREM and CIP Characterization of Complex Superstructures in Cu‐Co Related Perovskites
Authors: Ruiz‐González Luisa , Boulahya Khalid , Parras Marina , Alonso José , González‐Calbet José M.
Published: August 2003

Two compositions in the La‐Ba‐Cu‐Co‐O system − La2Ba3Cu2Co3O13 and La2Ba3Cu3Co2O13 − have been synthesized and characterized by means of SAED (Selected Area Electron Diffraction) and HREM (High Resolution Electron Microscopy). The La2Ba3Cu2Co3O13 phase leads to a fivefold perovskite superstructure along the c axis, which can be described as formed by the recurrent intergrowth of the two alternating blocks ···PP··· and ···POhP··· (P = pyramid and Oh = octahedron). Pyramidal and octahedral sites are randomly occupied by Cu/Co cations, while La/Ba cations exhibit an ordered distribution. The La2Ba3Cu3Co2O13 composition gives rise to a mixture of phases in which a new phase showing a threefold superstructure due to the sequence ···POhP··· coexists with a fivefold superstructure with the same polyhedra sequence (···PPPOhP···) as the previous one, but a disordered arrangement of lanthanum‐barium cations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Characterisation of Ternary Cage Compounds with Adamantane‐Like M4P4Si2 (M = Al, Ga, In) Core Structures
Authors: von Hänisch Carsten
Published: August 2003

The reactions of [LiAl(PH2)4] or [NaAl(PH2)4] with Et2SiCl2 or iPr2SiCl2 yield the dialkyldiphosphanylsilanes Et2Si(PH2)2 (1) and iPr2Si(PH2)2 (2), respectively. Both compounds were identified by NMR spectroscopy as well as mass spectrometry. Compound 2 reacts with MEt3 (M = Al, Ga, In) to form the cage compounds [iPr2Si{P(H)MEt2}2]2 (3: M = Al, 4: M = Ga, 5: M = In). These three clusters were fully characterised by NMR and IR spectroscopy as well as by single‐crystal X‐ray diffraction. The central structural motif of 3−5 is an adamantane‐like cage composed of four metal, four phosphorus and two silicon atoms. They are the first ternary clusters with these combinations of elements and crystallise isotypical in the triclinic space group P$\bar 1$
; the lattice constants are: 3: a = 1129.0(6), b = 1164.8(8), c = 1750.6(8) pm; α = 83.63(5), β = 81.53(4), γ = 73.39(5)°; 4: a = 1125.9(7), b = 1159.0(7), c = 1744.7(7) pm; α = 83.71(4), β = 81.89(4), γ = 73.05(5)°; 5: a = 1147.4(2), b = 1174.7(2), c = 1753.3(4) pm; α = 85.32(3), β = 82.03(3), γ = 73.40(3)°. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Silver(I) Complex Crystals Switched by a Water Molecule
Authors: Arii Hidekazu , Saito Yamato , Funahashi Yasuhiro , Ozawa Tomohiro , Jitsukawa Koichiro , Masuda Hideki
Published: August 2003

The reaction of AgPF6 and cis,cis‐1,3,5‐triaminocyclohexane (TACH) in a 1:1 ratio in methanol solution gave two different coordination polymer crystals depending on the presence/absence of water. The crystal structure in the absence of water is a one‐dimensional, tube‐like polymer with formula {[AgI(TACH)]PF6}n, while in the presence of water the structure is a three‐dimensionally expanded complex network built up from cage units containing a water molecule, {[AgI3(TACH)4](PF6)3·H2O}n; this structure is induced even by a trace amount of water. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Redox Chemistry of Actinide Ions in Wells−Dawson Heteropolyoxoanion Complexes
Authors: Chiang Ming‐Hsi , Soderholm L. , Antonio Mark R.
Published: August 2003

The redox behavior has been characterized for several actinide (An) complexes with the monovacant Wells−Dawson anion, of the form [Ann+(α‐2‐P2W17O61)2]n−20 (An = Th4+, U4+, Np4+, Pu4+, and Am3+). Two complexes, with An = U4+ and Am3+, show redox activity under oxidizing conditions, which is attributed to the actinide oxidation. Am3+ is oxidized to Am4+ with an E1/2 = +1.21±0.01 V, and U4+ oxidizes to U5+ with a measured E1/2 = +0.55±0.01 V vs. Ag/AgCl. Although the cyclic voltammetry (CV) data are consistent with a reversible redox couple, bulk oxidative electrolysis of [U4+(α‐2‐P2W17O61)2]16− results in the decomposition of this complex to produce uranyl acetate and the free monovacant Wells−Dawson anion. In contrast, all of the CV data from the actinide coordination complexes differ from equivalent data obtained from the [α‐2‐P2W17O61]10− ligand itself. There are two complexed An4+ ions, Np and Pu, that undergo reduction over the same potential range as the ligands themselves. In situ X‐ray spectroelectrochemistry is used to quantify the actinide response. The Np4+/Np3+ redox behavior is a classically single ion process, with a formal potential of −0.84±0.01 V that was determined from a Nernst plot of X‐ray absorption near‐edge structure (XANES) data. The Pu4+/Pu3+ formal reduction potential in the complex [Pu(α‐2‐P2W17O61)2]n− was determined to be −0.17±0.01 V using the same methodology. However, in this latter case, the slope of the Nernst plot indicates that 0.72±0.03 electrons are involved in the reduction. This is a significant deviation from the 1 electron expected for the Pu couple, and is discussed in terms of the concomitant reduction of the P−W−O framework of the Wells−Dawson anion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Two Polymeric Complexes of Norfloxacin with Iron(II) and Their Magnetic Properties
Authors: Qu Zhi‐Rong , Zhao Hong , Xing Li‐Xin , Wang Xi‐Sen , Chen Zhen‐Feng , Yu Zhi , Xiong Ren‐Gen , You Xiao‐Zeng
Published: August 2003

The reaction of H‐Norf with (NH4)2Fe(SO4)2·6H2O and Fe(OH)3 (or Fe2O3) affords Fe(H‐Norf)2(SO4)·2H2O (1) and Fe(Norf)2·4H2O (2), respectively, both of which have 2D polymeric structures. Their interesting magnetic properties are also reported. Crystal data for 1: monoclinic, P21/c, a = 23.166(1), b = 10.0492(4), c = 7.7264(3) Å, β = 98.379(1)°, V = 1779.50(13) Å3, Z = 2; for 2: monoclinic, P21/c, a = 5.8411(12), b = 21.685(4), c = 13.265(3) Å, β = 99.20(3)°, V = 1658.6(6) Å3, Z = 2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Structural and Magnetic Characterization of a Linear Trinuclear Copper Complex Formed through Ligand Sharing
Authors: Song Yufei , Gamez Patrick , Roubeau Olivier , Lutz Martin , Spek Anthony L. , Reedijk Jan
Published: August 2003

Reaction of bis(2‐hydroxybenzyl)‐1,3‐diamino‐2‐propanol (H2bhbdp) with copper perchlorate in methanol leads to the assembly of a trinuclear complex with the general formula [Cu3(bhbdp)2(CH3OH)2(ClO4)2] (1). The complex was characterized by X‐ray crystallography, Ligand Field, IR and ESR spectroscopy, and magnetic susceptibility. The structure of the complex contains a linear trinuclear array of copper ions [the Cu(1)−Cu(2)−Cu(1a) angle is 180° by symmetry], in octahedral, square planar and octahedral environments, respectively. The external Cu1 and Cu1a centers are coordinated by two amine nitrogens, two phenolate oxygen donors, one methoxide oxygen and one oxygen from a perchlorate, while the central Cu2 is coordinated by four phenolate oxygens through ligand sharing. A strong antiferromagnetic interaction between the adjacent CuII ions dominates the magnetic properties of 1 leading to an S = 1/2 ground state which is fully populated below 150 K. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Pendent Arm Formation and Extension accompanying Macrocycle Synthesis − A New Class of Ryongamines?
Authors: Harrowfield Jack , Kim Yang , Lee Young Hoon , Thuéry Pierre
Published: August 2003

Reaction of the CuII complex of the podand hexamine “sen”, CH3C(CH2NHCH2CH2NH2)3, with formaldehyde and nitroethane under basic conditions provides, as one of the principal products, a complex containing a new ligand which is not only macrocyclic but which has resulted also from reactions to extend one podand arm, to introduce an aminal bridge and to oxidise one of the donor‐N atom units to an imine. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Efficient Asymmetric Synthesis of Δ‐ and Λ‐Enantiomers of (Bipyridyl)ruthenium Complexes and Crystallographic Analysis of Δ‐Bis(2,2′‐bipyridine)(2,2′‐bipyridine‐4,4′‐dicarboxylato)ruthenium: Diastereoselective Homo‐ and Heterochiral Ion Pairing Revisited
Authors: Caspar Régis , Amouri Hani , Gruselle Michel , Cordier Christine , Malézieux Bernard , Duval Raphäel , Leveque Hubert
Published: August 2003

In our original article,[1] the captions for Figures 2, 3 and 4 (page 501) are incorrect. We wrongly attributed the CD curves with the solid line to the Δ‐enantiomers 4a, 4a and 5a and those with dotted lines to the �‐enantiomers 3b, 4b and 5b. The correct captions are as follows: Figure 2. CD curves for 3a (dotted line) and 3b (solid line) in acetonitrile Figure 3. CD curves for 5a (dotted line) and 5b (solid line) in acetonitrile Figure 4. CD curves for 4a (dotted line) and 4b (solid line) in acetonitrile
Seismic response of multi‐supported structures by proper orthogonal decomposition
Authors: Tubino Federica , Carassale Luigi , Solari Giovanni
Published: August 2003

The seismic analysis of structures is usually carried out considering the ground motion as fully‐correlated in space and determining the structural response by pseudo‐deterministic methods such as the response spectrum technique. Actually, the partial correlation of the seismic acceleration may influence heavily the behaviour of spatially extended structures, such as bridges, viaducts or pipelines. In order to take its partial correlation into account, the seismic ground motion is schematized as a stochastic process dependent on time and on space; the hypotheses of stationarity and homogeneity are used to obtain simple and general results. The influence of the partial correlation of the seismic ground motion on the structural response is investigated by introducing suitable Equivalent Spectra. The acceleration of the support‐points of the structure is represented by the Proper Orthogonal Decomposition (POD), defining the modes of the earthquake. The method is formulated for any kind of multi‐degree‐of‐freedom system and is applied, as a case study, to an ideal single‐storey multi‐supported frame with an axially rigid beam. In the case of two supports, the POD decouples the pseudo‐static and the dynamic contributions to the structural response. This property is preserved for structural systems with many supports, where only the lower modes of the earthquake, usually the first two POD modes, are responsible for the structural response. Copyright © 2003 John Wiley & Sons, Ltd.
Robust active vibration suppression control with constraint on the control signal: application to flexible structures
Authors: Forrai A. , Hashimoto S. , Funato H. , Kamiyama K.
Published: August 2003

A unified mathematical framework, sustained by experimental results, is presented for robust controller design taking into account the constraint on the control signal. The design procedure is exemplified for an active vibration suppression control problem with applications to flexible structures. The considered experimental set‐up is a three‐storey flexible structure with an active mass driver placed on the last storey. First, the considered flexible structure is identified and the model's parametric uncertainties are deduced. Next, control constraints are presented for the robust control design problem, taking into account the restriction imposed on the control signal. Finally, the effectiveness of the control system is tested through experiments, when the input disturbance is assumed to be a sinusoidal one as well as a historical earthquake record (1940 El Centro record). Copyright © 2003 John Wiley & Sons, Ltd.
Seismic risk assessments and GIS technology: applications to infrastructures in the Friuli–Venezia Giulia region (NE Italy)
Authors: Codermatz Raffaella , Nicolich Rinaldo , Slejko Dario
Published: August 2003

This paper illustrates the seismic risk preliminary estimates of two different groups of structures located on the territory of the Friuli–Venezia Giulia region (NE Italy) : the first group includes some special industrial plants, and the second group includes bridges and tunnels belonging to the regional highway network. The part of the study on special industrial plants tries to evaluate the degree of expected damage, taking into account their structural typology and ground shaking expressed in terms of macroseismic intensity. The second part of the study is an application of the HAZUS methodology to the tunnels and bridges of a highway network: the combination of expected ground shaking and the construction characteristics lead to very different risk levels, especially when considering the bridges. The resulting damage levels to bridges and tunnels are still only indicative because of the fragility curves used in the evaluations: they were developed for existing bridge and tunnel structural typologies in the U.S.A. Moreover, both examples show the power of GIS technology in storing, elaborating, and mapping spatial data. Copyright © 2003 John Wiley & Sons, Ltd.
Comparison of spectral ratio techniques for estimation of site effects using microtremor data and earthquake motions recorded at the surface and in boreholes
Authors: Rodríguez Víctor H. S. , Midorikawa Saburoh
Published: August 2003

The authors apply soil response estimation techniques employing accelerograms for fifteen earthquakes recorded at the Yokohama Strong Motion Network and its vertical array of nine sites, plus microtremor data recorded at all 150 sites. Assessment of the reliability of surface to reference site spectral ratios, and horizontal to vertical spectral ratios of S‐waves, coda, and microtremors, relied on cross‐validation with both surface to borehole spectral ratios, and theoretical soil response functions for vertically incident SH plane waves calculated from the vertical array recordings and logging data, respectively. The results indicate the following: (1) the reference site method provides more accurate soil response estimations; (2) the H/V of microtremors provides relatively better soil response estimations than its S‐wave and coda counterparts; and (3) the H/V of microtremors provides coincident soil response estimations at two‐thirds of the sites when considering no more than ±30% mismatch in the determination of the predominant periods. The matching of parameters obtained from the analysis of microtremors, combined with their relatively low economic cost and the possibility of recording without strict spatial or time restrictions turns microtremors into a particularly appealing approach. Copyright © 2003 John Wiley & Sons, Ltd.
A method of calculating the non‐linear seismic response of a building braced with viscoelastic dampers
Authors: Choi Hyun , Kim Wook‐Bae , Lee Sang‐Jo
Published: August 2003

Buildings are continually subject to dynamic loads, such as wind load, seismic ground motion, and even the load from internal utility machines. The recent trend of constructing more flexible high‐rise buildings underscores the importance of including viscoelastic dampers in building designs. Viscoelastic dampers are used to control the dynamic response of a building. If the seismic design is based only on the linear response spectrum, considerable error may occur when calculating the seismic response of a building; rubber viscoelastic dampers show non‐linear hysteretic damping that is quite different from viscous damping.

This study generated a non‐linear response spectrum using a non‐linear oscillator model to simulate a building with viscoelastic dampers installed. The parameters used in the non‐linear damper model were obtained experimentally from dynamic loading tests. The results show that viscoelastic dampers effectively reduce the seismic displacement response of a structure, but transmit more seismic force to the structure, which essentially increases its seismic acceleration response. Copyright © 2003 John Wiley & Sons, Ltd.
Effect of causal and acausal filters on elastic and inelastic response spectra
Authors: Boore David M. , Akkar Sinan
Published: August 2003

With increasing interest in displacement spectra and long‐period motions, it is important to check the sensitivity of both elastic and inelastic response spectra to the filtering that is often necessary to remove long period artifacts, even from many modern digital recordings. Using two records of very different character from the M=7.1, 1999 Hector Mine, California, earthquake, we find that the response spectra can be sensitive to the corner periods used in causal filtering, even for oscillator periods much less than the filter corner periods. The effect is most pronounced for inelastic response spectra, where the ratio of response spectra computed from accelerations filtered at 25 and 200 sec can be close to a factor of 2 for oscillator periods less than 5 sec. Published in 2003 by John Wiley Sons, Ltd.
Soil–structure interaction in yielding systems
Authors: Avilés Javier , Pérez‐Rocha Luis E.
Published: August 2003

The effects of soil–structure interaction in yielding systems are evaluated, including both kinematic and inertial interaction. The concepts developed previously for interacting elastic systems are extended to include the non‐linear behavior of the structure. A simple soil–structure system representative of code‐ designed buildings is investigated. The replacement oscillator approach used in practice to account for the elastic interaction effects is adjusted to consider the inelastic interaction effects. This is done by means of a non‐linear replacement oscillator defined by an effective ductility together with the known effective period and damping of the system for the elastic condition. To demonstrate the efficiency of this simplified approach, extensive numerical evaluations are conducted for elastoplastic structures with embedded foundation in a soil layer over elastic bedrock, excited by vertically propagating shear waves. Both strength and displacement demands are computed with and without regard to the effect of foundation flexibility, taking as control motion the great 1985 Michoacan earthquake recorded at a site representative of the soft zone in Mexico City. Results are properly interpreted to show the relative effects of interaction for elastic and yielding systems. Finally, it is demonstrated how to implement this information in the context of code design of buildings. Copyright © 2003 John Wiley & Sons, Ltd.
Formic Acid Catalyzed Rearrangement of Thevinols (=4,5‐Epoxy‐3,6‐dimethoxy‐α,17‐dimethyl‐6,14‐ethenomorphinan‐7‐methanols) and Their Vinylogous Analogues: Effects of 5β‐Methyl Substitution
Authors: Grundt Peter , Martinez‐Bermejo Fernando , Lewis John W. , Husbands Stephen M.
Published: August 2003

In a limited number of cases, 14‐alkenylcodeinones (=14‐alkenyl‐7,8‐didehydro‐4,5‐epoxy‐3‐methoxy‐17‐methylmorphinan‐6‐ones) can be obtained by formic acid treatment of thevinols (=4,5‐epoxy‐3,6‐dimethoxy‐α,17‐dimethyl‐6,14‐ethenomorphinan‐7‐methanols), but under these conditions the equivalent 14‐alkenyl‐7,8‐dihydrocodeinones undergo further rearrangement (Scheme 1 and Table). Introduction of a 5β‐methyl group allows the 18,19‐dihydrothevinol precursors to be rearranged to 14‐alkenyl‐7,8‐dihydrocodeinones, but similar manipulation of the vinylogues of these thevinols is generally unable to prevent full rearrangement to 5,14‐bridged thebainone derivatives.
Nucleotides. Part LXXI
Authors: Sigmund Harald , Pfleiderer Wolfgang
Published: August 2003

A new labelling technique attaching fluorescein via a carbamoyl linker directly to the amino groups of the nucleobases was developed. The amino groups were first converted to the phenoxycarbonyl derivatives (→10, 15, 19, 58), which reacted under mild conditions with 5‐aminofluorescein to give the corresponding N‐[(fluorescein‐5‐ylamino)carbonyl] derivatives (→11–14, 16, 17, 20, 59, 60). The introduction of the 5‐aminofluorescein residue into properly protected adenylyl‐adenosine dimers (→39, 40) and trimer (→50) worked well, and final deprotection of these uniformly blocked precursors led on treatment with DBU (1,8‐diazabicyclo[5.4.0]undec‐7‐ene), in one step to dimer 41 and trimer 51. Synthesis of an appropriately protected monomeric phosphoramidite building block (→75) was more difficult, since introduction of the 2‐(4‐nitrophenyl)ethyl residue into the fluorescein moiety in 59 led mainly to trisubstitution to give 61 including the urea function. Formation of the adenylyl dimer 66 and trimer 67 proceeded in the usual manner by phosphoramidite chemistry; however, deprotection of 67 with DBU was incomplete since the O‐alkyl group at the urea moiety was found to be very stable. Finally, the appropriate phosphoramidite building block 75 could be synthesized by the sequence 59→72→73→74→75. The phosphoramidite 75 was used for the synthesis of dimer 77 and trimer 79 by solution chemistry, as well as for that of various oligonucleotides by the machine‐aided approach on solid support carrying the fluorophore at different positions of the chain (→84–87). The attachment of the fluorescein fluorophor via a short carbamoyl linker onto the 6‐amino group of 2′‐deoxyadenosine enables such molecules to function very well in fluorescence‐polarization experiments.
Synthesis and Biological Evaluation of 14‐Alkoxymorphinans. Part 19
Authors: Schüllner Falko , Meditz Ruth , Krassnig Roland , Morandell Günther , Kalinin Valery N. , Sandler Ellen , Spetea Mariana , White Angela , Schmidhammer Helmut , Berzetei‐Gurske Ilona P.
Published: August 2003

The 14‐O‐benzylnaltrexones 3–6 were prepared from naltrexone (2) in several steps. The novel compounds were biologically evaluated in radioligand binding and in [35S]GTPγS functional assays in comparison to the reference compound naltrexone. In the binding assay, compounds 3–6 exhibited preference for κ opioid receptors, while the parent compound naltrexone shows preference for μ receptors. In the functional assay, μ antagonist potency of compounds 3–6 was in the range of naltrexone, while κ antagonist potency was considerably higher for most novel compounds in comparison to naltrexone.
Induced Circular Dichroism and Magnetic Circular Dichroism Spectra of Maleimide and Related Molecules
Authors: Kawamura Masahiro , Higashi Miwako
Published: August 2003

The induced circular dichroism (ICD) spectra of the inclusion complexes of maleimide, phthalimide, and naphthalene‐2,3‐dicarboximide with β‐ or γ‐cyclodextrin (CDx) have been measured. The structure of the CDx inclusion complexes are interpreted by the signs and shapes of ICD spectra compared with the results of PPP calculations. In maleimide and naphthalene‐2,3‐dicarboximide, the ICD spectra of the β‐CDx inclusion complex are very similar to those of the γ‐CDx inclusion complex in spite of the differences in dimensions between the cavity of β‐CDx and that of γ‐CDx. In phthalimide, the ICD spectra of the β‐CDx inclusion complex are very different from those of the γ‐CDx inclusion complex. The split‐type ICD bands at 220–235 nm show that the dimer of phthalimide is formed in the presence of β‐CDx.
Metabolism of Deuterated Isomeric 6,7‐Dihydroxydodecanoic Acids in Saccharomyces cerevisiae – Diastereo‐ and Enantioselective Formation and Characterization of 5‐Hydroxydecano‐4‐lactone (=4,5‐Dihydro‐5‐(1‐hydroxyhexyl)furan‐2(3H)‐one) Isomers
Authors: Garbe Leif‐A. , Tressl Roland
Published: August 2003

The chemical synthesis of deuterated isomeric 6,7‐dihydroxydodecanoic acid methyl esters 1 and the subsequent metabolism of esters 1 and the corresponding acids 1a in liquid cultures of the yeast Saccharomyces cerevisiae was investigated. Incubation experiments with (6R,7R)‐ or (6S,7S)‐6,7‐dihydroxy(6,7‐2H2)dodecanoic acid methyl ester ((6R,7R)‐ or (6S,7S)‐(6,7‐2H2)‐1, resp.) and (±)‐threo‐ or (±)‐erythro‐6,7‐dihydroxy(6,7‐2H2)dodecanoic acid ((±)‐threo‐ or (±)‐erythro‐(6,7‐2H2)‐1a, resp.) elucidated their metabolic pathway in yeast (Tables 1–3). The main products were isomeric 2H‐labeled 5‐hydroxydecano‐4‐lactones 2. The absolute configuration of the four isomeric lactones 2 was assigned by chemical synthesis via Sharpless asymmetric dihydroxylation and chiral gas chromatography (Lipodex ® E). The enantiomers of threo‐2 were separated without derivatization on Lipodex ® E; in contrast, the enantiomers of erythro‐2 could be separated only after transformation to their 5‐O‐(trifluoroacetyl) derivatives. Biotransformation of the methyl ester (6R,7R)‐(6,7‐2H2)‐1 led to (4R,5R)‐ and (4S,5R)‐(2,5‐2H2)‐2 (ratio ca. 4 : 1; Table 2). Estimation of the label content and position of (4S,5R)‐(2,5‐2H2)‐2 showed 95% label at C(5), 68% label at C(2), and no 2H at C(4) (Table 2). Therefore, oxidation and subsequent reduction with inversion at C(4) of 4,5‐dihydroxydecanoic acid and transfer of 2H from C(4) to C(2) is postulated. The 5‐hydroxydecano‐4‐lactones 2 are of biochemical importance: during the fermentation of Streptomyces griseus, (4S,5R)‐2, known as L‐factor, occurs temporarily before the antibiotic production, and (−)‐muricatacin (=(4R,5R)‐5‐hydroxy‐heptadecano‐4‐lactone), a homologue of (4R,5R)‐2, is an anticancer agent.
Low Temperature 1H‐, 19F‐, and 31P‐PGSE Diffusion Measurements. Applications to Cationic Alcohol Complexes
Authors: Martínez‐Viviente Eloísa , Pregosin Paul S.
Published: August 2003

The problems associated with low‐temperature pulsed‐gradient spin‐echo (PGSE) NMR diffusion measurements are discussed. The influence of convection is overcome by employing a coaxial insert inside a normal 5 mm NMR tube. By means of this configuration, correct diffusion constants and temperature‐independent hydrodynamic radii can be obtained. Low‐temperature 1H‐, 19F‐, and 31P‐PGSE measurements on unstable cationic alcohol complexes of palladium and tungsten (in MeOH and CH2Cl2) are reported. For [W(Cp)(adamant‐1‐ol)(CO)3](CF3SO3), a strong hydrogen bond between the alcohol OH group and the trifluoromethanesulfonate anion is demonstrated.
Methyl Fluorocarbonyl Disulfide (FC(O)SSMe): A Theoretical Study on the Structural and Conformational Properties of Its Neutral Ground State and Lowest‐Lying Cationic State
Authors: Erben Mauricio F. , Della Védova Carlos O.
Published: August 2003

In this work, we present a theoretical study on the structural and conformational properties of FC(O)SSMe in its neutral and cationic ground states. The structure of the neutral molecule, as deduced from HartreeFock (HF), Density Functional Theory (DFT), and MøllerPlesset (MP2) methods, agrees with the experimentally determined value for the CSSC dihedral angle (CS bonds gauche with respect to each other) and with the syn preference of the SSCO dihedral angle (CO bond syn with respect to the SS bond). The calculated values for these two dihedral angles are 81.9 and 4.2 degrees, respectively. From the energy difference of the anti vs. syn conformer computed at the CCSD(T)/6‐311++G** level of theory, a 3% contribution of a less‐stable conformer at room temperature is proposed. The potential barrier of rotation about the SS bond is 5.7 kcal/mol (B3PW91/6‐311++G** approximation). The FC(O)SSMe molecule adopts a planar structure after ionization, the anti conformer (CSSC dihedral angle 180°) being the most‐stable form. For the first ionization of the title compound, the adiabatic ionization potential (IPad) derived from the three mentioned theoretical methods (using the 6‐311++G** basis sets) is 8.48, 9.06, and 8.99 eV, whereas the vertical ionization potential (IPver) is 8.96, 9.79, and 9.62 eV, respectively (experimental value: 9.0 eV). The results are compared with previous experimental studies carried out for the neutral and charged species interpreted on the basis of the Natural Bond Orbital (NBO) analysis. From these calculations, the importance of the anomeric and mesomeric effects becomes evident. The preferred conformation can be quantitatively explained by evaluation of donor/acceptor interaction energies.
Synthesis of Polyfunctional Aromatic Ring Systems (Phloroglucide Analogs) under Microwave Irradiation
Authors: Khalafi‐Nezhad Ali , Rad Mohammad Navid Soltani , Hakimelahi Gholam Hossein
Published: August 2003

An efficient and rapid synthesis of phloroglucide analogs under microwave irradiation is described. The solid‐phase condensation reaction of the 4‐halo‐2,6‐bis(hydroxymethyl)phenols 1a,b with other substituted phenols in the presence of ZnCl2 afforded the target molecules in much higher yields than by classical solution‐phase synthesis and allowed us to prepare new phloroglucide analogs possessing sensitive functional groups difficult to access by established means.
New Acylated Triterpene Saponins from Polygala arenaria
Authors: Mitaine‐Offer Anne‐Claire , Miyamoto Tomofumi , Laurens Véronique , Delaude Clément , Lacaille‐Dubois Marie‐Aleth
Published: August 2003

Eight new acylated triterpene saponins 1–8 were isolated from the roots of Polygala arenaria as four inseparable (E)/(Z) mixtures of the 4‐methoxycinnamoyl and 3,4‐dimethoxycinnamoyl derivatives by repeated MPLC over silica gel. Their structures were established mainly by 600‐MHz 2D‐NMR techniques (1H,1H‐COSY, TOCSY, NOESY, HSQC, HMBC) as 3‐O‐(β‐D‐glucopyranosyl)presenegenin 28‐(O‐β‐D‐galactopyranosyl‐(1→4)‐O‐[β‐D‐glucopyranosyl‐(1→3)]‐O‐β‐D‐xylopyranosyl‐(1→4)‐O‐α‐L‐rhamnopyranosyl‐(1→2)‐{4‐O‐[(E)‐4‐methoxycinnamoyl]}‐β‐D‐fucopyranosyl) ester and its (Z)‐isomer (1/2), 3‐O‐(β‐D‐glucopyranosyl)presenegenin 28‐(O‐β‐D‐galactopyranosyl‐(1→4)‐O‐[β‐D‐glucopyranosyl‐(1→3)]‐O‐β‐D‐xylopyranosyl‐(1→4)‐O‐α‐L‐rhamnopyranosyl‐(1→2)‐{4‐O‐[(E)‐3,4‐dimethoxycinnamoyl]}‐β‐D‐fucopyranosyl) ester and its (Z)‐isomer (3/4), 3‐O‐(β‐D‐glucopyranosyl)presenegenin 28‐(O‐β‐D‐glucopyranosyl‐(1→3)‐O‐α‐L‐arabinopyranosyl‐(1→4)‐O‐α‐L‐rhamnopyranosyl‐(1→2)‐{4‐O‐[(E)‐4‐methoxycinnamoyl]}‐β‐D‐fucopyranosyl) ester and its (Z)‐isomer (5/6), and 3‐O‐(β‐D‐glucopyranosyl)presenegenin 28‐(O‐β‐D‐glucopyranosyl‐(1→3)‐O‐α‐L‐arabinopyranosyl‐(1→4)‐O‐α‐L‐rhamnopyranosyl‐(1→2)‐{4‐O‐[(E)‐3,4‐dimethoxycinnamoyl]}‐β‐D‐fucopyranosyl) ester and its (Z)‐isomer (7/8) (presenegenin=(2β,3β)‐2,3,27‐trihydroxyolean‐12‐ene‐23,28‐dioic acid). In our in vitro lymphocyte proliferation assay (Jurkat T‐leukemia cells), a fraction containing 1–4 showed a concentration‐dependent immunomodulatory effect. This effect was not found for the prosapogenin (tenuifolin=3‐O‐(β‐D‐glucopyranosyl)presenegenin), underlining the importance of the acyloligosaccharidic moiety.
Cytotoxic Pentacyclic Triterpenoids from the Rhizome of Astilbe chinensis
Authors: Sun Hongxiang , Zhang Jianxin , Ye Yiping , Pan Yuanjiang , Shen Yueao
Published: August 2003

Guided by in vitro antineoplastic tests, four cytotoxic pentacyclic triterpenoids, 3β‐hydroxyolean‐12‐en‐27‐oic acid (1), 3β‐hydroxyurs‐12‐en‐27‐oic acid (2), 3β,6β‐dihydroxyolean‐12‐en‐27‐oic acid (3), and 3β‐acetoxyolean‐12‐en‐27‐oic acid (4) were isolated from the rhizome of Astilbe chinensis. Their structures were determined on the basis of chemical evidence and extensive spectroscopic methods including one‐dimensional and two‐dimensional NMR. These compounds showed cytotoxic activities against HO‐8910, Hela and HL60 cell lines. In addition, β‐sitosterol palmitate, daucosterol, and β‐sitosterol have also been isolated.
Novel Sesquiterpenes from the Fungus Lactarius piperatus
Authors: Wang Ying , Yang Sheng‐Ping , Yue Jian‐Min , Chow Sharon , Kitching William
Published: August 2003

Four novel sesquiterpenes, namely 7α,8β,13‐trihydroxy‐5,13‐marasmanolide (2), isoplorantinone (5), 4,8,14‐trihydroxyilludala‐2,6,8‐triene (6), and 8‐hydroxy‐8,9‐secolactara‐1,6‐dien‐5,13‐olide (10), together with six known ones, 7α,8β‐dihydroxy‐5,13‐marasmanolide (1), 7α,8α‐dihydroxy‐5,13‐marasmanolide (3), isolactarorufin (4), blennin A (7), blennin D (8), and lactarorufin (9), were isolated from the ethanolic extract of Lactarius piperatus. The structures of these sesquiterpenes, representing diversified structural types, were determined mainly by spectroscopic methods, especially 2D‐NMR techniques. The structure of 6 was further confirmed by a single‐crystal X‐ray‐diffraction determination.
Simultaneous Determination of Chromium(VI) and Aluminum(III) by Adsorptive Stripping Voltammetry with Pyrocatechol Violet
Authors: Vargas Miguel Cámara , Renedo Olga Domínguez , Arcos Martinez M. Julia
Published: August 2003

A new methodology is presented for the simultaneous determination of chromium(VI) and aluminum(III) by differential‐pulse adsorptive stripping voltammetry (DPAdSV) with Pyrocatechol Violet (PCV) as a complexing agent. In this procedure, a partial least‐squares regression (PLS) is used for the resolution of the strongly overlapping voltammetric signals from mixtures of CrVIand AlIIIin the presence of PCV. The procedure was successfully applied to the determination of these metals in river water.
Binuclear Nickel(II) and Cobalt(III) Complexes with Dissimilar Bridges: Synthesis, Spectroscopy, Crystal Structure, and Magnetism
Authors: Wang Qing‐Lun , Yu Li‐Hua , Liao Dai‐Zheng , Yan Shi‐Ping , Jiang Zong‐Hui , Cheng Peng
Published: August 2003

Two novel binuclear nickel(II) and cobalt(III) complexes with two or three dissimilar bridges, [Ni2(tacn)2(μ‐N3)2(μ‐O2CPh)](ClO4)⋅H2O (1) and [Co2(tacn)2(μ‐N3)(μ‐OH)(μ‐O2CPh)](ClO4)3 (2) (tacn=1,4,7‐triazacyclononane), were synthesized and structurally as well as magnetically characterized. Both compounds have a discrete binuclear structure, bridged by two N3− ions and one carboxylato group of the benzoate ion for 1 and one N3− ion, one carboxylato group of the benzoate ion, and one hydroxy group for 2; the macrocyclic ligand tacn acts as terminal ligand. The magnetic data of compound 1 were analyzed by means of Ĥ = −2JŜ1Ŝ2−D(Ŝ12+Ŝ22), leading to J = 19.6 cm−1, g=2.07, D = 4.01 cm−1, and zJ′ = $\rm{-}$0.32 cm−1. The ferromagnetic interaction is discussed on the basis of the structural features.
New Long‐Chain Esters and Adenine Analogs from the Leaves of Formosan Bridelia balansae
Authors: Tsai Yeh‐Hsin , Chen Ih‐Sheng , Tsai Ian‐Lih
Published: August 2003

Six new compounds, including the two long‐chain esters balansenate I (=6,8,11‐trimethyldodecanoic acid (2E)‐3‐methylhexadec‐2‐enyl ester; 1) and balansenate II (=10,12,15‐trimethylhexadedecanoic acid (2E)‐3‐methylhexadec‐2‐enyl ester; 2), the eburicane‐like triterpenoid bridelone (=hexadecahydro‐4,4,10,13,14‐pentamethyl‐17‐(5‐methyl‐1,4‐dimethylenehexyl)‐3H‐cyclopenta[a]phenanthren‐3‐one; 3), the ‘deimino‐xanthine', bridelonine (=5‐(3‐methylbut‐2‐enyl)pyrrolo[3,4‐d]imidazole‐4,6(1H,5H)‐dione; 6), and the two adenine analogs 9‐(3‐methylbut‐2‐enyl)adenine (7) and 1‐(3‐methylbut‐2‐enyl)adenine (8), besides three known compounds, i.e., N6‐(3‐methylbut‐2‐enyl)adenine (4), 3‐(3‐methylbut‐2‐enyl)adenine (5), and adenine (9), were isolated from the leaves of Formosan Bridelia balansae. The novel skeleton of 6 consists of a fused pyrrolidine‐2,5‐dione and imidazole moiety. The already known adenines 7 and 8 were isolated for the first time from a plant. The structures of the isolated compounds were elucidated by spectroscopic analyses.
Synthesis and Evaluation of Chromogenic and Fluorogenic Analogs of Glycerol for Enzyme Assays
Authors: González‐García Eva Maria , Grognux Johann , Wahler Denis , Reymond Jean‐Louis
Published: August 2003

The branched glycerol analogs 1 and 2 were prepared. Mono‐ester derivatives of these triols undergo a chromogenic or fluorogenic reaction in the presence of NaIO4. In contrast, both the diesters and the triols are themselves not chromogenic or fluorogenic. Diester derivatives of these triols can be used as probes for lipases. The tris‐phosphate derivative of 1 is a fluorogenic substrate for various phosphatases.
Metal Complexes of Functionalized Sulfur‐Containing Ligands. Part XIX
Authors: Stachel Hans‐Dietrich , Immerz‐Winkler Elisabeth , Poschenrieder Hermann , Windt Andreas , Weigand Wolfgang , Drescher Norbert , Wünsch Ralf
Published: August 2003

The title compounds were prepared starting from the dihydropyrrolones 4–6. Nucleophilic displacement and ring closure yielded the 1H‐pyrrolo[3,2‐c]isothiazol‐5(4H)‐ones 8 and 10. The fused systems formed salts with strong acids and electrophiles (15, 16), as well as with bases. Oxidation led either to S(2)‐oxides (18a, 20a) or to the corresponding bicyclic sultams (18b, 20b), depending on the reaction conditions. The sulfinamide 18a was also obtained from the known 1,2‐dithiolopyrrolone S‐oxide 21 by a ring‐opening/ring‐closure reaction sequence. O‐Methylation of 8 furnished the ‘azafulvene' 17. The oxidative addition of [Pt(η2‐C2H4)L2] (24a: L=Ph3P, 24b: L=1/2 dppf, 24c: L=1/2 (R,R)‐diop) to 18a and 20a led to the cis‐amido‐sulfenato Pt complexes 25 and 26a–c, respectively.
Synthesis, and Antimycobacterial and Cytotoxic Evaluation of Certain Fluoroquinolone Derivatives
Authors: Sheu Jia‐Yuh , Chen Yeh‐Long , Tzeng Cherng‐Chyi , Hsu Shu‐Lin , Fang Kuo‐Chang , Wang Tai‐Chi
Published: August 2003

Certain 1‐ethyl‐ and 1‐aryl‐6‐fluoro‐1,4‐dihydroquinol‐4‐one derivatives were synthesized and evaluated for antimycobacterial and cytotoxic activities. Preliminary results indicated that, for 1‐aryl‐6‐fluoroquinolones, both 7‐(piperazin‐1‐yl)‐ and 7‐(4‐methylpiperazin‐1‐yl) derivatives, 9b and 11a, are able to completely inhibit the growth of M. tuberculosis at a concentration of 6.25 μg/ml, while the 7‐[4‐(2‐oxo‐2‐phenylethyl)piperazin‐1‐yl] derivative 13 exhibits only 31% growth inhibition at the same concentration. For 1‐ethyl‐6‐fluoroquinolones, both 7‐[4‐(2‐oxopropyl)piperazin‐1‐yl]‐ and 7‐[4‐(2‐oxo‐2‐phenylethyl)piperazin‐1‐yl]‐derivatives, 2a and 2b, respectively, show complete inhibition, while their 2‐iminoethyl and substituted phenyl counterparts 3a and 2c are less active. In addition, the 6,8‐difluoro derivative was a more‐favorable inhibitor than its 6‐fluoro counterpart (2b vs. 2d). These results deserve full attention especially because 2a, 2b, 9b, and 11a are non‐cytotoxic at a concentration of 100 μM. Furthermore, compound 9b proved to be a potent anti‐TB agent with selective index (SI)>40 and an EC90 value of 5.75 μg/ml.
Glycosylidene Carbenes. Part 32
Authors: Mangholz Sissi E. , Briner Karin , Bernet Bruno , Vasella Andrea
Published: August 2003

Acylation and sulfonylation of the N,N′‐unsubstituted glucosylidenespirodiaziridines 1A/1B 95 : 5 with Ac2O, BzCl, FmocCl, TsCl, (naphthalen‐2‐yl)sulfonyl, and (2,4,6‐triisopropylphenyl)sulfonyl chloride, and concomitant rearrangement gave the acylated and sulfonylated gluconolactone hydrazones 2B–2G in 40–83% yield (Scheme 2). Similarly, the galacto and manno analogues 3A/3B 95 : 5 and 5A/5B 55 : 45 and the mannofuransoylidene‐diaziridine 30 were acetylated and tosylated to give 4A, 4B, 6, 31A, and 31B (55–73% yield; Schemes 2 and 5). 15N‐Labelling of 11A/11B and 14A/14B showed that the pseudoequatorial NH of the gluco diaziridines 1 and the pseudoaxial NH of the galacto diaziridines 3 were preferentially acetylated and tosylated (Scheme 3). Sulfonylation of the N‐methylated diaziridines 19A/19B 72 : 28, 22A/22B 85 : 15, 25A/25B 85 : 15, 28A/28B 80 : 20, and 33A/33B/33C/33D 76 : 4 : 12 : 8 yielded the N‐methyl‐N‐tosylglyconolactone hydrazones 20, 23, 26, 29, and 34 (44–66%; Schemes 4 and 5). The methylated N‐atom of the diaziridines proved more reactive, irrespective of the configuration at C(2) and C(4). The products were readily hydrolysed to glyconolactones.
Reactions of Phosphate Radicals with Monosubstituted Benzenes. A Mechanistic Investigation
Authors: Rosso Janina A. , Caregnato Paula , Mora Verónica C. , Gonzalez Mónica C. , Mártire Daniel O.
Published: August 2003

The kinetics and reaction mechanism of phosphate radicals with substituted benzenes, PhX (X=OH, Me, H, Cl, MeO, and CHO), were studied by flash photolysis and continuous irradiation of aqueous solutions containing potassium peroxodiphosphate (K4[(PO3)2O2]). The rate constants for the reactions of phosphate radicals with the aromatic contaminants PhX were measured and the reaction intermediates and products detected. A correlation between the logarithm of the rate constant for every substrate with H2PO4., HPO4.−, and PO4.2− and the logarithm of the dissociation constant Ka for H3PO4, $\rm{ H_2 PO_4^ -}$, and $\rm{ HPO_4^{2 - }}$ was found. A general mechanism is proposed (Scheme 1), which accounts for the experimental results.
Chemical Constituents from the Whole Plant of Euphorbia altotibetic
Authors: Li Pan , Feng Zhang Xiao , Ye Deng , Huan Wang , Da Gang Wu , Dong Luo Xiao
Published: August 2003

Four new jatrophane diterpenoids, altotibetin A (1), altotibetin B (2), altotibetin C (3), altotibetin D (4), and nine known compounds, β‐sitosterol, cycloart‐23‐ene‐3β,25‐diol, cycloart‐25‐ene‐3β,24‐diol, lupeol acetate, scopoletin, kaempferol, uracil, uridine, astragalin, and daucosterol have been isolated from the whole plant of Euphorbia altotibetic Pauls. Their structures were established by spectral methods, and the configurations of 1 and 2 were confirmed by X‐ray analysis.
Nucleotides. Part LXXII
Authors: Beier Markus , Pfleiderer Wolfgang
Published: August 2003

The synthesis of various N‐methylated nucleosides (m6A, m3C, m4C, m3U) is described. These minor nucleosides can be obtained by simple methylation with diazomethane of [2‐(4‐nitrophenyl)ethoxy]carbonyl(npeoc)‐protected nucleosides. These methylated compounds are easily further derivatized to fit into the scheme of the [2‐(dansyl)ethoxy]carbonyl (dnseoc) approach for RNA synthesis (dansyl=[5‐(dimethylamino)naphthalen‐1‐yl]sulfonyl). Various oligoribonucleotides containing N6‐methyladenosine were synthesized, underlining the usefulness of the dnseoc approach, especially for the synthesis of natural tRNA‐derived oligoribonucleotide sequences.
Novel Anti‐Inflammatory Constituents of Artocarpus rigida
Authors: Lu Yi‐Huang , Lin Chun‐Nan , Ko Horng‐Huey , Yang Sheng‐Zehn , Tsao Lo‐Ti , Wang Jih‐Pyang
Published: August 2003

A novel phenolic compound containing an oxepine ring, artocarpol I (1), and a new biphenylpropanoid, artocarpol J (2), were isolated from the root bark of Artocarpus rigida. The structures, including relative configurations, were elucidated by spectroscopic data. Compound 1 and artocarpol J peracetate (3) strongly inhibited in a concentration‐dependent manner the formyl‐Met‐Leu‐Phe (fMLP)/cytochalasin B (CB)‐stimulated superoxide anion formation in neutrophils with IC50 values of 17.1±0.40 and 20.5±2.60 μM, respectively. Biogenetically, all the novel phenolic compounds isolated from this plant seem to be derived from stilbene.
Helix Formation and Folding in γ‐Peptides and Their Vinylogues
Authors: Baldauf Carsten , Günther Robert , Hofmann Hans‐Jörg
Published: August 2003

A complete overview of all possible periodic structures with characteristic H‐bonding patterns is provided for oligomers composed of γ‐amino acids (γ‐peptides) and their vinylogues by a systematic conformational search on hexamer model compounds employing ab initio MO theory at various levels of approximation (HF/6‐31G*, DFT/B3LYP/6‐31G*, SCRF/HF/6‐31G*, PCM//HF/6‐31G*). A wide variety of structures with definite backbone conformations and H‐bonds formed in forward and backward directions along the sequence was found in this class of foldamers. All formally conceivable H‐bonded pseudocycles between 7‐ and 24‐membered rings are predicted in the periodic hexamer structures, which are mostly helices. The backbone elongation in comparison to α‐ and β‐peptides allows several possibilities to realize identical H‐bonding patterns. In good agreement with experimental data, helical structures with 14‐ and 9‐membered pseudocycles are most stable. It is shown that the introduction of an (E)‐double bond into the backbone of the γ‐amino acid constituents, which leads to vinylogous γ‐amino acids, supports the folding into helices with larger H‐bonded pseudocycles in the resulting vinylogous γ‐peptides. Due to the considerable potential for secondary‐structure formation, γ‐peptides and their vinylogues might be useful tools in peptide and protein design and even in material sciences.