bluuebunny/crossref_metadata_2025 huggingface dataset:
Nodal Nomenclature II—Specific Nomenclature for Parent Hydrides, Free Radicals, Ions, and Substituents
Authors: Lozac'h Noël , Goodson Alan L.
Published: December 2003

Nodal nomenclature is compared with classical organic nomenclature, and the procedure by which an organic compound is given a nodal name is described. Parent hydride–especially hydrocarbon–names are derived from the names of structure graphs and are modified to incorporate descriptions of heteroatoms, unsaturation, free valences, and ionic charges. It is also shown how the substitutive method, though not an integral part of the nodal system, may nevertheless be used as a way to simplify the structure graphs without impairing the logic of the nodal system. For this purpose, it is indicated how to use prefixes or suffixes generally formed according to IUPAC Rules. The rôle of substitution in organic nodal nomenclature is more restricted than in classical nomenclature because many classical substituents are treated as part of the parent hydrides. The concept of “characteristic group” is not used in nodal nomenclature for similar reasons, and the term “principal substituent” is preferred to “principal characteristic group”.
Hydroxide Ion‐Initiated Deuteration of Very Weak CH Acidsunder Phase Transfer Catalysis Conditions
Authors: Halpern Marc , Feldman David , Sasson Yoel , Rabinovitz Mordecai
Published: December 2003

The deuteration of organic compounds with pKa values of up to ca. 34 has been achieved by a special type of phase transfer catalysis. As is well known, hydroxide ions can be extracted into an organic phase from aqueous sodium hydroxide in the presence of quaternary ammonium salts. It has now been shown that these extracted hydroxide ions are more basic than the hydroxide ions at the interface. Exploiting this observation, diphenylmethane, 10,11‐dihydrodibenzo[a,d]cycloheptene and xanthene (pKa = 34, 31, and 27, respectively) could be deuterated quantitatively.
13C‐NMR INADEQUATE Spectrum with Broad Band Decoupling by Supercycles
Authors: Bolte Peter , Klessinger Martin , Wilhelm Konrad
Published: December 2003

The informational value of 13C‐13C coupling constants has hardly yet been exploited, because they were extremely difficult to measure in molecules with 13C in natural abundance. Use of the “incredible natural abundance double quantum transfer experiment” method improves the situation. The combination of this method with an effective pulse sequence for proton decoupling now permits routine measurement of J(13C, 13C).
Synthesis of Anti‐Inflammatory α‐Arylalkanoic Acids by 1,2‐Aryl Shift. New Synthetic Methods (42)
Authors: Giordano Claudio , Castaldi Graziano , Uggeri Fulvio
Published: December 2003

α‐Arylalkanoic acids have acquired importance as anti‐inflammatory agents and are now in great demand on the pharmaceutical front. Hence, the need has arisen for new and improved, economical synthetic procedures suitable for their preparation and manufacture on an industrial scale. For many years the synthetic approach to this class of compounds was restricted to the Willgerodt and Darzen reactions. More recently, several methods have been developed which are based on the 1,2‐aryl shift in acetals of α‐functionalized alkyl aryl ketones. This new approach starts from the oxythallation of alkyl aryl ketones first described by Taylor and McKillop in 1971. Asymmetric syntheses of some important arylakanoic acids have also been developed on this basis. The highly toxic thallium salts may be replaced, inter alia, by catalytically effective metal salts.
Determination of Connectivities via Small Proton‐Carbon Couplings with a New Two‐Dimensional NMR Technique
Authors: Kessler Horst , Griesinger Christian , Lautz Jörg
Published: December 2003

The novel two‐dimensional NMR technique H,C‐COLOC enabled the constitutions of the photolysis products 1 and 2 referred to in the preceding article to be determined. In H,C‐COLOC spectroscopy, use is made of proton‐carbon coupling over two and three bonds. This technique, in which the homonuclear proton coupling are absent, offers several advantages over conventional H,C shift correlations using long‐range couplings.
Nickel‐Catalyzed Reduction of Carbon Monoxide by Hexamethyldisilane: a New Reaction Leading to a Novel Synthesis of Siloxanes
Authors: Vollhardt K. Peter C. , Yang Zhen‐Yu
Published: December 2003

CO as oxidizing agent for Me3SiSiMe3 facilitates a novel synthesis of siloxanes. The catalyst used is nickel on kieselgur. Particularly good conversions and yield were obtained in the presence of H2. In this way, “C” is converted into CH4 (RCH3).
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[(Me2N)2SF2]2⊕, a Sulfur(VI) Dication
Authors: Henle Hartmut , Hoppenheit Reinhard , Mews Rüdiger
Published: December 2003

The ability to electrophilically methylate a cation such as 2 demonstrates the extraordinary preparative potential of [CH3OSO]⊕X⊖. The reagent methylates 1 exclusively at the thiazyl nitrogen, and the salts 3 of the sulfur(VI) dication are obtained via salts 2. Compounds 3a, X = AsF6, and 3b, X = SbF6, are stable solids.
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The First C4B6 Carbaborane
Authors: Köster Roland , Seidel Günter , Wrackmeyer Bernd
Published: December 2003

A novel type of organocarbaborane, the nido‐cluster 2, was prepared from the “monomeric” organo‐closo‐carbaborane 1 using a redox method, which should be generally applicable. The positions of the ten skeletal atoms in 2 can be assigned by NMR spectroscopy.
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High‐Pressure Phases of KSi, KGe, RbSi, RbGe, CsSi, and CsGe with the NaPb‐Type Structure
Authors: Evers Jürgen , Oehlinger Gilbert , Sextl Gerhard , Weiss Armin
Published: December 2003

Six novel phases of the 1:1‐silicides and ‐germanides of K, Rb, and Cs have been synthesized using a high‐temperature method (4 GPa, 600°C); under normal conditions they are metastable. The six compounds crystallize in the cubic KGe‐type at normal pressure; the nine phases belong to the tetragonal NaPb‐type, which have previously only been found in stannides and plumbides of the alkali metals. The constant axes ratio c/a ≈ 1.63 suggests geometrical relationships of the NaPb‐type.
25Mg‐NMR: A Method for the Characterization of Organomagnesium Compounds, their Complexes, and Schlenk Equilibria
Authors: Benn Reinhard , Lehmkuhl Herbert , Mehler Klaus , Rufińska Anna
Published: December 2003

Predominantly covalent Mg—C bonds are present in dicyclopentadienylmagnesium, as indicated by 25Mg‐NMR spectroscopy. The large range of the 25Mg chemical shifts (ca. 200 ppm) also facilitates clarification of other controversial bonding behavior. For the investigation of Schlenk equilibria [eq. (a)], the method has the advantage that all three species can be identified directly.
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Microbial Asymmetric Catalysis—Enantioselective Reduction of Ketones [New Synthetic Methods (45)]
Authors: Sih Charles J. , Chen Ching‐Shih
Published: December 2003

Microbial asymmetric reduction of ketones is a method widely used for the preparation of chiral alcohols. The present progress report deals with the basic concepts that govern enantioselectivity of enzymes and intact cells. Strategies to control the stereochemical course of microbial reductions of carbonyl compounds and the relationship of substrate structure to enantioselectivity are considered.
Phosphaallenes
Authors: Appel Rolf , Fölling Peter , Josten Bernhard , Siray Mustafa , Winkhaus Volker , Knoch Falk
Published: December 2003

Novel, independent syntheses of phosphacumulenes are reported for the 1‐phosphaallene 1 and the 1,3‐diphosphaallene 2. 1 is prepared via a Wittig reaction from R PCO and Ph3PCPh2. 2 is obtained from the same educt with RP(X)SiMe3; as desired, the reactions can be performed using either a two‐step (XH) or one‐step (XLi) procedure.
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Structure of a “Y‐Conjugated” Dilithium Salt of an α,α′‐Keto Dianion: 1,3‐Dilithiodibenzyl Ketone‐(Me2NCH2CH2NMe2)2
Authors: Dietrich Hans , Mahdi Waruno , Wilhelm Dieter , Clark Timothy , von Ragué Schleyer Paul
Published: December 2003

The first X‐ray structure analysis of a monomeric dilithium salt with an α,α′‐keto dianion was successfully carried out on the TMEDA complex 1. With approximate C2 symmetry, 1 is chiral. Comparison of the experimentally determined structure with that calculated semiempirically (MNDO) reveals good overall agreement. According to ab initio calculations, 2 has an analogous structure.
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Photochemistry of Alkyltransition‐Metal Complexes
Authors: Alt Helmut G.
Published: December 2003

Alkyltransition‐metal complexes play an important role in catalytic processes (e.g. Ziegler‐Natta low‐pressure polymerization, hydroformylation, Fischer‐Tropsch synthesis), in the biochemistry of humans and animals (e.g. coenzyme B12), and in the classical theory of the chemical bond (e.g. multicenter bonding). The chemistry of alkyltransition‐metal complexes is 30 years old, but only with the '70s came the understanding necessary for the systematic synthesis of thermally stable representatives of this class of compounds by blocking preferred decomposition pathways—e.g. β‐hydrogen elimination—by the introduction of suitable ligands. In this article it is shown that thermally stable alkyltransition‐metal complexes can be dealkylated under mild conditions (even at 12 K) with the help of UV light, thus producing highly reactive intermediates which can be trapped and used preparatively. Some alkyl complexes which do not react thermally with unsaturated compounds, e.g. olefins, under the influence of UV light display high activity as polymerization catalysts.
Synthesis of the all‐L‐Configurated Cyclohexadepsipeptide cyclo‐[L‐Val‐L‐Lac]3 by the Peoc/Acid Chloride Method
Authors: Kunz Horst , Lerchen Hans‐Georg
Published: December 2003

The cyclization of linear depsipeptides is known to be especially difficult when only building blocks having the same configuration are present or when the amino acid residues are not N‐methylated. Ring closure to give 1 was accomplished with the acid chlorides of Peoc‐protected depsipeptides, despite simultaneous occurrence of both complicating factors.
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Crown Ether Complexes of Phosphonium Salts — The X‐Ray Structure Analysis of [(Ph3PMe)2·[18]Crown‐6][PF6]2
Authors: Allwood Billy L. , Colquhoun Howard M. , Crosby John , Pears David A. , Stoddart J. Fraser , Williams David J.
Published: December 2003

A higly symmetric cation consisting of two phosphonium ions and a crown ether molecule is obtained in crystalline 1. In 1 the direction PMe…Me′P′ coincides with the symmetry axis; the 18C6 host is oriented at right angles to this. All methyl H atoms are bound by discrete H bridges at individual O atoms. These H bridges are in each case directed towards the “rear side” of the crown ether ring.
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Synthesis and Structure of a (Carbene)(η2‐olefin)W(CO)4 Complex
Authors: Angermund Klaus , Grevels Friedrich‐Wilhelm , Krüger Carl , Skibbe Volker
Published: December 2003

A strong metal‐ligand π‐back bonding is the reason for the trans‐arrangement of carbene‐ and olefin‐ligand in the complex 1, for which an X‐ray structure analysis is available. Because of the ligand arrangement, a cyclization to the metallacyclobutane, an important intermediate in olefin metathesis, is impossible.
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DNA Methylation: Site‐Specific Methylations Cause Gene Inactivation
Authors: Doerfler Walter
Published: December 2003

In the molecular biology of eukaryotic organisms, the elucidation of mechanisms involved in the regulation of gene expression has assumed an important role. All cells of an organism carry the same genes, but differ in the patterns of genes they express. There is an increasing amount of evidence that cancer cells exhibit a pattern of gene expression which can be very different from that of normal cells. One of the molecular signals that has been recognized in the regulation of gene expression in eukaryotes is the modified nucleotide 5‐methylcytosine (5‐mC). Through experiments in well‐characterized eukaryotic systems, evidence has been adduced that the introduction of 5‐mC into highly specific sequences, particularly into the 5′ and promoter regions of a gene, can cause gene inactivation. Viral and other eukaryotic systems have helped in the recognition of this cause‐and‐effect relationship. Inactive genes are frequently hypermethylated in the promoter region; active genes are hypomethylated. However, these correlations are not always as simple and straightforward. The biochemical mechanisms by which site‐specific DNA methylations cause gene inactivation have not yet been determined. It is plausible to postulate that promoter methylations could somehow affect the binding of cellular enzymes involved in recognizing the promoter of a gene. Structural alterations of DNA promoter sequences arising from DNA methylations could also be important. DNA methylation is likely to represent a long‐term inactivation signal, since it is presently thought that patterns of DNA methylation can be changed only by DNA replication and specific inhibition of post‐replicative maintenance methylation.
The Dendralenes—a Neglected Group of Highly Unsaturated Hydrocarbons
Authors: Hopf Henning
Published: December 2003

Dendralenes are acyclic and cyclic cross‐conjugated polyolefins derived from 3‐methylene‐1,4‐pentadiene. This review summarizes and compares, for the first time, the methods developed for the synthesis of this class of hydrocarbons. Because of their particular arrangement of π‐electrons, the dendralenes are novel substrates for addition and rearrangement reactions, and model compounds for spectroscopic studies.
Chemoenzymatic Synthesis of a Functional Gene for Human Gamma Interferon
Authors: Engels Joachim , Leineweber Michael , Uhlmann Eugen
Published: December 2003

Chemoenzymatic gene synthesis in combination with cloning in E. coli enables the synthesis of larger proteins such as human gamma interferon. Chemical DNA synthesis followed by enzymatic coupling and cloning of the individual gene segments and ligation of the subfragments then yields the gene for the biologically active gamma interferon.
Basic Principles of Protease‐Catalyzed Peptide Bond Formation
Authors: Jakubke Hans‐Dieter , Kuhl Peter , Könnecke Andreas
Published: December 2003

The stereospecific formation of peptide bonds under mild conditions and without side reactions is still a formidable task in peptide synthesis. One approach that springs to mind, namely the use of the naturally occurring catalyst involved in the biosynthesis of proteins, the ribosomal peptidyl transferase, cannot be realized in practice. The fact, however, that the natural cleavage of proteins is carried out by other enzymes, namely the proteases, together with the reversibility of these cleavage reactions in principle, has led to an interesting synthetic concept. Proteases normally catalyze the enzymatic degradation of proteins and peptides by hydrolytic cleavage of the peptide bond in an exergonic reaction. The use of physicochemical principles in order to influence the equilibrium, the concentration of products, and the kinetic parameters of the reaction results in the successful application of the catalytic properties of proteases to peptide synthesis. The purpose of this review is to describe and summarize the methods used in such approaches and to attempt a systematic categorization. The principles are applied to the synthesis of such practically relevant products as aspartame and human insulin.
Reactive Organometallic Compounds Obtained from Metallocenes and Related Compounds and Their Synthetic Applications
Authors: Jonas Klaus
Published: December 2003

Progress in the synthesis of organometallic compounds via the partial or total degradation of metallocenes and related compounds under mild reaction conditions is reviewed. These degradation reactions permit highly reactive organo‐transition metal complexes to be prepared which can in turn be used in a wide range of synthetic reactions. Examples include catalytic reactions such as the cobalt‐catalyzed hydrogenation of benzene and the manganese‐catalyzed cyclotrimerization of butadiene as well as stoichiometric syntheses of mono‐ and polynuclear transition metal complexes, some of which have novel structural features.
The Glycine Receptor of Rat Spinal Cord: Exploring the Site of Action of the Plant Alkaloid Strychnine
Authors: Betz Heinrich
Published: December 2003

The amino acid glycine is a major neurotransmitter in the spinal cord of all vertebrates and is involved in the control of various motor and sensory functions. By binding to specific receptors of the neuronal plasma membrane, glycine produces an increase in chloride permeability and thus a hyperpolarization, i.e., an inhibition of glycine‐sensitive neurons. This inhibitory action of glycine is reversibly blocked by the plant alkaloid strychnine. We have used strychnine for the biochemical characterization and isolation of the glycine receptor of rat spinal cord. Our results show that the glycine receptor is a large membrane protein which contains three different polypeptides. Based on the currently available data we propose a structural model of the glycine receptor and discuss its relation to other proteins of the neuronal membrane that are involved in the transmission of nerve impulses.
Photochemically Initiated, Electron‐Transfer‐Catalyzed Diels‐Alder Reactions of Electron‐Rich Dienophiles
Authors: Mlcoch Jiri , Steckhan Eberhard
Published: December 2003

Photochemically excited triphenylpyrylium tetrafluoroborate catalyzes Diels‐Alder reactions that proceed via an electron‐transfer chain mechanism. By means of a “redox umploung”, an electron‐rich alkene (En) is transformed into the radical cation, which functions as an appropriate electron‐poor dienophile (Sens⊕ = triphenylpyrylium).
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Gas‐Phase Reactions of Organic Compounds on Raney Nickel
Authors: Bock Hans , Wolf Hans Peter
Published: December 2003

The comparison of catalyzed and uncatalyzed thermal gas‐phase reactions of model organic compounds showed that reactions in the presence of Raney nickel proceed at appreciably lower temperature with remarkable selectivity. For example, 2‐propanol is dehydrogenated to acetone on quartz wool only at 970 K, whereas on Raney nickel it is fifty percent converted already at room temperature and 10−2 mbar.
Comparison of Theoretical and Experimental Deformation Densities in SO Bonds
Authors: Fuess Hartmut , Bats Jan W. , Cruickshank Durward W. J. , Eisenstein Miriam
Published: December 2003

Marked similarities are found between the experimental electron‐density maps for sodium thiosulfate, Na2S2O3, and the theoretical maps for amidosulfuric acid, NH2SO3H. Quantum chemical calculations and determinations of the deformation density in the region of the SO bond and the lone pair on oxygen are reported.
Solvent Exchange on Magnesium([15]Crown‐5) Complexes—a First‐ and Second‐Order Reaction
Authors: Dickert Franz L. , Waidhas Manfred F.
Published: December 2003

The mobility of solvate molecules has been investigated NMR spectroscopically on the hydrophobic metal complex 1 in inert solvents. It was possible, for the first time, to observe how the solvent exchange converts from a reaction of second order into one of first order on increasing the concentration. DMF‐exchange in 1 is 104 times slower than in [Mg(DMF)6]2+ this can be attributed to an increased interaction between Mg2+ and DMF by the coordination of [15]crown‐5. This finding is of interest in connection with the transport of ions by biological membranes.
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A Macrobicyclic Receptor Molecule for the Diquat Dication
Authors: Allwood Billy L. , Kohnke Franz H. , Stoddart J. Fraser , Williams David J.
Published: December 2003

A 1:1 complex of [diquat]2+ and a tailor‐made derivative of dibenzo[30]crown‐10 has been investigated in solution as well as in the solid phase. The crown ether is rigidified by an o‐(CH2O)2C6H4 bridge joining the two annelated benzene rings. Complicated exchange reactions in solution were studied NMR spectroscopically. X‐ray structure analyses have been carried out on the host molecule and the complex.
Z‐[(η5‐C5H5)(CO)2FePC(OSiMe3)(tBu)], a Phosphaalkenyl‐Complex with FeP Single Bond
Authors: Weber Lothar , Reizig Klaus , Boese Roland , Polk Michael
Published: December 2003

The stable monomeric complex 2 is the first phosphaalkene in which a transition metal complex fragment is bound directly to the P atom; 2 was prepared from the ferriophosphane 1 and pivaloyl chloride. The FePCO skeleton of 2 is planar; the lone pair on the phosphorus is not required for electronic saturation of the metal.
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Simplification of Spectra for the Determination of Coupling Constants from Homonuclear Correlated 2D NMR Spectra
Authors: Kessler Horst , Oschkinat Hartmut
Published: December 2003

Without additional measurements having to be made, coupling constants can be determined from H,H‐COSY spectra using the DISCO (Difference and Sums in COSY spectra) method. The structure elucidation of compounds with complicated 1H‐NMR spectra, e.g., natural products, is thereby facilitated.
Proton Exchange between Arenium Ions and Arenes in the Gas Phase
Authors: Kuck Dietmar , Ingemann Steen , de Koning Leo J. , Grützmacher Hans‐Friedrich , Nibbering Nico M. M.
Published: December 2003

A new application of Fourier transform ion cyclotron resonance mass spectrometry is the investigation of the proton exchange reaction in the collision complexes formed between simple arenium ions and arenes. Only for degenerate reactions (R  R′) is a (surprisingly slow) exchange process observed (R  R′  H or CH3; R  H, R′  CH3).
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Selective 1H, 13C‐NOE Difference Spectroscopy for the Elucidation of Structures
Authors: Bigler Peter , Kamber Matthias
Published: December 2003

Structure elucidations are also possible for compounds with strongly overlapping 1H‐NMR signals employing a new procedure based on the use of the heteronuclear Overhauser effect. This 1D procedure requires only relatively short measuring times, and a knowledge of the coupling constants is not necessary. The capability of the method is demonstrated on a tricyclic β‐Keto ester containing a lactone bridge.
Applications of Synthetic Peptides
Authors: Moser Rudolf , Klauser Stephan , Leist Thomas , Langen Hanno , Epprecht Thomas , Gutte Bernd
Published: December 2003

Peptide chemists are increasingly concerned with the synthesis of polypeptides of biological and medical interest. This article describes several important applications of synthetic peptides in biochemistry, molecular biology, immunology, and medicine. Synthetic peptides may be useful in structure‐function studies of polypeptides, as peptide hormones and hormone analogues, in the preparation of cross‐reacting antibodies, and in the design of novel enzymes. Peptide chemists can actively contribute to progress in these fields if they are aware of the current problems in the life sciences.
Heterogeneous Redox Catalysis on Ti/TiO2 Cathodes—Reduction of Nitrobenzene
Authors: Beck Fritz , Gabriel Wolfgang
Published: December 2003

A novel ceramic electrode for redox catalysis was prepared from etched titanium sheet which was covered with a solution of titanium acetylacetonate in HNO3 and heated at 450°C. Noteworthy are the current densities recorded (for example 5 A/dm2) on such an activated electrode. This electrode has been used for the reduction of nitrobenzene. It proceeds as follows with reformation of Ti(OH)4:
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Solid Phase Synthesis (Nobel Lecture)
Authors: Merrifield Robert Bruce
Published: December 2003

A solid phase as “protecting group” in peptide synthesis—this was the original idea of Bruce Merrifield, who received the 1984 Nobel Prize for Chemistry. In his lecture, he describes the development of the Merrifield synthesis. In principle, all difunctional educts that may be selectively protected at one end and activated at the other can undergo reactions on solid supports.
Reactions of Per(chloro, fluoro)ethanes with Aryloxide and Alkoxide Ions — Evidence for Chlorophilic Attack on CCl Bonds
Authors: Li Xing‐ya , Pan He‐qi , Jiang Xi‐kui , Zhan Zheng‐yun
Published: December 2003

The synthesis of aryl‐ and alkyl per(chloro, fluoro) ethyl ethers 2 is achieved by reaction of nucleophiles ROK with the substrates 1 (X, YCl, F). This is the first confirmed example for the attack of oxygen nucleophiles on the CCl bond. The ethers 2 are only obtainable with difficulty by others routes.
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Increased Production of Specific Antibodies by Presentation of the Antigen Determinants with Covalently Coupled Lipopetide Mitogens
Authors: Jung Günther , Wiesmüller Karl‐Heinz , Becker Gerhard , Bühring Hans‐Jörg , Bessler Wolfgang G.
Published: December 2003

A new concept for the production of antibodies consists in preparing a conjugate from the “lipid membrane anchor” N‐palmitoyl‐S[2,3‐bis(palmitoyl‐oxy) propyl]cysteiny1 serine and the antigen—for example, a tetradecapeptide. These conjugates are potent immunogens, which, within a few days, induce the production of high titers of antigen‐specific antibodies (IgG and IgM), both in vivo and in vitro, with only one application and without either carrier proteins or Freund's adjuvant. It has already been possible to produce monoclonal antibodies with these new low‐molecular‐weight, chemically defined conjugates, which are obtainable via Merrifield synthesis.
Mechanisms of Biological Ion Transport — Carriers, Channels, and Pumps in Artificial Lipid Membranes
Authors: Läuger Peter
Published: December 2003

The cell membrane contains specific systems for passive and active transport of ions between the cytoplasm and the extracellular medium. For a number of small and medium‐sized transport molecules like valinomycin and gramicidin A, extensive structural and kinetic data are available and it is possible in these cases to understand the transport function on the basis of their molecular structure. Incorporation into artificial bimolecular lipid membranes opens up the possibility of studying the kinetic properties of biological transport systems in detail.
Isocyanomethylenetriphenylphosphorane
Authors: Zinner Gerhard , Fehlhammer Wolf Peter
Published: December 2003

The novel compound 2 combines the structural elements of α‐metalated isocyanides and Wittig reagents. Like its “storable form” 1 it is extraordinarily reactive. For example, metal‐coordinated 2 undergoes [3 + 2]‐cycloadditions with heteroallenes, nitriles, acetylenes, and olefins to give metal‐C bonded five‐membered heterocycles.
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Molecular Mechanism of Action of the Antibiotic Rifampicin
Authors: Hartmann Guido R. , Heinrich Peter , Kollenda Margit C. , Skrobranek Bernhard , Tropschug Maximilian , Weiß Wolfgang
Published: December 2003

The lipophilic antibiotic rifampicin is successfully used in the treatment of tuberculosis. On the molecular level it interferes with the metabolism of Eubacteria by blocking RNA synthesis. This effect is the consequence of the tight binding of the drug to a single and highly specific binding site on the DNA‐dependent RNA polymerase. The enzyme‐bound drug strongly inhibits RNA chain initiation and chain elongation. This inhibition can be explained by the influence of enzyme‐bound rifampicin on binding sites for the reaction products diphosphate and RNA. In order to reach its target the antibiotic must penetrate into the cytoplasm of the bacteria. Mutants have been discovered which are resistant to rifampicin because its uptake from the medium is significantly reduced. The gene responsible for this effect has been cloned. It confers on bacterial cells with highly sensitive RNA polymerases a remarkable resistance to the drug.
Oxidation of 2‐Propanol at Ti/Cr2O3 Anodes
Authors: Schulz Harry , Beck Fritz
Published: December 2003

Quantitative current yields without formation of CrIII salts are achieved in the oxidation of 2‐propanol to acetone at ceramic Ti/Cr2O3 anodes. The postulated reaction mechanism is analogous to that formulated by Westheimer for homogeneous oxidation with chromic acid. The lifetimes of the electrodes, however, are too short for use of the reaction on an industrial scale.
Molecular Biological Background of the Species and Organ Specificity of Influenza A Viruses
Authors: Scholtissek Christoph
Published: December 2003

Influenza is one of the great plagues which is not yet under control. The reason for this is the immense variability of the infecting agent, the influenza A viruses. These viruses behave like a chameleon: they adapt very rapidly to varying environments. New strains are “synthesized,” which can escape the immune response of the host, cross species barriers, and become highly pathogenic. We are beginning to understand the molecular background of this extraordinarily high variability. The genome of influenza A viruses consists of eight single‐stranded RNA segments, each of which constitutes a gene. The total base sequence of the eight RNA segments of several strains is known. If a suitable organism becomes doubly infected with two different influenza A strains, each of the RNA segments behaves like a chromosome. This means that by reassortment of the 16 RNA segments, 28 −2 = 254 new combinations (= reassortants) are theoretically possible, each having different properties. Furthermore, mutations in the various RNA segments are relatively easily tolerated. Another great problem resides in the enormous reservoir of different influenza A viruses in the animal kingdom, especially in feral waterbirds. In these birds the avian influenza A viruses normally cause at most mild symptoms, and therefore these viruses are distributed over and between continents. Bearing this in mind it appears to be necessary to develop new ideas as to how to overcome this great plague.
Physicochemical and Cytochemical Investigations on the Binding of Ethidium and Acridine Dyes to DNA and to Organelles in Living Cells
Authors: Zimmermann Herbert W.
Published: December 2003

Ethidium and acridine dyes are classical model substances for studying the binding of small, pharmacologically active molecules to DNA. Intercalation between the DNA base pairs is nearly always proposed as the most important type of binding. According to our investigations, however, there is a second type of binding, which also occurs when the concentration of the bound molecules is low and will be referred to here as external or preintercalative binding. The experimental binding isotherms show that the binding constant for intercalation KS1 is considerably smaller than that for external binding KS2 (KS1 > KS2). This surprising result is not due to the binding enthalpy (ΔH ≈ ΔH) but to the binding entropy (ΔS > ΔS). Electrostatic interactions between the dye and the DNA represent the most important contribution to both types of binding; they are supplemented by hydrogen bonds and hydrophobic interactions. The behavior of a substance in living cells, however, cannot be reliably predicted from its in vitro binding to DNA. Very few substances are bound to the DNA of the nuclear chromatin in cell culture; for example, dyes often accumulate instead in the lysosomes. In some cases the dye binds specifically and very efficiently to the mitochondria of the living cell, especially to the mitochondrial membranes, the sites of oxidative phosphorylation.
Synthesis of the all‐L‐Configurated Cyclotetradepsipeptide cyclo[‐L‐Val‐L‐Lac‐]2 by the Combined Protection/Activation Method with the 2,4‐Bis(methylthio)phenoxycarbonyl Group
Authors: Kunz Horst , Lasowski Hans‐Jürgen
Published: December 2003

The first chemical cyclization of tetradepsipeptides such as 1, which contain only building blocks with the same configuration and without N‐methyl groups, has been achieved with the new, activatable 2,4‐(MeS)2C6H4OCO (Bmpc) protecting group. The initially formed cyclic mixed anhydride spontaneously eliminates CO2 to give 2.
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Thin Layer Chromatographic Separation of Stereoisomeric Dipeptides
Authors: Günther Kurt , Martens Jürgen , Schickedanz Maren
Published: December 2003

The separation of enantiomeric and diastereomeric dipeptides without derivatization is possible on commercially available TLC plates. Examples are the separation of the pairs 1 and 2, and 3, respectively.
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Ordering of Ionic Solutes in Dilute Solutions through Attraction of Similarly Charged Solutes—A Change of Paradigm in Colloid and Polymer Chemistry
Authors: Ise Norio
Published: December 2003

EXAFS measurements indicate the presence of a quasi lattice‐like ordering of simple ions in dilute solutions. Small‐angle X‐ray scattering (SAXS) measurements on dilute aqueous solutions of synthetic macroions, polynucleotides, and proteins show a single broad peak; a binary mixture of synthetic macroions of different molecular weight gives a new scattering curve that is entirely different from the composite curve of the constituents before mixing. This would indicate that the macroions are distributed in a fairly regular way in the solution. The intermacroion spacing (2Dexp) obtained by the Bragg equation is found to be smaller than the average spacing (2D0) calculated from the polymer concentration. Furthermore, the 2Dexp value decreases with increasing number of charges per macroion. This finding is confirmed by studies on model systems, e. g. on monodisperse ionic latex particles, which are large enough (diameter: about 3000 Å) to be seen under the ultramicroscope. It follows, from the inequality relation 2Dexp<2D0, that there is an attraction between ionic species of like‐charge. This conclusion contradicts prevailing views in colloid chemistry; it has been pointed out that such a behavior can be explained in terms of a new theory, in which counterions between the macroions or ionic latex particles play a decisive role.
Enantiomer Separation of (R,S)‐2‐(tert‐Butyl)‐3‐methyl‐4‐imidazolidinone, a Chiral Building Block for Amino Acid Synthesis
Authors: Fitzi Robert , Seebach Dieter
Published: December 2003

For corrigendum see DOI:10.1002/anie.198607662
Evidence for Equilibria between μ‐Alkyne and Alkylidyne Complexes of Tungsten Alkoxides: [W2(OR)6(μ‐C2R′2)] ⇌ 2[(RO)3W ≡ CR′]
Authors: Chisholm Malcolm H. , Conroy Brian K. , Huffman John C. , Marchant Nancy S.
Published: December 2003

The cleavage of alkynes in the coordination sphere of metals forms the basis of a new synthesis of alkylidyne‐capped W3‐complexes. Reaction of the alkynes R′C  CR′with [W2(OCH2tBu)6(py)2] in the molar ratio 1:3 leads to formation of the complexes [W3(μ3‐CR′)(OCH2tBu)9]; the rate of formation of these complexes depends on R′(Et ∼ ph > Me)—evidence for the equilibria formulated in the title.
A Receptor‐Mediated Pathway for Cholesterol Homeostasis (Nobel Lecture)
Authors: Brown Michael S. , Goldstein Joseph L.
Published: December 2003

How does the healthy organism regulate cholesterol metabolism? The answer to this question was obtained, inter alia, by studies on patients with a genetic disease, familial hypercholesterolemia.Michael S. BrownandJoseph L. Goldsteinrecognized thereby the key role of the receptor for the cholesterol‐transport protein LDL. The receptor is a well‐characterized protein; studies afforded insights into endocytosis and the pathway by which the receptors enter and leave the cell. Genetic defects in the LDL receptors give rise to an accumulation of cholesterol in plasma and premature arteriosclerosis.
Thermally Induced Redox Reaction of Carbonyl Compounds and Alcohols in a Radical Chain Reaction: Comproportionation to Two Hydroxyalkyl Radicals
Authors: Malwitz Dietmar , Metzger Jürgen O.
Published: December 2003

The “molecule‐induced” homolytic cleavage of a C‐H bond, according to Equation (a), is probably the initiating step in the thermally induced redox reaction between a carbonyl compound and an alcohol. As intermediates in the two‐step process, which is a chain reaction, in contrast to the photochemically or the radically induced redox reaction, hydroxyalkyl radicals are formed.
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Model Experiments on the Phytotoxicity of Halogenated Hydrocarbons
Authors: Grimmer Gernot , Schmidt Werner
Published: December 2003

The hypothesis, that chlorinated hydrocarbons damage conifers under the influence of light is supported by the following finding: The photodegradation of β‐carotene in cyclohexane is very slow with simulated sunlight in the absence of oxygen; it is accelerated significantly by alkyl and aryl chlorides, and drastically so by bromides and iodides.
Structures with Oligomeric Condensed Clusters in Indium Oxomolybdates
Authors: Simon Arndt , Mertin Wilhelm , Mattausch Hansjürgen , Gruehn Reginald
Published: December 2003

Clusters of five linearly condensed Mo6O12 units are contained in the novel indium oxomolybdate In3Mo11O17, direct demonstration of which was accomplished by high‐resolution transmission electron microscopy. Linear polycations In are located between the oxoanions. The results signal a broad chemistry of “oligomeric” clusters (from individual Mo6 octahedra to infinite chains of octahedra) and a multitude of possible polycations of the main group metals.
Carbonyl Olefinating Carbene‐Tungsten Complexes and Their Suitability as Catalysts in Olefin‐Metathesis
Authors: Kauffmann Thomas , Abeln Renate , Welke Siegfried , Wingbermühle Dorothea
Published: December 2003

Noteworthy properties as CH2 transferring agents are exhibited by the tungsten complexes having the postulated structures 1 and 2, which are prepared in situ. They are the first tungsten complexes that are suitable for carbonylolefination (1 reacts with aldehydes and ketones, 2 preferentially with ketones); they are more stable than the known molybdenum complexes of this kind, and 2 can catalyze olefin metathesis. The solvent has a large effect on all of these reactions.
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Charge Separation in Excited States of Decoupled Systems—TICT Compounds and Implications Regarding the Development of New Laser Dyes and the Primary Process of Vision and Photosynthesis
Authors: Rettig Wolfgang
Published: December 2003

The understanding of the dual fluorescence of certain aromatic systems has greatly advanced in recent years. The accompanying large charge separation has been shown to be linked to a twisted (or small overlap) arrangement of the chromophores. Recent theoretical models are able to describe the excited‐state twisting of both single bonds (TICT compounds) and double bonds (olefins) in a unified picture. These models can help to elucidate the photophysical behavior of many organic, inorganic, and biologically relevant compounds, and their application to laser dyes and fluorescent probes provides a route to new “tailor‐made” fluorescent materials. Applied to the primary processes of vision and photosynthesis, these models can lead to a deeper understanding of basic photobiological processes.
Flash Photolysis of Os(CO)5 in Benzene Solution. Detection of Os(CO)4 Benzene by Fast Time‐Resolved IR Spectroscopy
Authors: Church Stephen P. , Grevels Friedrich‐Wilhelm , Kiel Gong‐Yu , Kiel William A. , Takats Josef , Schaffner Kurt
Published: December 2003

The formation and decomposition of the short‐lived species Os(CO)4 · benzene in benzene are best studied by the methods quoted in the title. The generation of Os(CO)4·benzene was achieved by flash photolysis of Os(CO)5 in benzene. On the basis of kinetic findings, a dissociation mechanism with reversible cleavage of benzene is proposed for the decomposition. Os(CO)4 is finally trapped by CO with re‐formation of Os(CO)5 or by Os(CO)5 with formation of Os2(CO)9.–The CO‐stretching vibration pattern of Os(CO)4·benzene is consistent with a C2v‐structure for the Os(CO)4 unit.
Elucidation of the Structure of Pharmacologically Active Magnesium L‐Aspartate Complexes
Authors: Schmidbaur Hubert , Müller Gerhard , Riede Jürgen , Manninger Gebhard , Helbig Joachim
Published: December 2003

Magnesium therapy (infact prophylaxis, suppression of stress symptoms etc.) has proven successful on using complexes of magnesium with natural amino and polycarboxylic acids. Presumably their activity is due to formation of weak complexes, from which the magnesium is released again after transport. As has now been demonstrated, L‐aspartic acid reacts as a di‐ to tridentate ligand depending on the pH. On the basis of X‐ray crystallographic, spectroscopic and electrochemical data, a model has been designed which is consistent with medicopharmacological findings.
Direct Measurement of the “Isokinetic Rate Constant” in Additions of Diarylcarbenium Ions to 2‐Methyl‐2‐butene
Authors: Schneider Reinhard , Mayr Herbert
Published: December 2003

The isokinetic rate constant kiso is of general importance. On the one hand, it is applicable for the compound with the isokinetic substituent at all temperatures, and, on the other, for all members of an isokinetic series at the isokinetic temperature. It has now been possible to measure kiso for the first time. In the case of the compounds, 1, X = Y = Me is the isokinetic substituent.
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Biochemistry of Oxidative Stress
Authors: Sies Helmut
Published: December 2003

As a normal attribute of aerobic life, structural damage to organic compounds of a wide variety (DNA, proteins, carbohydrates and lipids) may occur as a consequence of oxidative reactions. Oxidative damage inflicted by reactive oxygen species has been called “oxidative stress”. Biological systems contain powerful enzymatic and nonenzymatic antioxidant systems, and oxidative stress denotes a shift in the prooxidant/antioxidant balance in favor of the former. Diverse biological processes such as inflammation, carcinogenesis, ageing, radiation damage and photobiological effects appear to involve reactive oxygen species. This field of research provides new perspectives in biochemical pharmacology, toxicology, radiation biochemistry as well as pathophysiology.
Sulfur Oxides as Ligands in Coordination Compounds
Authors: Schenk Wolfdieter A.
Published: December 2003

Donor molecules undergo dramatic changes in their chemical properties on coordination to a transition‐metal atom. Highly reactive species can be trapped and studied as ligands. Conversely, stable compounds can be activated to undergo novel reactions. Sulfur dioxide complexes have generally been studied from a structural viewpoint, their reactivity having been somewhat neglected. The unstable sulfur oxides SO, S2O, and S2O2 are still often regarded as laboratory curiosities. Their successful stabilization in transition‐metal complexes has now made them accessible to detailed study, in the course of which many relationships to the chemistry of SO2 complexes have become apparent.
Heterometallic Polyhydride Raft Formation: A Comparison of Syntheses using Alkoxides of Copper and Gold
Authors: Sutherland Bruce R. , Ho Douglas M. , Huffman John C. , Caulton Kenneth G.
Published: December 2003

Relatively strong Cu–H and Cu–Cu interactions are the main reason that the most hydride‐rich cluster so far observed, the neutral cluster 3, is formed upon reaction of the Re2H8 complex 1 with 2. Complex 1 reacts with the gold complex 4, which is analogous to 2, to give the hexahydrido complex 5, for which the formula represents both a symmetrical and an unsymmetrical isomer.
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Azulene as Unusual η6‐Ligand and as η6:η4‐Bridge in Mo‐Complexes
Authors: Töfke Susanne , Behrens Ulrich
Published: December 2003

In the mononuclear complex (azulene)(benzene)molybdenum, 1, the azulene ligand behaves as if it consisted of a fulvene and a diene moiety. This is also true of the binuclear complexes obtained by reaction of 1 with [(H3CCN)3M(CO)3] (M = Cr, Mo, W). In 1, the η6‐coordinated azulene is nonplanar; the binuclear complexes exhibit fluxional behavior in solution, which was still observed at 193 K and results in only five signals in the 1H‐NMR spectrum.
2H,2H‐COSY and 2H,2H,13C‐RELAY NMR Experiments for the Analysis of Deuteriated Compounds
Authors: Moskau Detlef , Günther Harald
Published: December 2003

Determination of the homonuclear coupling between and the correlation of 13C nuclei via vicinal deuterium nuclei has been achieved by 2D NMR spectroscopy. [D5]Pyridine was used to show that the only 0.1‐ to 0.2‐Hz 3J(2H,2H) values lead to significant cross signals in the COSY experiment and that the RELAY experiment is a promising alternative when 2H,13C correlation and 2H,2H COSY NMR spectroscopy fail owing to overlapping of signals.
Directed Homogeneous Hydrogenation [New Synthetic Methods (65)]
Authors: Brown John M.
Published: December 2003

Stereochemical control is a major concern in the application of homogeneous catalysis to organic chemistry. In this context, the directed hydrogenation of olefins employing cationic rhodium or iridium catalysts has considerable potential, for very high selectivity can be attained under mild reaction conditions. The only requirement is a polar functional group in proximity to the double‐bond which remains bound to the metal during the catalytic cycle and thereby controls the Stereochemical course of hydrogen delivery through the constraints of chelation. The substituent is most frequently a hydroxy group OH but can also be an ester, amide or carbamate group; other groups remain to be scrutinized. In cyclic compounds, directed hydrogenation can lead to face‐selectivity, and the polar substituent may be in the β‐, γ‐, or δ‐position to the double‐bond. Acyclic stereoselection ensues with β‐ or γ‐substituents in appropriate compounds, and the configuration of reduced product is predictable on the basis of simple rules. The application of optically active rhodium complexes leads to useful kinetic resolution procedures.
Synthesis of the Four‐Membered Metallacycle [Cp2Ti(AsPh)3] via the in situ Reduction of [Cp2 TiCl2]
Authors: Mercando Paul , DiMaio Anthony‐Joseph , Rheingold Arnold L.
Published: December 2003

The title compound 1 contains an almost planar TiAs3 ring: the three phenyl rings are arranged alternately “upwards” and “downwards”. The two cyclopentadienyl rings are not equivalent at room temperature in solution. 1 is the first cyclic titanium derivative containing elements of the 5th group as ring members which has been characterized by X‐ray structure analysis.
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Genetic Engineering with Plants
Authors: Eckes Peter , Donn Günter , Wengenmayer Friedrich
Published: December 2003

Today there are no longer any basic problems involved in isolating and characterizing plant genes. Our knowledge of the structure and function of the genes so far sequenced provides a beginning understanding of gene regulation in plants. In connection with the recently developed methods of gene transfer to plant cells, the most important application is the production of plants with new characteristics through genetic engineering. Since the genes can be transferred from any kind of plant—indeed even from any organism—completely new possibilities are opened up for plant breeding.
Polyphosphorus Compounds—New Results and Perspectives
Authors: Baudler Marianne
Published: December 2003

In contrast to the numerous known and often technically important mono‐ and diphosphorus compounds with phosphorus in its maximum oxidation state, polyphosphorus compounds led only a shadowy existence up to about twenty years ago. One of the reasons for this was the properties of such compounds, which made their handling and structural characterization difficult. This problem was solved by the development of modern preparative techniques and, especially, by the further methodological development of nuclear magnetic resonance spectroscopy. Thus, a fascinating new branch of phosphorus chemistry has been opened up in recent years. The first comprehensive review on this subject was published five years ago. Since then, research on this “element‐near” chemistry of phosphorus has produced further impressive advances with the result that a surprisingly large variety of compounds with skeletons consisting of chains or rings of phosphorus atoms is known today. However, the recent observation of the spontaneous formation of the “aromatic” pentaphosphacyclopentadienide ion, P, during the synthesis of phosphorus‐richer polyphosphides from phosphorus‐poorer compounds in solution and the discovery of the inversion of phosphorus in tetra‐ and pentacyclic organophosphanes demonstrate that this field is still capable of producing surprises.