Showing papers in "Angewandte Chemie in 1981"
523 citations
TL;DR: The present paper will review this new field of microbial α-glucosidase inhibitors which has been studied with particular intensity during the past ten years and highlights the most interesting representative of this homologous series, acarbose, a pseudotetrasaccharide exhibiting a very pronounced inhibitory effect on intestinal α-GLUCosidases.
Abstract: α-Glucosidases are among the most important carbohydrate-splitting enzymes. They catalyze the hydrolysis of α-glucosidic linkages. Their substrates are—depending on their specificity—oligo- and polysaccharides. Microbial inhibitors of α-amylases and other mammalian intestinal carbohydrate-splitting enzymes studied during the last few years have aroused medical interest in the treatment of metabolic diseases such as diabetes. Moreover, they extend the spectrum of microbial secondary metabolites which comprises an enormous variety of structures. They also contribute considerably to a better understanding of the mechanism of action of α-glucosidases. These inhibitors belong to different classes of substances. Those studied most thoroughly are microbial α-glucosidase inhibitors which are members of a homologous series of pseudooligosaccharides of the general formula (4). They all have a core in common which is essential for their inhibitory action, a pseudodisaccharide residue consisting of an unsaturated cyclitol unit, and a 4-amino-4,6-dideoxy- glucose unit. The—in many respects—most interesting representative of this homologous series is acarbose (5), a pseudotetrasaccharide exhibiting a very pronounced inhibitory effect on intestinal α-glucosidases such as sucrase, maltase and glucoamylase. The present paper will review this new field of microbial α-glucosidase inhibitors which has been studied with particular intensity during the past ten years.
428 citations
TL;DR: Qualitative and quantitative structure/activity relationships of the aryldihydropyridines can be deduced from their biological data.
Abstract: The aryldihydropyridines first prepared by Hantzsch almost 100 years ago have recently been found to be highly effective calcium antagonists with suitable pharmacological profiles. An illustrative example is dimethyl-l,4-dihydro-2,6-dimethyl-4-(o-nitrophenyl)pyridine-3,5-dicarboxylate (Nifedipine) which is already employed therapeutically. This substance lowers the frequency of attack of angina pectoris and reduces blood pressure. The discovery of the therapeutic activity of this class of substances initiated renewed investigation of the Hantzsch condensation and the synthesis of numerous 4-aryldihydropyridines and related compounds. Qualitative and quantitative structure/activity relationships of these substances can be deduced from their biological data.
415 citations
TL;DR: A recent survey as mentioned in this paper summarizes facts and speculations fitting into the hypothesis of polymeric antitumor agents on a molecular and cellular level, which could serve as guidelines in the thicket of facts arising from the innumerable attempts to contribute to the solution of the cancer problem.
Abstract: During the last 80 years polymer science developed from H. Staudinger’s controversial hypothesis of the existence of macromolecules to highly sophisticated applications such as polymers in medicine. Within the field of pharmacologically active polymers, the area of polymeric antitumor agents is a new and attractive field, where polymer scientists try to combine the advantages of macromolecular systems with the requirements of tumor therapy. That is to say, that polymer chemists have to enter neighboring fields, for example, the rapidly developing area of the life sciences. This interdisciplinary thinking may lead to new concepts, which could serve as guidelines in the thicket of facts arising from the innumerable attempts to contribute to the solution of the cancer problem. The present survey does not review the whole field of polymeric antitumor agents, but summarizes facts and speculations fitting into the hypothesis of antitumor agents on a molecular and cellular level.
285 citations
273 citations
TL;DR: The first successful synthesis of mesomeric-stabilized phosphorus-carbon compounds with coordination number 2, seventeen years ago, was followed nine years later by the preparation of the imino-phosphanes whose intensive investigation has continued to the present day as discussed by the authors.
Abstract: Just as the octet rule had prevented the discovery of the inert-gas compounds, the systematic search for phosphorus-carbon- and phosphorus-nitrogen-compounds having (p-p)π-multiple bonds was hindered by the double bond rule. The first successful synthesis of mesomeric-stabilized phosphorus-carbon compounds with coordination number 2, seventeen years ago, was followed nine years later by the preparation of the imino-phosphanes whose intensive investigation has continued to the present day. A dramatic development has now begun in the phospha-alkene and -alkyne fields, and a large variety of preparative methods have been found. Several compounds of this type are amazingly stable, however they do not participate in typical ylide reactions such as the Wittig reaction. In contrast, the PC double bond is more comparable to that of olefins, which has been confirmed by the occurrence of E,Z-isomers and pericyclic reactions of phospha-l,5-hexadienes.
257 citations
TL;DR: Clusters of main group elements are not rare. On the contrary, it is becoming difficult to avoid the discovery of new substances of this type as discussed by the authors, and the great majority of homonuclear bonded structures are already present in the solid phases of simple systems.
Abstract: Clusters of main group elements are not rare. On the contrary, it is becoming difficult to avoid the discovery of new substances of this type. Clusters are the natural intermediate stages between an element and its isolated atoms or ions. In the form of polycations and polyanions they offer models for the stepwise oxidation and reduction of an element and represent a bridge between the elements. The great majority of homonuclear bonded structures are already present in the solid phases of simple systems. Mobilization of these clusters as molecules represents a great challenge.
246 citations
TL;DR: A review of the structure and bonding of molybdenum transition metal complexes is given in this article, as well as syntheses and reactions of these complexes are discussed. But this paper is restricted to molybenzum complexes.
Abstract: Numerous nitrido complexes of transition metals show very short metal-nitrogen bond lengths, suggesting MN-triple bonds. At present, compounds of this type are being intensively investigated. In particular the molybdenum complexes are considered as model substances for the study of at least an intermediate step of N2-assimilation. This article contains a review of the structure and bonding, as well as syntheses and reactions of these complexes.
228 citations
227 citations
TL;DR: In this paper, eine sturmische Entwicklung auf dem Gebiet der Phospha-alkene und -alkine is discussed, e.g., eine Verwandtschaft der PC-Doppelbindung zu Olefinen, welche durch das Auftreten von E,Z-Isomeren sowie durch pericyclische Reaktionen an P-1,5-hexadien-Derivaten bestatigt wird.
Abstract: Wie die Oktettregel der Entdeckung der Edelgasverbindungen im Wege stand, so behinderte die Doppelbindungsregel lange Zeit die systematische Suche nach Phosphor-Kohlenstoff- und Phosphor-Stickstoff-Verbindungen mit (p-p)π-Mehrfachbindungen. Auf die erste Synthese mesomeriestabilisierter Kohlenstoffverbindungen von Phosphor mit der Koordinationszahl 2 vor siebzehn Jahren, die neun Jahre spater beschriebene Herstellung von Iminophosphanen, deren Erforschung bis heute andauert, folgt nun eine sturmische Entwicklung auf dem Gebiet der Phospha-alkene und -alkine. Etliche Mitglieder dieser Stoffklassen, fur die ein Bundel von Syntheseverfahren bereitsteht, erweisen sich als erstaunlich stabil. Typische Ylid-Reaktionen, wie die Wittig-Reaktion, gehen die Phospha-alkene nicht ein. Vielmehr zeigt sich eine Verwandtschaft der PC-Doppelbindung zu Olefinen, welche durch das Auftreten von E,Z-Isomeren sowie durch pericyclische Reaktionen an Phospha-1,5-hexadien-Derivaten bestatigt wird.
223 citations
TL;DR: Fluorine-containing compounds have been extensively studied in the literature as mentioned in this paper, and the main motivating force behind the developments in this field were, above all, the unusual properties the numerous compounds acquire on introduction of fluorine substituents.
Abstract: Since the days of the “Manhattan Project” our knowledge of the chemistry of fluorine-con-taining compounds has increased tremendously. At first only considered out of curiosity, this area of research bordering between inorganic and organic chemistry has developed from modest beginnings to such a complexity of interesting ramifications that it would be very difficult to review all aspects in detail. The motivating force behind the developments in this field were, above all, the unusual properties the numerous compounds acquire on introduction of fluorine substituents. The spectrum of unusual modes of behavior extend from extreme stabilization in fluorine-containing polymers and blood-substitutes to drastic increases in reactivity in pharmacologically and phytomedicinally active substances and in dyes. Moreover, one physical peculiarity of the fluorine atom, its magnetic moment, opens a new route to the decyphering of metabolic processes.—Parallel to the ever increasing number of fluorinated compounds there has been a concomitant increase in the variety of methods of synthesis and reagents, which is frequently difficult to overview in entirety, even for the specialists. Older, simple methods such as halogen metathesis with metal fluorides and electrofluorination are being refined as far as higher selectivity is concerned, and completely new, very reactive substances such as hypofluorites and noble-gas fluorides enable fascinating reactions on complex substrates, e. g. steroids and nucleobases. The present review is an attempted documentation and classification of the methods as well as a critical appraisal, not least from the standpoint of efficiency and economic aspects.
TL;DR: The electrically induced fusion and entrapment of membrane-impermeable substances and genes in cells provide a new tool for the productions of a wide range of cells with manipulated functions, which could be used for the solution of a number of problems in cell biology, medicine and technology.
Abstract: Exposure to electrical fields can reversibly increase the electrical conductivity and permeability of a cell membrane, which regulates and directs the exchange of materials and information between the cell and its environment. If cell membranes (or artificial lipid membranes) are exposed to a field pulse of high intensity and short duration (ns to μs), local electrical breakdown occurs in them. This electrical breakdown is associated with a large permeability change in the membrane, which is such that substances or particles (up to the size of genes) which cannot normally permeate through the membrane, are able to traverse the membrane into the cell. The original properties of the membrane are restored within μs to min, depending on the experimental conditions and the membrane properties.
Electrical breakdown in the zone of contact between the membranes of cells (or lipid vesicles), which have been made to adhere to each other by the action of weak inhomogeneous alternating electrical fields, leads to fusion of these cells with formation of a single cell having new functional characteristics. The electrical fusion method is very mild, and the yield of fused cells is high.
The electrically induced fusion and entrapment of membrane-impermeable substances and genes in cells provide a new tool for the productions of a wide range of cells with manipulated functions, which could be used (or are being used) for the solution of a number of problems in cell biology, medicine and technology.
The application of electrical membrane breakdown to clinical diagnostics, the development of cellular carrier systems for the selective transport of drugs to a site of action within the organism and the potential applications of electrically induced fusion for breeding salt-tolerant crop plants for converting solar energy into ethanol, for synthesizing natural materials and manipulating genes, are described.
TL;DR: In this article, weisen sehr geringe Metall-Stickstoff-Bindungslangen auf, die denen von MN-Dreifachbindungen entsprechen.
Abstract: Zahlreiche Nitrido-Ubergangsmetall-Komplexe weisen sehr geringe Metall-Stickstoff-Bindungslangen auf, die denen von MN-Dreifachbindungen entsprechen. Verbindungen dieses Typs werden derzeit intensiv untersucht. Insbesondere die Molybdankomplexe werden als Modellsubstanzen fur das Studium zumindest eines Teilschritts der N2-Assimilation angesehen. Der vorliegende Beitrag gibt einen Uberblick uber Struktur und Bindungsverhaltnisse sowie uber Synthesewege und Reaktionen dieser Komplexe.
TL;DR: In the case of the reduced halides of the lanthanoids as discussed by the authors, the metal-metal bonds are linked together by metal clusters of the same type, which can be seen as a way of connecting the two types of structures.
Abstract: The chemistry of metals in low valence states is marked by the frequent occurrence of metal clusters, which are easily recognizable when they occur as molecular units. Many metal-rich compounds of transition metals with p-elements (3rd to the 6th main groups) are closely related to the corresponding halides, since they are built up from metal clusters of the same type. The clusters are however, linked together (condensed) by metal-metal bonds. This principle of construction holds particularly well in the case of the novel reduced halides of the lanthanoids.
TL;DR: In this paper, the Elektronenarmen Ubergangsmetalle V, Nb, Ta, Mo, W and Re bilden in den hochsten Oxidationsstufen tetraederformige Thioanionen with bemerkenswerten Eigenschaften.
Abstract: Die elektronenarmen Ubergangsmetalle V, Nb, Ta, Mo, W und Re bilden in den hochsten Oxidationsstufen tetraederformige Thioanionen mit bemerkenswerten Eigenschaften. Die farbenprachtigen Thiometallate werden durch Festkorperreaktion oder in Losung aus den Oxometallaten erhalten. Aus Thiometallaten lassen sich durch neuartige intramolekulare Redox-Prozesse bei gleichzeitiger Kondensation Poly(thiometallate) mit gemischten Valenzen gewinnen. Die Metall-Schwefel-Bindung reagiert sowohl nucleophil als auch elektrophil; bei der Mo–S-Bindung ist diese Eigenschaft von biochemischem Interesse. Als Komplexliganden ermoglichen die Thiometallate die Erzeugung von Multi-Metall-Komplexen. Daruber hinaus zeichnen sie sich durch vielseitiges Koordinationsverhalten sowie einzigartige elektronische Eigenschaften aus; wegen der ausgepragten Elektronendelokalisation existieren Thiometallato-Komplexe mit unterschiedlicher Elektronenpopulation. MoS42- hat auserdem Bedeutung fur bioanorganische Fragen, z. B. das Nitrogenase-Problem und den Cu-Mo-Antagonismus.
TL;DR: In the course of the last decade the chemistry of insecticides was expanded with the discovery of new cyclopropanecarboxylic acid esters of specific structure, far superior in action to the hitherto known insecticides of other substance classes or the natural prototypes from the group of pyrethrum constituents.
Abstract: In the course of the last decade the chemistry of insecticides was expanded with the discovery of new cyclopropanecarboxylic acid esters of specific structure, far superior in action to the hitherto known insecticides of other substance classes or the natural prototypes from the group of pyrethrum constituents. The discovery quickly precipitated a host of wide-ranging studies on the synthesis of these compounds. The development of selective methods of synthesizing complicated small rings called for a comprehensive repertoire: thus, synthesis of the compounds on an industrial scale makes use of sigmatropic rearrangement, radical addition, and nucleophilic ring closure with carbanions. These new industrial syntheses have acquired particular topicality because of their use of stereospecific and enantioselective methods.
TL;DR: In this article, a series of electroanalytical methods provides information on the electrode reaction mechanisms in the Kolbe electrolytic process, where carboxylic acid anions decarboxylate to form radicals which couple to form e.g. long chain alkene derivatives having pheromone activity, or add to ole-fins.
Abstract: Electrolysis allows the reactivity of a substrate to be changed, or its polarity to be reversed (“redox umpolung”). The carbon skeleton and the functional groups of a synthetic building block can thus be utilized more economically, and at the same time the number of reaction steps in multistage syntheses can be reduced. The tools necessary for an electrolytic process are a cell, a power source, electrodes, and an electrolyte, the latter being chosen in accordance with the reduction or oxidation potential of the substrate. A series of electroanalytical methods provides information on the electrode reaction mechanisms. At the anode, arenes, phenolic ethers, and electron-rich olefins dimerize via intermediate radical cations. In the Kolbe electrolysis, carboxylic acid anions decarboxylate to form radicals which can couple to form e.g. long chain alkene derivatives having pheromone activity, or add to ole-fins. At the cathode, activated olefins hydrodimerize via radical anions or, in the presence of appropriate reagents, can be acylated, alkylated, and carboxylated. Pinacols, crossed hydrodimers, and cyclic and arylated compounds are accessible via the cathodically produced radicals, while the formation of strained small rings or the reductive addition of halides to carbonyl compounds takes place through intermediate carbanions.
TL;DR: In this article, the Entdeckung der hochleitfahigen Molekulkristallen aus CT-Komplexes is discussed. But, auch die chemischen and physikalischen Prozesse, die sich hierbei abspielen, and die Ursachen fur die quasimetallische Leitfachigkeit sind noch weitgehend umstritten, are in die Diskussion der Eigenschaften ebenso einbezogen werden
Abstract: Polymere, die wie Polyacetylen ein ausgedehntes π-Elektronensystem in der Hauptkette haben oder wie Poly-p-phenylen aus einer Folge aromatischer Ringe bestehen, sind im nativen Zustand ausgezeichnete Isolatoren; sie konnen im festen Zustand zu elektrisch leitfahigen CT-Komplexen mit einer metallahnlichen Leitfahigkeitscharakteristik oxidiert oder reduziert werden. Die chemischen und physikalischen Prozesse, die sich hierbei abspielen, und die Ursachen fur die quasimetallische Leitfahigkeit sind noch weitgehend umstritten. Die physikalisch-chemische Realstruktur der Materialien, d. h. ihre komplexe Morphologie und Textur, mus in die Diskussion der Eigenschaften ebenso einbezogen werden wie die Erfahrungen uber Struktur-Eigenschafts-Beziehungen bei den „organischen Metallen”, d. h. bei hochleitfahigen Molekulkristallen aus CT-Komplexen niedermolekularer organischer Verbindungen. Die Entdeckung der hochleitfahigen Polymerkomplexe hat ein neues interdisziplinares Forschungsgebiet eroffnet, das die Polymerwissenschaft, die Festkorper- und Halbleiterphysik und die organische Festkorperchemie beschaftigt. Man darf annehmen, das sich hieraus zahlreiche neuartige Werkstoffe und technische Anwendungen ergeben werden.
TL;DR: The principle of replication, i.e. the spontaneous self-multiplication of a carrier of information, can be shown to be a general property of certain macromolecular systems and the question of whether or not chemical evolution resulted directly in the nucleic acid/protein system has to be answered.
Abstract: Using layer silicates as models, the principle of replication, i.e. the spontaneous self-multiplication of a carrier of information, can be shown to be a general property of certain macromolecular systems. Errors in replication and feedback together with environmental influences may lead to mutants with higher or lower replication rates, thus enabling evolution. In the light of these findings, the question of whether or not chemical evolution resulted directly in the nucleic acid/protein system, i.e. the genetic principle common to all living systems known up to now, has to be answered. It seems conceivable that as a first step a much simpler replicating system was formed: such a system might then have undergone an evolution of replicating systems, resulting in the final nucleic acid/protein system.
TL;DR: The negative ion mass spectra measured with a commercial instrument and the electron energies used (20-70 eV) are not suitable either for molecular weight or for structure determination as discussed by the authors.
Abstract: “It appears that negative ion mass spectra measured with a commercial instrument and the electron energies used (20–70 eV) are not suitable either for molecular weight or for structure determination—”. This was the conclusion of a paper appearing in 1965 which expressed the then almost universal opinion on the importance of negative ion mass spectrometry in the structure analysis of organic compounds[8]. The fact that quinones and aromatic nitro compounds were exceptions to this rule was rather taken as substantiation of this opinion. The potential value of the work originating from the laboratories of Manfred von Ardenne was first realized with the development of chemical ionization. This technique gave a firm foundation to negative ion spectrometry in the area where it is complementary to that of positive ions.
TL;DR: In this paper, the Photoelektronen-Spektroskopie bestens bewahrt: So gelingt es with dieser Echtzeit-Messonde bei den meisten Pyrolysen, in Millimol-Ansatzen and innerhalb weniger Stunden, the Temperaturen fur die verschiedenen Zersetzungskanale zu ermitteln, die Hauptprodukte zu charakterisieren and gegebenenfalls deren Ausbeute z
Abstract: Zur Analyse und zur Optimierung zahlreicher Gasreaktionen in stromenden Systemen hat sich die Photoelektronen-Spektroskopie bestens bewahrt: So gelingt es mit dieser Echtzeit-Messonde bei den meisten Pyrolysen – in Millimol-Ansatzen und innerhalb weniger Stunden –, die Temperaturen fur die verschiedenen Zersetzungskanale zu ermitteln, die Hauptprodukte zu charakterisieren und gegebenenfalls deren Ausbeute zu verbessern. Bei geeigneter Versuchsfuhrung lassen sich kurzlebige und/oder reaktive Molekule wie P2, Thioformaldehyd oder Silabenzol nachweisen. Von Vorteil ist die PE-spektroskopische Gasanalytik insbesondere bei der Suche nach Heterogen-Katalysatoren, die innerhalb eines Tages zwischen 300 und 1300 K mit Gasgemischen wechselnder Zusammensetzung getestet werden konnen. PE-Spektrometer eignen sich zum ”on line„-Anschlus an Rechner; tragbare Gerate fur den Laborbetrieb befinden sich in Entwicklung.