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  • 1995-1999  (7,108)
  • 1980-1984  (5,175)
  • 1965-1969  (6,329)
  • 1920-1924  (3,414)
  • General Chemistry  (21,202)
  • Ultrastructure
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  • 1
    Electronic Resource
    Electronic Resource
    Megasporogenesis in Arabidopsis thaliana L.: an ultrastructural study (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 99-109 
    Details
    ISSN: 1432-2145
    Keywords: Key words Arabidopsis thaliana ; Megasporogenesis ; Meiosis ; Ultrastructure ; Cellular polarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In this study, megasporogenesis of the plant model Arabidopsis thaliana was investigated by electron microscopy for the first time. The data described here could constitute a reference for future investigations of Arabidopsis mutants. During the beginning of meiosis the megaspore mother cell shows a polarity created by unequal distribution of organelles in the cytoplasm. Plastids accumulate in the chalazal region and long parallel saccules of endoplasmic reticulum, small vacuoles and some dictyosomes are found in the micropylar region. Plasmodesmata are abundant in the chalazal cell wall. The nucleus is almost centrally localized and contains a prominent excentric nucleolus and numerous typical synaptonemal complexes. After the second division of meiosis the four megaspores are separated by thin cell walls crossed by numerous plasmodesmata and do not show significant cellular organization. The young functional megaspore is characterized by a large nucleus and a large granular nucleolus. The cytoplasm is very electron dense due to the abundance of free ribosomes and contains the following randomly distributed organelles: mitochondria, a few short saccules of endoplasmic reticulum, dictyosomes and undifferentiated plastids. However, there is no apparent polarity, except for the distribution of some small vacuoles which are more abundant in the micropylar region of the cell. The degenerating megaspores are extremely electron dense and do not show any substructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004970050178
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  • 2
    Electronic Resource
    Electronic Resource
    Ultrastructural study of the destructive and repair processes in pulmonary inflammation and following endobronchial laser therapy (1999)
    Springer
    Virchows Archiv 435 (1999), S. 13-19 
    Details
    ISSN: 1432-2307
    Keywords: Key words Inflammation of the lung ; Biopsy ; Ultrastructure ; Laser therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Examination of 127 biopsy specimens from 45 patients with inflammatory lung diseases showed changes consistent with increased permeability of the capillary endothelial cells as an initial stage in the development of the inflammatory reaction. Associated interstitial oedema, deformation of the interalveolar septa, and structural disorganization of alveolar epithelium cells occur, and local microcirculatory problems result in tissue hypoxia and fibrosis. The ultimate morphological picture is determined largely by the intensity of repair. Laser biostimulation minimizes the inflammation and stabilizes fibroplastic process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004280050389
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  • 3
    Electronic Resource
    Electronic Resource
    Evaluation of muscle capillary basement membrane in inflammatory myopathy (1999)
    Springer
    Virchows Archiv 435 (1999), S. 58-61 
    Details
    ISSN: 1432-2307
    Keywords: Key words Capillary basement membrane ; Inflammatory myopathy ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The capillary basement membranes from 16 skeletal muscle biopsies from patients with a clinical and histological diagnosis of inflammatory myopathy and from six controls were analysed ultrastructurally and morphometrically. Resin sections from 244 endomysial capillaries were examined by light microscope, and the results were correlated with findings seen in electron micrographs of these capillaries. The ultrastructural morphometric measurements and the statistical analysis showed that the capillary basement membrane was thick and multilaminated in 87% specimens affected by inflammatory myopathy. No thick or multilaminated basement membrane was observed in controls. In inflammatory myopathy the endomysial space next to the capillaries contained an increased amount of collagen fibrils and showed signs of a chronic reparative process. It is suggested that the thick multilaminated basement membrane in inflammatory myopathy represents an advanced stage of vascular regeneration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004280050395
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  • 4
    Electronic Resource
    Electronic Resource
    Immunohistochemical, conventional and immunoelectron microscopical characteristics of periodic acid-Schiff-positive granules in the mouse brain (1999)
    Springer
    Acta neuropathologica 98 (1999), S. 31-38 
    Details
    ISSN: 1432-0533
    Keywords: Key words Polyglucosan body ; Periodic ; acid-Schiff-positive granules ; Mouse brain ; Immunohistochemistry ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Periodic acid-Schiff-positive granules (PGs) appear in the mouse brains in relation to advancing age. The exact location and pathophysiological significance of PGs, however, are not fully understood. The incidence, staining properties, and topographical distributions of PGs in the brains of 17 AKR mice ranging in age from 7 to 18 months were examined histochemically and immunohistochemically using antibody KM279 raised against a polyglucosan. In addition, to define the precise site of PG formation, we investigated the brains of 4 AKR mice of 24 months of age using conventional and immunoelectron microscopy. PGs were seen in all mice examined and the levels were increased with age. The PGs were located predominantly in the hippocampus and, to a lesser extent, in the cerebellum and olfactory bulb. Immunohistochemically, PGs in the hippocampus and cerebellum were labeled uniformly with KM279. On immunoelectron microscopy with this monoclonal antibody, the fibrillar or membranous structures corresponding to PGs seen using light microscopy were labeled specifically with gold particles. With conventional electron microscopy, fibrillar or membranous structures were seen along with synaptic vesicles and dense-core granules. Moreover, around the cells containing PGs, a few synaptic junctions with neighboring cells were observed, indicating that the cells contributing to formation of PGs were neuronal cells. The positive immunoreactivity of AKR mouse PGs for the antibody KM279 suggests that the PGs and similar structures in other species may share a common antigenicity. Thus, it is assumed that PGs in AKR mice might result from some abnormalities in glucose metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004010051048
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  • 5
    Electronic Resource
    Electronic Resource
    The visualization of a new class of traumatically injured axons through the use of a modified method of microwave antigen retrieval (1999)
    Springer
    Acta neuropathologica 97 (1999), S. 335-345 
    Details
    ISSN: 1432-0533
    Keywords: Key words Amyloid precursor protein ; immunoreactivity ; Axonal injury ; Microwave antigen retrieval ; Traumatic brain injury ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Antibodies to the amyloid precursor proteins (APP) have become routine markers for detecting traumatically induced axonal injury (AI) in animals and man. Unfortunately, the techniques used to visualize these proteins are not compatible with routine electron microscopic (EM) analysis. In the current communication, we describe a method for the ultrastructural visualization of antibodies to APP and, using this method, we identify a previously unrecognized population of traumatically injured axons. Rats were subjected to an impact acceleration traumatic brain injury and allowed to survive 30 min to 3 h postinjury. The animals were then perfused, their brains sectioned on a vibratome and the sections prepared for immunocytochemistry using a computer-controlled microwave capable of temperature regulation. The use of temperature-controlled microwave energy unmasked APP antigenic epitopes without sacrificing ultrastructural detail. The APP antibody was found in two distinct populations of reactive axons that differed in size, morphology, location, and temporal progression. Comparable to previous descriptions, one population showed traumatically related reactive changes that led to swelling and disconnection. The other population, however, revealed unanticipated changes reflected in nodal and paranodal swelling of small continuous fibers that showed no evidence of disconnection during the time periods assessed. These studies provide new insight into the complexity of the pathobiology of AI, while describing a novel approach for enhancing APP immunoreactivity at the EM level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004010050996
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  • 6
    Electronic Resource
    Electronic Resource
    Synaptology and ultrastructural characteristics of laryngeal cricothyroid and posterior cricoarytenoid motoneurons in the nucleus ambiguus of the rat (1999)
    Springer
    Anatomy and embryology 200 (1999), S. 301-311 
    Details
    ISSN: 1432-0568
    Keywords: Key words Intrinsic laryngeal motoneurons ; Cholera toxin HRP ; Ultrastructure ; Swallowing ; Respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The laryngeal motoneurons innervating the cricothyroid muscle (CT) are located in the semicompact formation just ventral to the rostral part of the compact formation of the nucleus ambiguus. The motoneurons innervating the posterior cricoarytenoid muscle (PCA) are located in the loose formation. We retrogradely labeled the CT and the PCA motoneurons using cholera toxin subunit B-conjugated horseradish peroxidase, and determined the ultrastructure and synaptic organization of these neurons. The CT and the PCA motoneurons had the appearance of α-motoneurons, i.e., large, oval or polygonal cells containing well-developed organelles and a prominent spherical nucleus. Two kinds of neurons were recognized among the PCA motoneurons. The one (PCA-A) was significantly smaller than the other (PCA-B). The average number of axosomatic terminals in a section was significantly largest in the PCA-B (56.6), smaller in the PCA-A (36.0), and smallest in the CT (32.3) neurons. Most of the axosomatic terminals (64.7%) contained pleomorphic vesicles and made symmetric synaptic contacts (Gray’s type II) with the PCA-A neurons, while more than 60% contained round vesicles with asymmetric synaptic contacts (Gray’s type I) in the CT (69.5%) and the PCA-B (60.6%) neurons. A few terminals associated with subsurface cisterns were present on all laryngeal motoneurons. These results indicated that the CT motoneurons may receive mostly excitatory terminals, whereas the PCA muscle may be regulated by neurons having many inhibitory terminals, and neurons having many excitatory terminals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004290050281
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  • 7
    Electronic Resource
    Electronic Resource
    Bunina bodies in amyotrophic lateral sclerosis on Guam: a histochemical, immunohistochemical and ultrastructural investigation (1999)
    Springer
    Acta neuropathologica 98 (1999), S. 150-156 
    Details
    ISSN: 1432-0533
    Keywords: Key words Amyotrophic lateral sclerosis ; Bunina body ; Guam ; Immunohistochemistry ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract An investigation of Bunina bodies is important when studying the pathoetiology and pathomechanisms involved in amyotrophic lateral sclerosis (ALS). It may serve as a clue essential for the study of the pathogenesis of Guamanian amyotrophic lateral sclerosis (ALS-G), and it may provide a means of answering the question of whether ALS-G is the same disease as classical ALS or a different entity. In ALS-G, however, no precise histochemical, immunohistochemical, or detailed ultrastructural examination has been published to date. To elucidate the pathological differences/similarities of Bunina bodies between classical ALS and ALS-G, we performed histochemical, immunohistochemical, topographic and ultrastructural examinations. Histochemically, hematoxylin and eosin, Masson’s trichrome, methylgreen-pyronin, phosphotungstic acid-hematoxylin, Klüver-Barrera, Bodian and periodic acid-Schiff staining were utilized. Immunohistochemical examination was performed using antibodies for cystatin C, ubiquitin, Tau-2, Cu/Zn superoxide dismutase, phosphorylated neurofilament and glial fibrillary acidic protein. Histochemical findings were consistent with those previously described for classical ALS. The immunohistochemical study showed that in ALS-G Bunina bodies were intensely labeled by an anti-cystatin C antibody. Topographic examination demonstrated that Bunina bodies were distributed in the spinal anterior horns and Clarke’s column in the spinal cord. Ultrastructurally, Bunina bodies were composed of electron-dense amorphous/ granular material accompanied by vesicular structures and neurofilaments. The results of the present study have revealed that the pathological features of Bunina bodies in ALS-G are identical to those seen in classical ALS. These findings strongly suggest that a similar degenerative process occurs in the spinal anterior horn cells in both ALS-G and classical ALS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004010051063
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  • 8
    Electronic Resource
    Electronic Resource
    Ultrastructural localization of phosphorylated eIF2α [eIF2α(P)] in rat dorsal hippocampus during reperfusion (1999)
    Springer
    Acta neuropathologica 98 (1999), S. 493-505 
    Details
    ISSN: 1432-0533
    Keywords: Key words Ischemia ; Protein synthesis ; Translation ; Ultrastructure ; Hippocampus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract During post-ischemic brain reperfusion there is a substantial reduction of protein synthesis in selectively vulnerable neurons. Normal protein synthesis requires a functional translation initiation complex, a key element of which is eukaryotic initiation factor 2 (eIF2), which in a complex with GTP introduces the met-tRNAi. Phosphorylation of Ser51 on the α subunit of eIF2 [eIF2α(P)] generates a competitive inhibitor of eIF2B, thereby preventing the replenishment of GTP onto eIF2, thus blocking translation initiation. It has been shown that the conditional expression of an eIF2α mutant (Asp substituted for Ser51) imitating the negative charge of Ser51 (P) induces apoptosis. During the first 10 min of post-ischemic reperfusion, there is an approximately 20-fold increase in eIF2α(P) seen in the cytoplasm of CA1 hippocampal neurons, and, by 1 h, there is also accumulation of eIF2α(P) in the nucleus. We utilized post-embedding electron microscopical immunogold methods to examine the localization of eIF2α(P) during reperfusion. Immunogold particles (10 nm) were concentrated chiefly along the rough endoplasmic reticulum and in association with the membranes of the nuclear envelope in CA1 neurons. Aggregations of gold particles in the nucleus were concentrated: (1) within and around the nucleolus, (2) associated to strands of heterochromatin, and (3) along putative nuclear filaments. The presence of eIF2α(P) in the nucleolus probably reflects its association with nascent ribosomal subunits. The β-subunit of eIF2 has a zinc finger and polylysine blocks analogous to those on other proteins that affect transcription. The association of eIF2α(P) with chromatin may have important implications for transcription.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004010051115
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  • 9
    Electronic Resource
    Electronic Resource
    Structural identification and characterization of arteries and veins in the placental stem villi (1999)
    Springer
    Anatomy and embryology 199 (1999), S. 407-418 
    Details
    ISSN: 1432-0568
    Keywords: Key words Placenta ; Vascular wall ; Smooth muscle cell ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The vascular wall structure in the human full-term placental villi of normal pregnancy was studied by means of light and electron microscopy with an improved technique of perfusion fixation and tissue preparation. We observed 81 sections of stem villi that showed cross-sectional profiles of paired vessels in their center. Both vascular walls contained a large amount of extracellular matrix and no elastic lamina between smooth muscle cells of the media, making identification of the artery and the vein quite difficult at first sight. We then noted that the density of the smooth muscle cell population was always considerably higher in one than the other, and identified the former as artery and the latter as vein on the basis of their connection with larger arteries and veins running on the chorionic plate. Between the paired vessels, the artery had a smaller caliber than the vein, and the ratio of venous to arterial caliber was distributed from 1.0 to 2.5. The thickness of media was usually thicker in the vein than in the artery. Clusters of elastic fibers were found occasionally in the media of arteries and veins, and basement membrane-like materials were associated frequently with the elastic fibers and were distributed widely in the media as well as in the adventitia. In the veins, the smooth muscle cells of the most superficial part of the media contained well-developed rough endoplasmic reticulum and Golgi apparatus, indicating differentiation to secrete extracellular matrices. The present study revealed the difference of wall structure between arteries and veins in the placental stem villi for the first time at the ultrastructural level, and suggested differentiation of venous smooth muscle cells, possibly by some influence from the luminal side.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004290050239
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  • 10
    Electronic Resource
    Electronic Resource
    The anchoring zone in the human placental amnion: bunches of oxytalan and collagen connect mesoderm and epithelium (1999)
    Springer
    Anatomy and embryology 200 (1999), S. 81-90 
    Details
    ISSN: 1432-0568
    Keywords: Key words Elastic fibre system ; Microfibrils ; Collagen type IV ; Ultrastructure ; Immunocytochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  This study deals with the examination of the elastic fibre system as well as collagen fibrils and collagen type IV in the amnion of the human chorionic plate of uncomplicated pregnancies at term. In organs other than placenta, the elastic fibre system comprises elastic fibres, elaunin and oxytalan microfibrils. The investigation was performed by light and electron microscopy and immunocytochemistry. Abundant oxytalan fibres were present in all amnionic layers, while no elastic fibres were found. Oxytalan microfibrils formed a broad subepithelial layer and were intermingled with collagen fibrils in the subjacent compact layer and in the amnionic mesoderm. Light microscopically, bunches containing orcein-stained oxytalan and collagen-type-IV-immunostained microfibrils were seen rising from the amnionic mesoderm perpendicularly towards the epithelial layer, where they obviously inserted. It can be assumed that the subepithelial microfibrillar layer and the following compact layer form an anchoring zone between the amnionic mesoderm and the epithelium that may contribute to the maintenance of strength. The ultrastructure of the bunches clearly showed collagen fibrils mixed with oxytalan microfibrils. No collagen type I-immunostaining was found in the bunches. After pretreatment of cryostat sections with elastase, oxytalan-orcein-staining was absent, but collagen type IV-immunoreactivity was not altered. Furthermore, after oxytalan-orcein-staining resp. anti-collagen type IV incubation, all positive fibres revealed an identical morphological pattern. We propose that oxytalan and collagen type IV may represent further members of the microfibril complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004290050262
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  • 11
    Electronic Resource
    Electronic Resource
    Familial inclusion body myopathy with desmin storage (1999)
    Springer
    Acta neuropathologica 97 (1999), S. 509-514 
    Details
    ISSN: 1432-0533
    Keywords: Key words Hereditary inclusion body myopathy ; Desmin storage myopathy ; Ultrastructure ; Immmunocytochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We report two adult familial cases of inclusion body myopathy (IBM) with desmin storage in skeletal muscle. Clinically, both patients presented late-onset, progressive, symmetrical, both proximal and distal muscle weakness. Muscle biopsy findings were identical in both cases and consisted of marked variability in fiber size, increased number of central nuclei and vacuolation involving 10% of fibers. Single or multiple vacuoles were located subsarcolemmally or in the center, and were rimmed by basophilic material. At the ultrastructural level, tubulofilamentous nuclear and cytoplasmic inclusions of 16–21 nm in diameter were frequently observed. In addition, large subsarcolemmal and central deposits composed of electron-dense granular material were present in many fibers. Immunocytochemistry revealed staining for desmin, vimentin and ubiquitin within both inclusions and vacuolated fibers. Possible structural and functional associations between these two types of muscle changes remain unclear. They may either represent two coexistent disease processes or merely reflect an abnormal form of muscle fiber degradation, with unidentifiable specificity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004010051021
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  • 12
    Electronic Resource
    Electronic Resource
    Larva-adult relationships in an ancestral dipteran: A re-examination of sensillar pathways across the antenna and leg anlagen of Chaoborus crystallinus (DeGeer, 1776; Chaoboridae) (1999)
    Springer
    Development genes and evolution 209 (1999), S. 103-112 
    Details
    ISSN: 1432-041X
    Keywords: Key words Imaginal disc ; Axonal trajectories ; Ultrastructure ; Chaoborus (Insecta ; Diptera)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In one of his classical studies on insect metamorphosis, Weismann compared the imaginal anlagen of the ancestral phantom midge, Chaoborus, with those of advanced brachycerans. We have expanded his findings on the relationships between larval and imaginal organs using electron microscopy and cobalt backfilling of the antenna and leg anlagen and the axonal trajectories of corresponding larval sensilla. We show that both primordia are confluent with the larval antennae and ”leg” sensilla (an ancestral Keilin organ), respectively. These fully developed larval organs represent the distal tips of the imaginal anlagen rather than separate cell clusters. The axons of the larval antenna and leg sensilla project across the corresponding anlagen to their target neuromeres within the central nervous system (CNS). Within the discs, nerves composed of these larval axons, developing afferent fibres and efferences ascending from the CNS are found. Both the structure of the primordia and the axonal trajectories thus relate the situation found in advanced brachycerans with that seen in more ancestral insects. In addition, the larval antennae, legs, wings and even the eyes possess very similar afferent pioneer trajectories supporting the idea that the described pattern is generally used in the ontogeny of sensory systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050232
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  • 13
    Electronic Resource
    Electronic Resource
    Isolation and characterization of a Clostridium sp. with cinnamoyl esterase activity and unusual cell envelope ultrastructure (1999)
    Springer
    Archives of microbiology 172 (1999), S. 139-149 
    Details
    ISSN: 1432-072X
    Keywords: Key wordsClostridium xylanolyticum ; Cinnamic acid ; Esterase ; Lignocellulose ; Sporogenesis ; Ultrastructure ; Cell envelope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microorganisms that hydrolyse the ester linkages between phenolic acids and polysaccharides in plant cell walls are potential sources of enzymes for the degradation of lignocellulosic waste. An anaerobic, mesophilic, spore-forming, xylanolytic bacterium with high hydroxy cinnamic acid esterase activity was isolated from the gut of the grass-eating termite Tumilitermes pastinator. The bacterium was motile and rod-shaped, stained gram-positive, had an eight-layered cell envelope, and formed endospores. Phylogenetic analysis based on 16S rRNA indicated that the bacterium is closely related to Clostridium xylanolyticum and is grouped with polysaccharolytic strains of clostridia. A wide range of carbohydrates were fermented, and growth was stimulated by either xylan or cellobiose as substrates. The bacterium hydrolysed and then hydrogenated the hydroxy cinnamic acids (ferulic and p-coumaric acids), which are esterified to arabinoxylan in plant cell walls. Three cytoplasmic enzymes with hydroxy cinnamic acid esterase activity were identified using non-denaturing gel electrophoresis. This bacterium possesses an unusual multilayered cell envelope in which both leaflets of the cytoplasmic membrane, the peptidoglycan layer and the S layer are clearly discernible. The fate of all these components was easily followed throughout the endospore formation process. The peptidoglycan component persisted during the entire morphogenesis. It was seen to enter the septum and to pass with the engulfing membranes to surround the prespore. It eventually expanded to form the cortex, verification for the peptidoglycan origin of the cortex. Sporogenic vesicles, which are derived from the cell wall peptidoglycan, were associated with the engulfment process. Spore coat fragments appeared early, in stage II, though spore coat formation was not complete until after cortex formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050753
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  • 14
    Electronic Resource
    Electronic Resource
    Studies of lectin receptors of rat microglia in culture: receptor distribution and internalization (1999)
    Springer
    Experimental brain research 124 (1999), S. 89-99 
    Details
    ISSN: 1432-1106
    Keywords: Key words Microglial culture ; Brain macrophages ; Isolectin ; Ultrastructure ; Intracellular pathway
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The present study examined the lectin labeling of diverse morphological forms of microglia in culture. Similar to amoeboid microglial cells in vivo, polymorphic microglia showed lectin labeling at their plasma membranes, as well as in a few cytoplasmic vesicles and vacuoles. This labeling pattern was observed in cultured microglia incubated with isolectin at 4°C for 30 min. Five minutes after the temperature was raised to 37°C, the surface lectin receptors appeared to be internalized, as shown by the occurrence of many subsurface lectin-labeled vesicles, vacuoles and tubule-like structures. With longer incubation (up to 1–2 h at 37°C), many lysosomes and a few trans-Golgi saccules and associated lysosome-like structures became labeled. Concomitant with these changes was a reduction of lectin labeling at the plasma, with labeling having vanished in most of the cells after 1–2 h of incubation. By 24 h, only a few cells retained surface lectin labeling. It appears, therefore, that irrespective of morphology, lectin labeling (including its intracellular pathway) of microglia in culture parallels that of amoeboid microglia in vivo. This would offer a useful model for the study of lectin turnover in microglia and help to explain the roles of such receptors in microglial differentiation and function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050603
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  • 15
    Electronic Resource
    Electronic Resource
    Light and electron microscopic immunohistochemical observations of p75 nerve growth factor receptor-immunoreactive dermal nerves in prurigo nodularis (1999)
    Springer
    Archives of dermatological research 291 (1999), S. 14-21 
    Details
    ISSN: 1432-069X
    Keywords: Key words p75 nerve growth factor receptor ; (p75 NGFr) ; Immunoreactivity ; Ultrastructure ; Prurigo nodularis ; Nerve fiber
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Prurigo nodularis is an inflammatory skin disease characterized by neurohyperplasia. Neurotrophins and their receptors play a critical role in nerve growth, differentiation, maturation and maintenance, including cutaneous nerve fiber growth and innervation. They may also be responsible for events related to the growth and differentiation control of keratinocytes. To explore the exact distribution of the p75 low-affinity nerve growth factor receptor (p75 NGFr) in the cutaneous nerve components, p75 NGFr immunofluorescence as well as ultrastructural immunohistochemical studies were performed on prurigo nodularis lesional skin and normal human skin samples. The immunofluorescence results revealed that nerve fibers and bundles were increased in number and size in lesional upper dermis with stronger p75 NGFr immunoreactivity than in the corresponding normal tissue. At the ultrastructural level, a lot of nerve fibers clustered together in the prurigo nodularis dermal tissue. The axons were enlarged and branched, but the axons themselves seldom showed any NGFr immunoreactivity. The Schwann cell bodies were extended and irregularly shaped, and tended to separate into many branches enveloping the axons. The Schwann cell membrane showed strong p75 NGFr immunoreactivity. The perineurium cells also revealed strong p75 NGFr immunoreactivity. The Schwann cells inside the perineurium were less p75 NGFr-immunoreactive than those outside the perineurium. The membrane of certain basal keratinocytes showed NGFr immunoreactivity as well. The present results indicate that overexpression of p75 NGFr in Schwann cells and perineurium cells could contribute to the neurohyperplasia in prurigo nodularis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004030050378
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  • 16
    Electronic Resource
    Electronic Resource
    The effects of cold-restraint stress on urinary bladder wall compared with interstitial cystitis morphology (1999)
    Springer
    Urological research 27 (1999), S. 454-461 
    Details
    ISSN: 1434-0879
    Keywords: Key words Cold-restraint stress ; Urinary bladder ; Interstitial cystitis ; Mast cell ; Urothelium ; Ultrastructure ; Ruthenium red ; Flow cytometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Stress is associated with many diseases of unknown aetiology. This study demonstrates the effects of cold-restraint stress on the morphology of the urinary bladder. Additionally, it compares the results obtained with the morphology of the interstitial cystitis. The animals were subjected to three hours of cold-restraint stress and then starved for 48 h. The morphology and histochemistry of the urinary bladder was investigated with light and electron microscopy. The proliferative activity was analysed via flow cytometry. Increased and degranulated mast cells in the mucosa, leucocyte infiltration in the lamina propria, vacuole formation in the urothelial cells, loose tight junction, dilated intercellular spaces and altered proliferative activity were observed in the stress group when compared with the control. The increase in the number of mast cells and especially degranulated mast cells and vacuole formation and the loose tight junction of the urothelium correlated with the histopathological findings of interstitial cystitis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002400050135
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  • 17
    Electronic Resource
    Electronic Resource
    Anatomical and ultrastructural changes of the floral nectary ofPisum sativum L. during flower development (1999)
    Springer
    Protoplasma 206 (1999), S. 57-72 
    Details
    ISSN: 1615-6102
    Keywords: Anatomy ; Floral nectary ; Modified stomata ; Phloem ; Pisum sativum ; Stereology ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The floral nectary ofPisum sativum L. is situated on the receptacle at the base of the gynoecium. The gland receives phloem alone which departed the vascular bundles supplying the staminal column. Throughout the nectary, only the companion cells of the phloem exhibited wall ingrowths typical of transfer cells. Modified stomata on the nectary surface served as exits for nectar, but stomatal pores developed well before the commencement of secretion. Furthermore, stomatal pores on the nectary usually closed by occlusion, not by guard-cell movements. Pore occlusion was detected most frequently in post-secretory and secretory glands, and less commonly in pre-secretory nectaries. A quantitative stereological study revealed few changes in nectary fine structure between buds, flowers secreting nectar, and post-secretory flowers. Dissolution of abundant starch grains in plastids of subepidermal secretory cells when secretion commenced suggests that starch is a precursor of nectar carbohydrate production. Throughout nectary development, mitochondria were consistently the most plentiful organelle in both epidermal and subepidermal cells, and in addition to the relative paucity of dictyosomes, endoplasmic reticulum, and their associated vesicles, the evidence suggests that floral nectar secretion inP. sativum is an energy-requiring (eccrine) process, rather that granulocrine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279253
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  • 18
    Electronic Resource
    Electronic Resource
    Structure and function of the human oocyte-cumulus-corona cell complex before and after ovulation (1999)
    Springer
    Protoplasma 206 (1999), S. 270-277 
    Details
    ISSN: 1615-6102
    Keywords: Cumulus oophorus ; Ovarian follicle ; Fertilization ; Ultrastructure ; Immunocytochemistry ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The fine structure of the human cumulus oophorus has been reviewed on the basis of scanning and transmission electron microscopic observations as well as of immunofluorescence data. Tissues sampled from preovulatory ovarian follicles and cumulus-enclosed oocytes and fertilized eggs (collected from the oviduct or obtained during in vitro fertilization procedures) have been evaluated from a microtopographic and morphodynamic point of view in order to better clarify the possible role of this population of cells. In particular, the following aspects have been studied and discussed: the presence of multiple close contacts (modulated by the interposition of the zona pellucida) between the oocyte surface and the long microvillous evaginations projecting from the inner aspect of corona cells surface (through these structures the intraovarian cumulus oophorus may control oocyte growth and metabolism up until the time of ovulation); the occurrence of different subpopulations of cells (steroid-synthetic cells, cells producing adhesive proteins, leukocytes, macrophages) in the postovulatory, extraovarian cumulus oophorus surrounding oocytes, zygotes and early developing embryos. All these elements found in the cumulus mass may positively act, through their paracrine activities, on the chemical composition of the microenvironment in which fertilization occurs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288215
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  • 19
    Electronic Resource
    Electronic Resource
    Ultrastructural features of the myocardium of children with dilated cardiomyopathy (1999)
    Springer
    Heart and vessels 14 (1999), S. 52-56 
    Details
    ISSN: 1615-2573
    Keywords: Endomyocardial biopsy ; Dilated cardiomyopathy ; Children ; Ultrastructure ; Basal lamina layering of capillary
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We analyzed the electron-microscopic features of endomyocardial biopsy from pediatric patients with dilated cardiomyopathy (DCM). The specimens examined were taken from the right ventricle of ten patients aged from 2 to 15 years (mean 9.7 years). Biopsy specimens from eight patients with congenital heart disease (tetralogy of Fallot), aged from 3 to 12 (mean 7.3 years), and ten adult patients with DCM, aged from 32 to 60 (mean 45 years), were also examined. Patients considered to have endocardial fibroelastosis, arrhythmogenic right ventricular cardiomyopathy, specific cardiomyopathy, or coronary heart disease were excluded from this study. Specimens from pediatric patients with DCM showed various degrees of ultrastructural abnormalities of myocytes, including myofibrillar fragmentation, mitochondrial abnormalities, and intracellular edema. The ultrastructurally determined contractility failure index based on the severity of myocardial degeneration at the electronmicroscopic level was 4.9 ± 1.1. This value was significantly higher than that in patients with tetralogy of Fallot (0.9 ± 0.6,P 〈 0.001) but was not significantly different from that in adult patients with DCM (6.1 ± 2.6). The index of pediatric patients with DCM who died within 3 years was high (6.0 ± 0.8). Basal lamina layering of a capillary (BLL) in the myocardium was revealed in 1 of the 10 (10%) pediatric patients with DCM and in 6 of the 10 (60%) adult patients with DCM (P 〈 0.05). No BLL was noted in the patients with tetralogy of Fallot. These findings may be related to the pathogenesis of DCM in children and adults.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02481742
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  • 20
    Electronic Resource
    Electronic Resource
    Effect of high-level oxygen exposure on the peroxidase activity and the neuromelanin-like pigment content of the nerve net in the earthworm, Lumbricus terrestris (1999)
    Springer
    Cell & tissue research 295 (1999), S. 349-354 
    Details
    ISSN: 1432-0878
    Keywords: Key words Neuromelanin ; Neuron ; Peroxidase ; Oxygen metabolism ; High-definition light microscopy ; Electron microscopy ; Ultrastructure ; Cytochemistry ; Substantia nigra ; Lumbricusterrestris (Annelida)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Histochemical examination of 1-μm tissue sections from the dorsal nerve plexus of the earthworm, Lumbricus terrestris, reveals multiple brown intraneuronal granules. These granules contain material morphologically and histochemically consistent with neuromelanin. When viewed with transmission electron microscopy, these were seen as single membrane-enclosed biphasic granules with diameters of 370–730 nm. Exposure of L. terrestris to high-level environmental oxygen resulted in an increase in the number of neuromelanin-like pigment granules within the neurons of the circular muscle layer. As measured by ortho-phenylenediamine hydrochloride, the endogenous peroxidase activity of extracts from worms incubated in high-level environmental oxygen was 51% more than controls. The endogenous peroxidase activity was localized in situ with 3,3-diaminobenzidine (DAB) and was found to increase in and around the neuromelanin-like pigment-containing neurons within the circular muscle layer. These studies suggest that the nerve net of L. terrestris may serve as a model to study the role of neuromelanin production in oxidative stress and its relationship to endogenous peroxidases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051241
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  • 21
    Electronic Resource
    Electronic Resource
    Echinococcus granulosus: praziquantel treatment against the metacestode stage (1999)
    Springer
    Parasitology research 85 (1999), S. 999-1006 
    Details
    ISSN: 1432-1955
    Keywords: Key wordsEchinococcus granulosus ; Praziquantel ; Metacestode ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The efficacy of praziquantel against the metacestode of Echinococcus granulosus was studied by means of in vitro incubations or in vivo experiments. The results of in vitro incubations indicated that the effectiveness of praziquantel was higher when the parasite material comprised cysts from cyst masses than in the case of intact cysts that retained their adventitial layer. Ultrastructural alterations in the germinal layer of collapsed cysts incubated in vitro were detected. The results obtained in mice after 4 months of treatment demonstrated no significant difference between the control and treated groups with regard to the number and wet weight of developed cysts. However, ultrastructural alterations were detected in the cyst tissue that were similar to those described in the in vitro experiment. In contrast, the effect of chemoprophylaxis on the number and the wet weight of developed cysts was extremely significant as compared with the control value, the efficacy being 99.41% and 98.32%, respectively. Moreover, ultrastructural observations of the cyst tissue revealed loss of its integrity, and no intact cyton was observed in the germinal layer of the developed cyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004360050672
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  • 22
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    Electronic Resource
    Morphology and ultrastructure of the anterior adhesive areas of the capsalid monogenean parasites Benedenia rohdei from the gills and B. lutjani from the pelvic fins of Lutjanus carponotatus (Pisces: Lutjanidae) (1999)
    Springer
    Parasitology research 85 (1999), S. 399-408 
    Details
    ISSN: 1432-1955
    Keywords: Key words Monogenea ; Capsalidae ; Benedenia rohdei ; B. lutjani ; Ectoparasites ; Lutjanus carponotatus ; Glands ; Ultrastructure ; Adhesion ; Attachment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The anterior adhesive areas of Benedenia rohdei from the gills and B. lutjani from the pelvic fins of Lutjanuscarponotatus at Heron Island, Australia, were studied using scanning and transmission electron microscopy. All specimens were fixed when detached from host tissue. Both monogenean species have two disc-like anteroventral attachment organs, each of which has an anterolateral adhesive area divided into three adjacent zones by tegument from the ventral surface of the attachment organ. A rod-shaped secretion and a smaller, roughly spherical secretion are associated with the anterior adhesive areas in both species; a third type of secretion occurs anteriorly but outside these adhesive areas. The electron-dense spherical secretory bodies released onto the anterior adhesive zones in these Benedenia spp. are of a single type and differ ultrastructurally from those previously reported in monogeneans living on teleost hosts. A correlation, therefore, between secretion morphology and host type is not supported. No relationship was found between parasite microhabitat and secretion morphology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004360050566
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  • 23
    Electronic Resource
    Electronic Resource
    Electrophysiological and ultrastructural correlates of cryoinjury in sciatic nerve of the freeze-tolerant wood frog, Rana sylvatica (1999)
    Springer
    Journal of comparative physiology 169 (1999), S. 351-359 
    Details
    ISSN: 1432-136X
    Keywords: Key words Freeze tolerance ; Sciatic nerve ; Cryoinjury ; Dehydration ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We investigated function and ultrastructure of sciatic nerves isolated from wood frogs (Rana sylvatica) endemic to the Northwest Territories, Canada, following freezing at −2.5 °C, −5.0 °C, or −7.5 °C. All frogs frozen at −2.5 °C, and most frogs (71%) frozen at −5.0 °C, recovered within 14 h after thawing began; however, frogs did not survive exposure to −7.5 °C. Sciatic nerves isolated from frogs frozen at −7.5 °C were refractory to electrical stimulation, whereas those obtained from frogs surviving exposure to −2.5 °C or −5.0 °C generally exhibited normal characteristics of compound action potentials. Frogs responded to freezing by mobilizing hepatic glycogen reserves to synthesize the cryoprotectant glucose, which increased 20-fold in the liver and 40-fold in the blood. Ultrastructural analyses of nerves harvested from frogs in each treatment group revealed that freezing at −2.5 °C or −5.0 °C had little or no effect on tissue and cellular organization, but that (lethal) exposure to −7.5 °C resulted in marked shrinkage of the axon, degeneration of mitochondria within the axoplasm, and extensive delamination of myelin sheaths of the surrounding Schwann cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600050231
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  • 24
    Electronic Resource
    Electronic Resource
    Intranuclear inclusions of meningioma associated with abnormal cytoskeletal protein expression (1999)
    Springer
    Brain tumor pathology 16 (1999), S. 86-91 
    Details
    ISSN: 1861-387X
    Keywords: Meningioma ; Intranuclear inclusion ; Immunohistochemistry ; Ultrastructure ; Intermediate filament
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We describe a case of meningothelial meningioma with a large number of intranuclear inclusions. Morphologically, these are divided into cytoplasmic inclusions and nuclear vacuoles. The cytoplasmic inclusion has a limiting membrane with cell organelles and filaments. Inclusions of this type are generally eosinophilic, like the cytoplasm. However, there are many inclusions that are more eosinophilic than the cytoplasm or that have a ground-glass appearance. Some of them may contain fine or coarse granules. On the other hand, the nuclear vacuole lacks a limiting membrane and appears empty. In most of the inclusions of this type, there is a faintly basophilic substance in the margin. Generally, the cytoplasmic inclusions are as immunopositive as cytoplasm with vimentin, but some of these cytoplasmic inclusions are more reactive. Under the electron microscope, abnormal aggregation of intermediate filaments is recognized in the cytoplasmic inclusions. It is considered that a strong reaction of cytoplasmic inclusions with vimentin immunostaining is due to abnormal aggregation of intermediate filaments. The present study distinctly demonstrates abnormal localization of intermediate filaments in the cytoplasmic inclusions, and it is suggested that the cytoskeleton participates in the evolution of the cytoplasmic inclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02478908
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  • 25
    Electronic Resource
    Electronic Resource
    Nucleophilic Aromatic Substitution of Hydrogen in the Reaction of tert-Alkylamines with Nitrosobenzenes - Synthesis and NMR Study of N-(tert-Alkyl)-ortho-nitrosoanilines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 29-35 
    Details
    ISSN: 1434-193X
    Keywords: Nitrosobenzenes ; ortho-Nitrosoanilines ; 2-Nitroso-1,3-phenylenediamines ; Nucleophilic aromatic substitution ; Oxidative nucleophilic substitution of hydrogen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of primary amines bearing tertiary alkyl groups (e.g. R-NH2; R = tBu, 1-adamantyl) with nitrosobenzenes has been found to proceed by oxidative nucleophilic aromatic substitution of hydrogen, thereby affording N-(tert-alkyl)-ortho- and -para-nitrosoanilines. The replacement of hydrogen proceeds more rapidly than the replacement of ortho- or para-nitro or -bromo substituents. With p-nitronitrosobenzene, both ortho-hydrogen atoms are substituted to afford N,N′-di(tert-alkyl)-4-nitro-2-nitroso-1,3-phenylenediamines 8a,b. The addition of oxidizing agents (e.g. MnO2) increases the yield of products. 1H-, 13C-, 14N- and 15N-NMR studies have confirmed the structures of the compounds under investigation. In ortho-nitrosoanilines, the rotamer with the nitroso group syn to the amino group is favored.
    Additional Material: 3 Tab.
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  • 26
    Electronic Resource
    Electronic Resource
    Photochemistry of 9,10-Dicarbonyl-9,10-dihydroanthracene - A Source of 9,10-Dehydroanthracene? (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 57-60 
    Details
    ISSN: 1434-193X
    Keywords: Benzyne ; Dehydroanthracene ; Matrix isolation ; Photochemistry ; Bergman reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -9,10-Didehydroanthracene (1) is an interesting derivative of p-benzyne that has been subject of several studies. In contrast to an earlier report, the photochemical decarbonylation of 9,10-dicarbonyl-9,10-dihydroanthracene (2) does not lead to 1 but rather to the ring-opened ene-diyne 4. The key intermediate for this reaction is keto carbene 7 which is formed by monodecarbonylation of 2. Carbene 7 is labile towards visible-light irradiation and easily looses the second CO molecule to give 4. Carbene 7 and diyne 4 are characterized by IR and UV/Vis spectra, the IR spectra are compared to calculations at the B3LYP/6-31G(d,p) level of theory.
    Additional Material: 2 Ill.
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  • 27
    Electronic Resource
    Electronic Resource
    Reversal Diastereofacial Selectivity in the n-Butyllithium Addition to O-Protected N-Trimethylsilylimines of (2S)-Lactal: Enthalpic versus Entropic Contributions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 61-65 
    Details
    ISSN: 1434-193X
    Keywords: Nucleophilic addition ; Solvent effect ; Reversal of diastereoselectivity ; Temperature effect ; Imines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Commonly observed, but rarely explored, is the possibility of modifying the diastereomeric excess (de%) by means of temperature. A complete reversal in the diastereofacial selectivity could be obtained whenever the diastereoisomers concerned are differentially favored by enthalpy and entropy. The enthalpic or entropic dominance of a diastereoisomer depends greatly on the reaction solvent used.
    Additional Material: 1 Ill.
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  • 28
    Electronic Resource
    Electronic Resource
    Syntheses of Donor-Acceptor-Substituted 2,6-Stellanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 73-81 
    Details
    ISSN: 1434-193X
    Keywords: Donor-acceptor systems ; Cage compounds ; Stelladione ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A number of condensations could be carried out using tricyclo[3.3.0.03,7]octane-2-one (stellanone, 4) and tricyclo[3.3.0.03,7]octane-2,6-dione (2,6-stelladione, 5) as starting materials. The components for condensations were 2-trimethylsilyl-1,3-dithiane (6), 1,1-bis(trimethylsilyl)-1H-cyclopropa[b]naphthalene (7), its 3,6-dimethoxy-substituted analogue 8, fluorene (12), xanthene (13), diethyl malonate (14), and malononitrile (15). The condensation reactions with 5 yielded mono- and disubstituted products, among them were the donor-acceptor-substituted 2,6-stellanes 33-35. The structures of 18 (prepared from stellanone and fluorene), 19, 24, 27, 31 and 32 (synthesized by condensation of 2,6-stelladione and 2-trimethylsilyl-1,3-dithiane and malononitrile, respectively) were determined by X-ray crystallography.
    Additional Material: 1 Ill.
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  • 29
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    Electronic Resource
    Synthesis of ω-Nitro Acids and ω-Amino Acids by Ring Cleavage of α-Nitrocycloalkanones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 87-90 
    Details
    ISSN: 1434-193X
    Keywords: Water ; α-Nitrocycloalkanones ; ω-Nitro acids ; Surfactant ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of various α-nitrocycloalkanones 1 with aqueous 0.05 M NaOH, at 80 °C, in the presence of cetyltrimethylammonium chloride (CTACl) as a cationic surfactant, produces ω-nitro acids 2 in good yields. Reduction of the latter with HCOONH4/Pd-C, in methanol, at 80 °C affords ω-amino acids 3. The synthesis of methyl 9-oxodecanoate (8) is also reported.
    Additional Material: 2 Tab.
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  • 30
    Electronic Resource
    Electronic Resource
    On the Selective O-Alkylation of Ambident Nucleophiles - The Synthesis of Thiohydroxamic Acid O-Esters by Phase-Transfer Reactions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 97-106 
    Details
    ISSN: 1434-193X
    Keywords: O-Alkylation ; Ambident nucleophile ; Thiazolethione ; Thiohydroxamic acid ; Phase-transfer reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -O-Alkylation of cyclic thiohydroxamic acids 1 and 3-5 has been studied with a view to developing an efficient method for the synthesis of N-(alkoxy)pyridine-2(1H)-thiones and N-(alkoxy)thiazole-2(3H)-thiones. Four issues have been addressed and the following conclusions can be drawn: (i) Thiones 1 and 5 exist as O-H acids in the solid state. (ii) According to NMR investigations (1H, 13C), the thione structures should be largely retained in CDCl3, [D6]DMSO, and CD3OD solutions of acids 1, 3-5, as is also the case for pyridinethione salts 2a-h. (iii) O-Alkylation of pyridinethione salts occurs in competition with S-alkylation. Selective O-alkylation is however possible, if thiohydroxamate salts with large countercations, such as M = NBu4, are treated with hard alkylating reagents in polar aprotic media. (iv) As tetrabutylammonium thiohydroxamates, such as 2f, are highly useful in the synthesis of cyclic thiohydroxamic acid O-esters, we have developed an efficient protocol for the preparation of N-(alkoxy)pyridine-2(1H)-thiones directly from acid 1 using phase-transfer conditions (alkyl halide or sulfonic acid ester, CH3CN, K2CO3, Bu4NHSO4). This method has proved particularly successful for the synthesis of N-(alkoxy)thiazole-2(3H)-thiones 11, 20-28, which were obtained in yields of up to 87%.
    Additional Material: 2 Ill.
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  • 31
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    Stereoselective Synthesis of the Pheromone (R)-(-)-Sulcatol, and Its Enantiopure (R)- and (S)-1-Mono-, -1,1-Di-, and -1,1,1-Trifluoro Analogues[1] (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 117-127 
    Details
    ISSN: 1434-193X
    Keywords: Fluorine ; Pheromones ; Sulfoxides ; Sulcatol ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The pheromone (R)-(-)-sulcatol (10a) and three of its enantiomeric mono-, di-, and trifluoro analogues 10b-d have been synthesized, in six steps and with good overall yields, starting from chiral (R)-2-methyl-5-[(4-methylphenyl)sulfinyl]pent-2-ene (1) and commercially available fluorinated or non-fluorinated acetates.Supporting information for this article is available on the WWW under http://www.wileY-Vch.de/contents/jc_2046/1999/98375_s.pdf or from the author.
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  • 32
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    Stereoselective Synthesis of Enantiomerically Pure β-Fluoroalkyl γ-Butyrolactones by Sulfoxide-Directed Lactonization (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 111-115 
    Details
    ISSN: 1434-193X
    Keywords: Fluorine ; Lactones ; Annulation ; Ketene ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Enantiomerically pure α,α-dichloro β-fluoroalkyl γ-p-tolylthio γ-butyrolactones trans-6a-c have been obtained with excellent stereocontrol (〉 98:2) and enantiomeric purity (〉 98:2) by sulfoxide-directed lactonization (Marino's annu-lation reaction) of β-fluoroalkyl vinyl sulfoxides (R)-(E)-5a-c with dichloroketene. Highly chemoselective dechlorination and desulfurization reactions performed on trans-6c efficiently provided the β-chlorodifluoromethyl γ-butyrolactone (S)-8c, the absolute stereochemistry of which was determined by X-ray diffraction analysis of its γ-p-tolylthio precursor (2R,3S)-7c.
    Additional Material: 1 Ill.
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  • 33
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    Nickel- or Iron-Catalyzed Coupling of Lithiated Methylthiomethyl p-Tolyl Sulfone with Lithiated Alkyl Sulfones to Give Methylthioalkenes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 163-165 
    Details
    ISSN: 1434-193X
    Keywords: Alkenes ; Methylthiomethyl sulfone ; Carbenoids ; Hetero-substituted carbanions ; Vinyl sulfides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of methylthiomethyl p-tolyl sulfone with alkyl sulfones when lithiated gives regioselectively vinyl sulfides in high yields in the presence of Ni(acac)2 or Fe(acac)3.
    Additional Material: 2 Ill.
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    Experimental Evidence for Intramolecular Attractive Nonbonded C-F…H-C Interactions in 2′,3′-Dideoxy-4′-(fluoromethyl)nucleosides - Through-Space JCF and JHF NMR Coupling Constants, Correlation with Empirical Parameters of Solvent Polarity and Single-Crystal X-ray Structures (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 187-196 
    Details
    ISSN: 1434-193X
    Keywords: Fluorinated dideoxynucleosides ; Through-space interactions ; Hydrogen bonds ; Long-range coupling constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A collection of 5′-O-benzyl-2′,3′-dideoxy-4′-(fluoromethyl)nucleosides carrying both purinic and pyrimidinic nucleobases (uracil, 5-Br-uracil, 5-O2N-uracil, 6-Cl-purine and inosine) were synthesized in both the α and the β form. Through-space-transmitted 6JCF NMR coupling constants between F and C-6 (pyrimidinic base) or C-8 (purinic base) were observed for all of the α anomers of the compounds examined, whilst the corresponding 7JHF coupling constants were resolved only for the 5-substituted uracil derivatives. The absolute values of all the through-space couplings were found to decrease monotonically with increasing solvent polarity (CDCl3, MeOD, [D6]acetone, [D6]DMSO). This trend suggests that the through-space interaction is mediated by an intramolecular (sp3)C-F…H-C(sp2) hydrogen bond. The possibility of any relevant solvent-induced conformational change influencing the F/base mutual spatial relationship in the molecules investigated was ruled out by heteronuclear steady-state 1H{19F}-NOE experiments. A linear correlation was observed between 6JCF and 7JHF coupling constants and the Kamlet-Taft's hydrogen bond basicity parameter β. The crystal structures of the α and β anomers of the 5-nitrouracil nucleoside show evidence that the H-6 of the nucleobase forms hydrogen-bond-like interactions involving the O-benzyl oxygen atom in the β anomer, and that in the case of the α anomer this is replaced by the F atom of the fluoromethyl group.
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    Electronic Resource
    2,3-Dialkynyl-1,4-diazabuta-1,3-dienes as Novel π-Systems: Synthesis, Structure, and Electronic Properties (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 205-214 
    Details
    ISSN: 1434-193X
    Keywords: Alkynes ; Cyclic voltammetry ; Diazabutadienes ; Electronic structure ; UV/Vis spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The introduction of alkynyl groups into the 2,3-positions of the 1,4-diazabuta-1,3-diene (DAD) backbone succeeds along two complementary synthetic routes either by condensing triisopropylsilyl-terminated dialkynyl-1,2-diones with primary aromatic amines or by a palladium-mediated alkynylation of bis(imidoyl chlorides). X-ray crystallographic analyses of two dialkynyl DAD derivatives reveals their planar (E-s-trans-E) conformations in the solid state. However, the central CC bond of both DAD backbones investigated has a length of 1.491(2) Å, and is therefore too long to indicate efficient delocalization across the DAD core. The UV/Vis spectra of dialkynyl DADs demonstrate that their absorptions in comparison to those of non-alkynyl DADs are bathochromically shifted by more than 40 nm, thereby demonstrating the suitability of the title compounds for developing NIR chromophores. The electron absorption properties of differentially N,N′-disubstituted dialkynyl DADs gave no indication for a push-pull effect across the DAD skeleton and suggest the ynimine moiety as the active chromophore of dialkynyl DADs. The electrochemical properties of the title compounds were determined by cyclo- and steady state voltammetry and show that introducing alkynyl groups leads to more easily reducible DAD systems. Again, the perception of dialkynyl DADs as covalently linked, but electronically decoupled ynimine units is corroborated by the redox potential of a differentially N,N′-disubstituted dialkynyl DAD. Similar conclusions were drawn from semiempirical MO (PM3) calculations of dialkynyl DADs.
    Additional Material: 5 Ill.
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  • 36
    Electronic Resource
    Electronic Resource
    Synthesis and Biological Activity of Phosphonate Analogs of Mannose 6-Phosphate (M6P) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 447-450 
    Details
    ISSN: 1434-193X
    Keywords: Phosphonate analogs ; Mannose 6-phosphate (M6P) ; M6P receptors ; Recognition markers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two phosphonate analogs of mannose 6-phosphate (M6P) have been synthesized. The isosteric analog 1 was obtained by a Wittig-Horner reaction at position 6 of a sugar aldehyde. The non-isosteric analog 2 was obtained by a Michaelis-Arbuzov rearrangement of a 6-bromo derivative. In contrast to the non-isosteric analog 2, the isoster 1 was shown to bind to M6P receptors as effectively as does M6P itself, thus demonstrating the considerable potential of the system in drug design.
    Additional Material: 1 Ill.
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  • 37
    Electronic Resource
    Electronic Resource
    Isopulegol as a Model Compound: Metalation and Substitution of an Allylic Position in the Presence of an Unprotected Hydroxy Function (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 459-462 
    Details
    ISSN: 1434-193X
    Keywords: Electrophilic substitution ; Metalations ; Monoterpene ; Protective groups ; Superbase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -When treated with butyllithium and potassium tert-butoxide for 2 h at 0 °C in hexanes, the unsaturated monoterpenic alcohol isopulegol is simultaneously deprotonated at the hydroxy function and the allylic methyl group. The metaloxy allylmetal species thus generated can be silylated, alkylated, carboxylated and oxidized to afford the expected products in good to excellent yields. Thus, a specific protection of hydroxy groups is not required, alcohols being instantaneously converted by superbases into alcoholates.
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  • 38
    Electronic Resource
    Electronic Resource
    Isolation of Cross-Coupling Products in Model Studies on the Photochemical Modification of Proteins by Tiaprofenic Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 497-502 
    Details
    ISSN: 1434-193X
    Keywords: Proteins ; Cross coupling ; Drug research ; Photochemistry ; Toxicology ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -To gain insight into the chemical nature of drug-induced photoallergy, model studies have been carried out on the photochemical modification of proteins by tiaprofenic acid. Irradiation of decarboxylated tiaprofenic acid (DTPA) in the presence of p-cresol leads to C-C- and C-O-connected p-cresol “dimers”, together with DTPA hydrodimers. The p-cresol-DTPA cross-coupling product was not detected in this reaction. However, a product of this type is formed using a more hindered phenol, such as 2,6-di-tert-butylphenol. Similar results are obtained when tiaprofenic acid (TPA) or its methyl ester are used as photosensitizers. The observed formation of “dimers” can be related to protein photo-crosslinking, through the coupling of two tyrosine units. On the other hand, phenol-(D)TPA cross-coupling may be relevant to the understanding of drug-protein photobinding.
    Additional Material: 5 Ill.
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  • 39
    Electronic Resource
    Electronic Resource
    Diastereoselective Addition of Chiral (2-Lithiophenyl)acetaldehyde Acetals to Various Imines as Key Step in the Asymmetric Synthesis of 1-Aryltetrahydroisoquinolines, Part 4 (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 503-517 
    Details
    ISSN: 1434-193X
    Keywords: Enantiomerically pure (2-bromophenyl)acetaldehyde acetals ; Halogen-metal exchange ; Diastereoselective addition to imines ; Asymmetric synthesis ; Tetrahydroisoquinolines ; NMDA antagonists ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A novel asymmetric synthesis of 1-aryl-1,2,3,4-tetrahydroisoquinolines has been developed. The key step in this synthesis is the diastereoselective addition of homochiral (2-lithiophenyl)acetaldehyde acetals to the sulfonylimine 25 and to the arylimines 28 and 31. The best diastereoselectivity is obtained by addition of the bis(2-methoxypropan-2-yl)-substituted 1,3-dioxolane 6e to benzylidene-p-anisidine (31) with an HPLC-determined diastereomeric ratio 32c/33c = 92.1:7.9. The N-tosyl and the N-(4-methoxyphenyl) groups of the addition products 26d, 27d, 32c, and 33c are cleaved with sodium in liquid ammonia and ammonium cerium(IV) nitrate, respectively, to yield the primary amines 35 and 36. The acid-catalysed cyclization of the sulfonamides 26d and 27d and the carbamates 37 and 38, prepared from 35 and 36, leads to the enantiomerically pure dihydroisoquinolines 40 and 41, respectively. During the cyclization of the sulfonamides 26d, 27d and the carbamates 37, 38 the chiral auxiliary - the diol 39 - is cleaved unchanged and can be recovered in good yields.
    Additional Material: 4 Tab.
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  • 40
    Electronic Resource
    Electronic Resource
    Ligand Effects on the Diastereoselectivities of Samarium Diiodide Promoted Pinacol Coupling (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 565-572 
    Details
    ISSN: 1434-193X
    Keywords: Pinacol coupling ; Aldehydes ; Samarium diiodide ; 1,2-Diols ; Diastereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The samarium diiodide pinacol coupling of benzaldehyde and cyclohexanecarboxaldehyde in the presence of a variety of polyethylene glycols, including derivatives containing carbohydrates has been studied. Whereas such complexing agents allow for the formation of 1,2-diols, in the case of benzaldehyde the erythro-isomer predominates with diastereoselectivities of up to 7:1, while with cyclohexanecarboxaldehyde a stereoselectivity of up to 10:1 was observed but in favor of the threo-isomer. This divergence in the stereoselectivity of these two aldehydes suggests the presence of two different mechanisms occurring in these pinacol coupling reactions.
    Additional Material: 5 Ill.
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  • 41
    Electronic Resource
    Electronic Resource
    Thermal Rearrangements of Di- and Triphenyl-Substituted Benzocyclobutenes and Corresponding o-Quinodimethanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 551-563 
    Details
    ISSN: 1434-193X
    Keywords: Benzocyclobutenes ; o-Quinodimethanes ; Pericyclic reactions ; Retrodisproportionation ; 9-Anthryl radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -7,8-Dimethoxy-7,8-diphenyl- (1c), 7,8-dimethyl-7,8-diphenyl- (1d), 7-methoxy-7,8,8-triphenyl- (1e), 7-methyl-7,8,8-triphenyl- (1f), 7-isocyano-7,8,8-triphenyl- (1g), and 7,7,8-triphenylbenzocyclobutene (1h) are amenable to a variety of thermal rearrangements following initial electrocyclic ring-opening to the corresponding 7,8-diphenyl- (2c,d) and 7,8,8-triphenyl-o-quinodimethanes (2e-h). meso-1c was found to undergo a facile meso/rac isomerization at room temperature, indicating that other processes such as a symmetry-forbidden disrotatory ring-opening or a stepwise reaction compete with the symmetry-allowed conrotatory process. An estimate of the energy profile of the 1c/2c reaction system was made by kinetic simulation in combination with oxygen trapping of the intermediate o-quinodimethanes (2c) and semiempirical PM3 calculations, and revealed that the barrier for the symmetry-forbidden pathway is merely about 4 kJ·mol-1 higher than that for the symmetry-allowed one. o-Quinodimethanes 2c, 2g, 2e, and 2h underwent further electrocyclic hexatriene-cyclohexadiene ring-closure to give 4a,10-dihydroanthracene derivatives at temperatures between 20 and 80 °C. The 4a,10-dihydroanthracenes were further transformed to 9,10-disubstituted anthracenes by elimination of methanol or HCN, as well as to 9,10-substituted 9,10-dihydroanthracene derivatives. ESR and ENDOR spectroscopic detection of related 9-anthryl radicals lends support to the view that 9,10-dihydroanthracene products are formed by a homolytic hydrogen-transfer reaction (retrodisproportionation). By way of contrast, the aforementioned transformations play only a minor role in the case of methyl-substituted benzocyclobutenes 1d, 1f as here they are overruled by faster 1,5-H shift reactions of the corresponding o-quinodimethanes 2d, 2f, leading to styrene derivatives.
    Additional Material: 11 Ill.
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  • 42
    Electronic Resource
    Electronic Resource
    Synthesis of Pentathiepanes and Isolation of the Conformers Based on High Inversion Barrier of the Pentathiepane Ring (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 597-605 
    Details
    ISSN: 1434-193X
    Keywords: S Heterocycles ; Cyclic oligosulfides ; Pentathiepanes ; Conformational analysis ; Sulfuration ; Ring inversion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Acenaphtho[1,2-a]acenaphthylene (1) was sulfurated with elemental sulfur to give a pentathiepane derivative (2). A dynamic NMR spectrum analysis revealed that the two naphthalene rings of 2 are chemically nonequivalent up to 100 °C. The pentathiepane ring of 2 was shown to adopt a chair conformation both in solution and crystals. In accordance with the NMR spectrum analysis, the sulfuration of 5-phenylacenaphtho[1,2-a]acenaphthylene (12) gave a pair of conformers (16a and 16b), which were isolated in pure form. The Friedel-Crafts acetylation of 2, followed by dithioacetalization with 1,2-ethanedithiol, also gave a pair of isolable conformers (18a and 18b). These two pairs of conformers isomerized, as a result of the ring inversion, to each other in solution at room temperature in the first-order kinetics. The activation parameters for this process, Ea, ΔH#, and ΔS#, were determined. Based on the experimental observations, a probable mechanism for the inversion process is proposed.
    Additional Material: 2 Ill.
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  • 43
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    Electronic Resource
    Cerium(III) Chloride Catalyzed Michael Reaction of 1,3-Dicarbonyl Compounds and Enones in the Presence of Sodium Iodide Under Solvent-Free Conditions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 617-620 
    Details
    ISSN: 1434-193X
    Keywords: Cerium(III) chloride heptahydrate ; Catalysis ; 1,3-Dicarbonyl compounds ; Enones ; Michael reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Cerium(III) chloride heptahydrate in the presence of sodium iodide catalyses the Michael addition of 1,3-dicarbonyl compounds to α,β-unsaturated ketones and α,β-unsaturated aldehydes with extraordinary efficiency. The very mild conditions allow high chemoselectivity as shown by the absence of the typical side reactions, which can be observed in the conventional base-catalyzed processes. More interestingly, when at least one of the starting materials is liquid at room temperature, the reaction can also be performed without solvents. The CeCl3· 7 H2O/NaI catalyst system can be easily separated from the reaction mixture and it can be reused without an appreciable loss of activity. Advantages of the present procedure, which utilizes cheap and “friendly” reagents, over the previously reported ones, are discussed.
    Additional Material: 1 Ill.
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  • 44
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    Electronic Resource
    Synthesis of γ-Amino- and δ-Amino-Functionalised Ethers, Amines, or Silanes by Hydroaminomethylation of Heterofunctionalised Allylic Compounds (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 653-660 
    Details
    ISSN: 1434-193X
    Keywords: Hydroaminomethylation ; Rhodium ; Catalysis ; Carbonylation ; Heterofunctionalised allylic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Heterofunctionalised allylic ethers 1, silanes 5, and amines 9 are hydroformylated in the presence of primary or secondary amines 2 to form the corresponding γ-amino- and δ-amino-functionalised compounds. The rhodium(I)-catalysed reaction sequence proceeds by aldehyde formation and subsequent reductive amination to generate the corresponding functionalised secondary or tertiary amines. This selective one-pot hydroaminomethylation procedure establishes access to γ-amino- and δ-amino-functionalised ethers, amines or silanes with potential biological activity.
    Additional Material: 4 Tab.
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  • 45
    Electronic Resource
    Electronic Resource
    Biomimetic Oxidation of Denaverine Hydrochloride (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 679-683 
    Details
    ISSN: 1434-193X
    Keywords: Biomimetic oxidations ; Cytochrome P450 ; Metalloporphyrins ; Denaverine ; Metabolism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The behavior of denaverine (1) in various chemical model systems based on metalloporphyrins as catalysts was investigated to determine the possible oxidative metabolism. The resulting derivatives were compared to a biological model system and in vivo metabolism in rat and human.
    Additional Material: 2 Tab.
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  • 46
    Electronic Resource
    Electronic Resource
    A Comparison of Chemical and Photochemically Induced Reduction of Some 2(4),5-Dihydro-1,2,4-triazines and Aromatic 1,2,4-Triazines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 685-689 
    Details
    ISSN: 1434-193X
    Keywords: Single-electron transfer ; Ring contractions ; 1,4-Dihydro-1,2,4-triazine ; Photochemical reduction ; Chemical reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Chemical reduction (Zn/AcOH) of the arene 1 and of 2(4),5-dihydro-1,2,4-triazine 7 has been reinvestigated, resulting in the amendment of literature data concerning this reaction. Chemical, electrochemical, and photochemically induced reductions and ring contractions of 1,2,4-triazine derivatives have been compared. The first example of a triaryl-1,4-dihydrotriazine has been prepared. Some further evidence is presented that supports the proposed mechanism of the photochemically induced reduction and ring contraction of 1,2,4-triazines.
    Additional Material: 2 Tab.
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  • 47
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    Electronic Resource
    Preparation of 2,3,5-Tri-O-benzyl-4-thio-L-arabino-furanosides and the Corresponding 4′-Thionucleoside Analogues (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 691-696 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; 4-Thiofuranosides ; Nucleosides ; Reaction mechanisms ; NOE measurements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabino-furanose (9) has been prepared from D-xylose via the 1,4-dithio-L-arabino-furanoside 8. The crucial step of the reaction, i.e. the intramolecular cyclization of the open-chain dithioacetal 5, has been achieved in a yield of 90% by applying tetrabutylammonium iodide as promoter. Reaction of 9 with bis(trimethylsilyl)uracil or -thymine led to the benzyl derivatives 12 and 13 from which the deprotected 4′-thionucleoside analogues 14 and 15 have been prepared by debenzylation with boron tribromide.
    Additional Material: 1 Ill.
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  • 48
    Electronic Resource
    Electronic Resource
    Steric and Electronic Effects in the Diastereoselective Catalytic Epoxidation of Cyclic Allylic Alcohols with Methyltrioxorhenium (MTO) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 785-790 
    Details
    ISSN: 1434-193X
    Keywords: Epoxidations ; Diastereoselectivity ; Allylic alcohols ; Homogeneous catalysis ; Methyltrioxorhenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The steric effects of allylic substituents in the epoxidations with methyltrioxorhenium/urea/hydrogen peroxide adduct (MTO/UHP) have been assessed for a series of 3-alkyl-substituted cyclohexenes. The trans selectivity increases with the size of the substituent and the diastereoselectivities follow an excellent linear correlation with the steric substituent constants of Taft (Es) or Charton (ν). Good cis selectivity is observed in the epoxidation of the cyclic allylic alcohols 2-cyclopentenol and 2-cyclohexenol due to a hydroxy-directing effect through hydrogen bonding; however, for 2-cycloheptenol and 2-cyclooctenol hydrogen bonding is ineffective and steric interactions cause a higher trans selectivity. The conformationally fixed cis- and trans-5-tert-butyl-2-cyclohexenols serve as suitable substrates for gauging the dihedral angle of the transition states for the oxygen transfer in these epoxidations. Thus, the MTO/UHP oxidant favours a quasi-equatorial arrangement of the hydroxy group for effective hydrogen bonding (hydroxy-group directivity), in analogy to m-chloroperbenzoic acid (m-CPBA) and dimethyldioxirane (DMD), and a dihedral angle of ca. 130° is suggested.
    Additional Material: 2 Ill.
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  • 49
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    Electronic Resource
    Catalytic Oxyselenenylation-Deselenenylation Reactions of Alkenes - Stereoselective One-Pot Conversion of 3-Alkenols into 2,5-Dihydrofurans (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 797-803 
    Details
    ISSN: 1434-193X
    Keywords: Phenylselenenyl sulfate ; Selenium-catalyzed reactions ; Stereoselective syntheses ; Dihydrofurans ; Tetrahydrofurans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A stereoselective multi-step one-pot procedure for converting 2-methoxycarbonyl-3-alkenols into 3-methoxycarbonyl-2,5-dihydrofurans, using only catalytic amounts of diphenyl diselenide and an excess of ammonium persulfate, has been developed. The erythro alkenols give the trans dihydrofurans, while the threo stereoisomers give the corresponding cisproducts. The configurations of the starting alkenols were deduced from those of the intermediate phenylseleno tetrahydrofurans, which were independently obtained from reactions of the alkenols with stoichiometric amounts of phenylselenenyl sulfate.
    Additional Material: 3 Tab.
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  • 50
    Electronic Resource
    Electronic Resource
    The Synthesis of Imidazol Sugars Which Mimic Cyclic Carboxonium Ions Formed During the Glycosidase-Catalysed Hydrolysis of Oligo and Polysaccharides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 893-898 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Amino sugars ; Imidazole ; Glycosidases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Some naturally occurring carbohydrates, of which several hydroxy groups had been selectively protected, were condensed with formamidine to give the expected imidazole derivatives in the D-arabino (9), D-lyxo (12), L-xylo (17), D-threo (21), and in the L- and D-erythro (24) series. Introduction of a strong leaving group at the remaining free alcohol function of these products led at once to intramolecular SN2 cyclisation to the corresponding bicyclic aza sugar derivatives. This was followed by total deprotection to give the target aza sugars in the L-xylo (7), L-ribo (14), D-arabino (19), as well as in the D-threo (22) and the L- and D-erythro (26) series. Inhibitory assays with four glycosidases showed that the D-arabino aza sugar 19 is the only potent inhibitor (for an α-mannosidase of jack bean).
    Additional Material: 1 Tab.
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  • 51
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    Electronic Resource
    Preparation and Characterization of Bridged Naphthoxazinium Salts (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 923-930 
    Details
    ISSN: 1434-193X
    Keywords: Bridged benzo[a]phenoxazinium salts ; Diazo compounds ; Cyclocondensation ; Absorption ; Fluorescence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -By condensation of bridged 4-arylazo-substituted 3-hydroxyanilines 18 and bridged or unbridged 4-arylazo-substituted 1-naphthylamines 19-23 with bridged 1-naphthylamines 15-17 and 3-aminophenols 14, respectively, in the presence of perchloric acid, bridged naphthoxazinium perchlorates 24-30 have been prepared. The spectral properties of the products have been compared with those of the bridged phenoxazinium salt 31 as well as with data for some unbridged analogues.
    Additional Material: 1 Ill.
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  • 52
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    Electronic Resource
    3-Trifloxy-3-trifluoromethylpropeniminium Triflate: Reaction with Aromatic Amines - An Efficient Synthesis of 2-Trifluoromethylquinolines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 937-941 
    Details
    ISSN: 1434-193X
    Keywords: Iminium salts ; Triflic anhydride ; Arylamines ; 2-Trifluoromethyl quinolines ; 3-Trifluoromethyl-cinnamaldehydes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of iminium triflates 2 and 7 with various aromatic amines were investigated. The 2-Rf-substituted quinolines 3 and 8 were prepared in excellent yields by the reaction of 2 and 7, respectively, with substituted anilines. The reactions of 2 and 7 with diarylamines proceeds, suprisingly, to afford the corresponding 3-Rf-substituted cinnamaldehydes 4 and 9.
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  • 53
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    Electronic Resource
    Synthesis Mediated by Ring-Closing Metathesis - Applications in the Synthesis of Azasugars and Alkaloids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 959-968 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Alkaloids ; Castanospermine ; Metathesis ; Azasugars ; Manzamine A ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the ring-closing metathesis (RCM) reaction to the construction of a wide variety of nitrogen-containing ring systems is described. The examples include pyrrolizidine, indolizidine, and quinolizidine derivatives related to azasugars. A formal total synthesis of castanospermine (5) is presented. The utilisation of two RCM steps in the synthetic sequence leading to the multicyclic ABCDE nucleus 7 of the complex alkaloid manzamine A (6) is discussed.
    Additional Material: 3 Ill.
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  • 54
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    Hydrogen Transfer Hydrozirconation of Alkenes with iBuZrCp2Cl Catalyzed by Lewis-Acidic Metal Compounds Containing Al, Zn, Si, Ag, and Pd (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 969-971 
    Details
    ISSN: 1434-193X
    Keywords: Hydrogen transfer ; Zirconium ; Alkenes ; Isobutylzirconocene chloride ; Lewis acid catalysis ; Lewis acid catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The hydrozirconation reaction of monosubstituted alkenes with iBuZrCp2Cl can be significantly accelerated by catalytic amounts of various Lewis acidic metal compounds, most notably AlCl3, Me3SiI, and Pd complexes, such as Li2PdCl4 and Cl2Pd(PPh3)2.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/99042_s.pdf or from the author.
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    Synthesis of the Enantiomers of (Z)-21-Methyl-8-pentatriacontene, the Major Component of the Female-Produced Contact Sex Pheromone of the Yellow-Spotted Longicorn Beetle, Psacothea hilaris (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 981-984 
    Details
    ISSN: 1434-193X
    Keywords: Alkenes ; Chirality ; Longicorn beetle ; Pheromones ; Psacotheahilaris ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Both the enantiomers of (Z)-21-methyl-8-pentatriacontene (1), the major component of the female-produced contact sex pheromone of the yellow-spotted longicorn beetle (Psacotheahilaris), were synthesized by starting from the enantiomers of citronellol (2)
    Type of Medium: Electronic Resource
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  • 56
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    Pseudorotaxanes and Catenanes Containing a Redox-Active Unit Derived from Tetrathiafulvalene (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 985-994 
    Details
    ISSN: 1434-193X
    Keywords: Catenanes ; Molecular machines ; Pseudorotaxanes ; Template-directed synthesis ; Tetrathiafulvalenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two bis(2-oxy-1,3-propylenedithio)tetrathiafulvalene-containing acyclic polyethers and two macrocyclic polyethers, each incorporating one bis(2-oxy-1,3-propylenedithio)tetrathiafulvalene unit and one p-phenylene ring, have been synthesized. The two acyclic polyethers are bound by cyclobis(paraquat-p-phenylene) with pseudorotaxane geometries in solution. The two macrocyclic polyethers have been mechanically interlocked with this tetracationic cyclophane to form [2]catenanes in a kinetically controlled self-assembly process. The X-ray crystallographic analysis of one of the two [2]catenanes and 1H-NMR-spectroscopic studies of both compounds showed that the p-phenylene ring of the macrocyclic polyether is located inside the cavity of the tetracationic cyclophane, while the bis(2-oxy-1,3-propylenedithio)tetrathiafulvalene unit resides alongside. The [2]pseudorotaxanes and [2]catenanes show broad bands around 780 nm, arising from the charge-transfer (CT) interaction between the electron-donor tetrathiafulvalene-(TTF-)type unit and the electron-acceptor units of the tetracationic cyclophane. 1H-NMR-spectroscopic studies have shown that the [2]pseudorotaxanes dissociate into their separate components upon oxidation of the TTF-type unit, as a result of disruption of the CT interaction and electrostatic repulsion between the tetracationic host and the newly formed monocationic guest. The subsequent reduction of the guest to its neutral state affords back the pseudorotaxane-type complex restoring the original equilibrium. The results obtained from electrochemical experiments are consistent with the reversible, redox-driven dethreading/rethreading process observed by 1H-NMR spectroscopy. Variable-temperature 1H-NMR-spectroscopic investigations have revealed two dynamic processes, both involving the relative movements of the mechanically interlocked components in the [2]catenanes. The two consecutive oxidation processes involving the TTF-type unit, observed electrochemically, are displaced toward more positive potentials compared with the free cyclic polyethers. The two reversible two-electron reduction processes, characteristic of free cyclobis(paraquat-p-phenylene), separate into four reversible one-electron processes because of the topological difference between the “inside” and “alongside” electron-acceptor units in the [2]catenane.
    Additional Material: 11 Ill.
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    Totally Regio- and Stereoselective P-O-to-P-C Rearrangement in the Synthesis of Chiral P-(o-Hydroxyaryl)diazaphospholidine P-Oxides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1099-1105 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Chiral synthons ; P-(o-Hydroxyaryl)diazaphospholidine P-oxides ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The totally regio- and stereoselective P-O-to-P-C rearrangement in the synthesis of various chiral P-(o-hydroxyaryl)diazaphospholidine P-oxides has been investigated. This reaction proceeds with excellent yields ranging from 72 to 92%, total retention of configuration at the phosphorus atom, and complete regioselectivity. An exception was found with naphthyl derivatives, which gave mixtures of two regioisomers. In all cases, the products generated have been unambiguously characterized by 1H-, 13C-, and 31P-NMR spectroscopy as well as by X-ray-diffraction analysis.
    Additional Material: 3 Ill.
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  • 58
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    Palladium-Catalyzed Cyclocarbonylation of o-Ethynylphenols and Vinyl Triflates To Form 3-Alkylidene-2-coumaranones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1137-1141 
    Details
    ISSN: 1434-193X
    Keywords: Cyclocarbonylation ; Alkynes ; Catalysis ; Palladium ; Vinyl triflates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -o-Ethynylphenols react with vinyl triflates, in the presence of tetrakis(triphenylphosphane)palladium(0) and under carbon monoxide, to form 3-alkylidene-2-coumaranones in good yield.
    Additional Material: 1 Tab.
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  • 59
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    S-Linked Thiomimetics of Phytoalexin-Elicitor-Active, Branched Oligosaccharides, Their Synthesis, Protein-Binding Ability and Phytoalexin-Inducing Activity (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1143-1152 
    Details
    ISSN: 1434-193X
    Keywords: Sulfur-linked thiooligosaccharides ; Oligosaccharin thio analogs ; Phytoalexin elicitor thio analogs ; Soybean glucan-binding assays ; Structure-activity relationships ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The sulfur-linked pentathiohexasaccharide 3I,3IV-di-β-D-glucopyranosylthiogentiotetraose (12) has been prepared by a convergent approach involving the reaction of 1,2,4-tri-O-acetyl-6-deoxy-6-iodo-3-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-3-thio-β-D-glucopyranose (10) with the sodium salt of 2,3,4-tri-O-acetyl-6-S-[2,4-di-O-acetyl-3,6-di-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-3,6-dithio-β-D-glucopyranosyl]-1,6-dithio-β-D-glucopyranose (4). A further reaction, involving the sodium salt of the peracetylated β-1-thio derivative of 12 with 1,2,3,4-tetra-O-acetyl-6-deoxy-6-iodo-β-D-glucopyranose (26), afforded the homologous sulfur-linked hexathioheptasaccharide 3II,3V-di-β-D-glucopyranosylthiogentiopentaose (28). Related sulfur-linked positional isomers 3II,3IV-di-D-β-glucopyranosylthiogentiotetraose (34) and 3III,3V-di-β-D-glucopyranosylthiogentiopentaose (39) have been prepared using analogous synthetic strategies. Thus, SN2 displacement of the iodine atom in 10 by the sodium salt of 2,4-di-O-acetyl-3,6-di-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-1,3,6-trithio-β-D-glucopyranose afforded a tetrathiopentasaccharide, which resulted in the pentathiohexasaccharide 34 by a sequence of reactions involving the 1-thioglycose 32 in reaction with 26. The hexathioheptasaccharide 39 was obtained conveniently by the reaction of 26 with the acetylated 1-thio-6I, 3II, 6II, 3IV, 6IV-pentathio derivative 37, followed by deacylation. The four isomeric pentathiohexa- and hexathioheptasaccharides 12,34 and 28,39, respectively, were all found to be active in eliciting phytoalexin accumulation in soybean cotyledon tissue and in binding to a glucan-binding protein of soybean, although to a lesser extent than the corresponding O-oligosaccharides, the alternate thiohexa- and thioheptasaccharides 12,28 being more active as compared to the geminally branched isomers 34,39.
    Additional Material: 3 Tab.
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  • 60
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    Intramolecular Copper- and Rhodium-Mediated Carbenoid Reactions of α-(Propargyloxy)silyl-α-diazoacetates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1213-1221 
    Details
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Carbenoids ; Silicon ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Copper(I) triflate catalyzes the transformation of α-[(2-alkynyl)oxy]silyl-α-diazoacetates 1a-g into 1,2-bis(2,5-dihydro-1,2-oxasilol-4-yl)ethenes 2 and/or 2H-1,2-oxasilines 3. With rhodium(II) perfluorobutyrate as catalyst, 1a-e furnish only 3 but no 2. Bicyclic 2-methoxyfurans 6 are formed when 1a,c,e (containing terminal alkyne functions) are treated with catalytic amounts of copper(I) chloride. The experimental observations are explained in terms of metal-mediated intramolecular cyclopropenation and subsequent metal-assisted ring-opening of the strained bicyclic cyclopropene leading to vinylcarbene-metal complexes. An unusual autoxidation of 2H-1,2-oxasilines 3a,c,e is also described.
    Additional Material: 1 Ill.
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    Syntheses of Cyclobutane Derivatives: Total Synthesis of (+) and (-) Enantiomers of the Oleander Scale Aspidiotus nerii Sex Pheromone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1201-1211 
    Details
    ISSN: 1434-193X
    Keywords: Pheromones ; Aspidiotus nerii ; Sex attractant ; Cyclobutane ; Enantiomeric purity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Synthesis of both enantiomers of the Aspidiotus nerii sex pheromone and their diastereomers has been achieved using, as a key step, an intramolecular ester enolate alkylation reaction for the formation of the cyclobutane ring with a good control of the relative configurations of the asymmetric centers. Stereoselective synthesis of a number of other trisubstituted cyclobutane derivatives also proves the versatility of the methodology used for the synthesis of the Aspidiotus nerii sex pheromone.
    Additional Material: 2 Ill.
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  • 62
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    Formation of Chiral N-Oxides from 2-Azabicyclo[3.3.0]octanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1249-1252 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohols ; Amine N-oxides ; Asymmetric synthesis ; Hydrogen bonds ; Structure determination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Enantiopure 2-azabicyclo[3.3.0]octanes 1a-d and ent-1e were oxidized with mCPBA to provide either diastereomeric pairs of N-oxides (2a/3a and 2b/3b) or diastereomerically pure compounds (2c,d and ent-2e). The structure of compounds 2a and ent-2e was confirmed by an X-ray study. The factors that affect the oxidation process are discussed.
    Additional Material: 2 Ill.
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    Non-Classical Epimerisation of (1S,2S,3S,4R,5R)-1-O-Methylcyclohexane-1,2,3,4,5-pentol (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1259-1263 
    Details
    ISSN: 1434-193X
    Keywords: Inositols ; Epimerisation ; Acetals ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Methoxycyclitol 4 was acetalized in a non-classical one-pot procedure with chloral/dicyclohexylcarbodiimide forming the 4-epi derivative 6. The stepwise deprotection of compound 6 is also described. Thus, decarbamoylation to the acetal 7 was achieved by heating 6 with methanolic sodium methoxide, and cleavage of the acid-stable trichloroethylidene moiety was realised in two steps via the corresponding ethylidene acetals 8 and 9; the ethylidene function was removed with aqueous trifluoroacetic acid (compound 10 from 6 via 9). Finally, the carbamoyl derivative 10 was converted into the tetra-O-acetyl product 12 via the tetrol 11.
    Additional Material: 2 Ill.
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    Reactions of Nepenthone with Chromium(II) Reagents in Neutral Aqueous Medium (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1265-1265 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -No abstract
    Type of Medium: Electronic Resource
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  • 65
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    Photoisomerization of Bicyclopropylidene and 1,2-Dimethylenecyclobutane in Rare-Gas Matrices: Towards the IR-Spectroscopic Identification of Tetramethyleneethane (2,3-Dimethylenebutane-1,4-diyl) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1291-1294 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; IR spectroscopy ; Photochemistry ; Diradicals ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Bicyclopropylidene (3) and 1,2-dimethylenecyclobutane (7) have been irradiated in rare-gas matrices. If 1,2-dimethylenecyclobutane (7) is exposed to the light of a KrF excimer laser (λ = 248 nm), an isomeric species is produced, showing an absorption at 793.1 cm-1 (argon matrix) or 791.2 cm-1 (xenon matrix) in the IR spectrum. The back reaction can be induced with light of λ = 254 nm. This photochemical interconversion, together with the comparison between the experimental and calculated band positions, supports the assignment of the IR absorption near 790 cm-1 to tetramethyleneethane (5).
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  • 66
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    A New Generation of Alkoxyl Radical Precursors - Preparation and Properties of N-(Alkoxy)-4-arylthiazole-2(3H)-thiones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1275-1290 
    Details
    ISSN: 1434-193X
    Keywords: Alkoxyl radical ; Cyclizations ; Radicals ; Tetrahydrofuran ; Thiazolethione ; Thiazolethione ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -N-(Hydroxy)thiazole-2(3H)-thiones 6-10 have been prepared in a short and efficient synthesis from p-substituted acetophenones. Alkylation of heterocycles 6-10 in the form of their potassium or tetraalkylammonium salts 11-15 affords N-alkoxy-4-arylthiazole-2(3H)-thiones 16-20 in good to satisfactory yields. The hitherto unknown thiones 16-20 have been subjected to a detailed structural investigation (NMR spectroscopy and X-ray crystallography) and furthermore to a mechanistic study in order to explore their utility as sources of oxygen-centered radicals in solution. From the results of these studies, the following conclusions can be drawn: (i) X-ray analyses of the p-chlorophenyl-substituted acid 9, of the O-alkyl derivatives 19c, 19f, and of the O-mixed anhydride 19k indicate short C-S bonds [C2-S2 = 1.637(5)-1.684(2) Å] and long N-O connectivities [N3-O1 = 1.369(3)-1.379(2) Å] in the thiohydroxamate functionalities. Furthermore, O-alkyl- or O-acyl substituents at O1 are twisted out of the thiazolethione plane by ca. 90°, which points to lone-pair repulsion between nitrogen and oxygen atom as the underlying structural motif of the cyclic thiohydroxamate derivatives. (ii) Alkylation of ambidentate thiohydroxamate anions (salts 11-15; oxygen and sulfur nucleophiles) affords almost exclusively O-esters 16-20 (alkylation at the oxygen atom). (iii) Based on the results of X-ray diffraction studies and on the 1H- and 13C-NMR spectra, guidelines for the characterization of N-(alkoxy)thiazolethiones 16-20 and 2-(alkylsulfanyl)thiazole N-oxides 21-25, i.e. the products of S-alkylation of thiohydroxamate salts 11-15, could be derived. (iv) Photolyses of substituted N-(4-pentenoxy)-4-arylthiazolethiones 16-20 in general and in particular of p-chloro derivatives 19 were carried out in the presence of the hydrogen donor Bu3SnH, and afforded substituted tetrahydrofurans 31 or tetrahydropyrans 32 as major products in good yields. The observed stereo- and regioselectivities of ethers 31 and 32 point to alkoxyl radicals 30 as reactive intermediates, which add intramolecularly by selective 5-exo-trig or 6-endo-trig pathways to the olefinic double bonds. In terms of synthetic access and ease of handling of the radical precursors, the p-chlorophenyl-substituted thiazolethiones 9 and 19 exhibit significant advantages over all the other thiones used in this study and are considered as excellent substitutes for the pyridinethiones as efficient sources of free alkoxyl radicals. Consequently, the present compounds may be of use in both mechanistic and synthetic studies.
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    Studies on the Synthesis of Natural Products with Bicyclo[4.4.0]decene Skeleton: Synthesis and Uncatalysed Intramolecular Diels-Alder Reactions of the Decatrienone Substrates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1377-1384 
    Details
    ISSN: 1434-193X
    Keywords: Natural products ; Intramolecular Diels-Alder reactions ; 2-Siloxycyclopropanecarboxylates ; 1,7,9-Decatrien-3-ones ; Octalones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Starting from enones 7 and 8 siloxydienes 9 and 12 were synthesized. Cyclopropanation and subsequent alkylation with sorbyl bromide provided tetrasubstituted siloxycyclopropanes 15 and 16 in good overall efficiency. Their ring cleavage with fluoride reagents gave 1,7,9-decatrienones 5 and 17; the latter was converted into the protected compound 6. The thermal intramolecular Diels-Alder reactions of 5 and 6 were compared with those of related trienones 3 and 4. Octalones 1, 2, 21, and 22 were formed as mixtures of three or four diastereomers. Thus, for the stereoselective construction of natural products such as α-eudesmol or dihydromevinolin alternative reaction conditions for the cycloaddition step have to be developed.
    Additional Material: 5 Tab.
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    A Stereoselective Synthesis of Nonracemic (+)-Desoxoprosophylline by a Tandem Wittig [2+3]-Cycloaddition Reaction (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1407-1414 
    Details
    ISSN: 1434-193X
    Keywords: L-Ascorbic acid ; (+)-Desoxoprosophylline ; Lactones ; Alkaloids ; Domino reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -L-Ascorbic acid serves as chiral starting material for the synthesis of (+)-desoxoprosophylline. The synthetic pathway includes the formation of an O-protected 5-azido-2,3-dideoxysugar which is subjected to a tandem Wittig [2+3]-cycloaddition reaction, leading to the heterocyclic core unit of (+)-prosophylline. Stereoselective hydrogenation and chain elongation yields the desired alkaloid.
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    A New Access to Diarylmaleic Anhydrides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1421-1426 
    Details
    ISSN: 1434-193X
    Keywords: Anhydrides ; Coupling reaction ; Enols ; Palladium ; Tin ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new three-step synthesis of diarylmaleic anhydrides 6, starting from 3-aryl-2-hydroxybut-2-enedioates 2, is reported.
    Additional Material: 1 Ill.
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    Synthesis, Reactions, and Properties of 2,8-Didehydronoradamantane Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1401-1406 
    Details
    ISSN: 1434-193X
    Keywords: 2,8-Didehydronoradamantane derivatives ; Cyclopropylcarbinyl ; Rearrangements ; Ring-opening reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -2,8-Didehydronoradamantan-9-one (2) was readily prepared by oxa-di-π-methane photorearrangement of brend-4-en-2-one (1). Other new 9-substituted 2,8-didehydronoradamantanes have also been prepared from 2, [i.e. 2,8-didehydronoradamantan-9-ol (3) and tosylhydrazone 4] and the ring-opening reactions have been studied. In acidic media, 2,8-didehydronoradamantan-9-ol (3) rearranges to the corresponding 2-substituted brend-4-ene derivatives. Exclusive formation of exo-2-substituted brend-4-enes supports the formation of a bridged bicyclobutonium ion. However, treatment of ketone 2 with PCl5 proceeds through a concerted mechanism by cleavage of the C-1-C-2 bond in 2 to give exo-2,5-dichlorotricyclo[4.2.1.03,8]non-4-ene (6). The tricyclo[4.2.1.03,8]nonane skeleton was also obtained by photochemically induced electron transfer reduction of 2 and reduction of 2 with Li/NH3, as well as by reduction of tosylhydrazone 4 with both NaBH3CN and BH3 × THF. On the other hand, Wolff-Kishner reduction of 2 gave the non-rearranged product, 2,8-didehydronoradamantane (10).
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    1-Alkoxycarbonyl-3-bromoazetidin-2-ones as Potential Elastase Inhibitors (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1441-1447 
    Details
    ISSN: 1434-193X
    Keywords: Azetidinones ; Enzyme inhibitors ; Kinetics ; Molecular modelling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Three 1-alkoxycarbonyl-3-bromoazetidin-2-ones have been prepared by reaction of (3S)-3-(tert-butoxycarbonyl)aminoazetidin-2-one with benzyl, trichloroethyl, and trifluoroethyl chloroformates followed by tBoc deprotection, diazotation of the exocyclic amino function and its substitution with potassium bromide. The 3-bromoazetidin-2-ones were obtained as racemic mixtures. Their hydroxide-catalyzed hydrolysis exclusively affords ring-opening products. Porcine pancreatic elastase (PPE) catalyzes the same reaction stereospecifically. Model building suggests that it is the (R) isomer that is enzymatically hydrolysed. The PPE-catalyzed hydrolysis is characterised by low kcat and Km values. Accordingly, these compounds behave as transient inhibitors of the enzyme.
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    Electrosynthesis of Aromatic Aldehydes by Palladium-Catalyzed Carbonylation of Aryl Iodides in the Presence of Formic Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1471-1473 
    Details
    ISSN: 1434-193X
    Keywords: Palladium ; Homogeneous catalysis ; Carbon monoxide ; Aromatic aldehyde ; Formic acid ; Carbonylation ; Electrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The palladium-catalyzed electrocarbonylation of aryl halides performed in the presence of formic acid under one atmosphere of carbon monoxide affords aromatic aldehydes in good to high yields.
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  • 73
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    Novel Diamino and Diimino Thioethers - Chiral Tridentate Ligands for Asymmetric Michael Reactions? (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1475-1479 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohols ; Asymmetric catalysis ; Chirality ; Michael additions ; Tridentate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Novel C2-symmetric enantiopure β,β′-diamino thioethers 1 and β,β′-diimino thioethers 2 have been prepared from chiral α-amino acids. Nine of these compounds have been screened as ligands, in combination with 13 metal salts, with a view to achieving the enantioselective catalysis of a Michael reaction of a β-oxo ester with methyl vinyl ketone resulting in an optimal ee of 17%.
    Additional Material: 2 Tab.
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  • 74
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    Reaction of the Carbanions of 2-(Alkylthio)thiolane 1-Oxides with Oxiranes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1481-1488 
    Details
    ISSN: 1434-193X
    Keywords: Thiolane 1-oxides ; Carbanions ; Oxiranes ; Asymmetric synthesis ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Carbanions of the 2-(alkylthio)thiolane 1-oxides 1 and 2 are generated and subjected to reaction with the epoxides 3-5. The resulting carbinols 6-11 are formed with high α diastereoselectivity, which is explained by a stabilization of the trans configuration of the carbanions in the activated complex. A minor γ stereoselectivity is also observed in case of the reactions with 4 and 5. The pure enantiomers (1S,2S,2′S)-9a and (1R,2R,2′S)-11b were obtained from 2 and (S)-4 or (R)-5, respectively, and their configurations were proved by X-ray structural analyses.
    Additional Material: 2 Ill.
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  • 75
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    A Convenient Preparation of Optically Active Diepoxyhenicosene (Leucomalure), Lymantrid Sex Pheromone, by Chiral HPLC (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1503-1506 
    Details
    ISSN: 1434-193X
    Keywords: Diepoxy sex pheromone ; Chiral HPLC ; Resolution ; Stereochemistry ; Diepoxyhenicosene ; Leucomalure ; Lymantrid satin moth ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From optically active (3Z,9Z)-cis-6,7-epoxy-3,9-henicosadiene (2), all stereoisomers of (3Z)-cis-6,7-cis-9,10-diepoxy-3-henicosene [leucomalure (1)], a sex pheromone component of the Satin moth, were prepared in addition to the cis-3,4-cis-6,7-diepoxy analog (3). Specifically, MCPBA oxidation of each enantiomer of this epoxydiene yielded a mixture of four compounds, namely two diastereomeric sets of leucomalure and the positional isomer, which were easily separable by chiral HPLC equipped with either a Chiralpak AD column or a Chiralcel OJ-R column. Their chemical structures were determined by 2D-NMR analyses, and it was further confirmed that the chiral HPLC columns also had a high capability of resolving the enantiomers of these diepoxides.
    Additional Material: 2 Ill.
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  • 76
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    Synthesis of N,N′-Disubstituted (1R,2R)-1,2-Diaminocyclohex-4-enes by a Ruthenium-Catalyzed Ring-Closing Metathesis Reaction (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1523-1526 
    Details
    ISSN: 1434-193X
    Keywords: Ruthenium ; Ring-closing metathesis ; Metathesis ; EPC synthesis ; 1,2-Diaminocyclohex-4-ene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure (1R,2R)-1,2-diaminocyclohex-4-ene derivatives have been synthesized by the ruthenium-catalyzed ring-closing metathesis reaction of (4R,5R)-N,N′-bis[(S)-1-phenylethyl]-4,5-diamino-1,7-octadiene dihydrochloride.
    Additional Material: 1 Ill.
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  • 77
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    An Efficient Procedure for Preparing γ-Hydroxy α,β-Unsaturated Sulfones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1545-1550 
    Details
    ISSN: 1434-193X
    Keywords: Takai-Hiyama-Nozaki-Kishi coupling ; Sulfones ; β-Ionone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromium(II)-mediated Barbier condensation of β-iodovinyl p-tolylsulfone with aldehydes and β-ionone afforded the title hydroxysulfones in good to excellent yields.
    Additional Material: 1 Ill.
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  • 78
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    Facile and General Synthesis of Polyphosphane Polyoxides with (O)PCP(O) Linkages (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1561-1569 
    Details
    ISSN: 1434-193X
    Keywords: Arbuzov reaction ; Phosphane oxide carbanion ; PCP linkage ; NMR spectroscopy ; Carbanions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyphosphane polyoxides with (O)PCP(O) linkages are powerful chelating agents for extraction of actinides from nuclear wastes. They are obtained either by the Michaelis-Arbuzov reaction of chloromethylphosphane oxides and phosphorus(III) esters, or by the reaction of phosphane oxide carbanions with chlorophosphanes. With the latter method, the addition of a phosphane oxide carbanion in excess allowed us to overcome a transmetallation reaction and thereby obtain polyphosphane polyoxides in good yields. The 1H-NMR spectra of the PCH2P groups show the influence of the different R groups attached to the phosphorus atoms. We determined the coupling constants and the chemical shifts of these spin systems.
    Additional Material: 1 Ill.
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  • 79
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    Synthesis, Fluorescence Properties, and Head-to-Tail Regioselectivity in the Photodimerization of a Donor-Acceptor-Substituted Anthracene (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1595-1600 
    Details
    ISSN: 1434-193X
    Keywords: Photochemistry ; Anthracenes ; Fluorescence spectroscopy ; Cycloaddition reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel 2,6-donor-acceptor-substituted anthracene, namely 6-methoxy-2-anthracene carboxylic acid (7), was synthesized. The emission of this compound exhibits significant solvatochromism. The fluorescence band position and intensity are also remarkably sensitive to H+. Irradiation of the anthracene 7 in solution yields the syn and anti head-to-tail dimers exclusively. A synergistic electronic effect between the donor and acceptor substituents is proposed to operate on the photophysical and photochemical properties of anthracene 7.
    Additional Material: 2 Ill.
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  • 80
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    Spectroscopic and Theoretical Investigations of Monocyclic Dioximes and Dimethoximes with Six-, Eight-, and Ten-Membered Rings (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1601-1609 
    Details
    ISSN: 1434-193X
    Keywords: Photoelectron spectroscopy ; Conformation analysis ; Ab initio calculations ; Through-space interactions ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dioximes 4-6 and the dimethoximes 7-9, which contain the functional groups in opposite positions of a six-, eight-, or ten-membered ring, were synthesized. Their conformational properties and transannular interactions were investigated by spectroscopic (PE, 13C NMR) and theoretical (MMX, AM1, ab initio HF, and B3LYP) methods. While the cyclooctane derivatives 5 and 8 have conformations favourable for through-space interactions of the π(C=N) orbitals, in the other compounds no such interactions can be ascertained. Through-space orbital interactions in the molecules with an eight-membered ring lead to a splitting of the π(C=N) MOs of 0.4 eV.
    Additional Material: 7 Ill.
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  • 81
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    Spectroscopic and Theoretical Investigations of Bicyclic Dioximes and Dimethoximes with Eight-Membered Rings (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1611-1617 
    Details
    ISSN: 1434-193X
    Keywords: Photoelectron spectroscopy ; Conformation analysis ; Ab initio calculations ; Through-space interactions ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bicyclic dioximes 4-6 and dimethoximes 7-9, which contain the functional groups in opposite positions of bridged eight-membered rings, were synthesized. Their conformational properties and transannular interactions were investigated by spectroscopic (PE, 13C NMR) and theoretical (MMX, AM1, ab initio HF, and B3LYP) methods. While in the 3,7-disubstituted bicyclo[3.3.1]nonane derivatives 5 and 8 the eight-membered ring has a CC conformation favourable for through-space interactions of the π(C=N) orbitals, in the bicyclo[3.3.0]octane derivatives 4 and 7 as well as the 2,6-disubstituted bicyclo[3.3.1]nonanes 6 and 9 the functional groups are in geometric orientations that are unfavourable for such interactions. Through-space orbital interactions in the molecules with favourable conformations lead to a splitting of the π(C=N) MOs of 0.4-0.6 eV.
    Additional Material: 7 Ill.
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  • 82
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    New Syntheses of Flavones from Diels-Alder Reactions of 2-Styrylchromones with ortho-Benzoquinodimethanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 135-139 
    Details
    ISSN: 1434-193X
    Keywords: Flavones ; Chromones ; ortho-Benzoquinodimethanes ; Diels-Alder reactions ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first reported cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodimethane afforded 2-[2-(3-aryl-1,2,3,4-tetrahydronaphthyl)]chromones. These cycloadducts were converted into the corresponding 2-[2-(3-arylnaphthyl)]chromones (benzoflavone derivatives) by bromination/dehydrobromination processes. These benzoflavone derivatives were also obtained in one-pot cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodibromomethane.
    Additional Material: 1 Ill.
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  • 83
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    Reactions of Nepenthone with Chromium(II) Reagents in Neutral Aqueous Medium (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 149-153 
    Details
    ISSN: 1434-193X
    Keywords: Morphine alkaloids ; 6,14-Ethenomorphinans ; Chromium(II) complex reagents ; Organochromium(III) complex intermediates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A synthetic method for the selective transformations of a selected morphine alkaloid in neutral aqueous medium is introduced. Full diastereoselectivity was achieved by the transformation of nepenthone (1) with [Cr(ida)(H2O)3] into 2a (20R) showing a complementary method as compared to the reactions with classical reagents to result in 2b (20S). A new unexpected morphine derivative 3 was prepared by a ligand-induced modification of the reaction which involves an unprecedented rearrangement.
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  • 84
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    Synthesis, Characterization, and Some Reactions of the Tricarbonylchromium Complexes of 1,3-Indandione and Ninhydrin (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 167-179 
    Details
    ISSN: 1434-193X
    Keywords: 1,3-Indandione ; Ninhydrin ; Chromium complexes ; Acetals ; Oxidation ; Hetero Diels-Alder reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The syntheses and characterization of the tricarbonylchromium complexes of 1,3-indandione and ninhydrin are described. As the direct complexation proved unsuccessful, the acetal route was tried. Although some complexes were obtained, complex deacetalization did not work in the case of ninhydrin. Finally, the oxidation of tricarbonyl(η6-1,3-indandione)chromium(0) with dimethyldioxirane gave the ninhydrin complex in 75% yield in equilibrium with the indantrione complex. The latter reacts in hetero Diels-Alder reactions with dienes with diastereoselective formation of spiro anellated pyran derivatives.
    Additional Material: 3 Ill.
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  • 85
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    Chiral Peptide Nucleic Acids (PNAs): Helix Handedness and DNA Recognition (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 197-204 
    Details
    ISSN: 1434-193X
    Keywords: DNA recognition ; Helical structures ; Induced chirality ; Peptide nucleic acid ; Thermal stability ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Peptide Nucleic Acids (PNAs) are DNA mimics in which the deoxyribose phosphate backbone has been replaced by a pseudo-peptide skeleton composed of N-(2-aminoethyl)glycine units; they bind to complementary DNA strands with high affinity and selectivity. In order to study the effect of stereogenic centers within the backbone on PNA preorganization and DNA binding properties, chiral PNA decamers were synthesized which contained thymine monomers derived from L-Leu and D- or L-Lys inserted either at C-terminus and/or in the middle of an achiral PNA strand. PNAs containing three chiral thymine monomers derived from L-Leu, D- or L-Lys, L-Asp, or D-Glu were also synthesized. CD spectral analyses showed that a charged chiral monomer inserted in the middle of the strand is able to induce a strong preference in the helix handedness of a PNA-PNA duplex. The effect is increased by the presence of three chiral charged monomers. The L-Lys- and L-Asp-PNAs induced a preference for the left-handed and the D-Lys and D-Glu-PNAs for the right-handed conformation. As expected, the PNA-DNA duplexes are dominated by the DNA strand and thus are right-handed with both D- and L-PNAs. However, the D-PNAs, being inherently right-handed, lead to more stable PNA-DNA duplexes than the L-PNAs. The lysine-based PNAs form more stable complexes with the DNA at low ionic strength, due to the electrostatic interactions between the charged lysine side chain and DNA.
    Additional Material: 10 Ill.
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  • 86
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    A New Cytotoxic Diterpene with the Dolabellane Skeleton from the Marine Sponge Sigmosceptrella quadrilobata (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 227-230 
    Details
    ISSN: 1434-193X
    Keywords: Diterpene ; Dolabellane ; Sigmosceptrella quadrilobata ; Sponge ; Antitumor agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new diterpene with the dolabellane skeleton 1 has been isolated from the sponge of the Indian Ocean, Sigmosceptrellaquadrilobata. Its structure elucidation, including absolute stereochemistry, was performed with the aid of MS, NMR, and CD data and by molecular modeling. Compound 1 is moderately cytotoxic against four tumor cell lines.
    Additional Material: 2 Ill.
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  • 87
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    Ectyoplasides A-B - Unique Triterpene Oligoglycosides from the Caribbean Sponge Ectyoplasia ferox (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 231-238 
    Details
    ISSN: 1434-193X
    Keywords: Saponins ; Terpenoids ; Sponges ; Ectyoplasiaferox ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two novel norlanostane triglycosides, ectyoplasides A (1) and B (2), have been isolated from the methanolic extracts of the Caribbean sponge Ectyoplasiaferox (Raspaliidae, Axinellida). Their structures have been established by extensive application of high-resolution FABMS and two-dimensional NMR techniques, supported by chemical and enzymatic degradation methods. Ectyoplasides A and B have been shown to possess identical sugar chains (composed of two β-galactose units and one α-arabinose unit), but to differ in their aglycone moieties, which possess nortriterpene skeletons with an unprecedented substitution pattern on ring A. Ectyoplasides A and B show moderate cytotoxic activity when tested in vitro towards various cell lines
    Additional Material: 1 Ill.
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  • 88
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    Reaction of Stabilised Phosphorus Ylides with Nitrogen Dioxide (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 251-254 
    Details
    ISSN: 1434-193X
    Keywords: Phosphonium ylides ; Nitrogen dioxide ; Oxidation ; Nitriles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of the stabilised ylides 14-23 with an excess of NO2 in CH2Cl2 at room temperature gives different results depending on the structure of the starting ylide. The monacyl ylides 14-16 give the corresponding α-oxo nitriles 4 together with Ph3PO · HNO3 (24) which has been fully characterised for the first time. Under the same conditions, the ylide 18 gives 2,4-dinitrobenzonitrile (26), Ph3PO, and benzoic acid. The other ylides examined all give 24 together with a variety of other products.
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  • 89
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    Reactions of Diphenyl Ether with Chlorine and Bromine Atoms Around 750 K - Relevance for Gas-Phase “Dioxin” Formation (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 261-265 
    Details
    ISSN: 1434-193X
    Keywords: Dioxins ; Gas-phase reactions ; Diphenyl ether ; Hydrogen abstraction ; ipso Substitution ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The title reactions have been studied to scrutinize rate data recently inferred for the two reverse steps - reaction of phenoxy radicals with chlorobenzene and bromobenzene - which were at variance with commonly accepted model values. Both with chlorine and bromine atoms, splitting to halobenzene and phenoxy radical was found to occur in competition with abstraction of o-, m-, p-hydrogen atoms. On this basis, the displacements of Cl and Br from the benzene ring by phenoxy radicals must have activation energies above 20 kcal/mol, and are therefore slow. As a consequence, formation of “dioxins” from halogenated phenols, in (slow) combustion, should proceed by combination of two (halo)phenoxy radicals rather than by displacement of (ortho-)halogen in a halophenol molecule.
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  • 90
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    Deprotonation of Amides and Polyfunctional Imides Probed by Heteronuclear NMR and Quantum Chemical Calculations (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 287-295 
    Details
    ISSN: 1434-193X
    Keywords: Ab initio calculations ; Amides ; Imides ; Acidity ; NMR spectroscopy ; Deprotonation site ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The site of deprotonation of several types of amide acids (carboxylic amides and imides, sulfonamides, cyanamide, N-hydroxyurea) has been investigated by quantum chemical calculations and heteronuclear NMR measurements. Relative energies of tautomeric ions deriving from protonation at the various sites were determined both in the gas phase and in water (by the IPCM continuum solvation method). NMR properties (nuclear shielding and electric field gradient) of the involved heteronuclei were calculated and compared with experimental 14N, 17O and 33S chemical shifts and relaxation rates. It is shown that the combination of theoretical and experimental tools allows a reliable prediction of spectral parameters and ultimately of the deprotonation site of polyfunctional acids.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98401_s.pdf or from the author.
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  • 91
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    Silicon-Controlled Intramolecular Thermal H-Ene Reaction - A New Access to a Key Intermediate of (±)-cis-γ-Irone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1825-1829 
    Details
    ISSN: 1434-193X
    Keywords: Ene reaction ; Allylsilane ; Annulation ; cis-γ-Irone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The primordial influence of the silyl group in an intramolecular thermal H-ene reaction is reported. The silyl group lowered the energy of the transition state and allowed the reaction to proceed at a lower temperature than that of the simple all-carbon analog, thereby excluding the formation of undesirable by-products. This sequence has been applied for new access to a key intermediate in the diastereoselective synthesis of (±)-cis-γ-irone with high chemocontrol and significantly improved overall yield.
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  • 92
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    On the Unexpected Stereochemical Outcome of the Magnesium in Methanol - Conjugate Reduction of an Exocyclic α,β-Unsaturated Ester (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1803-1809 
    Details
    ISSN: 1434-193X
    Keywords: Magnesium-methanol reduction ; Reductions ; α,β-Unsaturated esters ; Stereoselectivity ; (R)-(-)-Carvone ; Analogs of 1α,25-(OH)2-vitamin D3 ; Steroids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conjugate reduction of the exocyclic α,β-unsaturated ester 9 with magnesium in methanol gives a mixture of diastereoisomers containing predominantly the less stable 10a. Eventual structural identification rests on the X-ray diffraction analysis of tosylate 18.
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  • 93
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    Observation of Stereotopic Group Recognition in Chiral Borate Complexes in Solution (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1775-1786 
    Details
    ISSN: 1434-193X
    Keywords: Borate esters ; Molecular recognition ; NMR spectroscopy ; Enantioselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The borate ester of 1a and 2e exhibits complete quaternization of the boron center. An equilibrium is observed between the two diastereomeric complexes 3 and 4 formed by coordination to the boron center of either amino group of 2e. At -78°C, this equilibrium is slow on the NMR timescale and a diastereomeric ratio of about 3:1 is observed. At room temperature, a rapid equilibration is observed resulting in two NMR resonances (both 1H and 13C) for the dimethylamino groups of 2e in 3/4. Comparison with the NMR characteristics of the analogous borate complexes of 1h and 1j and of 2c and 2d shows that these resonances each correspond to both methyl groups of a single dimethylamino group. The chemical shift difference occurs solely from the difference between the time fractions that the dimethylamino groups are coordinated to the boron center, and forms, therefore, a direct measure of the ratio 3/4. This ratio amounts to 63:37 at room temperature, which was confirmed by a protonation titration experiment. The elucidation of these NMR characteristics of B(1a)(2e) allowed the more rapid evaluation of the enantiotopic group recognition in many other borate complexes, which range from 57:43 to 67:33 at room temperature. The recognition of the (after complexation) diastereotopic dimethylamino groups of 2e in the borate complex B(1a)(2e) was utilized in a consecutive methylation reaction, which yielded enantiomerically enriched ammonium salt 7. The enantiomeric excess proved to be identical to the diastereomeric excess observed in the preceding recognition event. Strong evidence is presented that complex 3 is indeed the major diastereomer present in a solution of 3/4, as expected from molecular models.
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  • 94
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    On the Unusual Dienophilicity of Trimethylsilylphosphaacetylene (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 363-371 
    Details
    ISSN: 1434-193X
    Keywords: Phosphaalkynes ; Diels-Alder reactions ; Ene reactions ; Homo [4 + 1] cycloaddition reactions ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The diphosphatricyclooctenes 8a, b are obtained from reactions of the phosphaacetylene 2 with the buta-1,3-dienes 6a, b through a reaction sequence involving Diels-Alder, ene, and intramolecular [4 + 2] cycloaddition reactions with the intermediates 7 and 9. An ab initio MO investigation at the MP2/6-31+G* level of theory has provided reasons why the postulated intermediates cannot be detected. The polycyclic products 8a, b were characterized in the form of the corresponding metal carbonyl complexes 10a, b, and 11. Reaction of the silylated phosphaalkyne 2 with cyclohexa-1,4-diene (12) furnishes the monophosphatricyclooctene 14; this reaction has also been studied by means of ab initio calculations. The result of the reaction of 2 with cyclopentadiene (15), however, is a complete surprise: the triphosphaspiropolycyclic system 17 is formed, apparently through Diels-Alder, homo-Diels-Alder, and homo [4 + 1] cycloaddition reactions with the intermediates 16 and 18.
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  • 95
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    Access to 4,5-Dinitro-1,3,5,7-octatetraene Systems (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 431-435 
    Details
    ISSN: 1434-193X
    Keywords: 3,4-Dinitrothiophene ring-opening ; Dinitrobutadienes ; Dinitrooctatetraenes ; Cycloisomerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reactions between 1,4-bis(diethylamino)-2,3-dinitro-1,3-butadiene (2), easily obtainable by ring-opening of 3,4-dinitrothiophene with diethylamine, and 2-substituted vinylmagnesium bromides gave good yields of the 4,5-dinitro-1,3,5,7-octatetraene derivatives 3a-e. With 1-phenylmagnesium bromide, conversely, only 3,4-dinitro-1,4-diphenyl-1,3,5-cyclooctatriene (4f) was obtained. From the unsubstituted dinitrooctatetraene 3a both the octatriene cycloisomer 4a and the valence tautomer of the latter (6a) could be isolated and characterized. The results obtained evidence an unfavourable effect of the two nitro groups on the cycloisomerization process of the octatetraene system.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 96
    Electronic Resource
    Electronic Resource
    Building Blocks for the Construction of Large Chloro-Functionalized, Hexagonal Oligophenylene Cycles (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 451-458 
    Details
    ISSN: 1434-193X
    Keywords: Cross-coupling ; Modular chemistry ; Repetitive synthesis ; Macrocycles ; Shape persistence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The synthesis of a variety of kinked oligophenylene building blocks is described. The synthetic strategy is repetitive, utilizes the Suzuki cross-coupling protocol, and involves potentially bifunctional building blocks (modules) which carry one functional group for coupling and one group which serves as place holder. After the coupling, the placeholder is converted into a coupling functionality for the next growth step. The building blocks also carry chloro-substituents which are unaffected by all transformations. For one of the large building blocks it is shown that it actually can be cyclized into an oligophenylene macrocycle with a chloro-substituent at each corner and a pair of hexyl chains at each side.
    Type of Medium: Electronic Resource
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  • 97
    Electronic Resource
    Electronic Resource
    Synthesis of C-Oligosaccharides That Mimic Their Natural O-Analogous Immunodeterminants in Binding to Monoclonal Immunoglobulins (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 471-476 
    Details
    ISSN: 1434-193X
    Keywords: C-Disaccharide ; C-Glycosides ; Carbohydrates ; Glycosylation ; Sugar lactone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -We have stereoselectively synthesized the analogues of the methyl β-glycosides of (1→6)-β-D-galacto-oligosaccharides (up to tetrasaccharide), in which the interglycosidic oxygen atoms are replaced by a methylene group.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 98
    Electronic Resource
    Electronic Resource
    Preparation of 1-Hydroxycyclopentanecarboxylic Acid Derivatives from a Chiral Equivalent of Glycolic Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 477-483 
    Details
    ISSN: 1434-193X
    Keywords: Radical reactions ; Glycolic acid ; Asymmetric synthesis ; Annulation ; Selenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The stereoselective preparation of 1-hydroxycyclopentanecarboxylic acid derivatives is reported. The key reaction is either a radical cyclization or a radical annulation mediated by the transfer of a phenylseleno group. The radical precursors are easily synthesized by two consecutive enolate alkylations. Excellent stereochemical control for the quaternary C(1) stereogenic center has been achieved.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 99
    Electronic Resource
    Electronic Resource
    Unprecedented Formation of a Benzo[d]azepine by Acid-Catalyzed Cyclization of a Camphor-Derived N-Formylenamine (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 519-522 
    Details
    ISSN: 1434-193X
    Keywords: Enamides ; Diformamides ; Cyclizations ; Nitrogen heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A convenient synthesis of (-)-N-styryl-N-[2-(1,7,7-trimethylbicyclo[2.2.1]hept-2-enyl)ethyl]formamide (2) was developed starting from natural (+)-camphor (3) via (-)-2-(bornen-2-yl)ethanol (6). Cyclization of the N-formylenamine 2 with the aid of 9-borabicyclo[3.3.1]non-9-yl triflate yielded a methanobridged octahydro-1H-benzo[d]azepine derivative.
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Synthesis of Chiral 4-(ω-Hydroxyalkyl)pyrazolidin-3-ones by Ring-Chain Transformation of α-Alkylidenelactones with Hydrazines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 525-525 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The configuration and/or formulae of the following compounds need to be corrected.(1′R,E)-3-(2-Benzyloxy-3-hydroxypropylidene)dihydrofuran-2-one(7c): Correct formula:(4S,5R,4′S)-5-(2,2-Dimethyl[1,3]dioxolan-4-yl)-4-(2-hydroxyethyl)pyrazolidin-3-one (11a): Original formula correct(4R,5S,1′R)-5-(1-Benzyloxy-2-hydroxymethyl)-4-(2-hydroxyethyl)pyrazolidin-3-one (11g): Correct formula:
    Type of Medium: Electronic Resource
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