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  • 2020-2022
  • 1995-1999  (7,064)
  • 1975-1979  (4,891)
  • General Chemistry  (11,144)
  • Electron microscopy
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  • 1
    Electronic Resource
    Electronic Resource
    Intimal-type primary sarcoma of the aorta (1999)
    Springer
    Virchows Archiv 435 (1999), S. 62-66 
    Details
    ISSN: 1432-2307
    Keywords: Key words Rhabdomyosarcoma ; Aorta ; Immunohistochemistry ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We report an intimal sarcoma presenting as an aortic aneurysm. A 68-year-old man suffered from chest pain and speech disturbance. Computed tomography showed a sacciform aneurysm of the aorta, which was resected, revealing a polypoid tumour measuring 1.5×2×2.5 cm projecting into the lumen. This proved to be a poorly differentiated high-grade sarcoma having morphological, immunophenotypic and ultrastructural features consistent with rhabdomyosarcomatous differentiation. Primary sarcomas of the aorta are extremely rare. Many cases have been diagnosed as ”intimal” on the basis of their site of origin, and they are not easy to classify from their histological pattern. Electron microscopy and the use of a more comprehensive panel of immunohistochemical markers should be applied in the histological classification of ”intimal” sarcoma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004280050396
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  • 2
    Electronic Resource
    Electronic Resource
    Melanin pigmented oncocytic metaplasia of the nasopharynx (1999)
    Springer
    Virchows Archiv 434 (1999), S. 455-457 
    Details
    ISSN: 1432-2307
    Keywords: Key words Melanin ; Oncocytic metaplasia ; Nasopharynx ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  A 64-year-old man presented with a history of discomfort of the throat of a few weeks’ duration. Nasoscopic examination revealed multiple small, brown pigmentations at the left suprapharynx, the base of the left nasal cavity and the pharyngeal openings of the auditory tube on both sides. Microscopically, the lesion showed a glandular pattern of oncocytic epithelium with abundant pigmented granules and melanophages in the surrounding stroma. Immunohistochemically, the dendritic cells in the basal layer were positive for S-100 protein. Electron microscopic study revealed numerous fully melanized melanosomes and hypertrophied mitochondria in the oncocytic cells. Oncocytic cells do not produce melanin for themselves, melanin granules apparently being transferred from the adjacent dendritic cells to the oncocytic cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004280050366
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  • 3
    Electronic Resource
    Electronic Resource
    A developmental study using three antibodies (VOBM1, VOBM2, and VOM2): immunocytochemical and electron microscopical analysis of the luminal surface of the rat vomeronasal sensory epithelium (1999)
    Springer
    Anatomy and embryology 199 (1999), S. 215-224 
    Details
    ISSN: 1432-0568
    Keywords: Key words Vomeronasal organ ; Microvilli ; Monoclonal antibody ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The development of the rat vomeronasal organ was studied morphologically and immunocytochemically, using the monoclonal antibodies (MAbs) VOBM1, VOBM2 and VOM2 that react with the luminal surface of the vomeronasal sensory epithelium. Postnatal day (P) 7, 14, 21, 28, 35 and adult animals were examined. The vomeronasal organ and the blood vessel of the organ markedly increased in size and the vomeronasal glands increased in number between P7 and P14. At P35, the shape of the vomeronasal organ was similar to that of the adult but its size was slightly smaller. Electron microscopy showed that only a few scattered microvilli were present on supporting cells, and receptor cells were immature at P7. At P21, well-branched microvilli of the receptor cells and many microvilli of the supporting cells were observed on the luminal surface of the sensory epithelium. At P35, most apical endings of supporting cells and receptor cells were covered with numerous microvilli. Less developed areas were also present at the luminal surface of the epithelium at P35. At P7, immunoreactivities of the three antibodies were observed as discontinuous thin-layered bands only on the luminal surface of the sensory epithelium and no immunoreactivity was observed in other regions of the vomeronasal organ. Immunoreactivities of the VOBM1, VOBM2 and VOM2 increased with age and were observed as continuous thin-layered bands on the luminal surface of the epithelium by P35. These finding suggest that the development of the vomeronasal organ continues after birth and that the organ may reach maturity just before puberty (P42–49).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004290050222
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  • 4
    Electronic Resource
    Electronic Resource
    A new combined Bodian-Luxol technique for staining unmyelinated axons in semithin, resin-embedded peripheral nerves: a comparison with electron microscopy (1999)
    Springer
    Acta neuropathologica 98 (1999), S. 323-329 
    Details
    ISSN: 1432-0533
    Keywords: Key words Unmyelinated fibers ; Peripheral nerve ; Electron microscopy ; Histochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Quantitation of unmyelinated fibers (UF) in peripheral nerves has classically relied upon ultrastructural morphometry. Because this method is time-consuming, it is not typically performed in routine analysis of nerve biopsies. We applied the Bodian-Luxol technique to detect unmyelinated axons by light microscopy on semithin sections from resin-embedded nerve tissue. Estimates were compared to ultrastructural counts. The staining appeared highly specific for axons. Excellent correlation was found between optic densities and the population of UF larger than 0.5 μm. The smallest profiles detected by light microscopy had a diameter close to 0.6 μm. This new technique is not a substitute for ultrastructural quantitative morphometry of UF, as very small unmyelinated axons, especially regenerating ones, can not be reliably visualized. However, it provides a valuable light microscopic method for evaluating axonal loss among UF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004010051088
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  • 5
    Electronic Resource
    Electronic Resource
    Breached cerebral glia limitans-basal lamina complex in Fukuyama-type congenital muscular dystrophy (1999)
    Springer
    Acta neuropathologica 98 (1999), S. 330-336 
    Details
    ISSN: 1432-0533
    Keywords: Key words Micropolygyria ; Electron microscopy ; Frontal lobe ; Perivascular space ; Dot-like structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have reported breaches of glia limitans (GL)-basal lamina (BL) complex with protruding neuroglial tissue in Fukuyama-type congenital muscular dystrophy (FCMD) fetus brain and suggested that some basic deficits in the GL-BL complex may have a pivotal role in formation of micropolygyria in FCMD. We therefore investigated the cerebral GL-BL complex in seven FCMD cases (12–27 years of age), in three cases of Duchenne muscular dystrophy (17–25 years of age) and in two non-neurological controls (28 and 33 years of age). The frontal lobe cortex was examined immunocytochemically using antibodies against collagen type IV and laminin in each case, and ultrastructurally in an adult case of FCMD. In FCMD, the BL of the cortical surface was frequently breached with protruding neural tissue that ultrastructurally showed frequent synapses, neurites that had parallel arranged microtubules, and astrocytic processes. The outermost surface of this tissue was only partly lined by a BL. In the region of the gyral adhesion of micropolygyria, the perivascular space of the apparently entrapped meningeal blood vessels was occupied by neuroglial tissue, which is assumed to have invaded through the occasionally seen breaches of the perivascular GL-BL complex. Electron microscopy of the intruding tissue showed frequent synapses, microtubule-containing neurites and astrocytic processes. No breached GL-BL complex was found in any of the non-FCMD cases. These findings indicate that in FCMD, the cerebral GL-BL complex continues to have a crucial deficit with resulting breaches through which neuroglial tissue protrudes, promoting adhesion of the adjacent cerebral gyri during brain development before and after birth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004010051089
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  • 6
    Electronic Resource
    Electronic Resource
    Motor neuron disease with predominantly upper extremity involvement: a clinicopathological study (1999)
    Springer
    Acta neuropathologica 98 (1999), S. 645-650 
    Details
    ISSN: 1432-0533
    Keywords: Key words Amyotrophic lateral sclerosis ; Autopsy ; Electron microscopy ; Immunocytochemistry ; Motor ; neuron disease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We report two autopsy cases of motor neuron disease (MND) patients with an unusual type of muscular atrophy predominantly affecting the shoulder girdle and the upper extremities with proximal dominance. Both patients are considered to be clinically categorized into the El Escorial suspected form of amyotrophic lateral sclerosis (ALS). At autopsy, they showed marked loss of spinal anterior horn cells accompanied by astrogliosis positively immunostained with anti-glial fibrillary acidic protein antibody at the cervical level. At the lumbosacral level, anterior horn neurons were relatively well preserved and Bunina bodies, ubiquitin-positive skein-like inclusions and Lewy body-like inclusions were observed in the remaining neurons. In one patient, brain stem motor neurons (nerves V, VII, XII) and motor cortex, including Betz cells, were also affected and the corticospinal tracts were degenerated at the level of the thoracic and lumbar spinal cord. Pathological findings of this patient are consistent with those of ALS. In the other patient, the motor cortex, brain stem motor nuclei and the corticospinal tracts were well preserved, which is pathologically compatible with progressive spinal muscular atrophy. These patients with such a peculiar pattern of progressive muscular atrophy should be placed in a subgroup of ALS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004010051131
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  • 7
    Electronic Resource
    Electronic Resource
    Subretinal macrophages in the developing eye of eutherian mammals and marsupials (1999)
    Springer
    Anatomy and embryology 200 (1999), S. 551-558 
    Details
    ISSN: 1432-0568
    Keywords: Key words Retina ; Development ; Retinal pigment epithelium ; Microglia ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Blood-borne mononuclear cells invade the developing retina via the hyaloid vasculature at the optic nerve head. Following removal of apoptotic cell debris they give rise to the network of resident microglia. The population of cells recently described in the peripheral subretinal space of developing human eyes may represent a further population of macrophages destined to become microglia. The aim of the present study was to confirm the presence of subretinal macrophages in the developing eye in other mammalian species and perform preliminary immunophenotypic analysis in rat tissues. The range of species chosen included eutherian mammals (rat and rabbit) and marsupials (wallaby and opossum). Ocular tissues from a range of developmental stages were studied by scanning electron microscopy and transmission electron microscopy. Distinctive networks of dendriform and pleomorphic macrophages were observed by scanning electron microscopy in the peripheral subretinal space of D2 rabbits, newborn and D2 rats and D75 wallaby. Transmission electron microscopic studies of D2 rabbit, newborn and D2 rat and all ages of North American opossum revealed cells with the ultrastructural features of macrophages in the peripheral subretinal space, cilio-retinal junction and between ciliary epithelial cells. Preliminary immunoperoxidase studies using a panel of anti-leukocyte monoclonal antibodies on frozen sections of rat ocular tissues (newborn, D2 and D4) revealed ED1+ Ox42+ ED2+ but Ox6– cells in the peripheral subretinal space, peripheral retina and ciliary body epithelia. The data confirms that subretinal macrophages are a feature of the developing eye in a broad range of mammalian species and immunophenotypic evidence leads the author to postulate that these cells arise from the ciliary body vasculature and may migrate into peripheral neural retina and mature into resident microglia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004290050303
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic properties of human liver and brain ferritin (1999)
    Springer
    European biophysics journal 28 (1999), S. 263-267 
    Details
    ISSN: 1432-1017
    Keywords: Key words Human liver ; Human brain ; Ferritin ; Electron microscopy ; Mössbauer spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Human brain (globus pallidus) and liver tissues were investigated by means of electron microscopy (EM), Mössbauer spectroscopy (MS) and SQUID magnetometry techniques. Based on MS measurements, the iron present was identified to be in the ferritin-like form (61–88%) and in the form of a low-spin iron species (the balance). Its overall concentration was estimated as 1.5(3) mg in the brain and 2.4(5) mg in the liver, per gram of lyophilized tissue. The average core diameter was determined by EM measurements to be equal to 7.5(1.3) nm for the liver and 3.3(5) nm for the brain. Magnetization measurements carried out between 5 and 300 K yielded an estimation of an average blocking temperature, KT BL, as equal to 6.7 K and 8.5 K for the liver and the brain, respectively. From the dependence of KT BL on the external magnetic field it was concluded that the ferritin-like cores in the studied samples can be regarded as non-interacting particles. Finally, the uniaxial magnetic anisotropy constant was determined to be 6×103 J/m3 for the liver and 4×104 J/m3 for the brain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490050208
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  • 9
    Electronic Resource
    Electronic Resource
    Infraterminal spreading and extrajunctional expression of nicotinic acetylcholine receptors in denervated rat skeletal muscle (1999)
    Springer
    Experimental brain research 125 (1999), S. 426-434 
    Details
    ISSN: 1432-1106
    Keywords: Key words Acetylcholine receptor ; Nicotinic ; Denervation supersensitivity ; Neuromuscular junction ; α-Bungarotoxin ; Immunocytochemistry ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Through the use of biotinylated-bungarotoxin and monoclonal antibodies, the nicotinic acetylcholine receptor (nAChR) was localized in the subneural apparatus of mammalian motor end plates of the flexor digitorum brevis muscle of the adult rat at the light and electron microscopic levels. Under normal conditions, nAChR was located in the primary post-synaptic membrane of the neuromuscular junction, and the depths of the junctional folds constituting the secondary post-synaptic membrane did not contain any nAChR. Up to 75 days after repeated transection of the related motor nerve (sciatic), there was no major alteration in the light-microscopic localization of junctional nAChR in the subneural apparatus, except for a moderate shrinkage and increased immunocytochemical reactivity of the subneural apparatus. At the electron microscopic level, however, immunocytochemical reactivity gradually occupied the entire extent of the secondary post-synaptic membrane, including the depths of the junctional folds, which exhibited extensive branching. In non-innervated portions of the muscle fibers, nAChR receptor appeared in a linear localization on the surfaces of denervated muscle fibers. This linear reaction was not continuous with the nAChR reaction of the motor end plates. It is concluded that denervation supersensitivity might not be due to spreading of junctional nAChR from the end-plate area, but rather to expression of nAChR in non-innervated portions of the muscle fiber and to the infraterminal (subsynaptic) spreading of nAChR into the depths of junctional folds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050699
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  • 10
    Electronic Resource
    Electronic Resource
    Recovery of synapses in axotomized adult cat spinal motoneurons after reinnervation into muscle (1999)
    Springer
    Experimental brain research 125 (1999), S. 19-27 
    Details
    ISSN: 1432-1106
    Keywords: Key words Nerve injury ; Nerve repair ; Retrograde reaction ; Regeneration ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Peripheral axotomy of adult cat spinal motoneurons induces a marked loss of synaptic boutons from the cell bodies and dendritic trees. The aim of the present study was to analyze the recovery of synaptic contacts in axotomized motoneurons following reinnervation into muscle. Adult cat spinal motoneurons were first deprived of their muscular contacts for 12 weeks and, then, allowed to reinnervate their target muscle. Two years later, regenerated motoneurons were labeled with horseradish peroxidase to allow quantitative ultrastructural analyses of the synaptic covering of the cell bodies and dendrites. Presynaptic boutons were classified according to their size and the shape of their synaptic vesicles. Results show that a recovery of synaptic covering occurs in the axotomized neurons after muscle reinnervation, but it affects various bouton types to different degrees. The number of S-type boutons synapsing with the soma was 70% higher after reinnervation than at 12 weeks after axotomy, while the number of F-type boutons had increased by only 13%. Compared with the normal situation, the number of S-type boutons synapsing with the proximal dendrites increased from 82% at 12 weeks after axotomy to 180% in the reinnervated state. In conclusion, in adult cat spinal motoneurons, the reestablishment of muscular contact is followed by a normalization of some of the synaptological changes induced by a prolonged state of axotomy. In certain respects restitution is incomplete, but in others it results in overcompensation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050653
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  • 11
    Electronic Resource
    Electronic Resource
    Phase and aggregation behaviour of double-chain cationic surfactants from the class of N-alkyl-N-alkyl′-N, N-dimethylammonium bromide surfactants (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 856-867 
    Details
    ISSN: 1435-1536
    Keywords: Key words Double chain surfactants ; Aggregates ; Phase diagrams ; Lamellar phases ; Electron microscopy ; SANS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We present the phase diagrams and the properties of newly synthesised double-chain cationic N-alkyl-N-alkyl′-N,N-dimethylammonium bromide surfactants [C x C y DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the systems studied form liquid-crystalline lamellar phases but with different morphologies: unilamellar vesicles at low surfactant concentrations, multilamellar vesicles and tubular aggregates for surfactant concentrations between 2 and 10 wt% and at even higher concentrations planar bilayers of surfactant molecules in the classical Lα phase. The phase diagrams were determined with macroscopic and microscopic methods (polarisation microscopy, freeze-fracture transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination and small-angle neutron scattering measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and viscosity measurements for phase characterisation were carried out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050462
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  • 12
    Electronic Resource
    Electronic Resource
    Synthesis of colloids and films of Pr, Er and Yb with nonaqueous solvents (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 164-173 
    Details
    ISSN: 1435-1536
    Keywords: Keywords Nanostructures ; Thin films ; Vapor deposition ; Electron microscopy ; Optical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Colloidal dispersions of Yb, Er and Pr have been prepared by chemical liquid deposition. The metals were cocondensed at 77 K with 2-methoxyethanol and ethanol to produce solvated metal atoms. The particle size of the dispersions was determined by transmission electron microscopy to range from 52 to 1080 Å; the particles had spherical shapes. After solvent evaporation under vacuum, active solids and amorphous powder were deposited over Cu and Al metal. Dispersion stability, particle size, UV/Vis absorption and zeta potential were studied. The solids prepared by solvent evaporation were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The films prepared on Al were studied by scanning electron microscopy. The most stable colloid was obtained using 2-methoxyethanol: several concentrations were stable for several months and the zeta potential indicated that this colloid stability is mainly due to solvation effects. FTIR spectroscopy of the solids indicated solvent incorporation in the film. This observation was corroborated by thermal analysis. Information on the thermal stability of the films was obtained by TGA. The UV/Vis absorption spectrum was measured at several concentrations under different conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050381
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  • 13
    Electronic Resource
    Electronic Resource
    Muscle and skin biopsies are a sensitive diagnostic tool in the diagnosis of CADASIL (1999)
    Springer
    Journal of neurology 246 (1999), S. 526-532 
    Details
    ISSN: 1432-1459
    Keywords: Key words CADASIL ; Cerebrovascular disease ; Skin biopsy ; Muscle biopsy ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a microangiopathic syndrome. Although the defective gene has been identified, genetic analysis may be effort some due to its large size and various mutations. Providing a reliable diagnostic marker would therefore be helpful. Electron microscopy has revealed characteristic electron-dense granular deposits in the basal lamina of vessels of patients with CADASIL. We investigated the sensitivity of skin and muscle biopsies for diagnosing CADASIL. We examined 30 family members of three unrelated German families affected by CADASIL. In 14 of the 21 affected individuals we performed skin and muscle biopsies; two patients were clinically asymptomatic. Under electron microscopy all muscle and skin biopsy specimens showed patches of granular and electron-dense material in the basal layer of both arterioles and capillaries. These findings confirm that general microangiopathy is a typical feature of this syndrome and is present in the early phase of the disease with or without clinical manifestation. Thus, as electron microscopy of skin biopsy specimens can establish the diagnosis of CADASIL with high certainty, it may be considered the method of first choice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004150050398
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  • 14
    Electronic Resource
    Electronic Resource
    A comprehensive analysis of selected diagnostic methods with respect to their usefulness in evaluating the biology of neoplastic cells in patients with laryngeal cancer (1999)
    Springer
    European archives of oto-rhino-laryngology and head & neck 256 (1999), S. 306-311 
    Details
    ISSN: 1434-4726
    Keywords: Key words Laryngeal cancer ; p53 ; Oncoprotein ; Ki67 ; Proliferating cell nuclear antigen (PCNA) ; DNA ploidy ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The difficult and complicated mechanism of cancer development with little knowledge about the biology of existing cancers can lead to a permanent search for new examination techniques to improve the precision of life expectancy in patients and the selection of the most efficient methods of treatment. The aim of this study was to analyze certain prognostic factors, i.e., p53, Ki67, proliferating cell nuclear antigen (PCNA), DNA ploidy and cell proliferating activity, as well as the degree of morphological differentiation and cell maturity evaluated on an ultrastructural level in patients with laryngeal cancers in connection with data obtained from follow-up examinations and the clinical course of the disease. Neoplastic tissue was taken from 120 patients with laryngeal cancers. All underwent surgical treatment, radiotherapy and combined treatment in the Department of Otolaryngology, Karol Marcinkowski University School of Medical Sciences, Poznań, Poland, and the Department of Otolaryngology – Head and Neck Surgery, Haukeland University, Bergen, Norway. Before beginning treatment all patients underwent histological verification of their neoplastic tissues. Histopathological examination proved that the majority of cases (95%) had a squamous cell carcinoma. The occurrence of changes within the lymph nodes of the neck (N) was significantly correlated with T, S, Ki67, metastases to lymph nodes, DNA ploidy, site and surgery performed. The degree of clinical progression (S) was intercorrelated with T, N, p53, Ki67, PCNA, DNA ploidy, site and laryngectomy. The occurrence of oncoprotein p53 in neoplastic cells was measured by the staining degree of their nuclei and was correlated with T, S, DNA ploidy, metastases to lymph nodes, PCNA and site. The degree of staining of neoplastic cells for the nuclear antigen Ki67 was correlated to T, N, G, S, DNA ploidy, metastases to lymph nodes and surgical treatment. The proliferative antigen PCNA in the examined population of patients was intercorrelated with T, p53, Ki67, metastases to lymph nodes and surgical treatment. The results obtained from DNA flow cytometry could be associated with N, G, p53, Ki67 and metastases to lymph nodes. On the basis of the results obtained, the techniques suggested for the morphological and biological evaluation of neoplastic cells in cancer of the larynx should include TNM classification + G + DNA + p53 + Ki67.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004050050252
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  • 15
    Electronic Resource
    Electronic Resource
    The cytoskeleton of the myenteric neurons during murine embryonic life (1999)
    Springer
    Anatomy and embryology 199 (1999), S. 459-469 
    Details
    ISSN: 1432-0568
    Keywords: Key words Differentiation ; Electron microscopy ; Histochemistry ; Microtubules ; Neurofilaments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The organization of the cytoskeleton has been studied during mouse differentiation in cells of the myenteric neuronal lineage. The entire gut was examined starting from day 12.5 of embryonic life (E12.5) until birth (P0). Immunocytochemistry was performed to evaluate the expression of five of the most represented neurofilaments proteins (the low, NF-L, medium, NF-M, and heavy, NF-H, molecular weight subunits, α-internexin and peripherin) and of two of the microtubule-associated proteins (MAP1 and MAP2a+2b). In parallel, the appearance in the differentiating myenteric neurons of filamentous and microtubular structures and their intracytoplasmatic distribution were observed under the electron microscope. A differential immunohistochemical expression of the structural proteins was found. Immature cells expressed α-internexin, peripherin, NF-M and MAP1 by day E12.5; α-internexin expression was strong in these cells, but gradually decreased with age and was practically absent in adulthood. Conversely, the expression of the other three proteins increased with cell differentiation and was still present in adulthood. NF-L and NF-H expression appeared later, by day E16.5, and was weak for the entire pre- and postnatal life. MAP2a+2b was never expressed. Under the electron microscope, at day E12.5 the cytoskeleton was already organized in filamentous and microtubular structures. At this age neurofilaments were few and mainly located in the cell processes, and microtubules were numerous and mainly assembled in the neuritic growth cones, together with synaptic vesicles. With ageing, neurofilaments and microtubules were ubiquitous in the neuron. Data obtained demonstrate that cytoskeletal proteins gradually accumulate in the cells of the neuronal lineage in parallel with the organization of the cytoskeletal structures, which in turn mediate important neural events by the earliest stages of murine embryonic life, including growth of nerve processes and initiation of axonal transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004290050244
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  • 16
    Electronic Resource
    Electronic Resource
    Outbreaks of gastroenteritis caused by SRSVs from 1987 to 1992 in Kyushu, Japan: Four outbreaks associated with oyster consumption (1999)
    Springer
    European journal of epidemiology 15 (1999), S. 175-180 
    Details
    ISSN: 1573-7284
    Keywords: Electron microscopy ; Epidemiology ; Non-bacterial Gastroenteritis ; Oyster ; Small round structured viruses (SRSVs)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract From 1987 to 1992, 18 outbreaks of acute non-bacterial gastroenteritis occurred in Kyushu district. The most common symptoms were diarrhea, vomiting, nausea and abdominal cramp. Small round structured viruses (SRSVs) were detected in 52 (44.8%) of 116 stool samples from 17 outbreaks by the electron microscopy (EM) method, and a significant increase in the antibody level was noted in 42 (80.7%) of 52 paired serum samples from 12 outbreaks by the immune electron microscopy (IEM) method and in 18 (51.4%) of 35 samples from 8 outbreaks by the western blot (WB) method. However, according to the WB method, antigen-antibody reaction was not observed to reference antigen strips (SRSV-9/Tokyo 86-510, 63kDa) in three of the 8 outbreaks. The detected virus was regarded as an etiologic agent for these outbreaks. In four of 5 outbreaks which appeared associated with eating raw oysters, there was a close relation between SRSV infection and consumption of raw oysters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007543924543
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  • 17
    Electronic Resource
    Electronic Resource
    Metaphase-specific cell death in meiotic spermatocytes in mice (1999)
    Springer
    Cell & tissue research 296 (1999), S. 359-369 
    Details
    ISSN: 1432-0878
    Keywords: Key words Apoptosis ; Electron microscopy ; Meiosis ; Spermatocytes ; Spermatogenesis ; Testis ; TUNEL ; Mouse (10 strains)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Apoptosis of male germ cells is a widespread but little-understood phenomenon in many animal species. The elucidation of its mechanisms could be useful in the understanding of male infertility. We have examined the distribution of dying cells with the terminal transferase-mediated nick-end labeling (TUNEL) method and by an electron-microscopic procedure in the testes of 10 mouse strains, viz., C57BL/10 (B10), SL/NiA (SL), C57BL/6 (B6), C3H/He (C3H), BALB/c (BALB), DBA2 (DBA), CBA/J (CBA), MRL/MpJ-+/+ (M+), MRL/MpJ-lpr/lpr (lpr), and wild-type NJL mice (Mus musculus musculus). In the testes of the B10, NJL, SL, B6, C3H, BALB, DBA, and CBA mice, very few TUNEL-positive cells are distributed in the seminiferous tubules, whereas in the testes of the M+ and lpr mice, many TUNEL-positive cells, which are restricted to stage XII seminiferous tubules, have been identified. The most important finding is that many metaphases of meiotic spermatocytes show a marked TUNEL-positive reaction. Some metaphases show apoptotic morphology electron-microscopically. These results suggest that the testes of MRL strains will provide a useful model for the study of the mechanism of metaphase-specific apoptosis in meiotic spermatocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051296
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  • 18
    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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  • 19
    Electronic Resource
    Electronic Resource
    Op/op mice defective in production of functional colony-stimulating factor-1 lack macrophages in muscularis externa of the small intestine (1999)
    Springer
    Cell & tissue research 295 (1999), S. 485-493 
    Details
    ISSN: 1432-0878
    Keywords: Key words Immunohistochemistry ; Electron microscopy ; Interstitial cells of Cajal ; F4/80 ; CSF-1 ; Kit-receptor ; Mouse (op/op)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The osteopetrotic (op/op) mutant mouse possesses an inactivating mutation in the colony-stimulating factor-1 (CSF-1) gene, which results in the absence of certain macrophages and in osteopetrosis, following a lack of osteoclasts. Studies of the op/op mouse indicate that CSF-1-dependent tissue macrophages may belong to a trophic and/or scavenger subpopulation, which through their effect on other cell types can significantly affect tissue functions, and that cells which are CSF-1 independent have antigen presentation and immunological functions.We have previously identified a cell system of regularly distributed macrophages in the muscularis externa of the small intestine and wanted to extend these studies to the op/op mouse.The present investigations with light- and electron-microscopic methods using fluorescent dextran, methylene blue and immunohistochemistry (F4/80, anti-kit receptor, anti-CD3, anti-CD45R/B220) show that macrophages are absent from the muscle layers, with only an occasional macrophage present in the subserosa. In the lamina propria and submucosa, macrophage numbers are reduced. In all other respects the muscularis externa appears normal, including normal organization and number of interstitial cells of Cajal. Control and op/op mice both lack cells expressing CD3 (T lymphocytes), CD45R/B220 (B lymphocytes) and mast cells in the muscularis externa. This leaves the muscularis externa macrophages as the most likely source of local cytokine production under such conditions as postoperative ileus and intussusception in infants, where the muscularis externa appears to be one target of cytokines. We conclude that the lack of macrophages, combined with the preservation of otherwise normal structure, will make the op/op mouse a valuable model by which to assess the functions and relative importance of the muscularis externa macrophages in relation to intestinal motility under normal and pathological conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051254
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  • 20
    Electronic Resource
    Electronic Resource
    Caveolin and its cellular and subcellular immunolocalisation in lung alveolar epithelium: implications for alveolar epithelial type I cell function (1999)
    Springer
    Cell & tissue research 295 (1999), S. 111-120 
    Details
    ISSN: 1432-0878
    Keywords: Key words Caveolin ; Caveolae ; Lung ; Alveolar epithelial type I cell ; Immunocytochemistry ; Electron microscopy ; Confocal laser scanning microscopy ; Rat (CD)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Caveolae are flask-shaped invaginations of the plasmalemma which pinch off to form discrete vesicles within the cell cytoplasm. Biochemically, caveolae may be distinguished by the presence of a protein, caveolin, that is the principal component of filaments constituting their striated cytoplasmic coat. Squamous alveolar epithelial type I (ATI) cells, comprising approximately 95% of the surface area of lung alveolar epithelium, possess numerous plasmalemmal invaginations and cytoplasmic vesicles ultrastructurally indicative of caveolae. However, an ultrastructural appearance does not universally imply the biochemical presence of caveolin. This immunocytochemical study has utilised a novel application of confocal laser scanning and electron microscopy unequivocally to localise caveolin-1 to ATI cells. Further, cytoplasmic vesicles and flask-shaped membrane invaginations in the ATI cell were morphologically identified whose membranes were decorated with anti-caveolin-1 immunogold label. Coexistent with this, however, in both ATI and capillary endothelial cells could be seen membrane invaginations morphologically characteristic of caveolae, but which lacked associated caveolin immunogold label. This could reflect a true biochemical heterogeneity in populations of morphologically similar plasmalemmal invaginations or an antigen threshold requirement for labelling. The cuboidal alveolar epithelial type II cell (ATII) also displayed specific label for caveolin-1 but with no ultrastructural evidence for the formation of caveolae. The biochemical association of caveolin with ATI cell vesicles has broad implications for the assignment and further study of ATI cell function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051217
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  • 21
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    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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  • 22
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    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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  • 23
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    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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  • 24
    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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  • 25
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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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  • 26
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    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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  • 27
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    Electronic Resource
    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.
    Additional Material: 2 Tab.
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  • 28
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    Electronic Resource
    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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  • 29
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    Electronic Resource
    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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  • 30
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    Electronic Resource
    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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  • 31
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    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.
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  • 32
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    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.
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  • 33
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    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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  • 34
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    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.
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  • 35
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    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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  • 36
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    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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  • 37
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    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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  • 38
    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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  • 39
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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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  • 40
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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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  • 41
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    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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  • 42
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    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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  • 43
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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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  • 44
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    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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  • 45
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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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  • 46
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    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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  • 47
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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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  • 48
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    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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  • 49
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    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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  • 50
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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.
    Additional Material: 1 Tab.
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  • 51
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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)
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  • 52
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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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  • 53
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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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  • 54
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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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  • 55
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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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    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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  • 57
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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.
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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.
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  • 60
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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
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  • 61
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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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  • 62
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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.
    Additional Material: 1 Ill.
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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.
    Additional Material: 2 Ill.
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  • 69
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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%.
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  • 70
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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.
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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.
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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.
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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.
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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.
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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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  • 76
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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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  • 77
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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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  • 78
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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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  • 79
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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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  • 80
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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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  • 81
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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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  • 82
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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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  • 83
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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
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  • 84
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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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    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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  • 86
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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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    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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  • 88
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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.
    Additional Material: 3 Ill.
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  • 89
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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.
    Additional Material: 6 Ill.
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  • 90
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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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    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.
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  • 92
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    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.
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    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.
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  • 94
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    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.
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    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.
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    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:
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  • 97
    Electronic Resource
    Electronic Resource
    Chemical Modification of the Structures and Functions of Proteins by the Cofactor Reconstitution Method (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 539-549 
    Details
    ISSN: 1434-193X
    Keywords: Protein engineering ; Cofactor reconstitution ; Non-natural molecules ; Hemoproteins ; Flavoenzymes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new strategy for the semi-synthesis of proteins and enzymes bearing non-natural functional groups is described. In line with our proposal that the replacement of native cofactors by modified cofactors may represent a useful and general methodology for introducing non-natural molecules into cofactor-dependent proteins and enzymes, we have shown that semi-synthetic cofactors bearing non-natural functional units can be incorporated in the proximity of the active sites of enzymes by cofactor reconstitution. A variety of non-natural building units such as a hydrophobic alkyl chain, a polyanion cluster, metal complexes, electron donors or acceptors, a photochromic moiety, peptides, and artificial receptors have successfully been introduced into hemoproteins (myoglobin, hemoglobin, and cytochrome b562) and their effects on the holoproteins have been examined. Incorporation of a long alkyl chain, for example, greatly facilitates conversion of a water-soluble protein into a membrane-bound protein. Attachment of a photosensitizer has enabled us to switch the enzyme activity by means of visible light. Artificial receptors introduced in the proximity of the active site can modulate the structures and activities of native proteins in response to specific guest molecules. This concept has been expanded to include flavoenzymes such as glucose oxidase. An immense variety of non-natural molecules are available that are potentially useful for protein engineering. By combination of the present cofactor reconstitution method with other techniques such as site-directed mutagenesis, chemical modification, peptide semi-synthesis, and non-natural amino acid incorporation using suppressor t-RNA, it should be possible to artificially manipulate native protein molecules with a similar degree of flexibility as that with which organic chemists manipulate small molecules.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 98
    Electronic Resource
    Electronic Resource
    A COCON Analysis of Proton-Poor Heterocycles - Application ofCarbon Chemical Shift Predictions for the Evaluation of Structural Proposals (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 579-586 
    Details
    ISSN: 1434-193X
    Keywords: Structure elucidation ; Computational method ; Natural products ; HMBC ; Constitutional analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the new computer program COCON (Constitutions from Connectivities) to the 2D-NMR data sets of three different complex natural products is described. The investigated compounds are proton-poor and therefore underdetermined systems. For such molecules the number of possible constitutions and the computational speed of COCON are of interest. Our investigation is focused on how methods of 13C-NMR chemical shift prediction can assist chemists with regard to refining the selection among the constitutions proposed by COCON.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 99
    Electronic Resource
    Electronic Resource
    The Reduction of α-X-Acetophenones (X = PhO, Br, Cl) in Hydrogen-Donating Solvents at Elevated Temperatures (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 607-616 
    Details
    ISSN: 1434-193X
    Keywords: Phenacyl halides ; Hydrogen donor ; Bond dissociation enthalpies ; Lignin ; DFT ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reduction of α-X-acetophenones (X = PhO, Br, Cl), as model compounds for lignin liquefaction studies, has been investigated in the presence of a hydrogen-donating solvent such as 9,10-dihydroanthracene (AnH2) or 2-propanol, between 373 and 573 K. With α-phenoxyacetophenone (PAP) in AnH2, acetophenone and phenol have been obtained with high selectivities. The mechanism involves the reverse radical disproportionation (RRD) with AnH2. Hydrodebromination of α-bromoacetophenone (BrAP) is quantitative at 423 K using AnH2 as a reducing agent. Now, the hydrogen transfer proceeds by an uninhibited radical chain mechanism with anthracenyl radicals as the chain carriers. For the kinetic analysis, the C-X (X = Br, Cl) bond dissociation enthalpies (BDEs) have been determined by means of very low pressure pyrolysis to give BDE(C-Br) = 271 kJ mol-1 and, as a lower limit, BDE(C-Cl) ≈ 309 kJ mol-1, at 298 K. The BDEs are quite at variance with recently published insights derived from an electrochemical study. For comparison, density functional theory calculations (DFT) have been performed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Influence of Transition-Metal Ions on the Aggregation Behavior of a Single-Chained Ammonium Amphiphile Carrying an o-Hydroxyazobenzene Unit (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 627-630 
    Details
    ISSN: 1434-193X
    Keywords: Surfactants ; H aggregates ; Ion pairs ; Copper(II) binding ; Copper ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A novel, single-chained ammonium amphiphile that carries an o-hydroxyazobenzene unit at the terminus of its hydrophobic chain has been synthesized. This compound forms ordered thread-like aggregates upon dispersion in water. These aggregates exhibit a phase transition at 56 °C. The o-hydroxyazobenzene unit binds several transition-metal ions in a 2:1 stoichiometry. Binding of these metal ions results in a lowering of the critical aggregation concentration. From the changes in the UV absorption spectrum it is concluded that the Cu2+ complex forms more tightly packed aggregates in water than the Zn2+ and Ni2+ complexes.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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