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  • 1995-1999  (2.764)
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  • Bone
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  • 1
    Digitale Medien
    Digitale Medien
    Ossifying intramuscular metastasis from colon cancer (1999)
    Springer
    Diseases of the colon & rectum 42 (1999), S. 1225-1227 
    Details
    ISSN: 1530-0358
    Schlagwort(e): Colon cancer ; Adenocarcinoma ; Intramuscular metastasis ; Bone ; Heterotopic ossification ; Soft tissue tumor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract PURPOSE: This report presents a patient who developed severe buttock pain because of an ossified intramuscular metastasis from a sigmoid colon cancer. METHODS: This is a case report and review of the literature for intramuscular metastasis from colon cancer. RESULTS: Computed tomography and magnetic resonance imaging showed a soft-tissue mass with heavy calcification. Histologically, mature compact bone was observed with adenocarcinoma cells dispersed among the bony trabeculae. CONCLUSION: When an intramuscular mass is seen, even if it contains extensive calcification, metastasis from colon cancer should be included in differential diagnosis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02238580
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  • 2
    Digitale Medien
    Digitale Medien
    Density predicts the activity-dependent failure load of proximal femora with defects (1999)
    Springer
    Skeletal radiology 28 (1999), S. 90-95 
    Details
    ISSN: 1432-2161
    Schlagwort(e): Key words DXA ; Bone ; Cadaver ; Biomechanics ; Metastases ; Fracture
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Objective. To determine whether the load-bearing capacity of human proximal femora with metastatic defects can be predicted from the bone mineral content. Design. The bone mineral content (BMC) of the total proximal femur was measured by dual-energy X-ray absorptiometry (DXA). The femurs were loaded so as to simulate stair ascent or external rotation. Patients. Simulated lytic defects were created using specialized cutting tools in the intertrochanteric region of 32 human cadaveric femora. Bone density measurements were made before and after creating defects. Results. A linear relation could be used to predict failure load from BMC or bone mineral density. The slope of the linear relation was greater for loads representing external rotation than for loads representing stair ascent. The linear relations suggest that the BMC measurements account for both the density of the host bone and the amount of bone removed by the defect. Conclusions. The data suggest that between 70% and 80% of the variation in failure load of human femora with lytic metastatic defects can be predicted from the BMC and that relations between BMC and failure load are sensitive to the type of loading. Combined with information on the loads associated with the activities of daily living, these data may be used to help identify patients in whom prophylactic stabilization might prevent a pathologic fracture.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002560050480
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  • 3
    Digitale Medien
    Digitale Medien
    Mikromorphologische Kieferveränderungen nach Bestrahlung (1999)
    Springer
    Mund-, Kiefer- und Gesichtschirurgie 3 (1999), S. 140-145 
    Details
    ISSN: 1434-3940
    Schlagwort(e): Schlüsselwörter Konfokale Laser-Scanning-Mikroskopie ; Dunkelfeldmikroskopie ; Bisbenzimidmarkierung ; Knochen ; Strahlenfolgen ; Radiogener Osteozytentod ; Key words Confocal laser scanning microscopy ; Microscopy ; Bisbenzimide labelling ; Bone ; Radiation effects ; Osteocytes ; Osteoradionecrosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Early radiation effects on human bone may lead to osteoradionecrosis (ORN). Direct bone cellular lesions [28] as well as fibrous degeneration of blood vessels [21] are considered to be pathologically relevant. Only few data on initial subclinical radiation effects are available. Patients were grouped according to the dose of radiation and clinical findings. Group 1: sound human bone of lower jaw, mostly collected during orthodontic surgery (n = 10 patients); group 2: specimens of lower jaw from patients with ORN (n = 12 patients); group 3: specimens of lower jaw from patients with head and neck cancer who were preoperatively treated with 36 Gy radiation; group 4: specimens of lower jaw from patients with head and neck cancer (n = 9) who were treated with 60–70 Gy radiation. Specimens were studied by confocal laser scanning microscopy (CLSM), by conventional light microscopy (DL) and by flourescence darkfield microscopy (DFM) after bisbenzimide staining (H 33258) of the viable cellular nuclei. For the correlating study of identical areas in CLSM and DL the specimens were prepared according to the sawing and grinding technique [8]. All the radiated bony specimens, regardless of the dose of radiation, showed areas of extensive or total loss of vitality of the osteocytes. This finding was also evident after 36 Gy and a short interval between radiation and sample collection (group 3). Additionally, in CLSM micromorphologic lesions of the lamellate structure were seen. With these results we can confirm the loss of vitality of the osteocytes as an initial radiation effect as described earlier [10, 23, 28]. In addition to these findings, alteration of the lamellate microstructure was found in the early phase after radiation. The functional and mechanical significance of these findings should be the subject of further studies.
    Notizen: Für die infizierte Osteoradionekrose (IORN) des Kiefers werden unterschiedliche pathogenetische Mechanismen initialer Strahlenfolgen im Knochen diskutiert: Wichtige Parameter sind dabei die direkte Zellschädigung der Osteozyten [28] und die Gefäßfibrosierung [21]. Bislang liegen wenige Kenntnisse zum Ausmaß der initialen, subklinischen Veränderungen vor. 4 Probengruppen wurden anhand verschiedener Patientenkollektive definiert: Gruppe 1: gesunde Unterkieferproben meist von orthodontischen Operationen (n = 10 Patienten); Gruppe 2: Unterkieferproben mit manifester IORN (n = 12 Patienten); Grruppe 3: Unterkieferproben nach 36 Gy präoperativer Radio(chemo)therapie (n = 9 Patienten); Gruppe 4: Unterkieferproben nach 60–70 Gy Bestrahlung ohne Hinweise auf IORN (n = 9 Patienten). Alle Proben wurden histotomographisch mit konfokaler Laser-Scanning-Mikroskopie (CLSM), durchlichtmikroskopisch (DL) und dunkelfeldmikroskopisch (DFM) nach Fluoreszenzmarkierung des intakten Zellkerns (Bisbenzimid H 33258) untersucht. Korrelierende Histologien identischer Probenareale erfolgten an Trenndünnschliffen [8]. Als Ergebnisse wurden gefunden: 1. Alle unterschiedlich bestrahlte Knochenproben zeigten Areale mit weitgehendem bis vollständigem Verlust vitaler Osteozyten. Diese Strahlenfolge trat auch schon nach 36 Gy und kurzem Intervall bis zur Operation (Gruppe 3) auf. 2. Im CLSM zeigten sich zusätzlich mikromorphologische Veränderungen der lamellären Struktur, die zwischen den Probengruppen progredient waren. Hieraus können folgende Schlußfolgerungen gezogen werden: 1. Der vorbeschriebene Vitalitätsverlust der Osteozyten [10, 23, 28] konnte als sehr frühe, initiale, radiogene Läsion bestätigt werden. 2. Zusätzlich zeigten sich Veränderungen der lamellären Mikroarchitektur des Knochens als frühe und im Gruppenvergleich progrediente Strahlenläsion. Die mikromechanisch funktionelle Bedeutung dieser Veränderung muß in weiterführenden Untersuchungen eruiert werden.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100060050118
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  • 4
    Digitale Medien
    Digitale Medien
    The limited value of radionuclide imaging at symptomatic knee prosthesis (1999)
    Springer
    European journal of orthopaedic surgery & traumatology 9 (1999), S. 251-254 
    Details
    ISSN: 1432-1068
    Schlagwort(e): Bone ; Scintigraphy ; symptomatic ; Knee ; Arthroplasty ; Os ; Scintigraphie ; Genou ; Arthroplastie ; Symptomatique
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Résumé Objectif: Evaluation de la scintigraphie osseuse dans l'arthroplastie totale de genou douloureux. Lieu: Hôpital universitaire, Maastricht et Hôpital Maasland, Sittard. Projet: Investigation clinique retrospective. Méthode: Les dossiers cliniques de 27 patients ayant subi une scintigraphie de l'os, ont été étudiés afin d'analyser les plaintes et la façon de décider le diagnostic. Ces patients avaient des symptômes persistants après l'arthroplastie totale du genou. En plus ont été étudiées les radiographies conventionelles et les scanographies isotopes, sans connaître les dossiers cliniques. Sur la base de ces données nous avons évalué les cas dans lesquels la scanographie isotope du genou a contribué de façon décisive au traitement future. Résultats: La scanographie isotope ne contribue pas à la planification du traitement, si l'examen physique ou les radiographies conventionelles n'ont pas apporté de diagnostic clinique. Il s'agissait ici de 37 % des patients de cette série. Dans les cas où le diagnostic clinique était fait, la scanographie isotope a influencé la décision de diagnostic de 65 % des patients. Cependant, pour les autres patients avec diagnostic clinique (35 %), ce ne fut pas le cas. Conclusion : La répresentation radionucléide est de valeur limitée dans le diagnostic d'une arthroplastie symptomatique totale du genou. Elle peut supporter ou rejeter un diagnostic clinique mais entraînera rarement un changement de traitement, dans l'absence de constatations anormales pendant les examens physiques ou radiologiques.
    Notizen: Summary Objective: Determination of the value of bone scanning in symptomatic total knee arthroplasties. Setting Academic Hospital Maastricht and Maasland Hospital Sittard. Design: Retrospective clinical investigation. Method: The clinical reports of 27 patients, who underwent a bone scintigraphic study, were investigated for complaints and analysis of diagnostic decision making. These patients had persistent symptoms after total knee arthroplasty. In addition, conventional radiographs and the isotope scans were studied without knowledge of the clinical records. Based on these data we evaluated in which cases isotope scanning of the knee had contributed decisively to the further treatment. Results: Isotope scanning did not contribute to the treatment planning if physical examination or conventional radiographs had not led to a clinical diagnosis. This comprised 37% of the patients in our series. If a clinical diagnosis was present, isotope scanning did influence decision making in 65% of the patients. However in the remaining patients with a clinical diagnosis (35%) this was not the case. Conclusion: Radionuclide imaging is of limited value in the diagnostic process of symptomatic total knee arthroplasty. It may support or reject a clinical diagnosis, but in the absence of abnormal findings at physical examinations or radiologic studies, it seldom will induce a change in treatment
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00573333
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  • 5
    Digitale Medien
    Digitale Medien
    Bone substitutes (1999)
    Springer
    European journal of orthopaedic surgery & traumatology 9 (1999), S. 161-165 
    Details
    ISSN: 1432-1068
    Schlagwort(e): Bone ; Bone substitutes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Biocompatible calcium phosphate ceramics has been used for several years in orthopeadic surgery. We have been using two new synthetic biphasic calcium phosphate ceramics (BCP) since September 1996 for bone defect filling in any orthopaedic or trauma operation where autograft use was not possible or even wanted. The first, Eurocer 400® has 300 to 500 micron wide macropores with a totally interconnected porosity. This salt seed like product can be used in bone defect filling, when solidity is not a major concern. The second, Eurocer 200® has not totally interconnected 200 micron large pores. Its main characteristic is a mechanical resistance up to 30 Mpa. We use it in any case of weight-bearing surgery. Different sizes and presentation forms are available and will be chosen according to the recipient site shape. We report one hundred and fifty cases with a six to thirty month follow-up. In one third of the patients hip revision surgery was addressed. Another third concerned recent trauma or sequelae cases,.whereas the last third involved cold orthopaedic procedures. General principles are the need of a living and non-infected site after thorough debridement if necessary. Osteocompatibility of calcium phosphate ceramic is confirmed by our results. We report no mechanical failure. In all cases X-rays show a progressive integration, with new bone formation. Our substitutes have been histologically studied in nine cases, four to fifteen months after implantation. New bone formation around and in the substitute is impressive. Indeed, their good mechanical properties without loss of biological quality is the most relevant feature of these BCPs, leading to a wider indication field; therefore we have now abandoned the use of any bony auto, allo or xenograft.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00542583
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  • 6
    Digitale Medien
    Digitale Medien
    Bone tunnel enlargement after anterior cruciate ligament reconstruction with the hamstring autograft and endobutton fixation technique A clinical, radiographic and magnetic resonance imaging study with 2 years follow-up (1999)
    Springer
    Knee surgery, sports traumatology, arthroscopy 7 (1999), S. 290-295 
    Details
    ISSN: 1433-7347
    Schlagwort(e): Key words Anterior cruciate ; ligament reconstruction ; Bone ; tunnel enlargement ; Hamstring ; tendons ; Magnetic resonance ; imaging ; Radiographic evaluation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Sportwissenschaft
    Notizen: Abstract The aim of this study was to describe the contrast-enhanced magnetic resonance imaging (MRI) appearance of bone tunnel enlargement detected on radiography after anterior cruciate ligament (ACL) reconstruction with semitendinosus and gracilis tendon endobutton (STG-endobutton) fixation technique. Fourteen patients with a STG-endobutton ACL reconstruction were examined 3 months (n = 1), 1 year (n = 1) and 2 years (n = 12) postoperatively. An age- and sex-matched group with a bone–patellar tendon–bone (BTB) autograft ACL reconstruction with similar follow-up was taken as control. Data on clinical examination, laxity and isokinetic muscle torque measurements, anteroposterior and lateral view radiography were obtained, and knee scores (Lysholm and Tegner) were collected. Contrast-enhanced MRI was performed in the STG-endobutton group with a 1.5-T imager. There were no statistical differences between the groups with respect to clinical findings, stability tests, or knee scores. In the STG-endobutton group the average femoral and tibial bone tunnel diameter detected on anteroposterior view radiography had increased at 2-year follow-up by 33% and 23%, respectively. On MRI the ligamentous graft itself was not enhanced by the contrast medium whereas periligamentous tissue within and around the STG graft bundles showed mild contrast enhancement. In conclusion, the MRI results suggest that enhancing periligamentous tissue accumulated in and around the STG graft associated with the tunnel expansion. In spite of the significant bone tunnel enlargement observed on the follow-up radiography the STG-endobutton knees were stable and the patients satisfied.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001670050166
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  • 7
    Digitale Medien
    Digitale Medien
    Advanced glycation endproduct-specific receptors in rat and mouse osteoblast-like cells: regulation with stages of differentiation (1999)
    Springer
    Acta diabetologica 36 (1999), S. 45-52 
    Details
    ISSN: 1432-5233
    Schlagwort(e): Key words Non-enzymatic glycosylation ; Advanced glycation endproducts ; Receptor for advanced glycation endproducts ; Diabetes mellitus ; Osteoblasts ; Bone ; Osteopenia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Advanced glycation endproducts have been implicated in the development of diabetic complications. In addition, these products could also mediate certain bone alterations such as diabetic osteopenia. Several receptors specific for advanced glycation endproduct-modified proteins have been characterized in different cell types, contributing to the recognition and degradation of senescent proteins. In the present report, we investigated the possible presence of advanced glycation endproduct-binding proteins on osteoblast-like cells. Both UMR106 and MC3T3E1 cell lines express specific advanced glycation endproduct-binding sites, with an affinity constant between 0.4 and 1.7 · 106 M−1, depending on the stage of osteoblastic differentiation; and with a receptor capacity of 1.5–2.0 · 107 sites/cell. Osteoblast-like cells were also found to participate both in the uptake and degradation of advanced glycation endproduct-modified bovine serum albumin at 37°C. Radiolabelled ligand blotting studies confirmed the presence of several membrane binding proteins, with apparent molecular masses of 50, 45–40, 30, 25 and 18 kDa; the major bands corresponded to 30 and 25 kDa proteins. This study provides evidence of the presence of advanced glycation endproduct-specific binding sites, and for their regulation with the stage of differentiation, in two osteoblast-like cells in culture.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005920050144
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  • 8
    Digitale Medien
    Digitale Medien
    Die aneurysmatische knochenzyste am kleinfinger (1999)
    Springer
    European journal of trauma 25 (1999), S. 230-236 
    Details
    ISSN: 1615-3146
    Schlagwort(e): Aneurysmatische Knochenzyste ; Knochentumor ; Hand ; Aneurysmal bone cyst ; Bone ; Hand
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Abstract The aneurysmal bone cyst localizised at the longfingers of the hand is an extremely rare clinical entity, particularly considering the age and the distinct aggressiveness in our case. In this specific case of a 53-year-old male the differentialdiagnosis as well as problems of the aneurysmal bone cyst with affection of the phalangeal bone will be discussed. Furthermore the various possibilities of therapy will be focussed on. At first the patient was treated with curettage followed by bone grafting. Already 5 months later a local recurrence appeared. The proximal phalangeal bone and the metacarpophalangeal joint V were almost distroyed. Aiming at preservation of a high funcionality of the hand we amputated the 5th finger in the metacarpophalangeal joint.
    Notizen: Zusammenfassung Die aneurysmatische Knochenzyste mit Lokalisation an der Hand, insbesondere an den Phalangen, ist ein extrem seltenes Krankheitsbild. Auch das Alter des Patienten und die ausgeprägte Aggressivität unseres Falles sind bemerkenswert. Anhand der Krankengeschichte eines 53jährigen Mannes mit Befall der Grundphalanx des fünften Fingers der rechten Hand werden die Problemstellung bzw. Differentialdiagnose verdeutlicht und die verschiedenen Therapiemöglichkeiten besprochen. In unserem Fall wurde zunächst eine Kürettage mit anschließender Spongiosaaufftüllung durchgeführt. Bereits nach fünf Monaten kam es zu einem aggressiven Rezidiv mit Zerstörung der gesamten Grundphalanx und des Grundgelenks, so daß wir uns schließlich unter Berücksichtigung der bestmöglichen Funktion der Hand für eine Amputation des Kleinfingers entschieden haben.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00596732
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  • 9
    Digitale Medien
    Digitale Medien
    Estrogen research (1999)
    Springer
    Reproduktionsmedizin 15 (1999), S. 405-409 
    Details
    ISSN: 1434-808X
    Schlagwort(e): Schlüsselwörter Estrogenrezeptoren ; Knochen ; Arteriosklerose ; Endometrium ; Zentralnervensystem ; Key words Estrogen receptors ; Bone ; Arteriosclerosis ; Endometrium ; Central nervous system
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary Almost each cell in the body is estrogen-receptive. The strength of estrogen influence on organs or organ systems, however, may vary. Thus, estrogen withdrawal may have more or less severe pathophysiological consequences. Recently, the existence of two estrogen receptors has been established (estrogen receptor α and β = ERα and ERβ and several splice variants of these two basic receptor types have been desribed). This, together with our increasing knowledge about tissue-specific enhancer and repressor genes now allows a better understanding of the organ-specific effects of estrogens. In view of gynecological endocrinology, hormone replacement therapy with estrogens is beneficial for most organs in the body (bone, cardiovascular system, CNS). However, pure estrogen therapy may have deleterious effects in the endometrium of the uterus because it may initiate the development of uterine cancer. In the uterus of most species studied so far, no ERβ but only the classical ERα gene has been described. Hence, drug companies have now intensively begun to search for ERβ-specific estrogens. The first, relatively specific, non-steroidal product that addresses primarily the ERβ is the drug raloxifen, which has been recently introduced clinically. However, also some natural phyto-estrogens appear to be ERβ-specific.
    Notizen: Zusammenfassung Fast jede Körperzelle ist estrogenrezeptiv. Es gibt allerdings Organe und Organsysteme, die besonders unter dem Einfluß von Estrogenen stehen und die sich bei Estrogenmangel krankhaft verändern können. Die vielfältigen Wirkungen von Estrogenen konnten nicht vollständig verstanden werden, solange die Existenz von nur einem Estrogenrezeptor quasi ein Dogma war. Erst die Klonierung eines zweiten (Estrogenrezeptor β = ERβ) sowie das bessere Verständnis von gewebespezifischen Enhancer- und Repressor-Genen konnten die vielfältigen und z. T. organspezifischen Wirkungen der Estrogene aufklären. Aus der Sicht der gynäkologischen Endokrinologie ist die Hormonersatztherapie mit Estrogenen für fast alle Organe des Körpers (Knochen, Herz-Kreislauf-System, Zentralnervensystem) segensreich. Eine nicht gestagenbegleitete Estrogentherapie kann allerdings verheerende Folgen am Endometrium mit Entwicklung eines Corpus-Karzinoms haben. Da der Uterus praktisch kein ERβ sondern nur den klassischen ERα exprimiert, hat eine intensive Suche nach ERβ-spezifischen Estrogenen begonnen. Ein erstes, halbwegs spezifisches nicht-steroidales Produkt scheint das kürzlich in die Klinik eingeführte Raloxifen zu sein, aber auch einige Phytoestrogene scheinen ERβ-spezifisch zu wirken.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004440050096
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  • 10
    Digitale Medien
    Digitale Medien
    Recognition and significance of pulmonary bone embolism (1999)
    Springer
    International journal of legal medicine 112 (1999), S. 195-197 
    Details
    ISSN: 1437-1596
    Schlagwort(e): Key words Trauma ; Calcification ; Bone ; Embolism ; Autopsy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Rechtswissenschaft
    Notizen: Abstract Embolism of bone marrow to the lungs is a quite frequent finding after trauma but transport and deposition of solid bone is rarely seen, which may simply be because pulmonary calcifications are not recognized as bone fragments. We report on three patients with embolism of bone spicules to small lung arteries of about 0.5 mm in diameter which were plentiful in two of the patients on postmortem examination. However, the true nature of the emboli was only recognizable after decalcification of lung tissues. It appears that trauma occurring in a septic bone lesion has the greatest chance to provoke bone embolism. The bone spicules do not usually occlude vessel lumina and thus do not severely disturb the blood circulation in the lungs. The bone fragments become covered by endothelium and can remain recognizable for months or even years.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004140050232
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  • 11
    Digitale Medien
    Digitale Medien
    Model for Intravital Microscopic Evaluation of the Effects of Arterial Occlusion-caused Ischemia in Bone (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 508-516 
    Details
    ISSN: 1573-9686
    Schlagwort(e): Angiogenesis ; Artery ; Bone ; Creeping substitution ; Leukocytes ; Osteocytes ; Reperfusion injury ; Trauma
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract An in vivo model has been developed for chronic observation of the effects of ischemia on cortical bone remodeling and perfused vascularity. Diaphragm occluders were implanted around the right common iliac artery of four rabbits and inflated to produce 10 h of ischemia to the limb. Microcirculation was monitored with intravital microscopy of injected fluorescent microspheres and FITC-Dextran 70 through a bone window, the tibial bone chamber implant (BCI). Bone resorption and apposition in the BCI were indicated with mineralization dyes. Between 2 and 12 h following release of the occluder, secondary ischemia/no-reflow and other evidence of reperfusion injury were observed. Vessel damage was suggested by abnormally high leakage of FITC-D70 from the few vessels perfused during secondary ischemia. In the weeks following occluder release perfused vasculature increased beyond pre-occlusion levels. Net bone resorption reached a maximum when vascularity passed normal levels. In order to further validate the arterial occlusion model for osteonecrosis, techniques for (1) confirming bone death and (2) detecting increased leukocyte adherence to endothelial cells were added. The dead cell stain Ethidium homodimer-1 was used to tag dead osteocytes immediately after occlusion and produced a measure designated “osteonecrosis index.” To detect leukocytes adhering to vessel walls, carboxyfluorescein diacetate, succinimidyl ester was injected at occluder release. An increase in the number of adherent leukocytes was detected. © 1999 Biomedical Engineering Society. PAC99: 8764Rr, 8717-d, 8719Tt
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1114/1.194
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  • 12
    Digitale Medien
    Digitale Medien
    Konfokale Laser-Scanning Mikroskopie (CLSM) (1998)
    Springer
    Mund-, Kiefer- und Gesichtschirurgie 2 (1998), S. 141-145 
    Details
    ISSN: 1434-3940
    Schlagwort(e): Schlüsselwörter Konfokale Laser-Scanning-Mikroskopie ; Knochen ; Histotomographie ; Key words Confocal laser scanning microscopy ; Bone ; Histotomography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Objectives: Fixation (formalin), decalcification (sections) or mechanical treatment (grinding) all bear the risk of artifacts occurring during hard-tissue histology. Because studies on the etiology of pathological changes mostly focus on subclinical lesions, artifacts can simulate early changes or even be superimposed on existing changes. The objective of this study was to determine how artifacts can be reduced. Material and methods: In confocal laser scanning microscopy (CLSM) a focused laser beam scans the surface of the specimens and penetrates into the tissue. The intensity of the remitted light is recorded. The confocal effect is due to an extremely small aperture (pinhole), excluding light from out-of-focus planes of the sample. By stepwise movement of the object table, a tomographic series of tomographic images is obtained. Sound cortical bone samples of the lower jaw (n = 20) were studied by light microscopy and by CLSM, visualizing identical areas of a ground sectioned sample after H & E staining. Additionally, embedded and fresh blocks of tissue of the same bone sample were studied histotomographically in the CLSM. Results: (1) Light microscopic micromorphology of cortical bone can be visualized adequately in the CLSM; (2) many structures that can be visualized by light microscopy only after special staining (e.g., osteozyte processes) can be visualized by the CLSM using sample blocks without pretreatment. Conclusion: (1) Nondestructive subsurface histotomography by CLSM totally excludes mechanical artifacts; (2) physicochemical artifacts can be handled more easily because fresh samples can be studied; (3) pseudo-three-dimensional imaging allows histological interpretation of the tissue that is equivalent to macroscopic tomographic techniques (CT, MRT).
    Notizen: Durch Fixierung (Formalin), Entkalkung (Schnitte) oder mechanische Bearbeitung (Schliffe) besteht bei der Hartgewebshistologie das Risiko physikalisch-chemischer oder mechanischer Artefakte. Da Studien zur Ätiopathogenese pathologischer Veränderungen meist auf subklinische Läsionen zielen, besteht die Gefahr, daß Artefakte frühe Veränderungen vortäuschen oder vorhandene überdecken. Es wird der Frage einer artefaktminimierten Histologie nachgegangen. Bei der konfokalen Laser-Scanning-Mikroskopie (CLSM) rastert ein monochromatischer Laserstrahl über die Probenoberfläche und dringt in das Gewebe ein. Die Intensität der remittierten Strahlung wird in einem Detektor gemessen. Durch eine konfokale Blende (pinhole) erreicht nur Laserlicht aus einer extrem dünnen In-Fokus-Ebene den Detektor, so daß schrittweises Bewegen des Objekttischs eine tomographische Serie von Einzelbildern visualisiert. Gesunde kortikale Knochenproben des Unterkiefers (n = 20) wurden durchlichtmikroskopisch und im CLSM untersucht: Dabei wurden identische Probenareale an Dünnschliffen nach HE-Färbung visualisiert. Außerdem wurden eingebettete und frische Gewebeblöcke derselben Knochenproben im CLSM histotomographiert. Als Ergebnisse wurden gefunden: 1. Lichtmikroskopische Mikromorphologie kortikalen Knochens ist im CLSM valide visualisierbar. 2. Viele lichtmikroskopisch erst nach Spezialfärbungen darstellbare Strukturen (z.B. Osteozytenfortsätze) können im CLSM an Probenblöcken ohne Vorbereitung mikroskopiert werden. Hieraus können folgende Schlußfolgerungen gezogen werden: 1. Die zerstörungsfreie Histotomographie des CLSM unter der Probenoberfläche vermeidet mechanische Artefakte völlig. 2. Physikalisch-chemische Artefakte werden kontrollierbar, da auch frische Proben mikroskopiert werden können. 3. Die pseudo-dreidimensionale Darstellung erlaubt eine histologische Gewebeinterpretation, die makroskopischen Schichtbildverfahren (CT, MRT) vergleichbar ist.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100060050049
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  • 13
    Digitale Medien
    Digitale Medien
    Neuer Hydroxylapatitzement für die kraniofaciale Chirurgie (1998)
    Springer
    Mund-, Kiefer- und Gesichtschirurgie 2 (1998), S. S37 
    Details
    ISSN: 1434-3940
    Schlagwort(e): Schlüsselwörter Kalzium ; Phosphat ; Hydroxylapatit ; Zement ; Knochenersatz ; Augmentation ; Key words Calcium ; Phosphate ; Hydroxyapatite ; Cement ; Bone ; Augmentation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary A new stoechiometric mixture of 27% dicalcium-phosphate (DCPA) and 73% tetra-calcium-phosphate (TTCP) can be prepared with water intraoperatively to a paste that subsequently sets to a structurally stabile implant composed of hydroxyapatite (HA). Primary setting time is about 20 min; pH during setting ranges from 6.5 to 8.5. There is no relevant curing heat or expansion or contraction. Compressive strength is about 50 MPa, tensile strength about 8 MPa. Over a period of about 4 h in physiological milieu, the cement converts to hydroxyapatite. This product is no longer redissolvable in normal body fluid. This cement can be used for non-load-bearing applications especially in craniofacial bone surgery. Cranial defects due to tumour or trauma as well as deficits in the facial skeleton may be reconstructed using this new biomaterial. In nine of ten patients we used the hydroxyapatite cement successfully for reconstructions in the craniofacial area. Fluid control of the operation field and implant site is extremely important and sometimes difficult to achieve. Further applications could be all non-load-bearing augmentations such as filling of blocked paranasal sinuses, of dentoalveolar cysts and defects following dental apectomy or fixation of implanted hearing-aid electrodes. The perspectives for the hydroxyapatite cement include its application as a carrier for osteogenic protein preparations, especially because of its isothermic reaction and intrinsic osteoconductive characteristics.
    Notizen: Zusammenfassung Ein neuer Kalziumphosphatzement besteht aus 73% Tetrakalziumphosphat und 27% Kalziumhydrogenphosphat. Er bindet bei Körpertemperaturen nach Zugabe von Wasser innerhalb von 20 min ab. Innerhalb von 4 h wird der Zement zu Hydroxylapatitkristallen umgesetzt und damit wasserunlöslich. Der Abbindeprozeß verläuft nahezu isotherm im pH-Bereich von 6,5–8,5 ohne Schrumpfung. Die Druckfestigkeit liegt im ausgehärteten Zustand oberhalb von 50 MPa, die Zugfestigkeit bei mehr als 8 Mpa. Der Zement ist für alle nicht lasttragenden Knochenaugmentationen und Knochenersatzanwendungen insbesondere am Gesichtsschädel geeignet. Bei 9 von 10 Patienten benutzten wir den Zement erfolgreich für Rekonstruktionen im kraniofazialen Bereich. Beim klinischen Einsatz muß besonders auf sorgfältige Trockenlegung des Operations- und Implantationsfelds geachtet werden. Weitere Anwendungsmöglichkeiten sind das Auffüllen von ausgeräumten und verblockten Schädelhöhlen, die Fixation von implantierten Hörelektroden in der Hals-Nasen-Ohren-Heilkunde sowie das Auffüllen von Zysten und Wurzelspitzenresektionsdefekten in der dentoalveolären Chirurgie. Besondere Perspektiven bietet der Hydroxylapatitzement wegen seiner isothermen Abbindereaktion und seiner intrinsischen osteokonduktiven Eigenschaften als Trägermaterial für osteogene Proteinkomplexe.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00014476
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  • 14
    Digitale Medien
    Digitale Medien
    Osseous hemangiopericytomas of unsuspected intracranial origin (1998)
    Springer
    Skeletal radiology 27 (1998), S. 98-102 
    Details
    ISSN: 1432-2161
    Schlagwort(e): Key words Hemangiopericytoma ; Brain ; Bone ; Metastasis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Two cases of osseous hemangiopericytoma are presented that were initially diagnosed as primary in origin, but later reclassified as metastases, after a history of resection for an intracranial tumor was discovered. An intracranial source should be excluded before an isolated osseous tumor is determined to be a primary hemangiopericytoma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002560050345
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  • 15
    Digitale Medien
    Digitale Medien
    Muscular dystrophy: Centronucleation may reflect a compensatory activation of defective myonuclei (1998)
    Springer
    Journal of biomedical science 5 (1998), S. 54-61 
    Details
    ISSN: 1423-0127
    Schlagwort(e): Muscular dystrophy ; Central nuclei ; Avian muscle ; Inflammation ; Dwarfism ; Lymphocyte ; Mechanochemical transducer ; Bone ; Steroid ; Fiber splitting
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Muscular dystrophy has long been believed to be characterized by degeneration and abortive regeneration of muscle fibers (the muscle degeneration theory), but unfortunately its pathogenesis is still unclear and an effective treatment has yet to be developed. As a challenge to the theory, we have proposed an alternative muscle-defective-growth theory and a further bone muscle growth imbalance hypothesis supposing possible defects in bone-growth-dependent muscle growth based on our findings in hereditary dystrophic dy mice (C57BL/6Jdy/dy). This review presents some new insights into the pathogenesis of the disease along with our hypothesis, focusing on the physiological meaning of centronucleation, one of the major pathological changes commonly observed in dystrophic muscles of man and experimental animals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02253356
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  • 16
    Digitale Medien
    Digitale Medien
    Cell behaviour in tubes (1998)
    Springer
    Experimental biology online 3 (1998), S. 1-15 
    Details
    ISSN: 1430-3418
    Schlagwort(e): Bone ; Cell behaviour ; Chondrocyte ; Endothelia ; Epitenon
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The motile behaviour, growth and reactions of osteoblasts, chondrocytes, epitenal cells and endothelia to culture on extended concave surfaces inside tubes is reported. Time-lapse video observations show that these cells can be successfully grown in quartz tubes for up to 21days. The cells would attach to the concave surfaces even when the radius of curvature was as low as 25 μm. The cells attached to the walls were not oriented. As culturing progressed the chondrocytes, osteoblasts and epitenon cells tended to detach from the walls of the tubes, forming long cords of cells attached to the walls at a few points only. Endothelial cells did not detach. These cords showed extensive lamellipodial activity at their points of attachment to the tube wall. The cells in these cords do not show contact inhibition of movement.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s00898-998-0002-6
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  • 17
    Digitale Medien
    Digitale Medien
    Humoral factor in children with neonatal Bartter syndrome reduces bone calcium uptake in vitro (1998)
    Springer
    Pediatric nephrology 12 (1998), S. 371-376 
    Details
    ISSN: 1432-198X
    Schlagwort(e): Key words: Neonatal Bartter syndrome ; Bone ; Cal- cium ; Heparin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. The neonatal Bartter syndrome (NBS) is associated with a complex disorder of mineral metabolism in children, including hypercalciuria, nephrocalcinosis, and diminished bone mineral density. Although cyclooxygenase inhibition usually brings about improvement in these findings, there is a variable component which is resistant to such therapy in many children. The factor mediating this disorder has not been identified. Blood and urine from 12 children with NBS were examined. When compared with samples from normal children and adults, all (NBS) sera reduced bone calcium uptake in a bone disc bioassay. This effect persisted in the presence of parathyroid hormone (PTH) antibody and PTH receptor blockade, indicating that neither PTH nor PTH related peptide was responsible. It was eliminated by indomethacin, suggesting that prostanoid generation was essential. Protamine was also inhibitory, as was the addition of ecteola, an anion binder. Activity could be recovered from ecteola by elution with hypertonic buffer. Urine samples from children with NBS had the same calcitropic effect. The agent was removed by ecteola and recovered by hypertonic elution. Activity was eliminated by protamine and by heparinase, but not by trypsin digestion. Size exclusion centrifugation showed that the activity was associated with a material between 10 and 30 kilodaltons. Finally, urine ecteola eluates from NBS patients raised serum concentrations of calcium after intraperitoneal injection in rats. These data suggest that children with NBS have a calcitropic substance in their serum and urine which is not found in normal individuals. The substance is heparin like, and mediates its effects through prostanoid production. These studies provide additional evidence against a direct renal cause of the urinary calcium disturbance characteristic of the disorder.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004670050468
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  • 18
    Digitale Medien
    Digitale Medien
    Cystic angiomatosis of bone with massive osteolysis of the cervical spine (1998)
    Springer
    European spine journal 7 (1998), S. 257-259 
    Details
    ISSN: 1432-0932
    Schlagwort(e): Key words Angiomatosis ; Bone ; Osteolysis ; Cervical spine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The case of a 21/2-year-old boy with diffuse cystic angiomatosis of bone is presented. No evidence of visceral involvement was recorded. The clinical, radiographic and histologic findings during the course of the disease process are discussed. At the age of 15 years the patient died of neurologic alterations developed due to massive osteolysis and collapse of the cervical spine, and severe dyspnoea, secondary to persistent bilateral pleural effusions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005860050069
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  • 19
    Digitale Medien
    Digitale Medien
    Intraosseous malignant peripheral nerve sheath tumor in a patient with neurofibromatosis (1998)
    Springer
    Skeletal radiology 27 (1998), S. 346-349 
    Details
    ISSN: 1432-2161
    Schlagwort(e): Key words Neurofibromatosis ; Malignant peripheral nerve sheath tumor ; Bone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Malignant peripheral nerve sheath tumors (MPNSTs) are uncommon sarcomas that almost always arise in soft tissue. They can develop in pre-existing neurofibromas or schwannomas, de novo from peripheral nerves, or following radiation therapy. Primary intraosseous MPNST is rare and has been reported most frequently in the mandible. Of the reported cases involving the long bones, none has been associated with neurofibromatosis type 1 (NF-1). We report a case of MPNST arising in the femur in a patient with NF-1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002560050395
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  • 20
    Digitale Medien
    Digitale Medien
    Vascularized knee joint transplantation in man: a report on the first cases (1998)
    Springer
    Transplant international 11 (1998), S. S487 
    Details
    ISSN: 1432-2277
    Schlagwort(e): Key words Knee joint ; Vascularized graft ; Bone ; Transplantation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Four transplantations of an allogeneic vascularized human knee joint were performed at the Trauma Center Murnau between April 1996 and July 1997. The indication for the procedure was the total loss of the knee joint including the extensor apparatus due to severe trauma. These were the first transplants of this type. Management of patients started with closure of soft-tissue defects. After successful completion, stabilization was achieved with femoral and tibial nails plus a temporary arthroplasty. AB0 compatibility and a negative cross-match were the main criteria for selecting patients for transplantation. Interlocking compression nails were used for osteosynthesis. Vascular anastomoses between graft and recipient vessels were established by the end-to-side technique. Immunosuppression was started as a quadruple induction therapy for 3 days, then reduced to a two-drug maintenance therapy with cyclosporine and azathioprine. Six months posttransplantation the osteotomies were bridged by callus and the patients became completely mobile. Radiographic and histological examinations revealed vital graft tissue.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001470050525
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  • 21
    Digitale Medien
    Digitale Medien
    Light- and electron-microscopic study of the distribution of axons containing substance P and the localization of neurokinin-1 receptor in bone (1998)
    Springer
    Cell & tissue research 293 (1998), S. 87-93 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Osteoclasts ; Osteoblasts ; Osteocytes ; Bone ; Substance P (SP) ; Neurokinin-1 receptor (NK1-R) ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  Substance P (SP) is a neuropeptide that is released from axons of sensory neurons and causes signal transduction through the activation of the neurokinin-1 receptor (NK1-R). The present study demonstrates the distribution of SP-like-immunoreactive (SP-LI) axons and the localization of NK1-Rs in rat bone tissue using the avidin-biotin-peroxidase complex method. Axons with SP-LI were commonly found near the trabecular bone in the temporal bone marrow, but they were only sparsely distributed in the mandible, femur, and tibia. Immunoreactivity for NK1-Rs was found on the plasma membrane and in the cytoplasm of the osteoclasts. In the osteoblasts and osteocytes, a small number of weak, punctate immunoreactive products of NK1-Rs were distributed close to the plasma membrane. At the electron-microscopic level, immunoreactivity for NK1-R was distributed mainly in the whole cytoplasm, except for the clear zone of the osteoclasts, and in pit-like structures along the plasma membrane. The NK1-R-immunoreactive structures in the cytoplasm were divided into two types of organelles, consisting of vesicular and vacuolar structures (probably transport vesicles and early endosomes). In the osteoblasts and osteocytes, the number of NK1-R-positive vesicular structures was fewer than in the osteoclasts. These results thus suggest that SP secreted by the sensory axons could directly modulate bone metabolism via NK1-Rs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051100
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  • 22
    Digitale Medien
    Digitale Medien
    Ultrastructural and lanthanum tracer examination of rapidly resorbing rat alveolar bone suggests that osteoclasts internalize dying bone cells (1998)
    Springer
    Cell & tissue research 293 (1998), S. 173-176 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Osteoclast ; Bone ; Bone resorption ; Alveolar bone ; Rat (Wistar)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  Glutaraldehyde-formaldehyde fixed undecalcified alveolar bone from 7-day-old rats was prepared for light and electron microscopy. Colloidal lanthanum was used as an ultrastructural tracer, and both random and semi-serial sections were examined. Lanthanum penetrated the infoldings of the ruffled border and some nearby vacuoles and vesicles. The majority of vacuoles and vesicles were lanthanum-free. Some osteoclast profiles contained a large vacuole with a cell enclosed in its interior. The enclosed cell exhibited an irregular nucleus containing condensed peripheral chromatin, intact cytoplasmic organelles, conspicuous rough endoplasmic reticulum and large blebs on the cell surface. These features are characteristic of osteoblasts or bone-lining cells or immature osteocytes which may be undergoing apoptosis or necrosis. The observation of remnants of cellular structures within internalized osteoclast vacuoles, together with the above results, suggests that osteoclasts engulf and probably degrade dying osteoblasts/bone-lining cells or immature osteocytes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051109
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  • 23
    Digitale Medien
    Digitale Medien
    Stress fractures (1998)
    Springer
    Clinical rheumatology 17 (1998), S. 47-51 
    Details
    ISSN: 1434-9949
    Schlagwort(e): Bone ; Fatigue ; Stress fracture ; Stress reaction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Stress fractures are being increasingly reported as a common cause of morbidity in both healthy populations and those withunderlying diseases involving abnormal bone. An insight into the types and pathogenesis of stress fractures is necessary to considering the diagnosis, management and prevention of such conditions. The classification, aetiology and aspects of management are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01450958
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  • 24
    Digitale Medien
    Digitale Medien
    Identifikation eines skelettierten Kleinkind-Schädels durch die molekularbiologische Untersuchung von Hirnresten (1998)
    Springer
    Rechtsmedizin 8 (1998), S. 109-111 
    Details
    ISSN: 1434-5196
    Schlagwort(e): Key words Identification ; Forensic osteology ; DNA typing ; PCR ; Brain ; Bone ; Schlüsselwörter Identifikation ; Forensische ; Osteologie ; DNA-Typisierung ; PCR ; Gehirn ; Knochen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Rechtswissenschaft
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Ein weitgehend skelettierter Kleinkind-Schädel konnte mittels forensisch-anthropologischer Befunderhebung klassifiziert und mittels erfolgreicher DNA-PCR-Typisierung am Hirnbrei, nicht jedoch am Schädelknochen identifiziert werden. Die vorgestellte Kasuistik belegt eindrücklich, daß eine sorgfältige forensisch-anthropologische Befunderhebung eine wesentliche Grundlage für die molekularbiologische Identifizierung an Skeletteilen bildet und daß auch an fortgeschritten fäulnisverändertem Gehirn bei feuchtem Lagerungsmilieu eine DNA-PCR-Typisierung erfolgreich sein kann.
    Notizen: Abstract The skull of a small child, which was largely devoid of soft tissue, was classified according to forensic/anthropological findings and could be identified on the basis of DNA typing by PCR using residual brain tissue, but not bone. This case illustrates the fact that careful forensic/anthropological investigation is an important basis for molecular biological identification from skeletal remains and that DNA typing by PCR may even be possible on brain tissue that has been exposed to damp conditions and is an advanced state of decomposition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001940050041
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  • 25
    Digitale Medien
    Digitale Medien
    Structure and Dynamics of Hydrogen Chelates. Part 1. NMR-spectroscopic studies in the quinazoline-2-acetonitrile series (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 236-250 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: To get informations on both the structure and dynamics of hydrogen chelates 1 of heteroaromatic systems, a great variety of quinazoline-2-acetonitrile chelates were synthesized (see 2-4). Similarly to the situation of the corresponding H-chelates in the pyrimidine-2-acetonitrile series, the investigation of these new derivatives 2-4 by NMR spectroscopic methods (DNMR, COSY, NOESY, ROESY, EXSY, HMQC, HMBC) confirms the presence of an equilibrium of the two possible H-chelate structures (two ‘rotamers’ I and II, i.e., (E)/(Z) isomers; see Scheme). The corresponding equilibria I ⇌ II were determined by complete 1H-NMR signal assignment at low temperatures (after freezing the rotational processes). In addition, the tautomer equilibria A ⇌ B (relative energies of the two minima of the nonsymmetrical double-well potential) for both ‘rotamers’ are ascertained by H,H and C,H couplings. The results are an important basis for the interpretation of both the UV/VIS absorptions and the dependence of fluorescence and fluorescence quantum yields on temperature.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810206
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  • 26
    Digitale Medien
    Digitale Medien
    Stereoselective Reactions of Phthalimido-Substituted Radicals Derived from (±)-Threonine: A comparison with reactions of N-phthaloyliminium ions (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 268-284 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Stereoselective reactions of phthalimido-substituted radicals derived from (±)-threonine with different radical traps are reported (Scheme 3, Table 1). A strong influence of the nature of the radical trap on the stereoselectivity was noticed. Small nucleophilic radical traps gave preferentially the syn products. The observed selectivities are explained with the A1,3 strain model and depend on steric and electronic effects (Fig. 2). Reactions with electrophilic radical traps such as diphenyl diselenide gave the anti diastereoisomers with moderate stereocontrol, presumably due to stereoelectronic effects. The same stereochemical outcome, i.e., preferential formation of the anti products, was observed for the reactions of the related N-phthaloyliminium ion (Scheme 5, Table 2). The stereochemistry of the ionic reaction is rationalized by a Felkin-Anh model (Fig. 3).
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810208
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  • 27
    Digitale Medien
    Digitale Medien
    Cyclopalladation of 1,1′-Azonaphthalene (= Di(naphthalen-1-yl)diazene): Isolation and characterization of two isomeric complexes (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 307-316 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The cyclopalladation of 1,1′-azonaphthalene (= di(naphthalen-1-yl)diazene; 2) with bis(hexafluoroacetyl-acetonato)palladium(II) (3; [Pd(hfa)2]) yields the ortho-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[1-(naphthalen-1-ylazo-κN2)naphthalen-2-yl-κC2]palladium(II) (4) as well as the peri-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[8-(naphthalen-1-ylazo-κN2)naphthalen-1-yl-κC1]-palladium(II) (5); their structures were corroborated by X-ray analyses. The formation of the novel peri-metallated product 5 containing a six-membered palladacycle strongly depends upon the reaction conditions.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810211
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  • 28
    Digitale Medien
    Digitale Medien
    The Photoisomerization Behavior of the (4-Hydroxycinnamoyl)-spermidines (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 342-352 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The photoisomerization behavior of three mono[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 1, 2, and 3, and three bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 4, 5, and 6, are investigated. The synthetic product (E)-1 could be almost quantitatively (〉 96%) converted into its isomer (Z)-1 under UV light irradiation. In the cases of (E)-2 and (E)-3, a mixture of (E)/(Z) ca. 1:2 was obtained, when the same conditions were applied. The comparison of their UV spectra provides the possible explanation for these different behaviors. Furthermore, it was noticed that the (Z) → (E) isomerization of the C=C bond took place during the purification by reverse-phase high-performance liquid chromatography (RP-HPLC), and the (E)/(Z)-mixture is thus inseparable. The same feature could be observed during the isolation of the (Z,Z)-N,N′-bis[3-(4-hydroxyphenyl)prop-2-enoyl]-spermidines, (Z,Z)-4, (Z,Z)-5, and (Z,Z)-6. Nevertheless, the fractions of (Z,Z)-5 and (Z,Z)-6 were in almost pure state collected, and their 1-NMR spectra are presented.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810215
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  • 29
    Digitale Medien
    Digitale Medien
    Preparation and Absolute Configuration of (-)-(E)-α-trans-Bergamotenone (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 153-162 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis, absolute configuration, and olfactive evaluation of (-)-(E)-α-trans-bergamotenone (= (-)-(1′S,6′R,E)-5-(2′,6′-dimethylbicyclo[3.1.1]hept-2′-en-6′-yl)pent-3-en-2-one; (-)-1), as well as its homologue (-)-19 are reperted. The previously arbitrarily attributed absolute configuration of 1 and of (-)-α-trans-bergamotene (= (-)-(1 S,6R)-2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1. 1]hept-2-ene; (-)-2), together with those of the structurally related aldehydes (-)-3a,b and alcohols (-)-4a,b, have been rigorously assigned.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810114
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  • 30
    Digitale Medien
    Digitale Medien
    New Synthesis and Chirality of (-)-4,4,4,4′,4′,4′-Hexafluorovaline (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 182-186 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (-)-(R)-4,4,4,4′,4′,4′-Hexafluorovaline hydrochloride ((R)-5) of 98% ee is prepared from β,β-bis(trifluoromethyl)acrylic acid (= benzyl 4,4,4-trifluoro-3-(trifluoromethyl)but-2-enoate; 1) in 4 steps with an overall yield of 9.6%. Key step is the separation of the TsOH salts of the diastereoisomers obtained by anti-Michael addition of (+)-(R)-1-phenylethylamine (2) to 1 (→ (R,R)-3). In contrast to the published (S)-chirality, the X-ray structure analysis of (R,S)-6 reveals, that (R)-chirality has to be assigned to the levorotatory (-)-4,4,4,4′,4′,4′-hexafluorovaline hydrochloride.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810117
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  • 31
    Digitale Medien
    Digitale Medien
    Tripodal Dodecadentate Ligands with Salicylamide and bipyridine binding sites for iron(II) and iron(III) coordination (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 207-218 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis and characterization of tripodal dodecadentate ligands with salicylamide and bipyridine binding sites for iron(II) and iron(III) are presented.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810203
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  • 32
    Digitale Medien
    Digitale Medien
    N,N-Dialkylcarbamato Complexes of the d10 cations of copper, silver, and gold (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 219-230 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of CuO'Bu with CO2, and iPr2NH in the presence of PPh3, gives the dialkylcarbamato complex [Cu(O2CNiPr2)(PPh3)2] (1). The CO2/R2NH system (R = Me, Et) in an appropriate organic medium reacts with Ag2O giving the corresponding N,N-dialkylcarbamato complexes of analytical formula [Ag(C2CNR2)] (R = Me, 2; R = Et, 3). The methyl derivative 2 was characterized by X-ray diffraction methods. Crystal data of 2: for [Ag2(O2CNMe2)2], C6H12Ag2N2O4, mol. wt. 391.9; monoclinic, space group P21/c, a = 12.08(1), b = 3.797(2), c = 11.316(7) Å, β = 113.37(6)°, V = 476.3 Å3, Z = 2, Dc = 2.732 g cm-3; μ(MoKα) = 40.64 cm-1, F(000) = 376.0; R = 0.059, Rw = 0.067; g.o.f. 1.27. The structure consists of dinuclear [(Ag2OCNMe2)2] units with slightly distorted linearly two-coordinated Ag-atoms containing bridging carbamato groups to form a substantially planar eight-membered ring with an intra-annular Ag—Ag distance of 2.837(2) Å; the dinuclear units are further joined by Ag—O bonds to form an infinite array. Compound 3, which is presumably dinuclear, as suggested by cryoscopic measurements in benzene, undergoes a structural fission with PPh3, giving the mononuclear triphenylphosphine derivative [Ag(O2CNEt2)(PPh3)2] (4). The amine-catalyzed conversion of Ag2O into Ag2CO3, in the presence of the iPr2NH/CO2 system, is also reported. Cl-Exchange from [AuCl(PPh3)] with [Ag(O2CNEt2)] (3) gives the first N,N-dialkylcarbamato complex of gold, namely [Au(O2CNEt2)(PPh3)] (5), which crystallizes in the monoclinic system: C23H25AuNO2P · 0.5 C7H16, mol. wt. 625.5, space group P21/c; a = 13.212(5), b = 12.25(1), c = 16.795(6) Å, β = 109.09(2)°, V = 2568(2) Å3, Z = 4, Dc, = 1.618 g cm-3; μ(AgKα) = 31.40 cm-1, F(000) = 1236.0; R = 0.058; Rw = 0.064; g.o.f. 2.121. The compound contains two-coordinated Au-atom, namely to the P-atom and to the O-atom of the monodentate carbamato group, the P—Au—O bond angle being 174.7(3)°. The reaction with MeI showed these compounds to react predominantly at the carbamato O-atom giving the corresponding urethanes R2NCO2Me. Evidence was gathered for the transient coordination of CO to Ag in 3.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810204
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  • 33
    Digitale Medien
    Digitale Medien
    1,3-Oxathiole and Thiirane Derivatives from the Reactions of Azibenzil and α-diazo amides with thiocarbonyl compounds (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 285-302 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reactions of α-diazo ketones 1a,b with 9H-fluorene-9-thione (2f) in THF at room temperature yielded the symmetrical 1,3-dithiolanes 7a,b, whereas 1b and 2,2,4,4-tetramethylcyclobutane-1,3-dithione (2d) in THF at 60° led to a mixture of two stereoisomeric 1,3-oxathiole derivatives cis- and trans-9a (Scheme 2). With 2-diazo-1,2-diphenylethanone (1c), thio ketones 2a-d as well as 1,3-thiazole-5(4H)-thione 2g reacted to give 1,3-oxathiole derivatives exclusively (Schemes 3 and 4). As the reactions with 1c were more sluggish than those with 1a,b, they were catalyzed either by the addition of LiClO4 or by Rh2(OAc)4. In the case of 2d in THF/LiClO4 at room temperature, a mixture of the monoadduct 4d and the stereoisomeric bis-adducts cis- and trans-9b was formed. Monoadduct 4d could be transformed to cis- and trans-9b by treatment with 1c in the presence of Rh2(OAc)4 (Scheme 4). Xanthione (2e) and 1c in THF at room temperature reacted only when catalyzed with Rh2(OAc)4, and, in contrast to the previous reactions, the benzoyl-substituted thiirane derivative 5a was the sole product (Scheme 4). Both types of reaction were observed with α-diazo amides 1d,e (Schemes 5-7). It is worth mentioning that formation of 1,3-oxathiole or thiirane is not only dependent on the type of the carbonyl compound 2 but also on the α-diazo amide. In the case of 1d and thioxocyclobutanone 2c in THF at room temperature, the primary cycloadduct 12 was the main product. Heating the mixture to 60°, 1,3-oxathiole 10d as well as the spirocyclic thiirane-carboxamide 11b were formed. Thiirane-carboxamides 11d-g were desulfurized with (Me2N)3P in THF at 60°, yielding the corresponding acrylamide derivatives (Scheme 7). All reactions are rationalized by a mechanism via initial formation of acyl-substituted thiocarbonyl ylides which undergo either a 1,5-dipolar electrocyclization to give 1,3-oxathiole derivatives or a 1,3-dipolar electrocyclization to yield thiiranes. Only in the case of the most reactive 9H-fluorene-9-thione (2f) is the thiocarbonyl ylide trapped by a second molecule of 2f to give 1,3-dithiolane derivatives by a 1,3-dipolar cycloaddition.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810209
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  • 34
    Digitale Medien
    Digitale Medien
    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810301
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  • 35
    Digitale Medien
    Digitale Medien
    Synthesis of Chiral C2-Symmetric Binucleating Ligands (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 491-506 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of a series of chiral enantiomerically pure C2-symmetric binucleating ligands is reported. Ligands of type 1-4, which consist of a phenolic or heterocyclic unit bridging two chiral dihydrooxazole rings. are readily accessible from chiral amino alcohols. Ligands 5a and 5b are composed of a cyclic urea or thiourea unit, respectively, and two 3,4-dihydro-2H-pyrrole rings containing a stereogenic center next to the N-atom. Compounds of this type are readily assembled from ethane-1,2-diamine and an imidothioic ester derived from pyroglutamic acid. These new ligands, which can coordinate two metals in close proximity to each other, are of interest regarding possible applications in asymmetric catalysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810304
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  • 36
    Digitale Medien
    Digitale Medien
    Stability and Lability of Dicopper Double-Stranded Helicates in Solution (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 548-557 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Stability constants have been measured for a series of ligands based on a 2,2′-(pyridine-2,6-diyl)bis[1H-benzimidazole] unit which forms dinuclear double-stranded helical complexes with copper(I). Variation of different structural parameters confirms the importance of the coordinate bond, the stacking interactions, and the weakly bridging pyridine units observed by X-ray crystallography. The stabilities of the complexes depend strongly on the solvent, and in MeCN, which is a good solvent for copper(I), the complexes are less stable and assemble in a stepwise manner. The interconversion of the enantiomers may be followed by 1H-NMR and takes place on a millisecond time scale around room temperature. The trends in lability are similar to those found for the stability of the complexes.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810308
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  • 37
    Digitale Medien
    Digitale Medien
    7-Deazapurine Oligodeoxyribonucleotides: The effects of 7-deaza-8-methylguanine on dna structure and stability (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 570-583 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oligodeoxyribonucleotides containing 7-deaza-2′-deoxy-8-methylguanosine (m8c7Gd; 2b) were prepared. For this purpose, the phosphonate 3a and the phosphoramidite 3b were synthesized and employed in solidphase oligodeoxyribonucleotide synthesis. The structures and the thermodynamic data of duplex formation of oligodeoxyribonucleotides containing 2b were investigated by temperature-dependent CD and UV spectra and compared with those containing 7-deaza-2′-deoxy-7-methylguanosine (m7c7Gd) or 7-deaza-2′-deoxy-guanosine (c7Gd; 2a). In general, compound 2b reduces the duplex stability. In case of the sequence d(m8c7G-C)4 (18), the B → Z transition was facilitated by the incorporation of 2b. Moreover, a single 7-deaza-8-methylguanine residue present in an oligodeoxyribonucleotide tract of guanine residues destabilizes the dG quadruplex significantly. This destabilization is more pronounced than in the case of 7-deazaguanine or 7-deaza-7-methyl-guanine.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810310
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  • 38
    Digitale Medien
    Digitale Medien
    Absolute rate Constants for the Addition of Malonyl Radicals to Alkenes in Solution (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 770-780 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Absolute rate constants and their Arrhenius parameters are obtained for the addition of a cyclic malonyl radical derived from Meldrum's acid to 20 mono- or 1,1-disubstituted alkenes in (±)-propylene oxide and for the addition of the open-chain di(tert-butyl)malonyl radical to six mono- or 1,1-disubstituted alkenes in 1,1,2-trichloro-1,2,2-trifluoroethane by time-resolved electron spin resonance spectroscopy. At room temperature, the radicals add at the unsubstituted C-atoms with rate constants ranging from 1.1. 105 M-1S-1 (acrolein) to 2.4. 106 M-1S-1 (1,1-diphenylethene). The frequency factors are in the narrow ranges of log (A/M-1S-1) = 8.7 ± 0.1 for the cyclic and log (A/M-1S-1) = 8.2 ± 0.2 for the open-chain malonyl species, whereas the activation energies vary from 12.9 kJ/mol (1,1-diphenylethene) to 21.7 kJ/mol (acrylonitrile). They correlate with the alkene ionization potentials and, more weakly, with the reaction enthalpy. No correlation was found between the activation energies and the alkene electron affinities. Hence, the results confirm and quantify the electrophilic nature of malonyl radicals in addition reactions.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810327
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  • 39
    Digitale Medien
    Digitale Medien
    Synthesis of the Spermidine Alkaloid (-)-(4R)-Dihydroisomyricoidine (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1303-1318 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An asymmetric synthesis of (-)-(4R)-dihydroisomyricoidine (28), a 13-membered amino lactam of type A, was performed by a diastereoselective Michael addition between the spermidine derivative 3 and the commercially available optically active ethyl carboxylate 4, and the cyclization of the resulting ω-amino acid 7 using diethyl phosphorocyanidate ((EtO)2POCN), followed by a Wittig reaction to introduce the (Z)-side chain. Some side reactions are also discussed.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810541
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  • 40
    Digitale Medien
    Digitale Medien
    New Types of Potentially Antimalarial Agents: Epidioxy-substituted norditerpene and norsesterpenes from the marine sponge Diacarnus levii (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1285-1292 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Natural free carboxylic acids from the hadromerid sponge Diacarnus levii (Kelly-Borges and Vacelet) were esterified to yield the new cyclic norditerpene peroxides ent-muqubilin benzyl ester (= (αR,3S,6R)-α,6-dimethyl-6-[(E)-4-methyl-6-(2,6,6-trimethyl-cyclohex-1-en-1-yl)hex-3-enyl]-1,2-dioxan-3-acetic acid benzyl ester; 6, diacarnoate B methyl ester(= (αS,3R,6R)-α,6-dimethyl-6-{2-(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-3-oxo-2,5,5,8a-tetramethylnaphthalen-1-yl)ethyl}-1,2-dioxan-3-acetic acid methyl ester; 9), and deoxydiacarnoate B benzyl ester (= (αS,3R,6R)-α,6-dimethyl-6-{2-[(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-2,5,5,8a-tetramethyl-1-naphthalenyl]ethyl}-1,2-dioxan-3-acetic acid benzyl ester; 10), which were isolated following extensive chromatography. The relative configuration of the peroxide/α-methylacetate moiety of 6, 9, and 10, was directly determined from their NMR spectra. The absolute configurations of the peroxide/α-methylacetate moiety was deduced from comparative 1H-NMR data of the (S)- and (R)-phenylglycine methyl ester derivatives 7 and 8 as well as 11/13 and 12/14, all obtained from a mixture of the precursors of 3, 6, and 10. The absolute configuration at the carbobicyclic moiety of enone 9 and of 10, is identical, as established by chemical interconversion, 9 and 10 belong to the normal labdane series according to empirical CD rules, applied either directly to 9 or to the parent (+)-sclareolide-derived enone 20. In contrast, molar rotation additivity rules suggest the ent-labdane configuration for 9 and 10. The epidioxides 1-3, 6, and 10 proved active in vitro against the malaria parasite Plasmodium falciparum; especially the previously isolated methyl 3-epinuapapuanoate (2) was active against a chloroquine-resistant strain, and this with a good security index.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810539
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  • 41
    Digitale Medien
    Digitale Medien
    3-Hydroxy-2-cyanoalk-2-enamides, and 2-Cyano-2-(tetrahydrofuran-2-ylidene)- and 2-Cyano-2-(tetrahydropyran-2-ylidene)acetamides: Synthesis, structure, and solvent-dependent (Z)/(E)-isomerismDedicated to Professor D. Seebach on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1319-1328 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 3-Hydroxy-2-cyanoalk-2-enamides, and 2-cyano-2-(tetrahydrofuran-2-ylidene)- and 2-cyano-2-(tetrahydropyran-2-ylidene)acetamides with N-alkyl and N-aryl substituents have been synthesized in three steps from cyanoacetic acid. Their conformations were investigated by X-ray crystallography and 1H-NMR ROESY spectroscopy at room temperature. The enolic compounds 1-3 adopt an extended conformation stabilized by a strong intramolecular O—H … O=C bond both in the solid state and in (D6)DMSO solution. In contrast, the structure of the cyclic derivatives 5a,b-8a,b is solvent-dependent. In the solid state and in CDCl3 solution, the compounds adopt an extended conformation of type I or III, while, in (D6)DMSO solution, their structures undergo time-dependent (Z)/(E)-isomerization structures (of type II or IV). This observation is compatible with a dipolar transition state of rotation. The kinetics of the isomerization are controlled by the N-substituent, the N-(t-Bu) derivatives 7a and 7b having the highest barrier of rotation around the C=C bond. The whole body of experimental evidence together with the results of molecular-mechanics calculations with I-IV, indicate that, in DMSO, two (E)/(Z)-isomers with two conformations are present, and that they undergo interconversion at room temperature with four different constants. The very fast exchange rates kI,II and kIII,IV in the NMR time-scale might be responsible for the detection of only two isomers.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810542
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  • 42
    Digitale Medien
    Digitale Medien
    Monoterpene Dimers from Lisianthius seemannii (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1393-1403 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new acylated dimeric secoiridoid glycoside, seemannoside A (2), has been isolated from the aerial parts of Lisianthius seemannii (GRISEB) O. KUNTZE (Gentianaceae). The structure was established by spectroscopic analysis (UV, MS, 1H- and 13C-NMR, and 2D-NMR experiments) and chemical reactions as (E-4′-O-p-coumaroyl)lisianthioside. The structure of the (Z)-isomer (seemannoside B, 3), also present in the plant, was confirmed by LC/UV/1H-NMR analysis. The active principle, 6, responsible for the antifungal activity of the apolar extract against Cladosporium cucumerinum, has been isolated. Its structure has been established by NMR spectroscopy and X-ray crystallographic analysis as a rare type of aglycone monoterpene dimer.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810548
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  • 43
    Digitale Medien
    Digitale Medien
    Asymmetric synthesis of pentono- and 6-deoxyhexono-δ-lactams via hetero-Diels-Alder reactions with nitroso dienophile (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1417-1428 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Asymmetric Diels-Alder reaction of the pentadienoic and hexadienoic acids 2a,b with the chiral chloronitroso derivative 3 gave the primary adducts 4a,b with good-to-excellent enantioselectivity. Subsequent as- or trans-dihydroxylation and hydrogenolytic cleavage of the N—O bond led to the 5-amino-5-deoxypentono-δ-lactams 13a, 14, 15a, and 16 in the D-ribose, L-arabinose, D-xylose, and L-lyxose series, respectively, and to the 5-amino-5,6-dideoxyhexono-δ-lactams 13b and 15b in the D-allose and D-glucose series, respectively.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810550
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  • 44
    Digitale Medien
    Digitale Medien
    Distamycin-NA: A DNA Analog with an Aromatic Heterocyclic Polyamide Backbone. Part 1. Synthesis and structural analysis of monomers and dimers containing the nucleobase uracil (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 14-34 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the monomeric building block 13 and its constitutional isomer 12 of a new type of DNA analog, distamycin-NA, is presented (Schemes 1 and 2). This building block consists of a uracil base attached to a thiophene core unit via a biaryl-like axis. Next to the biaryl-like axis on the thiophene chromophore, a carboxy and an amino substituent are located allowing for oligomerization via peptide coupling. The proof of constitution and the conformational preferences about the biaryl-like axis were established by means of X-ray analyses of the corresponding nitro derivatives 10 and 11. Thus, the uracil bases are propeller-twisted relative to the thiophene core, and bidentate H-bonds occur between two uracil bases in the crystals. The two amino-acid building blocks 12 and 13 were coupled to give the dimers 15 and 16 using dicyclohexylcarbodiimide (DCC) in THF/LiCl and DMF, respectively. While the dimer 15 showed no atropisomerism on the NMR time scale at room temperature, its isomer 16 occurred as distinct diastereoisomers due to the hindered rotation around its biaryl-like axis. Variable-temperature 1H-NMR experiments allowed to determine a rotational barrier of 19 ± 1 kcal/mol in 16. The experimental data were complemented by AM1 calculations.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810103
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  • 45
    Digitale Medien
    Digitale Medien
    [2+3] Cycloadditions of ‘Thiocarbonyl Ylides’ (= (Alkylidenesulfonio)methanides) and diazoalkanes with N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole])Part of the planned Ph.D. Thesis of T.G., University of Łódź.Dedicated to Professor Romuald Bartnik (University of Łódź) on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 66-77 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Heating of a mixture of N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole]; 1) and 2,5-dihydro-1,3,4-thiadiazole 2a or 2b gave the 1,3-dithiolanes 4a and 4b, respectively, via a regiospecific 1,3-dipolar cycloaddition of the corresponding ‘thiocarbonyl methanides’ 3a,b onto the C=S group of 1 (Schemes 1 and 2). The adamantane derivative 4b was not stable in the presence of 1H-imidazole and during chromatographic workup. The isolated 1,3-dithiole 5 is the product of a base-catalyzed elimination of 1H-imidazole from the initial cycloadduct 4b. The formation of the S,N-acetal 6 can be rationalized by a protonation of the ‘thiocarbonyl ylide’ 3b followed by a nucleophilic addition of 1H-imidazole. With the diazo compounds 8a-e (Scheme 3) 1 underwent a regiospecific 1,3-dipolar cycloaddition to give the corresponding 2,5-dihydro-1,3,4-thiadiazole derivatives 9, which spontaneously eliminated 1H-imidazole to yield (1H-imidazol-1-yl)-1,3,4-thiadiazoles 10. The structures of 10a and 10d were established by X-ray crystallography. In the case of diazodiphenylmethane (8f), the initial cycloadduct 9f decomposed via a ‘twofold extrusion’ of N2 and S to give 1,1′-(2,2-diphenylethenylidene)bis[1H-imidazole] (11; Scheme 3).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810108
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  • 46
    Digitale Medien
    Digitale Medien
    Synthesis of New Nucleosides by coupling of chloropurines with 2- and 3-deoxy derivatives of N-methyl-D-ribofuranuronamide (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 145-152 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of new deoxyribose nucleosides by coupling chloropurines with modified D-ribose derivatives is reported. The methyl 2-deoxy-N-methyl-3-O-(p-toluoyl)-α-D-ribofuranosiduronamide (α-D-8) and the corresponding anomer β-D-8 were synthesized starting from the commercially available 2-deoxy-D-ribose (1) (Scheme 1). Reaction of α-D-8 with the silylated derivative of 2,6-dichloro-9H-purine (9) afforded regioselectively the N9-(2′-deoxyribonucleoside) 10 as anomeric mixture (Scheme 2), whereas β-D-8 did not react. Glycosylation of 9 or of 6-chloro-9H-purine (17) with 1,2-di-O-acetyl-3-deoxy-N-methyl-β-D-ribofuranuronamide (13) yielded only the protected β-D-anomers 14 and 18, respectively (Scheme 3). Subsequent deacetylation and dechlorination afforded the desired nucleosides β-D-11, β-D-12,15, and 16. The 3′-deoxy-2-chloroadenosine derivative 15 showed the highest affinity and selectivity for adenotin binding site vs. A1 and A2A adenosine receptor subtypes.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810113
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  • 47
    Digitale Medien
    Digitale Medien
    Asymmetric Synthesis of (S)-5,5,5,5′,5′,5′,5′-Hexafluoroleucine (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 174-181 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (S)-5,5,5,5′,5′,5′-Hexafluoroleucine ((S)-13) of 81 % ee is prepared from hexafluoroacetone (l) and ethyl bromopyruvate (= ethyl 2-oxopropanoate) in 7 steps with an overall yield of 18% (Schemes 1 and 2). Key step in this sequence is the highly enantioselective reduction of the carbonyl group in α-keto ester 4 either by bakers' yeast (91 % ee) or by ‘catecholborane’ 6 utilizing an oxazaborolidine catalyst, yielding hydroxy ester (R)-5 with 99% ee. The absolute configuration was determined by X-ray analysis of the HCl adduct (S,R)-9b of (2S)-N-[(R)- l-phenylethyl]-5,5,5,5′,5′,5′-hexafluoroleucine ethyl ester.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810116
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  • 48
    Digitale Medien
    Digitale Medien
    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810201
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  • 49
    Digitale Medien
    Digitale Medien
    Preparation of N-Fmoc-Protected β2- and β3-Amino Acids and their use as building blocks for the solid-phase synthesis of β-peptidesPartially published in a preliminary communication [1]; β2 means that the NH2, group ist at C(3)(= C(β)) and the side chain at C(2) of the amino acid, and β3 indicates that both the NH2 group and the side chain are at C(3)( = C(β)). Fmoc = (9H-Fluoren-9-ylmethoxy)carbonyl.Dedicated to Professor A. I. Meyers, University of Colorado, Fort Collins, on the occasion of his 65th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 187-206 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: N-Fmoc-Protected (Fmoc = (9H-fluoren-9-ylmethoxy)carbonyl) β-amino acids are required for an efficient synthesis of β-oligopeptides on solid support. Enantiomerically pure Fmoc-β3-amino acids β3: side chain and NH2 at C(3)(= C(β)) were prepared from Fmoc-protected (S)- and (R)-α-amino acids with aliphatic, aromatic, and functionalized side chains, using the standard or an optimized Arndt-Eistert reaction sequence. Fmoc-β2- Amino acids (β2 side chain at C(2), NH2 at C(3)(= C(β))) configuration bearing the side chain of Ala, Val, Leu, and Phe were synthesized via the Evans' chiral auxiliary methodology. The target β3-heptapeptides 5-8, a β3- pentadecapeptide 9 and a β2-heptapeptide 10 were synthesized on a manual solid-phase synthesis apparatus using conventional solid-phase peptide synthesis procedures (Scheme 3). In the case of β3-peptides, two methods were used to anchor the first β-amino acid: esterification of the ortho-chlorotrityl chloride resin with the first Fmoc-β-amino acid 2 (Method I, Scheme 2) or acylation of the 4-(benzyloxy)benzyl alcohol resin (Wang resin) with the ketene intermediates from the Wolff rearrangement of amino-acid-derived diazo ketone 1 (Method II, Scheme 2). The former technique provided better results, as exemplified by the synthesis of the heptapeptides 5 and 6 (Table 2). The intermediate from the Wolff rearrangement of diazo ketones 1 was also used for sequential peptide-bond formation on solid support (synthesis of the tetrapeptides 11 and 12). The CD spectra of the β2- and β3-peptides 5, 9, and 10 show the typical pattern previously assigned to an (M) 31 helical secondary structure (Fig.). The most intense CD absorption was observed with the pentadecapeptide 9 (strong broad negative Cotton effect at ca. 213 nm); compared to the analogous heptapeptide 5, this corresponds to a 2.5 fold increase in the molar ellipticity per residue!
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810202
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  • 50
    Digitale Medien
    Digitale Medien
    Photoaddition of Ethyl 2,2-Dimethyl-5-oxo-5,6-dihydro-2H-pyridine-1-carboxylate to 2,3-dimethylbut-2-ene (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 303-306 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: On irradiation (350 nm) in the presence of excess 2,3-dimethylbut-2-ene, the newly synthesized title compound 5 affords as main products the unexpected cyclopropylpyrrolidine 10 (50%) and the spiro-oxetane 9 (25%).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810210
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  • 51
    Digitale Medien
    Digitale Medien
    Influence of Lewis Acids on the [4 + 2] Cycloaddition of N,N′-Fumaroylbis[(2R)-bornane-10,2-sultam] to Cyclopentadiene and application to various dienes (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 324-329 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Among seventeen different Lewis acids, TiCl4 was found to be the best catalyst for the [4 + 2] cycloaddition of cyclopentadiene to N,N′-fumaroylbis[(2R)-bornane-10,2-sultam] ((-)-1). Independently of the TiCl4 molar concentration, almost constant and complete (98-89% d.e.) diastereofacial π-selection was achieved in the Diels-Alder addition of (-)-1 to cyclopentadiene, cyclohexadiene, isoprene, and 2,3-dimethylbuta-1,3-diene.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810213
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  • 52
    Digitale Medien
    Digitale Medien
    N,Se-Acetals: Preparation and use in diastereoselective radical reactionsFor a preliminary communication of this work, see [1]. (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 353-373 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new facile synthesis of N,S- and N,Se-acetals starting from aldehydes and primary amines is presented (Schemes 3-5). These acetals are used as precursors for stereoselective radical deuteration and allylation reactions (Schemes 6 and 7, Tables 1 and 2). The stereochemical outcome of the reactions depends on the radical trap and the substituents at the N-atom. Deuterations give always anti products with moderate to high selectivities. The allylation reactions give either syn or anti products with low to moderate selectivities. The observed stereoselectivities can be explained with a model based on minimization of A1,3 strain and are controlled by steric and stereoelectronic effects.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810216
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  • 53
    Digitale Medien
    Digitale Medien
    Syntheses of O-Methylasparvenone-Derived Serotonin-Receptor Antagonists (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 525-538 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Based on O-methylasparvenone (1), a N-free 5HT2C antagonist with moderate affinity (pKi = 6.7), derivatives bearing dimethylamino (7), (dimethylamino)methyl (17, 18, 21, and 22), and aminomethyl substituents (26) in place of the benzylic OH group of 1 as well as pyrrolidine- (33) and piperidine-fused derivatives (29, 43, and 45) were synthesized. In contrast to the lead structure 1, these new ligands were active in vivo in the rat. The tricycles 33 and 45 display high affinities for the 5HT2C receptor (pKi = 8).
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810306
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  • 54
    Digitale Medien
    Digitale Medien
    [2+3] Cycloadditions of Azomethine Ylides with 1,3-Thiazole-5(4H)-thionesDedicated to Professor Max Viscontini on the occasion of his 85th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 558-569 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Thermal reactions of 1,2,3-trisubstituted aziridines 1 with 1,3-thiazole-5(4H)-thiones 6 in toluene yielded, in general, a mixture of two diastereoisomeric spirocyclic [2+3] cycloadducts. The formation of these products can be explained by a stereoselective electrocyclic ring opening of 1 to give an azomethine ylide 2 as the reactive intermediate, which is trapped immediately by 6 via a stereoselective 1,3-dipolar cycloaddition. Only in the case of trans-dimethyl 1-(4-methoxyphenyl)aziridine-2,3-dicarboxylate (trans-1a), four diastereoisomeric cycloadducts were formed (Scheme 4). This result is rationalized by an isomerization of the intermediate azomethine ylide cis-2a to trans -2a.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810309
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  • 55
    Digitale Medien
    Digitale Medien
    Protonic Quantum Correlations in the H-Bond Dynamics of Nucleic Acids. Part II. Correlations along the helical axis of protein-coding DNA of living organisms (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 584-601 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Due to their small mass, adjacent protons (or H-atoms) of molecular systems may exhibit quantum entanglement (or quantum correlations), even at ambient conditions. The considerable thermal disturbance and/or manybody interactions of condensed matter and the associated decoherence effect, however, cause this protonic entanglement to be restricted in space and time. Some aspects of entanglement and decoherence are mentioned. Extending our previous theoretical work, in the present paper the focus is on the possible existence of entangled protons belonging to the H-bonds of adjacent base pairs of B-type DNA. Based on the ‘working hypothesis’ that this effect does really exist, the most probable ‘positions’ for the appearance of protonic entanglement in DNA sequences are qualitatively determined. Furthermore, these ‘positions’ appear to correspond uniquely to dimers of adjacent base pairs of DNA. As a consequence, one can straightforwardly search for an enhanced appearance of such entangled H-bonds in DNA sequences of living organisms, using the existing DNA databases. A quantitative analysis of protein-coding DNA sequences of various organisms has been performed, the results of which provide strong evidence for the existence of the considered effect. The most striking finding may be summarized as follows: Quantum entanglement appears preferably between the third base of a codon and the first base of the following one. Quantitative estimates of this and further obtained results are presented. It is also shown that quantum-chemical considerations of stacking energies cannot account for the results. The new findings provide first evidence for the biological significance of entangled H-bonds.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810311
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  • 56
    Digitale Medien
    Digitale Medien
    An Advantageous Synthesis of 1D- and 1L-1,2,3,5/4-Cyclohexanepentol (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 688-694 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The title compounds D-10 and L-10 were prepared from 1 in eight steps and in a combined overall yield of 41-49%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810319
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  • 57
    Digitale Medien
    Digitale Medien
    Reaction of N,N'-dimethyl-2-nitroethene-1, 1-diamine with α,ß-unsaturated acyl isothiocyanates: Preparation of 1,3-thiazin-4-one and 4-nitro-1,2-thiazol-5(2H)-imine derivativesPresented in preliminary form at the ‘XII seminario cientifico’, centro nacional de investigaciones cientificas, habana, cuba, 1995 (M. I. G. T.) and at the ‘tenth international conference on organic synthesis’, Bangalore, India, 1994 (D. M. A.). (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 718-728 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of N,N'-dimethyl-2-nitroethene-1,1-diamine (8) with α,ß-unsaturated acyl isothiocyanates 9 affords 3,3-diamino-2-nitroacrylthioamides 10 (Scheme 2) in moderate-to-good yields. Cyclization of 10 under acidic conditions gives 1,3-thiazin-4-one derivatives of type 11. Oxidative cyclization of 10 with diethyl azodicaboxylate leads to 4-nitro-1,2-thiazol-5(2H)-imine derivatives 12.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810321
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  • 58
    Digitale Medien
    Digitale Medien
    Prenylated Flavanones from Monotes engleri: On-line Structure Elucidation by LC/UV/NMR (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 754-763 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The CH2Cl2 extract of Monotes engleri Gilg. (Dipterocarpaceae) showed antifungal activity against the yeast Candida albicans in our bioautographic TLC assays. After a first fractionation of the crude extract, the bioactivity was located in one of the fractions. To perform an efficient targeted isolation of the active compounds, LC/UV/MS and LC/UV/NMR analyses of the crude extract and the active fraction were performed. LC/UV/, LC/MS, and LC/NMR data (1D and 2D) allowed the identification of 1 as (2S)-2,3-dihydro-5,7-dihydroxy-{3-hydroxy-4-[(3-methylbut-2-enyl) oxy]phenyl}-4H-1-benzopyran-4-one, a new prenylated flavanone, named monoteson A. Subsequent isolation of 1 has permitted the determination of its absolute configuration on the basis of CD measurements. Theree other prenylated flavanoes 2-4 were isolated from the same extract. Compound 3 was identified as 2- (3, 5-dihydroxyphenyl) -2,3-dihydro-5, 7-dihydroxy-6, 8-bis (3-methylbut-2-enyl)-4 H-1-benzopyran-4-one, another new natural product, named monotesone B. The structures of 2 and 4 were established as selinone and lonchocarpol A, respectively. The antifungal activity against Candida albicans was determined for all compounds.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810325
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  • 59
    Digitale Medien
    Digitale Medien
    Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds part VIPart V: [1] Derivatives with Bidentate Ligands, Crystal Structures of tetrahedro- Decacarbonyl{μ-[1,1-bis(methylthio-χS)ethane]}tetrairidium ([Ir4(CO)10-(μ2-(MeS)2CHMe)]), tetrahedro-Tri-μ-carbonylheptacarbonyl{μ-{ethylidenebis- [diphenylphosphine]-χP:χP'}}tetrairidium ([Ir4(CO)10(μ2-(Ph2P)2CHMe)]), and tetrahedro-Tri-μ-carbonylheptacarbonyl{μ-{propane-1,3-diylbis[diphenylphosphine]-χP:χP'}}tetrairidium ([Ir4(CO)10(μ2-Ph2P(CH2)3PPh2)]) (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 781-791 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The disubstituted clusters[Ir4(CO)10(μ2-L—L)] with one edge-bridging ligand have a ground-state geometry with all COs terminal (L—L = (MeS)2CHMe, cluster 1) or with three edge-bridging COs (L—L = (Ph2P)2CHMe, cluste 2; L—L =Ph2P(CH2)3PPh2, cluster 3) in the solid state and in solution. A comparative 13C-NMR study of 1-3 shows that their respective ground-state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry-go-round of six COs about a unique trangular face and the rotation of terminal COs about one Ir-atom. The factors affecting the activation energy of the merry-go-round result from the relative bites of the bidentate ligands in the ground-state geometry, as shown by a comparison of the molecular structures of 2 and 3.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810328
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  • 60
    Digitale Medien
    Digitale Medien
    Kinetic Study of the Reaction of Pyridoxal 5′-Phosphate with Hydrazino Compounds of Pharmacological Activity (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 837-844 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the reaction between pyridoxal 5′-phosphate (PLP) with carbidopa, hydralazine, and isoniazid, in aqueous solution at variable pH and constant ionic strength of 0.1M was studied spectrophotometrically. The rate constants of formation and hydrolysis of the resulting Schiff base, and its stability were determined in a wide range of pH. A comparison is made of the formation rate constants with those of PLP with hydrazine. The reactivity shows the sequence isoniazid 〉 hydrazine 〉 carbidopa 〉 hydralazine in the whole range of pH studied. The Schiff bases studied are more stable than those formed by PLP and hexylamine and as stable as those described for the reactions of PLP with poly(L-lysine) or copolypeptides containing L-lysine.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810505
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  • 61
    Digitale Medien
    Digitale Medien
    Structure and Properties of Transition-Metal Complexes with Chiral C2-symmetric binucleating ligands (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 507-524 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The coordination behavior of chiral binucleating ligands of type 1-4 with various transition metals has been investigated. 1H-NMR Titration experiments with zinc(II) salts gave detailed structural information about the structure of the resulting zinc complexes. Ligand 1 forms an unusual C3-symmetric dinuclear zinc complex [Zn2CIL3] (8a) which was characterized by X-ray crystallography. Treatment of complex 8a with various carboxylic acids resulted in ligand-exchange reactions. With ligand 2, a hydroxo-bridged dinuclear copper complex 15 was synthesized and its structure elucidated by X-ray analysis. Solution studies UV and 1H-NMR spectroscopy of the reaction of ligand 3 with ZnII and NII salts revealed the formation of dimeric species of the type [M2X4L2]. Ligand 4 formed well-defined dinuclear complexes with NiII and CuII salts of which the corresponding NiII complex [Ni2(AcO)2(ClO4)2L] (22a) was characterized by crystal-structure analysis.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810305
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  • 62
    Digitale Medien
    Digitale Medien
    Warum Pentose- und nicht Hexose-Nucleinsäuren??. Teil VTeile I-IV der Reihe ‘Warum Pentose- und nicht Hexose-Nucleinsäuren?’, vgl. [1-4]. Die vorliegende Arbeit gilt als 9. Mitteilung in der Reihe ‘Chemie von α-Aminonitrilen’ 8. Mitteilung dieser Reihe vgl. [4]. Teile der hier publizierten Ergebnisse sind von J. H. an der Herbstversammlung der Schweizerischen Chemischen Gesellschaft in Bern am 16.10.1991 vorgetragen sowie in mehreren von A. E. gehaltenen und im Druck erschienenen Vorträgen erwähnt worden; vgl. [5-8].. (Purin-Purin)-Basenpaarung in der homo-DNS-Reihe: Guanin, Isoguanin, 2,6-Diaminopurin und Xanthin (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 375-474 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Why Pentose- and Not Hexose-Nucleic Acids? Purine-Purine Pairing in homo-DNA: Guanine,Isoguanine, 2,6-Diaminopurine, and XanthineThis paper concludes the series of reports in this journal [1-4] on the chemistry of homo-DNA, the constitutionally simplifie dmodel system of hexopyranosyl-(6′ → 4′)-oligonucleotide systems stidued in our laboratory as potentially natural-nucleic-acid alternatives in the context of a chemical aetiology of nucleic-acid structure. The report describes the synthesis and pairing properties of homo-DNA oligonucleotides which contain as nucleobases exclusively purines, and gives, together with part III of the series [3], a survey of what we know today about purine-purine pairingin homo-DNA. In addition, the paper discusses those aspects of the chemistry of homo-DNA which, we think, influence the way how some of the structural features of DNA (and RNA) are to be interpreted on a qualitative level.Purine-purine pairing occurs in the homo-DNA domain in great variety. Most prominent is a novel tridentate Watson-Crick pair between guanine and isoguanine, as well as one between 2,6-diaminopurine and xanthinone, both giving rise to very stable duplexes containing the all-purine strands in antiparallel orientation. For the guanine-isoguanine pair, constitutional assignment is based on temperature-dependent UV and CD spectroscopy of various guanine- and isoguanine-containg duplexes in comparison with duplexes known to be paired in the reverse guanine is replaced by 7-carbauguanine. Isoguanine and 2,6-diaminopurine also have the capability of self-pariring in the reverse-Hoogsteen mode, as previously observed for adenine and guanine [3]. In this type of pairing, the interchangeably. Fig. 36 provides an overall survey of the relative strength of pairing in all possible purine-purine combinations.Watson-Crick pairing of isoguanine with guanine demands the former to participate in its 3H-tautomeric form; hitherto this specific tautomer had not been considered in the pairing chemistry of isoguanine. Whereas (cumulative) purine-purine pairing in DNA (reverse-Hoogsten or Hoogsteen) seems to occur in triplexes and tetrapalexes only, its occurrence in duplexes in a characteristic feature of homo-DNA chemistry. The occurrence of purine-purine Watson-Crick base pairs is probably a consequence of homo-DNA's quasi-linear ladder structure [1][4]. In a double helix, the distance between the two sugar C-atoms, on which a base pair is anchored, is expected to be constrained by the dimensions of the helix; in a linear duplex, however, there would be no restrictions with regard to base-pair length. Homo-DNA's ladder-like model also allows one to recognize one of the reasons why nucleic-acid duplexes prefer to pair in antiparallel, rather than parallel strand orientation: in homo-DNA duplexes, (averaged) backbone and base pair axes are strongly inclined toward one another [4]; the stronger this inclination, the higher the preference for antiparallel strand orientation is expected to be (Fig. 16).In retrospect, homo-DNA turns out to be one of the first artificial oligonucleotide systems (cf. Footnote 65) to demonstrate in a comprehensive way that informational base pairing involving purines and pyrimidines is not a capability unique to ribofuranosyl systems. Stability and helical shape of pairing complexes are not necessary conditions of one another; it is the potential for extensive conformational cooperativity of hte backbone structure with respect to the constellational demands of base pairing and base stacking that determines whether or nor a given type of base-carrying backbone structure is an informational pairing system. From the viewpoint of the chemical aetiology of nucleic-acid structure, which inspired our investigations on hexopyranosyl-(6′ → 4′)-oligonucleotide systems in the first place, the work on homo-DNA is only an extensive model study, because homo-DNA is not to be considered a potential natural-nucleic-acid altenratie. In retrospect, it seems fortunate that the model study was carried out, because without it we could hardly have comprehended the pairing behavior of the proper nucleic-acid alternatives which we have studied later and which will be discussed in Part VI of this series.The English footnotes to Fig. 1-49 provide an extension of this summary.
    Zusätzliches Material: 49 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810302
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  • 63
    Digitale Medien
    Digitale Medien
    Synthesis and Properties of Monodisperse Chiral Dendrimers (up to Fourth Generation) with doubly branched building blocksPartially published in preliminary communications [1][2].: An intriguing solvent effect (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 603-631 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ‘Fully chiral’ dendrimers, containing a stereogenic center at each and every branching point, have been prepared using a chiral core triol with aromatic elongating units (cf. 27) and chiral branch diols (cf. 8, 12, and 24) as building blocks. The biggest dendrimer prepared is of the 4th generation (33: 46 building blocks, 93 stereogenic centers, 1028 possible stereoisomers), and has been obtained by a convergent growth approach in 32 steps starting from the biopolymer poly[(R)-3-hydroxybutanoic acid] (P(3-HB)). All compounds were shown to be monodisperse by MALDI-TOF mass spectrometry. Spin-lattice relaxation-time (T1) measurements and size-exclusion chromatography show typical features of structurally related achiral dendrimers. The influence of the chiral building blocks on the shape of the whole dendrimer has been investigated by chiroptical measurements: the specific rotation can be considered as average of all chiroptical properties of its constituent chiral units, independent of the solvent, the concentration, and the temperature. On the other hand, regularity in the circular dichroism (CD) spectra is completely lost with variation of the solvent (cf. Fig. 13).
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810313
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  • 64
    Digitale Medien
    Digitale Medien
    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810101
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  • 65
    Digitale Medien
    Digitale Medien
    Enantioselective Dicarbonylation of Styrene to Isotactic Poly[1-oxo-2-phenylpropane-1,3-diyl] with phosphinodihydrooxazole-palladium(ii) complexes: Model studies for enantioface selection preliminary communication (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 764-769 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The first steps, believed to be involved in the highly enantioselective copolymerization of styrene and carbon monoxide to poly[1-oxo-2-phenylpropane-1,3-diyl] with phosphinodihydrooxazole-palladium(II) complexes, were investigated. The insertion of carbon monoxide into [Pd(Me)(P^N)(solvent)] TfO (P^N = (S)-2-[2-(5H-benzo[b]phosphindol-5-yl)phenyl]4-benzyl-4,5-dihydrooxazole (1)) and of styrene into [Pd(Me)(P^N)(solvent)] TfO were highly regioselective (alkyl and acyl substituents trans to N); moreover, the olefin insertion took place with essentially complete enantioface discrimination.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810326
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  • 66
    Digitale Medien
    Digitale Medien
    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810501
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  • 67
    Digitale Medien
    Digitale Medien
    A Novel Hydrocarbon, 8,10-Dimethylidenetricyclo[7.1.1.02,7]undeca-2,4,6-triene: Synthesis of benzopinane skeleton via di-π-methane rearrangement of benzonorbornadiene systemDedicated to Professor Özer Bekaroǧlu on the occasion of his 65th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 828-836 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The [4 + 2] cycloadduct 17 of 2,3-dimethylidene-1,2,3,4-tetrahydro-1,4-methanonaphthalene and 4-phenyl-4H-1,2,4-triazole-3,5-dione (PTAD) was subjected to a triplet-sensitized di-π-methane rearrangement. Hydrolysis of the resulting urazol 18 gave the hydrocarbon 7. Hydrolysis of 18 at lower base concentrations led to isomeric stable semicarbazides 24 and 25, which were submitted NiO2 or MnO2 oxidation, to give the target compound 7, and oxidation products 26 and 27.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810504
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  • 68
    Digitale Medien
    Digitale Medien
    Cooperative Interactions of the Catalytic Nucleophile and the Catalytic Acid in the Inhibition of β-Glycosidases. Calculations and their validation by comparative kinetic and structural studies of the inhibition of glycogen phosphorylase b (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 853-864 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The difference between the strong inhibition of retaining β-glucosidases by the tetrazole 1 and the weak inhibition by the triazole 3 has been explained by the protonation by the enzymic catalytic acid of N(3) of 1, replaced by CH in 3. One also expects a contribution to the inhibition from the charge-dipole interaction between the enzymic catalytic nucleophile and the azole ring. The extent of this contribution was estimated from the calculated, distance-dependent heats of formation of the acetate-azole complexes. The calculations were validated by comparison of the charge-dipole interaction between phosphate and the inhibitors 1 and 3 in the glycogen phosphorylase b (GPb)-azole-phosphate complexes, as derived from differences in the Ki values for 1 and 3, while the structural invariance of the complexes was demonstrated by X-ray analysis. The difference between the charge-dipole interactions of (dihydrogen) phosphate and 1 or 3 as derived from Δ Ki is 1.1 kcal mol-1, while the calculated difference is 1.3 kcal mol-1. The calculated difference for the interaction of 1 or 3 with acetate, representing the catalytic nucleophile in β-glycosidases, is 2.0 kcal mol-1, while the differences of the binding energies as derived from the Ki values for the inhibition by 1 or 3 of different β-glycosidases range from 2.4 to 5.3 5 kcal mol-1. The calculated difference for 1 and the imidazole 6 is 2.5 kcal mol-1 in favour of 1, whereas the Ki-derived difference is 3.7 kcal mol-1 in favour of 6, equal to the calculated difference between 1 and the protonated imidazole 6. Thus, protonation by the catalytic acid and the charge-dipole interaction with the catalytic nucleophile contribute cooperatively to the binding of inhibitors possessing a trigonal anomeric centre bonded to a heteroatom.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810507
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  • 69
    Digitale Medien
    Digitale Medien
    Heterosupramolecular Chemistry: Synthetic strategies for the covalent and noncovalent assembly and organization of nanocrystals and molecules (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 902-915 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Described are the preparation of nanocrystals and the synthesis of molecules that may be covalently or noncovalently assembled in solution to yield heterosupermolecules possessing a well-defined heterosupramolecular function. Also described are preparative and synthetic methods that yield organized assemblies of heterosupermolecules possessing an addressable heterosupramolecular function. Finally, the development of these synthetic strategies to permit the covalent and noncovalent assembly and organization of a wide range of condensed phase and molecular components is outlined.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810511
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  • 70
    Digitale Medien
    Digitale Medien
    γ-Peptides Forming More Stable Secondary Structures than α-Peptides: Synthesis and helical NMR-solution structure of the γ-hexapeptide analog of H-(Val-Ala-Leu)2-OHDedicated to Professor E. J. Corey on the occasion of his 70th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 983-1002 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: For a comparison with the corresponding α- and β-hexapeptides H-(Val-Ala-Leu)2-OH (A) and H-(β-HVal-β-HAla-β-HLeu)2-OH (B), we have now prepared the corresponding γ-hexapeptide 1 built from the homochirally similar (S)-4-aminobutanoic acid, (R)-4-amino-5-methylhexanoic acid, and (R)-4-amino-6-methylheptanoic acid. The precursors were prepared either by double Arndt-Eistert homologation of the protected amino acids Boc-Val-OH, Boc-Ala-OH, and Boc-Leu-OH (Schemes 1 and 2), or by the superior route involving olefination/hydrogenation of the corresponding aldehydes (Boc-valinal, Boc-alaninal, and Boc-leucinal; Scheme 3). Conventional peptide-coupling methodology (EDC/HOBt) furnished the γ-hexapeptide 1 (through the intermediate γ-di- and γ-tripeptide derivatives 9-11). Analysis of NMR measurements in (D5)pyridine and CD3OH solution (COSY, TOCSY, HSQC, HMBC, ROESY) reveals that the γ-hexapeptide 1 adopts a right-handed helical structure ((P)-2.61 helix of ca. 5-Å pitch, containing 14-membered H-bonded rings) which is to be compared with the left-handed helix of the corresponding β-peptide B ((M)-31 helix of 5-Å pitch, 14-membered H-bonded rings) and with the familiar right-handed, so-called α-helix of α-peptides ((P)-3.61 helix of 5.4-Å pitch, 13-membered rings). Like the helix sense, the helix dipole reverses when going from α-, (N + → C) to β-(C + → N) to γ-peptides (N + → C). The surprising difference between the natural α-, and the analogous β- and γ-peptides is that the helix stability increases upon homologation of the residues.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810514
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  • 71
    Digitale Medien
    Digitale Medien
    Antitumor Agents. Part 184.Part 183: [1]. Syntheses and antitubulin activity of compounds derived from reaction of thiocolchicone with amines: Lactams, alcohols, and ester analogs of allothiocolchicinoidsDedicated to Prof. Dieter Seebach on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1023-1037 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 7-O-Substituted analogs of deaminodeoxycolchinol thiomethyl ether were synthesized and evaluated for their inhibitory effects on tubulin polymerization in vitro. Ketone 9, a key compound in this study, was derived from thiocolchicone 6 by reaction with aniline. Reaction of compound 6 with MeNH2 or BuNH2 gave tetracyclic lactams 7 and 8, respectively. Optically active alcohols 11a and 11b were obtained from racemic 11 by chemical resolution including a separation of the comphanate diastereoisomers 12a and 12b, followed by basic hydrolysis. The (aR,7R)-configuration of 12b was verified by X-ray crystallographic analysis. Almost all racemic and optically active 7-O-acyl or 7-O-aroyl compounds had strong inhibitory effects on the tubulin polymerization reaction, with IC50 values from 1.7 to 5.1 μM. A few agents, such as the lactams 7 and 8, the camphanates 12a and 12b, the cyclohexanecarboxylates 19a and 19b, and, most notably, the (7S)-benzoate 15a, had negligible effects on polymerization, yielding IC50 values greater than 40μM. Ketone 9 showed strong inhibition of tubulin polymerization comparable to that of thiocolchicone (6). Optically active alcohol 11a and acyl esters 13a and 14a with a (7S)-configuration were more active than the (7R)-esters 13b and 14b. However, the esters 15a-17a with a (7S)-configuration were less active than the (7R)-isomers 15b-17b, in which the (7R)-benzoate 15b was at least 15-fold more inhibitory than the (7S)-isomer 15a. For the most part, the agents causing strongest inhibition of polymerization also caused the greatest inhibition of [3H]colchicine binding. NMR and optical rotatory data indicate that, in polar solvents, the equilibrium in esters with a 7-O-aroyl substituent, i.e., 15a,b, 16a,b, and 17a,b, is reversed from (aS) to (aR) or from (aR) to (aS), as compared to nonpolar solvents.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810516
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  • 72
    Digitale Medien
    Digitale Medien
    α-Methylidene-γ-butyrolactones: Synthesis and evaluation of quinolin-2(1H)-one derivatives (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1038-1047 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: As a continuation of our previous studies on the synthesis and antiplatelet activity of quinolin-2(1H)-ones with an α-methylidene-γ-butyrolactone substituted at O(8), the O(6)- and N(1)-substituted isomers were synthesized and evaluated for antiplatelet activity against thrombin (Thr)-, arachidonic acid (AA)-, collagen (Col)-, and platelet-activating-factor (PAF)-induced aggregation in washed rabbit platelets. These compounds were synthesized from 6-hydroxyquinolin-2(1H)-one via alkylation and Reformatsky-type condensation (Schemes 1 and 2). All of them were found to inhibit the platelet aggregation perfectly which was induced by AA and Col. 6-Substituted isomers 5b-g exhibited very strong inhibitory activities against AA- and PAF- induced aggregation and are approximately ten times more potent than their 8-substituted counterparts. However, the 1-substituted (11a and 11b) and the 1,6-disubstituted (6) counterparts were relatively inactive. Their effects on the Ca2+-dependent vasoconstriction induced by high K+, and the phasic and tonic vasoconstrictions induced by norepinephrine (NE) in rat aorta were also evaluated. Except 5g, all of them were found to have significant inhibitory activity on the NE-induced phasic and tonic vasoconstrictions. Compounds 6 and 11b also exhibited strong inhibitory activity on high-K+ medium, Ca2+-induced vasoconstriction.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810517
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  • 73
    Digitale Medien
    Digitale Medien
    Aminocyclopentitols from N-Alkylpyridinium Salts: A photochemical approach (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1095-1104 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The photolysis of N-alkylpyridinium halides 9a-e in alkaline H2O gave 6-azabicyclo[3.1.0]hexenol derivatives 10a-e. N-Substituents bearing ether, acetal, and alcohol functions were found to do not adversely influence the photochemical reaction course. The free OH groups of the N-(3-hydroxypropyl) derivative 10d were protected by benzoylation. The ensuing dibenzoate 14 underwent stereocontrolled opening of the aziridine ring on reaction with MeSH/BF3 to give a thioether 15. With benzoic acid in CHCI3, 10d gave the 4-hydroxy-5-aminocyclopent-2-enyl benzoate 11. The meso-2-aminocyclopent-4-ene-1,3-diol 12 was obtained by hydrolysis of 11. On reaction with Boc2O and NaI, the aziridine ring of 14 was converted to a bicyclic compound 17. Hydrolysis of 17 provided the trans-1,3-diol 18, the epimer of 12. Face-selective dihydroxylation of Boc-protected 12 gave a meso-aminocyclopentanetetrol 23 which was characterized upon peracetylation. Dihydroxylation of 15 provided a racemic analogue of epi-mannostatin A (26).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810523
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  • 74
    Digitale Medien
    Digitale Medien
    An Alternative Synthesis of the Enantiomerically Pure Competitive NMIDA Antagonists SDZ 220-581 and SDZ EAB 515 (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 729-733 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An alternative synthesis of enantiomerically pure SDZ 220-881 (1a) and SDZ EAB 515 (1b) starting from L-Z-tyrosine is described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810322
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  • 75
    Digitale Medien
    Digitale Medien
    Diastereo- and Regioisomeric Bicyclic Thiohydantions from Chiral 1,3-Thiazolidine-2,4-dicarboxylic acids (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 744-753 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Bicyclic thiohydantoins were synthesized in a stereoselective manner by reacting (2R)/(2S)-diastereoisomer mixtures of 1,3-thiazolidine-2,4-dicarboxylic acids or their dimethyl diesters with PhNCS. 5,5-Dimethyl-1,3-thiazolidine-2,4-dicarboxylic acid with PhNCS led to a cyclization involving the C=O group at the C(2) center of the thiazolidine ring, while the acid's dimethyl diester gave cyclization involving the C=O group at C(4). In contrast, reactions involving unsubstituted 1,3-thiazolidine-2,4-dicarboxylic acid or its dimethyl diester led to thiohydantoins in which the ring closure had taken place only with the COO group at C(4). Independently of the direction of the ring closure, all reactions produce exclusively products with the (R)-configuration at C(2). The configurational assignments were based on 1H- and 13C-NMR studies, and confirmed by X-ray crystallographic analyses.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810324
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  • 76
    Digitale Medien
    Digitale Medien
    New Axially Chiral Bis(dihydrooxazoles) as Ligands in Stereoselective Transition-Metal Catalysis (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 676-687 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The new, axially chiral bis(4,5-dihydrooxazoles) 4 have been synthesized in a straightforward manner, starting from the substituted, racemic 1,1′-biphenyl-2,2′-dicarboxylic acids 1 and optically active amino alcohols 2. The adducts were resolved by medium-performance liquid chromatography (MPLC; see Scheme 1). Formation of Cu1 complexes of 4 was followed by 1H-NMR spectroscopy. The catalytic behavior of these complexes has been investigated by asymmetric cyclopropanation of styrene with ethyl diazoacetate. Beside the influence of steric factors, a significant electronic effect on asymmetric induction could also be observed (see Scheme 2 and Table).
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810318
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  • 77
    Digitale Medien
    Digitale Medien
    Synthesis of Bridgehead-Functionalized Bicyclo[3.2.1]octanes via intramolecular titanium- and tributylstannane-induced pinacol coupling (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 734-743 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the enantiomerically pure, bridgehead-functionalized bicyclo[3.2.1]octanes 11 and 16, containing a conformationally fixed trihydroxypropyl (aminodihydroxypropyl) unit, as well as the X-ray structure of 11 are described. These compounds are of interest as sugar surrogates in the preparation of DNA analogs. Compounds 11 and 16 became available in 10 and 12 steps, respectively, and in an overall yield of 11 and 4% from D-arabinose via a highly stereoselective pinacol coupling as the key step.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810323
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  • 78
    Digitale Medien
    Digitale Medien
    Synthesis and Structure Elucidation of a New Potent Sandalwood-Oil Substitute (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1349-1358 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New derivatives of campholenaldehyde (= 2-(2,2,3-trimethylcyclopent-3-enyl)ethanal bearing two cyclopropane moieties were synthesized, and the structure of the stereoisomer responsible for its exceptionally strong, diffusive, and natural sandalwood-oil scent, ((1S,2S)-1-methyl-2-{[1S,3R,5R)-1,2,2-trimethylbicyclo[3.1.0]hex-3-yl]methyl}cyclopropyl)methanol (13a), was elucidated.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810545
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  • 79
    Digitale Medien
    Digitale Medien
    Glycosylidene Carbenes. Part 27.Part 26: [1] Glucosidation of titanium dioxide with 1-aziglucoses: Preparation and characterization of modified titanium-dioxide surfaces (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1359-1372 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Titanium-dioxide surfaces have been glycosylated with the benzyl-, 4-fluorobenzyl-, and acetyl-protected diazirines 1-3. The modified TiO2 surfaces were characterized by contact-angle measurement, X-ray photoelectron spectroscopy (XPES), and time-of-flight secondary-ion mass spectrometry (ToF-SIMS). The main by-products of the glucosidation (mostly azines and trehaloses) were identified. Their physisorption slightly reduces the efficiency of the glucosidation by 1 mM solution of 1 or 2 in CH2Cl2, but this influence is neutralized by repeating the glucosidation, or by using a 100 mM solution of the diazirines. The immobilized, acetylated glucosyl moieties were deacetylated in situ. Calculations based on the XPES peaks of Ti 2p and F 1s for the TiO2 surface modified with 2 indicated 1.5 ± 0.9 immobilized glucosyl moieties per nm2.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810546
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  • 80
    Digitale Medien
    Digitale Medien
    Minor Coumarins from Calophyllum teysmannii var. inophylloide and Synthesis of Cytotoxic Calanone Derivatives (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1404-1416 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A Chemotaxonomic survey for biologically active compounds from Malaysian Calophyllum species led to the findings of the four new benzoylcoumarins 1a, 2, 3, and 4a (including the unusual prenylated 6-benzoylcoumann 1a), two uncommon coumarins 5 and 6a with a pyran-4-one moiety fused at C(6) and C(7), and compounds 7a, 9, and 10, all isolated from the bark of C. teysmannii var. inophylloide. Their structures were determined by spectroscopic analysis and chemical transformations. X-Ray crystal-structure determination of 2 provided information on the conformational preferences of substituents in this class of coumarins. The syntheses of the cytotoxic calanone (7a) and of some related coumarins are described.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810549
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  • 81
    Digitale Medien
    Digitale Medien
    New Enzyme Models of Chloroperoxidase: Improved stability and catalytic efficiency of iron porphyrinates containing a thiolato ligand (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1506-1520 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The heme-thiolate protein chloroperoxidase (CPO) catalyzes the chlorination of activated C—H bonds. A reaction mechanism is proposed for this enzymatic transformation (Scheme 1), and a new iron(III) porphyrinate complex 13 is synthesized containing pentafluorophenyl groups at two meso-positions and a thiophenolato ligand coordinating to the Fe-atom (Schemes 2 and 3). Due to the presence of the electron-withdrawing substituents, the catalyst 13 is appreciably resistant to oxidants (HOCl) and chlorinates, e.g., monochlorodimedone (5), with turnover numbers up to 1530. The redox potential of 13, E0 = - 134 mV, and the Soret band (λmax 448 nm) of the CO adduct of the reduced state of 13 are close to the corresponding values of the enzyme CPO.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810554
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  • 82
    Digitale Medien
    Digitale Medien
    Nucleotides. Part LVII.Part LVI: [1].. Synthesis of phosphoramidite building blocks of 2′-amino-2′-deoxyribonucleosides: New compounds for oligonucleotide synthesis (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1528-1544 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The chemical synthesis of 2′-amino-2′-deoxyribonucleosides of uracil, cytosine, adenine, and guanine, and their conversion into suitably protected 3′-phosphoramidite building blocks 35-40 for oligonucleotide synthesis are described. The aglycone and the 2′-amino functions were protected using the 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) group. The synthesis of the 3′-O-succinyl (3′-O-(3-carboxypropanoyl))-substituted starting nucleoside 41 is described and its behavior examined in solution and on solid phase with regard to an anticipated migration during 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) deprotection. Oligonucleotides were prepared using the new building blocks, and their hybridization properties were studied by UV-melting techniques.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810556
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  • 83
    Digitale Medien
    Digitale Medien
    Erratum (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1583-1583 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810559
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  • 84
    Digitale Medien
    Digitale Medien
    Supramolecular Chirality: Chiral hydrogen-bonded supermolecules from achiral molecular components (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1-13 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Chiral supermolecules may be obtained from suitable achiral molecular constituents associated through a dissymmetrizing interaction mode. This is the case for the supermolecules I-IV formed by hydrogen-bonding association between the achiral complementary components 1a,b and 2a,b,c. The crystal structures of the supermolecular pairs I-III and of the homochiral aggregate of two ternary supermolecules IV have been determined. The structural data are discussed.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810102
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  • 85
    Digitale Medien
    Digitale Medien
    Nucleotides. Part LVPart LIV: [1].. Synthesis and application of a novel linker for solid-phase synthesis of modified oligonucleotides (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 46-58 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Various bifunctional amino-protecting groups such as the phthaloyl, succinyl, and glutaryl group were investigated as potential linker molecules for attachment to solid-support materials. Pentane-1,3,5-tricarboxylic acid 1,3-anhydride (16) offered the best properties and reacted with the amino groups of differently sugar-protected adenosine (see 20 and 22), cytidine (see 29), and guanosine derivatives (see 32) to the corresponding 2-(2-carboxyethyl)glutaryl derivatives 23, 24, 30, and 33. The usefulness of the new linker-type molecules was demonstrated by the solid-support synthesis of the potentially antivirally active 3′-deoxyadenylyl-(2′-5′)-2′-adenylic acid 2′-{2-[(adenin-9-yl)methoxy]ethyl} ester (38) starting from the 2′-end with N6,N6-[2-(2-carboxyethyl)glutaryl]-9-{{2-[(4,4′-dimethoxytrityl)ethoxy]methyl}adenine (12).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810106
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  • 86
    Digitale Medien
    Digitale Medien
    Biocatalytic Deracemization of 1,4-Benzodiazepines in the Synthesis of Enantiomerically Pure Serine (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 85-92 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An efficient stereocontrolled synthesis of (S)-N-Cbz-serine (Cbz = benzyloxycarbonyl; 12) and of its (R)-enantiomer is reported. Kinetic resolution of the easily available racemic 3-(hydroxymethyl)-1,4-benzodiazepin-2-ones is performed in the key step via acetylation by the immobilized Mucor miehei lipase (Lipozyme IM) at 60°. This method is characterized by high enantiomer purity (ee's ges; 99%) of the intermediary alcohols (+)-8 and (+)-9 and acetates (-)-10 and (-)-11, as well as of the final products (S)- and (R)-N-Cbz-serine, simple recycling of the biocatalyst, complete recovery of 2-aminobenzophenones (3 and 4) and their recycling into production of 1,4-benzodiazepines, and possibility to selectively racemize ‘wrong’ enantiomers of the alcohols 8 and 9 in the presence of Amberlite CG 400.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810110
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  • 87
    Digitale Medien
    Digitale Medien
    A Study of the Metabolic Degradation of an insect juvenile hormone analog using different radiolabeling (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 163-173 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The fate of an insect juvenile hormone analog applied to the insect body of the flesh fly (Sarcophaga bullata) or the tsetse fly (Glossina palpalis), respectively, was studied using three different radiolabeled positions in the parent biologically active compound 1. Several metabolites were found and analyzed. A mechanism of degradation of the applied molecule was designed using a combination of several radioanalytical methods. A unique monitoring of the applied compound and its metabolites was provided, based on the different radiolabeling of the structure (cf. 1a-1c), and established their fate in an insect body during a 10-day experiment. A 14C and 3H radiolabeling, respectively, was employed to synthesize three different radiolabeled forms 1a-1c derived from the parent non-labeled 1. A combination of three different ways of radiolabeling resulted in an advantage in tracing the metabolic pathway of degradation of the employed compound 1 in its radiolabeled forms 1a-1c.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810115
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  • 88
    Digitale Medien
    Digitale Medien
    3rd Swiss course on medicinal chemistry (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 187-187 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810118
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  • 89
    Digitale Medien
    Digitale Medien
    Orbital-Symmetry Effects in Bimolecular Electron-Transfer Reactions: Back Electron TransferDedicated to Prof. Nicholas J. Turro on the occasion of his 60th birthday (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 670-675 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Previous work has indicated orbital-symmetry effects upon forward electron transfer in bimolecular systems, with magnitude similar to that encountered in rigid monomolecular systems. The present work, which employs back electron transfer, supports and extends these earlier findings.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810317
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  • 90
    Digitale Medien
    Digitale Medien
    Glycosylidene Carbenes part 26Part 25: [1]. The intramolecular F…HO hydrogen bond of 1,3-diaxial 3-fluorocyclohexanols (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 695-717 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: According to ab-initio calculations, the CF…HO H-bond in 1,3-diaxial 3-fluorocyclohexanol is characterized by d(F…H) = 2.08 Å, and ∠ (F…H—O) = 138°, and by ΔE between 1.2 and 4.1 kcal/mol, depending upon the reference system. Relative to the OH stretching frequency of axial cyclohexanol, the OH stretching frequency of 1,3-diaxial 3-fluorocyclohexanol is shifted by Δω = 7 cm-1. The rigid fluoro diols D-4 and L-4 were prepared from tetrahydroxy-p-benzoquinone in 11 steps and 1% overall yield. The IR spectrum of 4 in CCl4 soln. is characterized by Δν = 7 cm-1 for the axial and Δν = 44 cm-1 for the equatorial OH group. A relatively strong intramolecular CF…HO bond of 4 in CCl4 is evidenced by the large through-space coupling 5J(F,HO) of 9.3 Hz. Nevertheless, this FHO bond is disrupted in ethereal solvents, while the bifurcated O…HO bond subsists. In CCl4, the carbene generated from the glucosylidene-derived diazirine 5 reacted more rapidly with the axial OH group of D-4 and L-4 than with the equatorial one. This regioselectivity is in keeping with the weaker H-bond of the axial OH group. The regioselectivity is lower in ethers, but its solvent dependence does not parallel solvent basicity. This is not satisfactorily explained by the differential interaction of the ether solvents with the axial and equatorial OH groups, as evidenced by the solvent dependence of their chemical shift, but must also reflect the different interaction of the solvents with the carbene derived from 5, leading to ylides. The lower solvent dependence of the anomeric selectivity for the glycosidation of the equatorial OH group is a consequence of the coordination of the intermediate oxycarbenium ion with O—C(1) and O—C(3) rather than with the solvent. Under conditions of competitive glycosylation in CCl4, the fluoro alcohol D-22 reacted more slowly than the alcohol L-24, evidencing the intramolecular F…HO H-bond.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810320
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  • 91
    Digitale Medien
    Digitale Medien
    Synthesis and Odor of Chiral Partial Structures of Khusimone. Part 3Part 2: [1].. Short communication (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 40-45 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Khusimone (1), one of the main odor-donating compounds of vetiver oil, is subject of the following study on structure/odor relationship. The omittance of the methano bridge of the tricyclic khusimone should lead to the bicyclic partial structure (-)-2. Unexpectedly, (-)-2 could not be obtained since epimerization favored (-)-16. The stereochemical key step of the synthesis of the hydrazulene nucleus is based on a highly diastereoselective conjugate addition to a chiral oxocyclopent-1-ene-1-carboxylate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810105
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  • 92
    Digitale Medien
    Digitale Medien
    A Convenient Stereoselective Synthesis of (1R,2S,3R,4S)-3-(Neopentyloxy)isoborneol (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 78-84 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A convenient preparation of (1R,2S,3R,4S)-3-(neopentyloxy)isoborneol (= (1R,2S,3R,4S)-3-(2,2-dimethyl-propoxy)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol; 1a), a valuable chiral auxiliary, is described. The synthesis involves six steps starting from the readily available camphorquinone (5) and gives 1a in 48% overall yield. The key step is the chemoselective hydrolysis of the less hindered 1,3-dioxolane moiety in the camphorquinone di-acetal 4.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810109
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  • 93
    Digitale Medien
    Digitale Medien
    A Novel Solution- and Solid-Phase Approach to 2,4,5-tri- and 2,4,5,6-tetrasubstituted pyrimidines and their conversion into condensed heterocycles (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 646-660 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A novel general synthesis of 2,4,5-tri- and 2,4,5,6-tetrasubstituted pyrimidines 5a-d and 7a, e, f, g by condensation of thiouronium salts of type 3 with (ethoxymethylidene)malononitrile (4) and [bis(methylthio)methylidene]malononitrile (6), respectively, was first established in solution (Scheme 1) and successfully transferred onto solid support by using the polymer-bound thiouronium salt 11 (Scheme 3). Further investigations were directed toward a multidirectional cleavage procedure of the 2-(alkylsulfinyl) intermediates, obtained from the 2-(alkylthio)pyrimidines 7a (Scheme 2) or 12 and 14 (Schemes 3 and 4), with different nucleophiles to form highly substituted pyrimidines. In addition, fused-heterocycle derivatives 22a--h, 24a-c, and 26a-e were generated in good-to-excellent yields by condensation of 7a, e, h with versatile isocyanates and isothiocyanates, with subsequent alkylation (Scheme 5).
    Zusätzliches Material: 6 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810315
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  • 94
    Digitale Medien
    Digitale Medien
    Induction of an Enantiomeric Excess in a Calix[4]arene/Bipyridine-Based chiral copper(i) complex (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 661-669 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Introduction of the non-complexing chiral (S)-2-methylbutoxy substituent close to the complexing site of a bis[(bipyridinyl)methoxy]calixarene podand resulted in the induction of an enantiomeric excess of ca. 30 % in the corresponding chiral CuI complex. Structural investigations by high-resolution NMR studies led us to propose the left-handed prohelical [CuI(bpy)2] substructure for the major enantiomer.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810316
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  • 95
    Digitale Medien
    Digitale Medien
    Ruzicka-Preis 1998 (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 792-792 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810329
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  • 96
    Digitale Medien
    Digitale Medien
    Selective Derivatization of the Ionophore X-206 at C(22) Maintaining Potassium Binding (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 812-827 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The insecticidal polyether antibiotic X-206 (1) complexes potassium ions using nearly all of its O-atoms either for binding to the metal ion or for participation in a H-bonding network which helps to hold X-206 in the ionophoric tertiary structure. The group OH—C(22) is not involved in these processes. It was supposed that derivatization of this group would not affect the ionophoric properties and would produce insecticidally active compounds. The chemistry leading to selective modification of OH—C(22) via the intermediate 6 was developed. The potassium-binding properties and insecticidal activities of the MeCOO—C(22) and MeO—C(22) compounds 3 and 11, respectively, confirmed that derivatization of the peripheral OH—C(22) was a valid strategy for the synthesis of biologically active compounds.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810503
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  • 97
    Digitale Medien
    Digitale Medien
    Synthesis and Some Transformations of 2-Acetamido-5-amino-3,4,6-tri-O-benzyl-2,5-dideoxy-D-glucono-1,5-lactam (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 865-880 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The lactam 21 was obtained in an overall yield of 72% from the hydroxy amide 16 by oxidation with the Dess-Martin periodinane, acid-catalysed isomerization of the oxidation products in toluene, whereupon 18/19 precipitated, and reductive dehydroxylation of 18/19 (Et3SiH/BF3 · OEt2; Scheme 1). The amide 16 was obtained by ammonolysis of the N-acetylglucosamine-derived lactone 15. Depending on the oxidation method, 16 yielded the keto amide 17, the hydroxy lactams 18/19, and the pyrrolidinecarboxamide 20 in widely different proportions. The pyrrolidinecarboxamide 20 was not reduced under the conditions of the reductive dehydroxylation. Hydrogenolysis of the benzyl-protected lactam 21 gave the trihydroxy lactam 22, while reduction with NaBH4/BF3 · OEt2 led to the 2-acetamidopiperidine derivative 24 (Scheme 2). Selective (tert-butoxy)carbonylation of the lactam 21 (→ 25) followed by NaBH4 reduction and acid-catalysed solvolysis in EtOH led to the α-ethoxycarbamates 28/29. Similarly, (tert-butoxy) carbonylation of 1 (→ 31) followed by reduction to 32/33 and glycosidation yielded the ethoxycarbamate 34. Treatment of the GlcNAc-derived ethyl glycosides 28/29 with Me3SiCN/BF3 · OEt2 gave the equatorial amino nitrile 30. Under similar conditions, the Glc-derived glycoside 34 led to the iminooxazolidinone 35. In the presence of a larger proportion of Me3SiCN at 5°, 34 was transformed into the axial, selectively monodebenzylated amino nitrile 36.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810508
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  • 98
    Digitale Medien
    Digitale Medien
    Aldehyde-Promoted Addition of 2-(Trimethylsilyl)thiazole to α,α′-Dialkoxy Ketones: A new way to branched-chain monosaccharides (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 889-901 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of 2-(trimethylsilyl)thiazole (2-TST) with several ketones was tested in the presence or absence of aldehydes. The keto aldehyde 5 (Scheme 2) was prepared from 1 via the hydroxy aldehyde 4 in 3 steps. It reacted with 2-TST to give, after desilylation and acetylation, the bis-thiazole 6. The ketone 11, obtained from 4 in 3 steps, reacted with 2-TST to give, after desilylation, 12. The ketofuranose 17 (Scheme 3) reacted with 2-TST to yield exclusively the more stable D-gluco epimer 18. The reaction of the ketone 11 (Scheme 2) with 2-TST was faster in the presence of 1 equiv. of the keto aldehyde 5, suggesting that an aldehyde promotes the indirect and intermolecular addition of 2-TST to a ketone. We have studied the effect of several aldehydes on the rate of the reaction of the ketones 11 and 17 with 2-TST at different temperatures and at different concentrations of the ketones and of the aldehydes. Electrophilic aldehydes, and particularly 2-fluorobenzaldehyde (0.1 equiv.), promote the addition of 2-TST to electrophilic ketones.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810510
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  • 99
    Digitale Medien
    Digitale Medien
    Distamycin-NA: A DNA analog with an aromatic heterocyclic polyamide backbone. Part 2. Solid-phase synthesis of distamycin-NAs containing the nucleobase uracil: Unexpected solvent participation in the coupling step (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 916-931 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the Fmoc-protected amino acid 2 is presented. First attempts of amide-bond formation to the homodimer 4 in solution showed only poor coupling yields indicative for the low reactivity of the amino and carboxy groups in the building blocks 1 and 2, respectively (Scheme 1). Best coupling yields were found using dicyclohexylcarbodiimide (DCC) without any additive. The oligomerization of building block 2 adopting the Fmoc ((9H-fluoren-9-ylmethoxy)carbonyl) solid-phase synthesis yielded a mixture of N-terminal-modified distamycin-NA derivatives. By combined HPLC and MALDI-TOF-MS analysis, the N-terminal functional groups could be identified as acetamide and N,N-dimethylformamidine functions, arising from coupling of the N-terminus of the growing chain with residual AcOH or DCC-activated solvent DMF. An improved preparation of building block 2 and coupling protocol led to the prevention of the N-terminal acetylation. However, ‘amidination’ could not be circumvented. A thus isolated tetramer of 2, containing a lysine unit at the C-terminus and a N,N-dimethylformamidine-modified N-terminus, not unexpectedly, showed no complementary base pairing to DNA and RNA, as determined by standard UV-melting-curve analysis.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810512
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  • 100
    Digitale Medien
    Digitale Medien
    Second-Generation Trifluoromethyl-Substituted Chiral Dendrimers Containing Triply Branched Building Blocks: CF3 as sensitive NMR probe for ‘remote’ diastereotopicityPartially published in a preliminary communication [1]. (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 1003-1022 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (S)-4,4,4-Trifluoro-3-hydroxybutanoic acid was used as a starting material for the synthesis of dendritic branches (16-21, 30-32) which were attached to a chiral triol (6 or ent-6), derived from (R)-3-hydroxybutanoic acid, to give CF3-substituted dendrimers (33-36, 38-40) and dendritic compounds (37) of 1st and 2nd generation. The key steps in these syntheses are diastereoselective aldol additions of dioxanone enolates (building blocks and intermediates 6-15, 22, 23, and 25-28) and Williamson etherifications of benzylic-branch bromides with triols (intermediates and products 16-21, 28, and 30-40). The surfaces of the dendrimers are covered with MeO (33-35, 38-40) or allyloxy groups (36 and 37). The new dendrimers are characterized by NMR and mass spectroscopy. 19F-NMR Signals of the CF3 groups reveal constitutional heterotopicities caused by substituents which are separated from the F-nuclei by up to 15 bonds (through a 1,1′-biphenyl-4,4′-diyl spacer!) (Fig. 6).
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810515
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