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  • 2000-2004
  • 1995-1999  (876)
  • 1940-1944
  • 1900-1904
  • 1999  (876)
  • General Chemistry  (750)
  • breast cancer  (126)
  • Chemical Engineering
  • Engineering General
  • Nuclear reactions
Datenquelle
Materialart
Erscheinungszeitraum
  • 2000-2004
  • 1995-1999  (876)
  • 1940-1944
  • 1900-1904
Jahr
Schlagwörter
  • 101
    Digitale Medien
    Digitale Medien
    Differentially expressed genes associated with the metastatic phenotype in breast cancer (1999)
    Springer
    Breast cancer research and treatment 55 (1999), S. 125-134 
    Details
    ISSN: 1573-7217
    Schlagwort(e): breast cancer ; differential display ; gene expression ; invasion ; metastasis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We have previously shown that human breast carcinoma cells demonstrating an interconverted phenotype, where keratin (epithelial marker) and vimentin (mesenchymal marker) intermediate filaments are both expressed, have an increased ability to invade a basement membrane matrix in vitro. This increase in invasive potential has been demonstrated in MDA‐MB‐231 cells, which constitutively express keratins and vimentin, and in MCF‐7 cells transfected with the mouse vimentin gene (MoVi). However, vimentin expression alone is not sufficient to confer the complete metastatic phenotype in MoVi cells, as determined by orthotopic administration. Thus, in the present study, differential display analysis was utilized to identify genes that are associated with the invasive and/or metastatic phenotype of several human breast cancer cell lines. Forty‐four of 84 PCR fragments were differentially expressed as assessed by Northern hybridization analysis of RNA isolated from MCF‐7, MoVi, and MB‐231 cell lines. Polyadenylated RNA from a panel of poorly invasive, invasive/non‐metastatic, and invasive/metastatic breast carcinoma cell lines was used to differentiate between cell‐specific gene expression and genes associated with the invasive and/or metastatic phenotype(s). We observed that lysyl oxidase and a zinc finger transcription factor were expressed only in the invasive and/or metastatic cell line; whereas, a thiol‐specific antioxidant and a heterochromatin protein were down‐regulated in these cells. In contrast, tissue factor was expressed only in breast carcinoma cell lines having the highest invasive potential. These results suggest that specific genes involved in breast cancer invasion and metastasis can be separated by differential display methodology to elucidate the molecular basis of tumor cell progression.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006188129423
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  • 102
    Digitale Medien
    Digitale Medien
    Reduced expression of p27Kip1 protein is associated with poor clinical outcome of breast cancer patients treated with systemic chemotherapy and is linked to cell proliferation and differentiation (1999)
    Springer
    Breast cancer research and treatment 55 (1999), S. 159-165 
    Details
    ISSN: 1573-7217
    Schlagwort(e): breast cancer ; cell cycle ; cyclin‐dependent kinase inhibitor ; differentiation ; p27Kip1 ; prognosis ; proliferation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The cyclin‐dependent kinase inhibitor p27Kip1 is a negative regulator of cell proliferation. Its expression is known to be altered in a proteasome‐dependent manner without changes in DNA level. Reduced expression of p27Kip1 is associated with aggressive behavior in a variety of human cancers. We investigated expression of p27Kip1 protein in human breast cancer using immunohistochemistry to assess its biologic implication along with cell‐cycle analysis by flow cytometry. A total of 68 patients with invasive ductal cancer received adjuvant chemotherapy with cyclophosphamide, methotrexate, and 5‐FU every 3 weeks for six cycles. In epithelial cells of normal and benign breast disease, expression of p27Kip1 was well preserved while its expression markedly decreased in breast cancer (45 of 68). Expression of p27Kip1 is significantly reduced in poorly differentiated cancers and in the advanced stage of the disease. Levels of p27Kip1 expression correlated with cell populations in G0/G1 phase of the cell cycle. In survival analysis, p27Kip1 was useful to predict disease free survival but not overall survival of the patients after adjuvant chemotherapy. In summary, p27Kip1 seems to have a role in the cell proliferation and differentiation process during carcinogenesis of breast cancer. The results of the present study suggest that p27Kip1 can be used in predicting response to systemic chemotherapy in a subset of patients with breast cancer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006258222233
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  • 103
    Digitale Medien
    Digitale Medien
    G1‐S transition defects occur in most breast cancers and predict outcome (1999)
    Springer
    Breast cancer research and treatment 56 (1999), S. 103-110 
    Details
    ISSN: 1573-7217
    Schlagwort(e): cell cycle ; cyclins ; p16 ; p27 ; retinoblastoma protein ; breast cancer ; survival
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Cell cycle deregulation is frequently observed in tumors and has moreover been proposed to be a requirement for tumor development. By analyzing the expression of p27 by immunohistochemistry in 100 primary breast tumors and combining the analyses with our earlier characterization of cyclin E, D1, p16, and the retinoblastoma protein (pRB), we have been able to cover the majority of potential G1–S transition defects and observed that 90% of the tumors had alterations in one or several cell cycle regulatory proteins. Considerable variations in protein levels were found among tumors, with low p16 expression as the most common alteration followed by cyclin E or cyclin D1 overexpression, low p27 expression or pRB inactivation in decreasing prevalence. Tumors were grouped according to observed combinations of defects and the proliferative capacity was determined for each group by analyzing Ki–67 labeling index. Low proliferation was observed in tumors with: low p16; high cyclin Dl with normal or high p16 expression; and in tumors without cell cycle defects. Tumors with high cyclin E/low p27 or pRB defects showed higher proliferation. The survival differed noticeably for patients with various combinations of cell cycle defects, and four distinctive clusters were identified showing significantly different breast cancer specific survival (p 〈 0.0001) for both node-positive (p=0.0006) and node-negative patients (p 〈 0.0001). In summary, we have shown that G1-S transition defects are nearly obligatory in breast tumors and that the specific type of cell cycle defect influences the clinical behavior of the tumor.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006208419350
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  • 104
    Digitale Medien
    Digitale Medien
    Overexpression of basic fibroblast growth factor (FGF–2) downregulates Bcl–2 and promotes apoptosis in MCF–7 human breast cancer cells (1999)
    Springer
    Breast cancer research and treatment 56 (1999), S. 151-165 
    Details
    ISSN: 1573-7217
    Schlagwort(e): apoptosis ; basic FGF ; Bax ; Bcl–2 ; breast cancer ; MCF–7 cells
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Basic fibroblast growth factor (bFGF, FGF–2), a classical transforming factor, mitogen, and survival factor in multiple cell types, and has a paradoxic role in mammary epithelial cell transformation and proliferation. We have also demonstrated that recombinant FGF–2 uncharacteristically promotes cell death in MCF–7 human breast cancer cells. In this study, we investigated the effects of FGF–2 overexpression on survival in the same MCF–7 cells. In eight breast cancer cell lines and two nontransformed mammary epithelial cell lines, we demonstrated that high levels of Bcl–2 are only expressed in cells with undetectable levels of FGF–2 on western blot. In retrovirally transduced MCF–7 cells expressing both cytoplasm– and nucleus–localizing FGF–2 species and ones expressing only cytoplasm–localizing FGF–2 species, Bcl–2 levels were strongly decreased at both the mRNA and protein levels. Immunoprecipitation of Bax demonstrated a decreased association of Bax with Bcl–2 in these cells. Levels of Bax did not correlate with expression of FGF–2 in the 10 cell lines or in MCF–7 cells. The clonogenic potential of MCF–7 cells in tissue culture was decreased by the expression of FGF–2 and was additively suppressed by the chemotherapeutic agents etoposide and 5–fluorouracil in a dose and time dependent manner. MCF–7 cells overexpressing FGF–2 had a greater rate of programmed cell death at baseline and in response to etoposide and 5–fluorouracil in a TUNEL assay by immunofluorescent microphotography and by flow cytometric quantitation. The pro–apoptotic effect of FGF–2 overexpression on the chemosensitivity of these cells was confirmed by quantitative morphologic determination. These data demonstrate that the expression of FGF–2 downregulates Bcl–2 and promotes programmed cell death in MCF–7 human breast cancer cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006258510381
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  • 105
    Digitale Medien
    Digitale Medien
    Cisplatin–epirubicin–paclitaxel weekly administration in advanced breast cancer: A phase I study of the Southern Italy Cooperative Oncology Group (1999)
    Springer
    Breast cancer research and treatment 56 (1999), S. 237-250 
    Details
    ISSN: 1573-7217
    Schlagwort(e): breast cancer ; cisplatin ; epirubicin ; paclitaxel ; weekly administration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Purpose: Both cisplatin and epirubicin have been shown to enhance the antitumor activity of paclitaxel in vitro. Weekly administration could result in a substantial improvement in the therapeutic index of cisplatin and paclitaxel. This study was aimed at determining the MTDs of epirubicin and paclitaxel given weekly with a fixed dose of cisplatin. Patientsandmethods: Sixty–three breast cancer patients with advanced disease (24 locally advanced and 39 metastatic), who had not received prior chemotherapy (except adjuvant), received weekly cisplatin (CDDP) doses of 30 mg/m2 together with escalating doses of paclitaxel (PTX) and epirubicin (EPI) for a minimum of six cycles. The dose escalation was stopped if DLT occurred during the first six treatment cycles in 〉33% of patients of a given cohort. Results: Nine different dose levels were tested, for a total of 506 weekly cycles delivered. G–CSF support on days 3–5 of each week was also given in the last four cohorts (24 patients). An overall 11 patients showed DLT in the first six cycles. EPI and PTX doses up to 40 and 85 mg/m2/week, respectively, were safely delivered without G–CSF support. However, the actually delivered mean dose intensity was only 64 in this cohort. Therefore, the dose escalation continued with the addition of filgrastim from day 3 to day 5 each week. Doses of EPI and PTX up to 50 and 120 mg/m2/week were administered without observing DLT in the first six cycles in more than one third of the patients enrolled. No toxic deaths were observed. Only two patients had to be hospitalized because of sepsis. Grade 3–4 neutropenia, thrombocytopenia, and anemia occurred in 25, 9, and 16 patients, respectively. Alopecia was almost universal. Other nonhematologic toxicities were generally mild, being of grade 3–4 in only eight patients (fatigue and loss of appetite in two cases, diarrhoea in four cases, peripheral neuropathy and mucositis in one case).abstract
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006263226099
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  • 106
    Digitale Medien
    Digitale Medien
    Effective treatment of advanced estrogen–independent MXT mouse mammary cancers with targeted cytotoxic LH–RH analogs (1999)
    Springer
    Breast cancer research and treatment 56 (1999), S. 265-274 
    Details
    ISSN: 1573-7217
    Schlagwort(e): breast cancer ; cell death ; cell proliferation ; doxorubicin ; LH–RH analogs ; targeted chemotherapy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Cytotoxic agents linked to hormonal carriers provide new approaches to tumor therapy, and LH–RH receptors expressed by breast cancers can be used for targeting chemotherapeutic compounds. In the present study, large, advanced estrogen–independent MXT mouse mammary cancers were treated with cytotoxic LH–RH analog AN–152 containing doxorubicin (DOX) or AN–207 incorporating superactive derivative 2–pyrrolino–DOX (AN–201). These cytotoxic hybrid molecules were administered once i.v., close to their maximum tolerated doses, at various time intervals after transplantation of tumors. The cytotoxic LH–RH analogs and the radicals alone, given at earlier stages of tumor development, inhibited growth of MXT cancers. Cytotoxic LH–RH conjugate AN–207 had significantly stronger effect than its respective cytotoxic radical, particularly when larger tumors were treated, causing 95, 89, 100 and 96 tumor growth reduction when administered on days 1, 7, 10 or 14, respectively. AN–152, AN–201, and DOX, given on day 14, were virtually ineffective. Histological characteristics of tumor cell proliferation and cell death were analyzed in large MXT cancers 1–4 days after treatment with AN–207 and AN–201. AgNOR scores were decreased and apoptotic indices increased after treatment of tumors with AN–207 or AN–201, but enhanced apoptosis and decreased AgNOR numbers persisted longer in the case of AN–207. In contrast to AN–201, AN–207 also increased the extent of necrosis in tumors. In conclusion, on the basis of its powerful inhibitory effect on the aggressive MXT mouse mammary tumor, the cytotoxic LH–RH analog AN–207 could be considered for treatment of advanced human mammary carcinomas that express LH–RH receptors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006267327007
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  • 107
    Digitale Medien
    Digitale Medien
    Biomarkers for local recurrence after breast‐conservation — a nested case‐control study (1999)
    Springer
    Breast cancer research and treatment 57 (1999), S. 245-259 
    Details
    ISSN: 1573-7217
    Schlagwort(e): biological markers ; breast cancer ; ipsilateral breast tumor recurrences ; prognosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Purpose: A previous cohort study of 759 women with invasive T1‐T2 breast cancer operated on with breast‐conserving surgery in Stockholm between 1976 and 1986 indicated that age 〈50 years, no postoperative irradiation, and nodal involvement were independent risk factors for ipsilateral breast tumor recurrences (IBTR). The aim of the current study was to analyse if selected biological markers assayed in tumor specimens from these patients could add prognostic information, thereby helping to identify groups of patients at high versus low risk of IBTR. Methods: The study was designed as a case‐control study ‘nested’ within the cohort. The cohort was stratified according to nodal status and the use of postoperative irradiation. In these four strata, the cases were those 80 women who developed IBTR between 1977 and 1994. In each stratum, women without IBTR were randomly selected as controls (n=159). Median time at risk was 12 (8–18) years. The following factors were analysed: histopathological tumor grade according to Elston–Ellis, DNA ploidy, immunohistochemical staining for apoptosis, angiogenesis, Ki‐67 (MIB‐1), c‐erbB‐2, p‐53, waf‐1, and bcl‐2. The prognostic role of each factor was assessed using linear logistic regression methods. Results: In univariate analyses only age 〈50 years was identified as a significant risk factor for IBTR, whereas none of the studied biomarkers yielded statistically significant information. However, in a multivariate model, age, MIB-1-index, and tumor grade significantly influenced the risk for IBTR: the odds-ratio (OR) for age ≥50 years was 0.4, 95% confidence interval (CI) = 0.2–0.9; for medium or high grade tumors it was 0.4 (CI = 09–0.9); and for MIB-1-index 〉30%, 2.1 (CI = 1.0–4.4). In women ≥50 years, MIB-1-index 〉30% was associated with an OR of 3.5 (CI = 1.4–8.8) compared to those who were younger. Patients ≥50 years with MIB-1-index ≤30% were thus identified as a low-risk group with an OR of 0.2 (CI = 0.1–0.5). A possible high-risk group was patients 〈50 years with tumors showing a combination of c-erbB-2 and waf-1 immunoreactivity, with an OR of 6.7 (CI = 1.3–34.7). Conclusion: Women ≥50 years with MIB-1-index ≤30% constituted a subgroup with a low risk of IBTR. This observation raises the issue whether this group of patients might be spared postoperative irradiation following breast-conserving surgery. However, due to the methodology of the study, including the large number of comparisions, the presented results warrant cautious interpretation and should be regarded as tentative.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006281718793
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  • 108
    Digitale Medien
    Digitale Medien
    Antimetastatic effect of desmopressin in a mouse mammary tumor model (1999)
    Springer
    Breast cancer research and treatment 57 (1999), S. 271-275 
    Details
    ISSN: 1573-7217
    Schlagwort(e): breast cancer ; desmopressin ; metastasis ; tumor cell aggregation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We have investigated the effects of desmopressin (DDAVP), a synthetic analog of the natural hormone vasopressin, on experimental lung colonization of mammary tumor cells using a syngeneic BALB/c mouse model. Coinjection of DDAVP (1–2 μg/kg body weight) at the time of i.v. inoculation of F3II carcinoma cells or LM3 adenocarcinoma cells significantly inhibited the formation of experimental lung metastases. In both cases, the number of pulmonary nodules was reduced about 70%. Inhibition of metastasis was also obtained with i.v. administration of DDAVP 24 h after tumor cell inoculation. Interestingly, the inhibition of lung metastasis was not due to direct cytotoxic effects of DDAVP on mammary tumor cells. The in vitro formation of multicellular aggregates in the presence of citrated plasma from control and DDAVP‐treated mice was also examined. Control plasma rapidly induced a significant tumor cell aggregation. In contrast, in the presence of plasma from DDAVP‐treated mice, tumor cells remained as a single cell suspension. DDAVP may help to dissolve the protective fibrin shield of circulating tumor cells. Our data suggest, for the first time, that adjuvant DDAVP therapy may impair successful implantation of circulating mammary tumor cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006291607871
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  • 109
    Digitale Medien
    Digitale Medien
    Tamoxifen and fenretinide in women with metastatic breast cancer (1999)
    Springer
    Breast cancer research and treatment 57 (1999), S. 277-283 
    Details
    ISSN: 1573-7217
    Schlagwort(e): breast cancer ; dark adaptation ; fenretinide ; lipids ; tamoxifen ; transforming growth factor‐β
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Background: Tamoxifen and fenretinide combination therapy has been shown to be an active treatment regimen in metastatic breast cancer patients. This pilot study sought to determine whether the addition of fenretinide to tamoxifen would be associated with antitumor activity in metastatic breast cancer patients who had been previously treated with tamoxifen or who had hormone receptor negative disease. The effect of this therapy on circulating plasma transforming growth factor‐beta (TGF‐β) levels and serum lipids was also examined. Patientsand Methods: Thirty‐one patients were treated with tamoxifen (20mg po daily), and fenretinide (400mg po daily with a 3‐day drug holiday each month). Plasma TGF‐β testing was performed using isoform specific sandwich ELISA. Results: Twenty four of the 31 patients were evaluable for an antitumor response including 14 estrogen receptor (ER) positive patients who had failed prior tamoxifen therapy, seven ER‐negative patients, and three hormone therapy naive ER‐positive patients. There were no objective antitumor responses; three patients had stable disease for 8, 8, and 24 months. Five patients (16%) discontinued therapy for toxicity (one for grade 3 skin rash and four for abnormal dark adaptation). There was a statistically significant decrease in total cholesterol (median change per patient of −13.5 mg/dl; p=0.049, a 6.5% decrease), and an increase in HDL levels (median change per patient of +18 mg/dl, p=0.0001, a 35% increase) with tamoxifen and fenretinide therapy. TGF-β1 plasma levels were normal in 26 of 28 patients, and no changes in these levels post-treatment were demonstrated. Conclusions: Tamoxifen and fenretinide therapy is not an active combination in ER negative metastatic breast cancer or in patients whose disease has progressed on tamoxifen. This combination had a beneficial effect on total serum cholesterol and HDL levels with no associated rise in serum triglyceride levels. The 400 mg dose of fenretinide was associated with symptomatic nyctalopia in one-third of patients making it an unsuitable dose for use in breast cancer prevention studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006216409688
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  • 110
    Digitale Medien
    Digitale Medien
    p73 mutations are not detected in sporadic and hereditary breast cancer (1999)
    Springer
    Breast cancer research and treatment 58 (1999), S. 25-29 
    Details
    ISSN: 1573-7217
    Schlagwort(e): p73 ; mutation ; breast cancer ; sporadic
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Recently, a novel tumor suppressor gene, p73, was isolated and mapped to chromosome 1p36, a region commonly associated with loss of heterozygosity in neuroblastoma and other human malignancies, including breast cancer. The p73 gene shares considerable homology with the common tumor suppressor gene p53, both in composition and function. This study examines the potential participation of p73 in the pathogenesis of sporadic and hereditary breast cancers. Mutation analysis of 29 hereditary breast cancer cases revealed five independent silent mutations in the hereditary cases that are unlikely to play a role in tumor development. Mutation analysis of 48 sporadic breast tumors did not identify any unique variants. Eleven common polymorphisms scattered throughout the gene were also detected. Thus, mutations in the p73 gene appear to play little if any role in hereditary or sporadic breast cancer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006237031070
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  • 111
    Digitale Medien
    Digitale Medien
    The pure antiestrogen ICI 182780 is more effective in the induction of apoptosis and down regulation of BCL‐2 than tamoxifen in MCF‐7 cells (1999)
    Springer
    Breast cancer research and treatment 58 (1999), S. 87-97 
    Details
    ISSN: 1573-7217
    Schlagwort(e): antiestrogens ; apoptosis ; BCL‐2 ; breast cancer ; MCF‐7 ; tamoxifen ; ZM 182780
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract There is increasing evidence that induction of apoptosis by antihormones is an important mechanism in regard to their growth inhibitory action on hormone dependent tumors. In this report we have compared the efficiency of tamoxifen (Tam) and the pure antiestrogen ICI 182780 (ZM) to induce apoptosis in the estrogen dependent breast cancer cell line MCF‐7. Clear evidence for induction of apoptosis could be demonstrated after treatment with both antiestrogens. Application of the pure antiestrogen ZM led to a significantly higher induction of apoptosis compared to the partial agonistic compound Tam. The ability of the two compounds to induce apoptosis correlated with their growth inhibitory action. On the molecular level administration of ZM led to a time dependent steady decrease of BCL‐2 mRNA and protein. Administration of Tam also initially decreased the expression of BCL‐2. In contrast to ZM treatment, BCL‐2 expression increased again after 8 h of incubation with Tam. After 96 h Tam treated cells expressed BCL‐2 levels nearly as high as untreated cells. In general, ZM decreased BCL‐2 levels more effectively than Tam. Our results demonstrate that ZM and Tam possess quantitative and qualitative differences in their ability to down regulate BCL‐2 expression. The higher ability of the pure antiestrogen to down regulate BCL‐2 expression may explain the superiority of the pure antiestrogen to induce apoptosis and to inhibit the growth of MCF‐7 cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006338123126
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  • 112
    Digitale Medien
    Digitale Medien
    Bone marrow micrometastases in breast cancer patients (1999)
    Springer
    Breast cancer research and treatment 58 (1999), S. 123-130 
    Details
    ISSN: 1573-7217
    Schlagwort(e): bone marrow ; breast cancer ; micrometastases
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The presence of epithelial cells in bone marrow may be a prognostic factor in breast cancer, and so we evaluated their evolution in treated and untreated patients. A first bone marrow aspirate was obtained from 125 stage I/II breast cancer patients at diagnosis and repeated every 6–8 months; the samples were processed for leukocyte separation, used to prepare cytospin slides, stained with a pool of monoclonal antibodies (MoAb) recognising epithelial antigens, and immunocytochemically processed. The median follow-up was 48 months (range 15–82); 23 patients relapsed, and 14 died. MoAb positive cells were observed in 31.2% of first, 24.3% of second, and 27.8% of third aspirates. In 68/100 pairs of successive aspirates, bone marrow status remained unchanged; in 20 it became negative, and in 12 positive (not statistically significant even after adjusting for adjuvant therapy). An analysis based on Mantel and Byar's approach to time-dependent covariates using all 225 aspirates found no statistically significant prognostic difference between the patients with negative and positive bone marrow. Bone marrow status changed over time in about 1/3 of the patients; adjuvant therapy did not affect the probability of its becoming negative or positive. No significant association was found between bone marrow evolution and relapse or death, but the relatively high probability of a change in status over time cannot exclude the possibility that a positive aspirate during the course of breast cancer may be a negative prognostic factor.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006336100142
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  • 113
    Digitale Medien
    Digitale Medien
    Static disease on anastrozole provides similar benefit as objective response in patients with advanced breast cancer (1999)
    Springer
    Breast cancer research and treatment 58 (1999), S. 157-162 
    Details
    ISSN: 1573-7217
    Schlagwort(e): anastrozole ; breast cancer ; static disease
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Background. This paper reports on the clinical relevance of durable static disease (SD) (≥24 weeks) in breast cancer patients treated with the aromatase inhibitor anastrozole. Patients and methods. All patients were part of two prospective, randomised, multicentre studies in postmenopausal women with advanced disease in which megestrol acetate was compared with anastrozole 1 mg. Survival from initiation of treatment was analysed by the response type, i.e., complete response (CR)/partial response (PR), static disease (SD) (≥24 weeks), or progressive disease (PD), achieved on therapy. Results. Median survival with anastrozole 1 mg was similar between patients who obtained CR/PR and SD (≥24 weeks). Similarly, no difference in survival was observed in patients treated with megestrol acetate who achieved CR/PR and SD. With both treatments patients with CR/PR and SD had improved survival over those patients with PD within 24 weeks. There was no difference between treatment arms for patients showing PD within 24 weeks. Conclusions. These data confirm that durable SD (≥24 weeks) is a clinically useful remission criterion in postmenopausal women with advanced breast cancer with predictive value for overall survival. It also confirms the value of this endpoint with anastrozole, a new generation aromatase inhibitor.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006391902868
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  • 114
    Digitale Medien
    Digitale Medien
    Changes associated with delay of mammary cancer by retinoid analogues in transgenic mice bearing c-neu oncogene (1999)
    Springer
    Breast cancer research and treatment 58 (1999), S. 239-252 
    Details
    ISSN: 1573-7217
    Schlagwort(e): N-(4-hydroxyphenyl) retinamide ; arotinoid Ro 40-8757 ; breast cancer ; erbB2 expression ; IGF-1 levels ; toxicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Breast cancer is one of the common cancers and is a leading cause of cancer mortality in women. The TG.NK transgenic mouse line on FVB strain background expresses the c-neu oncogene under the control of a MMTV promoter in mammary tissue and appears to be a useful animal model for evaluation of strategies to delay or prevent mammary cancer. Fiber-rich nonpurified diet (NTP-2000) and some retinoid analogues have delayed mammary cancer in the TG.NK model. Four week old hemizygous TG.NK female mice with MMTV/c-neu (erbB2) activated oncogene were fed NTP-2000 diet containing the retinoid analogue 4-hydroxyphenylretinamide (4-HPR) at 7 mmol/kg or the arotinoid Ro 40-8757 at 1.5 and 2.5 mmol/kg for 26 weeks. The 4-HPR at 7 mmol/kg diet delayed the development of palpable tumors up to 24 weeks, but by 26 weeks, the incidence markedly increased and was closer to the NTP-2000 diet control group. However, the 4-HPR diet markedly decreased the average weight of the tumors at 26 weeks with no decrease in multiplicity. The 4-HPR also caused significant increase in liver weights without an effect on body weight. Arotinoid Ro 40-8757 caused marked decrease in the number and branching of mammary ducts, and inhibited mammary tumor development with significant decrease in the incidence, multiplicity, and tumor weights compared to the NTP-2000 diet control. Arotinoid also caused a significant dose-related increase in liver weights without a significant effect on body weights. At the doses tested, the arotinoid but not 4-HPR decreased the circulating levels of IGF-1. However, there was no association between the IGF-1 levels and the size, incidence, or absence of tumors when evaluated for any treatment group or for all mice in the study irrespective of treatment. The oncogene erbB2 (c-neu) and the growth factor EGF expression were more prominent in the small tumors of the mice treated with arotinoid than in the larger tumors of the control group. PCNA staining was observed in areas where there was high erbB2 and EGF staining. The delay in onset of mammary tumors by the above retinoid analogues may be related to the delay in development of mammary glands.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006315716713
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  • 115
    Digitale Medien
    Digitale Medien
    MMP-2 positivity and age less than 40 years increases the risk for recurrence in premenopausal patients with node-positive breast carcinoma (1999)
    Springer
    Breast cancer research and treatment 58 (1999), S. 285-291 
    Details
    ISSN: 1573-7217
    Schlagwort(e): breast cancer ; gelatinase A ; hematogenous metastasis ; prognostic factors ; 72 kDa type IV collagenase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Node-positive breast carcinoma is associated with a poor prognosis. Some patients benefit from adjuvant chemotherapy but new treatment modalities should still be developed in order to further increase the cure rate in this patient group. Prognostic factors are needed to define patients for such studies. Here, the prognostic value of matrix metalloproteinase-2 (MMP-2) and age was evaluated in 108 premenopausal, node-positive breast carcinoma patients treated with an adjuvant chemotherapy. Expression of MMP-2 protein was studied in paraffin-embedded tissue sections from primary tumors by using specific MMP-2 monoclonal antibody in an immunohistochemical staining. Age less than 40 years predicted 5-year recurrence free survival (RFS) as unfavorable, being 74% in patients 41–49 years of age and 54% in those under age 40 (p=0.02). The 5-year RFS rate was 85% in patients with an MMP-2 negative primary tumor while it was 65% in the MMP-2 positive patient group. This difference was not, however, statistically significant (p=0.07). Correlation between hematogenous metastasis and MMP-2 positivity in breast carcinoma was demonstrated for the first time (p=0.03). A risk group for a relapse was identified using MMP-2 immunohistochemistry and age. The RFS rate in patients less than 40 years with an MMP-2 positive primary tumor was only 50% while it was 74% in other premenopausal patients (p=0.007). Young age and MMP-2 positivity may, thus, associate with early relapse in node-positive breast carcinoma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006326513176
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  • 116
    Digitale Medien
    Digitale Medien
    A novel orthotopic model of breast cancer metastasis to bone (1999)
    Springer
    Clinical & experimental metastasis 17 (1999), S. 163-170 
    Details
    ISSN: 1573-7276
    Schlagwort(e): bone metastasis ; breast cancer ; model ; PTHrP
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Breast cancer affects approximately one woman in twelve and kills more women than any other cancer. If detected early, patients have a five year survival rate of 66%, but once metastatic disease has developed, there is no effective treatment. About 70% of patients with metastatic disease have bone involvement, while lungs and liver are the other common targets. Bone metastases cause severe pain, pathological fractures and hypercalcaemia and thus are a significant clinical problem. The development of new therapies for metastatic breast carcinoma depends on a better understanding of the mechanism of homing of the tumour cells to bone, liver and lungs and the factors required for their growth in these organs. Research on mechanisms of breast cancer metastasis, particularly to bone, has relied on in vitro studies or on tumour models in which the inoculation route is designed to promote delivery of tumour cells to a specific organ. Metastases in bone are achieved by inoculation into the right ventricle of the heart. To our knowledge there has been no report of a model of metastatic spread from the mammary gland to distant sites which reliably includes bone. In this paper, we describe our recent development of a novel murine model of metastatic breast carcinoma. The new model is unique in that the pattern of metastatic spread closely resembles that observed in human breast cancer. In particular, these murine breast tumours metastasise to bone from the primary breast site and cause hypercalcaemia, characteristics not normally found in murine tumours, but common in human disease. Furthermore, in a preliminary characterisation of this model, we show that secretion of parathyroid hormone-related protein, a role for which has been implicated in breast cancer spread to bone, correlates with metastasis to bone. This model therefore provides an excellent experimental system in which to investigate the factors that control metastatic spread of breast cancer to specific sites, particularly bone. The special advantage of this system is that it involves the whole metastasis process, beginning from the primary site. Existing models consider mechanisms that pertain to growth of tumour once the site has been reached. An understanding of the regulation of these factors by potential therapeutic agents could lead to improvement in therapies designed to combat metastatic disease. For the first time, this development will allow exploration of the molecular basis of site-specific metastasis of breast cancer to bone in a clinically relevant model.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006689719505
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  • 117
    Digitale Medien
    Digitale Medien
    ERK signalling in metastatic human MDA-MB-231 breast carcinoma cells is adapted to obtain high urokinase expression and rapid cell proliferation (1999)
    Springer
    Clinical & experimental metastasis 17 (1999), S. 649-654 
    Details
    ISSN: 1573-7276
    Schlagwort(e): u-PA ; cyclin D1 ; breast cancer ; ERK
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Increased urokinase plasminogen activator (u-PA) production is associated with tumor invasion and metastasis in several malignancies, including breast cancer. The mechanisms underlying constitutive u-PA expression are not well understood. We examined the relationship between the signal strength of the ERK pathway and the level of u-PA expression in the metastatic human breast cancer cell line MDA-MB-231. Treatment with the MEK1 inhibitor PD98059 resulted in decreased ERK1/2 phosphorylation and decreased u-PA mRNA and protein expression. Inhibition of ERK1/2 activity also led to decreased cell proliferation and to decreased cyclin D1 expression. Less than 5% of total ERK1/2 was phosphorylated in exponentially growing MDA-MB-231 cells, and ERK1/2 activity could be stimulated by okadaic acid. Okadaic acid did not stimulate u-PA expression, but induced strong expression of the cdk-inhibitor p21Cip1. These findings suggest that ERK1/2 signaling is tuned to a level which results in high u-PA expression and rapid cell proliferation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006741228402
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  • 118
    Digitale Medien
    Digitale Medien
    Increased levels of α6 integrins are associated with the metastatic phenotype of human breast cancer cells (1999)
    Springer
    Clinical & experimental metastasis 17 (1999), S. 323-330 
    Details
    ISSN: 1573-7276
    Schlagwort(e): breast cancer ; integrins ; metastasis ; progression ; xenograft model
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Integrins play an important role in interactions between cells and the extracellular matrix, and thus have a potential role in metastasis. Expression levels of α6, β1 and β4 integrin sub-units were measured in a panel of human breast cancer cell lines by RT/PCR, immunoprecipitation and flow cytometry. All the lines expressed α6, with the highest levels in the MDA-MB-231 and MDA-MB-435 cells. These grew the most aggressively and were metastastic in nude mice. Low levels of α6 protein were measured in breast cancer cells that were poorly tumorigenic and non-metastatic in nude mice, and there was an inverse relationship between ER and α6 expression. RT/PCR revealed that all lines expressed the 2 isoforms of α6, with the α6A isoform generally more abundant than α6B isoform. Clones of MDA-MB-435 were isolated by sterile sorting for cells with high or low α6 expression, and two variants established from metastases in nude mice were found to differ in α6 expression. When injected into nude mice, the α6-high variants produced significantly more lung metastases than the α6-low variants. β1 was abundant in all lines, while β4 was not detected in MDA-MB-134 cells, and in the MDA-MB-435 cells an alternately spliced variant of β4 was identified. Sequencing of the alternate variant revealed a novel sequence from a splicing event in the cytoplasmic tail of β4. None of the cells with this variant mRNA expressed detectable levels of β4 protein. Our results suggest that high α6 expression in human breast cancer cells is associated with tumorigenicity and metastatic potential.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006659230585
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  • 119
    Digitale Medien
    Digitale Medien
    Chemokines induce the cellular migration of MCF-7 human breast carcinoma cells: Subpopulations of tumour cells display positive and negative chemotaxis and differential in vivo growth potentials (1999)
    Springer
    Clinical & experimental metastasis 17 (1999), S. 389-396 
    Details
    ISSN: 1573-7276
    Schlagwort(e): breast cancer ; chemokine ; integrin ; metastasis ; migration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We previously reported that chemotactic cytokines (chemokines) induce the directional migration of cells derived from the breast carcinoma cell line MCF-7 in vitro, however it was apparent that only a small percentage of cells displayed the ability to migrate upon stimulation. In the present study three sub-lines derived from the parental MCF-7 cell line were selected for their ability to migrate in response to MIP-1α, MIP-1β or RANTES across Transwell filters of 8 μm pore size. The first round selection of migratory cells resulted in sub-populations which demonstrated an increased chemotactic response compared with parental cells. Cells migrating to MIP-1β were subjected to four further rounds of positive or negative selection, resulting in two sub-lines, MCF-7L4 and MCF-7U4 which displayed an increased and decreased chemotactic response respectively to MIP-1α MIP-1β and RANTES. No difference in chemokine receptor RNA message expression between these sub-lines and the parental MCF-7 line were detected, although increased levels of α3, α6 and αv integrin sub-units were shown for MCF-7L4 (positively selected sub-line) compared with MCF-7U4 cells. Moreover, the in vivo growth of cells derived from the two MCF-7 sub-lines was inversely correlated with their chemotactic response. The results of this study depict further the inherent heterogeneity in cancer, suggesting that the chemotactic response may influence the migratory traits of sub-populations within the tumour and potentially contribute to their in vivo behavior, growth and survival.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006657109866
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  • 120
    Digitale Medien
    Digitale Medien
    N-linked oligosaccharides and metastatic propensity in in vivo selected mouse mammary adenocarcinoma cells (1999)
    Springer
    Clinical & experimental metastasis 17 (1999), S. 437-444 
    Details
    ISSN: 1573-7276
    Schlagwort(e): breast cancer ; carbohydrate ; glycosylation ; invasion ; metastasis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Studies using metastatic variant selected in vivo from a cloned parental cell line demonstrate that the expression of β1-6 branched, N-linked carbohydrates and sialic acid were positively associated with in vitro invasiveness and inversely associated with metastatic potential, adherence, and in vivo growth rate. These results suggest that at least within one tumor model, a negative association occurs between metastatic potential and β1-6 branched oligosaccharide expression. In these studies two metastatic variants, Cl-66M1 and Cl-66M2, were selected following serial in vivo passage of Cl-66, a clonal cell line obtained from a mouse mammary adenocarcinoma cell line. The parent cell line and the two metastatic variants were approximately equal in their adherence to fibronectin, laminin, and collagen type IV coated plastic. In contrast, both Cl-66M1 and Cl-66M2 had a significantly increased ability to invade through matrigel invasion chambers and expressed significantly increased levels of β1-6 branched, N-linked carbohydrates, and sialic acid compared to the clonal parental cell line, Cl-66. Furthermore, the in vivo tumor growth rates of these selected variants were decreased compared to Cl-66 with the longest tumor volume doubling time observed with Cl-66M2.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006629119030
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  • 121
    Digitale Medien
    Digitale Medien
    Is the Fischer 344/CRJ rat a protein-knock-out model for dipeptidyl peptidase IV-mediated lung metastasis of breast cancer? (1999)
    Springer
    Clinical & experimental metastasis 17 (1999), S. 609-615 
    Details
    ISSN: 1573-7276
    Schlagwort(e): breast cancer ; Fischer 344/CRJ rats ; metastasis ; mutant DPP IV (G633R)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Fischer 344/CRJ rats harbor a G633R substitution in dipeptidyl peptidase IV (DPP IV) that leads to retention and degradation of the mutant protein in the endoplasmic reticulum (Tsuji E, Misumi Y, Fujiwara T et al. Biochemistry 1992; 31 (47): 11921–7 [1]). However, when these rats were used as a ‘protein knock-out’ model in further evaluating the previously established role of DPP IV in metastasis, lung colonization of the highly metastatic MTF7 rat breast cancer cell line was reduced by only 33% relative to normal Fischer 344 rats. To examine whether lung endothelia leak expression of mutant DPP IV and whether mutant DPP IV exhibits the same adhesion qualities as wild type DPP IV, detailed immunohistochemical, biochemical, transfection, and FACS analyses were performed to assess the surface expression of mutant DPP IV on lung endothelia and transfected HEK293 cells and adhesion assay to compare the adhesion qualities of wild-type and mutant DPP IV. Both endothelial and transfected HEK293 cells expressed mutant, enzymatically inactive DPP IV on their surfaces, albeit at greatly reduced levels when compared to expression of wild type DPP IV. Purified mutant DPP IV had identical adhesion qualities for lung-metastatic MTF7 cells as wild type DPP IV, and competitive inhibition of MTF7 lung colonization by truncated DPP IV confirmed involvement of mutant DPP IV in lung metastasis of Fischer 344/CRJ rats. Although metastasis appears to be mediated by several, often parallel mechanisms involving multiple tumor and host factors, these data indicate that altered expression of a single component can drastically change the outcome of metastatic disease.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006757525190
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  • 122
    Digitale Medien
    Digitale Medien
    Mycoplasma-Mediated Uptake of the Exogenous Human BRCA1 Gene by Hatching Blastocysts (1999)
    Springer
    Journal of assisted reproduction and genetics 16 (1999), S. 546-550 
    Details
    ISSN: 1573-7330
    Schlagwort(e): breast cancer ; mycoplasma ; Ureaplasma urealyticum ; foreign DNA ; gene transfer ; transgenic
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Purpose: Biological vectors for cell transfection are mainly viral in origin, with inherent shortcomings. Mycoplasmas are ubiquitous organisms that traverse cells easily. The objective was to determine if Ureaplasma urealyticum (T-mycoplasma) would vector exogenous BRCA1 DNA into blastocysts. Methods: Hatching mouse blastocysts (N = 70) were incubated in the presence of either viable or dead Ureaplasma urealyticum at 37°C for 1 hr. The blastocysts were exposed to human BRCA1 DNA lacking homology in the mouse genome for 2 hr, followed by DNase-I treatment and wash. Polymerase chain reaction and agarose gel electrophoresis analysis of amplified products were performed. Results: The BRCA1 gene was detected in the blastocysts only when viable Ureaplasma was present. PCR analyses of control Ureaplasma and untreated blastocysts were negative. Conclusion: Viable Ureaplasma organisms were shown to mediate the uptake of DNA fragments into blastocysts, resulting in transgenic mouse blastocysts with a normal human BRCA1 exon 11 gene.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1020553322073
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  • 123
    Digitale Medien
    Digitale Medien
    Clinical Relevance of Minimal Residual Cancer in Patients with Solid Malignancies (1999)
    Springer
    Cancer and metastasis reviews 18 (1999), S. 91-100 
    Details
    ISSN: 1573-7233
    Schlagwort(e): micrometastases ; immunohistochemistry ; minimal residual cancer ; marrow disease ; lymph node metastases ; breast cancer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract With the advent of new therapeutic modalities, the treatment options for oncologists can vary greatly depending upon the aggressiveness of the patient's cancer. Patients may receive no therapy, adjuvant therapy, aggressive adjuvant therapy (taxane based), monoclonal antibody therapy (e.g. Herceptin) or bone marrow transplantation. It is now mandatory to determine accurate prognostic patient profiles at diagnosis and during therapy to determine who would benefit most from a particular therapeutic regimen or to determine who should be shifted into more aggressive therapy. We now have ultra-sensitive methods of tumor cell detection that can determine the presence of minimal residual cancer (MRC) in marrow, stem cell product (SCP) and lymph node to help create these prognostic profiles. The author has conducted a critical review of the literature regarding the type of testing used to detect MRC, the incidence of MRC in marrow, SCP, and lymph node, and the clinical significance of MRC at diagnosis and during therapy. To date it is now clear that immunohistochemistry is a very useful diagnostic tool with adequate sensitivity to detect MRC. The presence of MRC at diagnosis in marrow and/or lymph node is associated with a poor prognosis for a number of disorders including breast cancer, neuroblastoma, gastrointestinal tumors, and lung cancer. In addition, the presence of MRC during therapy in marrow and/or SCP is associated with a very poor prognosis for patients with breast cancer. The use of testing for MRC in the patient provides prognostic information that may be of use to the oncologist.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006264420822
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  • 124
    Digitale Medien
    Digitale Medien
    Infusion Reactions Associated with the Therapeutic Use of Monoclonal Antibodies in the Treatment of Malignancy (1999)
    Springer
    Cancer and metastasis reviews 18 (1999), S. 465-471 
    Details
    ISSN: 1573-7233
    Schlagwort(e): monoclonal antibodies ; side effects ; toxicity ; lymphoma ; breast cancer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract With the FDA approval of Rituximab in 1998 for the treatment of lymphoma, and Trastuzumab in 1999 for the treatment of breast cancer, monoclonal antibodies were officially added to the therapeutic armamentarium against malignancy. Most of the side effects associated with these agents are due to antigen-antibody interactions on specific cells and tissues. One of the most predictable side effects of these products is a constellation of various systemic effects including flu-like syumptoms such as headache, fever, sweats, skin rash, shortness of breath, hypotension, nausea, and asthenia that occurs with the first infusion of such products. Rarely severe hypotension, bronchospasm, and hypoxia and even death have occurred. The pathophysiology of these reactions appears to be secondary to the release of cytokines as the antibodies bind do circulating antigen-expressing cells that are then removed in the reticuloendothelial system of the lungs, spleen and liver. In patients with large numbers of antigen-dense cells that have a high mitotic index, such as prolymphocytic leukemia, mantle cell lymphoma, or lymphosarcoma cell leukemia, there is a risk of true tumor lysis syndrome. One should be particularly cautious when treating patients with high numbers of circulating antigen-expressing cells in the setting of underlying cardiovascular or respiratory disease.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006341717398
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  • 125
    Digitale Medien
    Digitale Medien
    Antiestrogens – Tamoxifen, SERMs and Beyond (1999)
    Springer
    Investigational new drugs 17 (1999), S. 285-311 
    Details
    ISSN: 1573-0646
    Schlagwort(e): breast cancer ; estrogen-related diseases ; estrogen receptor ; ERβ ; chemoprevention
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Medizin
    Notizen: Abstract Estrogens play a central role in reproductive physiology. The cellular effects of estrogens are mediated by binding to nuclear receptors (ER) which activate transcription of genes involved in cellular growth control. At least two such receptors, designated ERα and ERβ, mediate these effects in conjunction with a number of coactivators. These receptors can directly interact with other members of the steroid receptor superfamily. A complex cross-talk exists between the estrogen-signaling pathways and the downstream signaling events initiated by growth factors, such as epidermal growth factor and insulin-like growth factors. Estrogens are also a causative factor in the pathogenesis of a variety of neoplastic and non-neoplastic diseases, including breast cancer, endometrial cancer, endometriosis, and uterine fibroids, among others. Antiestrogens, such as tamoxifen, are widely used for the treatment of breast cancer. Tamoxifen produces objective tumor shrinkage in advanced breast cancer, reduces the risk of relapse in women treated for invasive breast cancer, and prevents breast cancer in high-risk women. Although, initially developed as an antiestrogen, tamoxifen can also prevent postmenopausal osteoporosis as well as reduce cholesterol, due to its estrogen-agonist effects. Its estrogen-agonist activity, however, can lead to significant side-effects such as endometrial cancer and thromboembolic phenomena. This has led to the concept of “ideal” selective estrogen receptor modulators (SERMs), drugs that would have the desired, tissue selective, estrogen-agonist or -antagonist effects. Raloxifene is a SERM which has the desirable mixed agonist/antagonist effects of tamoxifen but does not cause uterine stimulation. “Pure” antiestrogens may provide very potent estrogen-antagonist drugs, but are likely to be devoid of beneficial effects on bone and lipids. Future drug development efforts should focus on developing superior SERMs that have a greater efficacy against ER-positive tumors and do not cause hot flashes or thromboembolism, and explore combination strategies to simultaneously target hormone-dependent as well as hormone-independent breast cancer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006348907994
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  • 126
    Digitale Medien
    Digitale Medien
    The Prophylactic Mastectomy Dilemma: A Support Group for Women at High Genetic Risk for Breast Cancer (1999)
    Springer
    Journal of genetic counseling 8 (1999), S. 163-173 
    Details
    ISSN: 1573-3599
    Schlagwort(e): prophylactic mastectomy ; breast cancer ; women at high genetic risk for breast cancer ; psychiatric evaluation ; psychosocial support ; support group ; genetic counseling ; education and health promotion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Psychologie
    Notizen: Abstract The goal of this pilot study was to test the usefulness of a six session psychoeducational support group for women at high genetic risk for breast cancer who were considering prophylactic mastectomy. The themes of the group sessions included overestimation of and anxiety about risk; desire for “hard data”; the emotional impact of watching a mother die of breast cancer; concerns about spouse reactions; self- and body image; the decision-making process; and confusion over whom to trust in decision making. Both the participants and the multidisciplinary leaders concluded that as a supplement to individual counseling, a support group is a beneficial and cost-effective treatment modality. Recommendations for the optimal format for such a group are described.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022834706495
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  • 127
    Digitale Medien
    Digitale Medien
    Photochemistry of 9,10-Dicarbonyl-9,10-dihydroanthracene - A Source of 9,10-Dehydroanthracene? (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 57-60 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Benzyne ; Dehydroanthracene ; Matrix isolation ; Photochemistry ; Bergman reaction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -9,10-Didehydroanthracene (1) is an interesting derivative of p-benzyne that has been subject of several studies. In contrast to an earlier report, the photochemical decarbonylation of 9,10-dicarbonyl-9,10-dihydroanthracene (2) does not lead to 1 but rather to the ring-opened ene-diyne 4. The key intermediate for this reaction is keto carbene 7 which is formed by monodecarbonylation of 2. Carbene 7 is labile towards visible-light irradiation and easily looses the second CO molecule to give 4. Carbene 7 and diyne 4 are characterized by IR and UV/Vis spectra, the IR spectra are compared to calculations at the B3LYP/6-31G(d,p) level of theory.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 128
    Digitale Medien
    Digitale Medien
    Reversal Diastereofacial Selectivity in the n-Butyllithium Addition to O-Protected N-Trimethylsilylimines of (2S)-Lactal: Enthalpic versus Entropic Contributions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 61-65 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Nucleophilic addition ; Solvent effect ; Reversal of diastereoselectivity ; Temperature effect ; Imines ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Commonly observed, but rarely explored, is the possibility of modifying the diastereomeric excess (de%) by means of temperature. A complete reversal in the diastereofacial selectivity could be obtained whenever the diastereoisomers concerned are differentially favored by enthalpy and entropy. The enthalpic or entropic dominance of a diastereoisomer depends greatly on the reaction solvent used.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 129
    Digitale Medien
    Digitale Medien
    Syntheses of Donor-Acceptor-Substituted 2,6-Stellanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 73-81 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Donor-acceptor systems ; Cage compounds ; Stelladione ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -A number of condensations could be carried out using tricyclo[3.3.0.03,7]octane-2-one (stellanone, 4) and tricyclo[3.3.0.03,7]octane-2,6-dione (2,6-stelladione, 5) as starting materials. The components for condensations were 2-trimethylsilyl-1,3-dithiane (6), 1,1-bis(trimethylsilyl)-1H-cyclopropa[b]naphthalene (7), its 3,6-dimethoxy-substituted analogue 8, fluorene (12), xanthene (13), diethyl malonate (14), and malononitrile (15). The condensation reactions with 5 yielded mono- and disubstituted products, among them were the donor-acceptor-substituted 2,6-stellanes 33-35. The structures of 18 (prepared from stellanone and fluorene), 19, 24, 27, 31 and 32 (synthesized by condensation of 2,6-stelladione and 2-trimethylsilyl-1,3-dithiane and malononitrile, respectively) were determined by X-ray crystallography.
    Zusätzliches Material: 1 Ill.
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  • 130
    Digitale Medien
    Digitale Medien
    Synthesis of ω-Nitro Acids and ω-Amino Acids by Ring Cleavage of α-Nitrocycloalkanones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 87-90 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Water ; α-Nitrocycloalkanones ; ω-Nitro acids ; Surfactant ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The reaction of various α-nitrocycloalkanones 1 with aqueous 0.05 M NaOH, at 80 °C, in the presence of cetyltrimethylammonium chloride (CTACl) as a cationic surfactant, produces ω-nitro acids 2 in good yields. Reduction of the latter with HCOONH4/Pd-C, in methanol, at 80 °C affords ω-amino acids 3. The synthesis of methyl 9-oxodecanoate (8) is also reported.
    Zusätzliches Material: 2 Tab.
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  • 131
    Digitale Medien
    Digitale Medien
    On the Selective O-Alkylation of Ambident Nucleophiles - The Synthesis of Thiohydroxamic Acid O-Esters by Phase-Transfer Reactions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 97-106 
    Details
    ISSN: 1434-193X
    Schlagwort(e): O-Alkylation ; Ambident nucleophile ; Thiazolethione ; Thiohydroxamic acid ; Phase-transfer reaction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -O-Alkylation of cyclic thiohydroxamic acids 1 and 3-5 has been studied with a view to developing an efficient method for the synthesis of N-(alkoxy)pyridine-2(1H)-thiones and N-(alkoxy)thiazole-2(3H)-thiones. Four issues have been addressed and the following conclusions can be drawn: (i) Thiones 1 and 5 exist as O-H acids in the solid state. (ii) According to NMR investigations (1H, 13C), the thione structures should be largely retained in CDCl3, [D6]DMSO, and CD3OD solutions of acids 1, 3-5, as is also the case for pyridinethione salts 2a-h. (iii) O-Alkylation of pyridinethione salts occurs in competition with S-alkylation. Selective O-alkylation is however possible, if thiohydroxamate salts with large countercations, such as M = NBu4, are treated with hard alkylating reagents in polar aprotic media. (iv) As tetrabutylammonium thiohydroxamates, such as 2f, are highly useful in the synthesis of cyclic thiohydroxamic acid O-esters, we have developed an efficient protocol for the preparation of N-(alkoxy)pyridine-2(1H)-thiones directly from acid 1 using phase-transfer conditions (alkyl halide or sulfonic acid ester, CH3CN, K2CO3, Bu4NHSO4). This method has proved particularly successful for the synthesis of N-(alkoxy)thiazole-2(3H)-thiones 11, 20-28, which were obtained in yields of up to 87%.
    Zusätzliches Material: 2 Ill.
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  • 132
    Digitale Medien
    Digitale Medien
    Palladium(0)-Catalyzed Asymmetric Synthesis of 1,2,3,4-Tetrahydro-2-vinylquinoxalines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 129-134 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Tetrahydro-2-vinylquinoxaline ; Cyclization ; Palladium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Reaction of (Z)-1,2-bis(methoxycarbonyloxy)but-2-ene (2) with various N,N-bis(arylsulfonyl)-o-phenylenediamines 1 was catalyzed by a palladium complex associated with chiral ligands to give optically active 1,4-bis(arylsulfonyl)-1,2,3,4-tetrahydro-2-vinylquinoxalines 3 with up to 62% ee. The use of (S)-MeOBIPHEP as the chiral ligand and N,N-bis(p-tolylsulfonyl)-o-phenylenediamine (1i) as the nucleophile led to the highest ee at 25 °C, regardless of the solvent used. The enantioselectivity of the cyclization is strongly affected by the nature of the substituents at the nitrogen atom.
    Zusätzliches Material: 4 Tab.
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  • 133
    Digitale Medien
    Digitale Medien
    Stereoselective Synthesis of Enantiomerically Pure β-Fluoroalkyl γ-Butyrolactones by Sulfoxide-Directed Lactonization (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 111-115 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Fluorine ; Lactones ; Annulation ; Ketene ; Sulfoxides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Enantiomerically pure α,α-dichloro β-fluoroalkyl γ-p-tolylthio γ-butyrolactones trans-6a-c have been obtained with excellent stereocontrol (〉 98:2) and enantiomeric purity (〉 98:2) by sulfoxide-directed lactonization (Marino's annu-lation reaction) of β-fluoroalkyl vinyl sulfoxides (R)-(E)-5a-c with dichloroketene. Highly chemoselective dechlorination and desulfurization reactions performed on trans-6c efficiently provided the β-chlorodifluoromethyl γ-butyrolactone (S)-8c, the absolute stereochemistry of which was determined by X-ray diffraction analysis of its γ-p-tolylthio precursor (2R,3S)-7c.
    Zusätzliches Material: 1 Ill.
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  • 134
    Digitale Medien
    Digitale Medien
    Reaction of Nitrosobenzene with 4-Methoxy-N-methyleneaniline (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 141-143 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Nitrosobenzene ; 4-Methoxy-N-methyleneaniline ; 1,3,5-Tris(4-methoxyphenyl)-1,3,5-triazinane ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -A 1:1 adduct produced in the reaction of nitrosobenzene (2) with 1,3,5-tris(4-methoxyphenyl)-1,3,5-triazinane (3) has been shown by X-ray diffraction structure analysis to be the N′-(4-methoxyphenyl)-N-phenyl-N-oxyformamidinium species 5.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 135
    Digitale Medien
    Digitale Medien
    A New Diastereoselective Synthesis of anti-α-Alkyl α-Hydroxy β-Amino Acids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 155-161 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Alkylation ; Oxazolines ; anti-α-Alkyl α-hydroxy β-amino acids ; Lithium dianion ; Penicillin G acylase ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -As part of an ongoing project concerning the synthesis of enantiomerically pure α-hydroxy β-amino acids, we have now developed a general strategy allowing the synthesis of anti-α-alkyl α-hydroxy β-amino acids. Our procedure involves the intermediate formation of trans-oxazolines, which are alkylated at C-5 with good to high diastereoselectivity and then hydrolysed under mildly acidic conditions, affording in quantitative yield the corresponding hydroxy amides. The starting (R)-3-amino-3-phenylpropanoic acid and (S)-3-aminobutanoic acid were obtained in enantiomerically pure form by selective enzymatic hydrolysis of the corresponding phenylacetylamides with penicillin G acylase.
    Zusätzliches Material: 3 Ill.
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  • 136
    Digitale Medien
    Digitale Medien
    Palladium(0)-Catalyzed Reaction of Acidic Anilines with (Z)-2-Butene-1,4-diyl Dicarbonate - Preparation of N-Aryl-4-vinyloxazolidin-2-ones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 181-186 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Palladium catalysis ; Homogeneous catalysis ; Anilines ; Alkylation ; Oxazolidinones ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Palladium-catalyzed reaction of acidic anilines with (Z)-2-butene-1,4-diyl dicarbonate affords N-aryl-4-vinyloxazolidin-2-ones. The success of the reaction depends on the acidity of the aniline and requires in situ conversion of the dicarbonate into carbamate carbonate by nucleophilic attack of the aniline conjugate base followed by palladium-catalyzed intramolecular cyclization.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 137
    Digitale Medien
    Digitale Medien
    Substituent Effects on the Vinylcyclopropane-Cyclopentene Rearrangement - A Theoretical Study by Restricted and Unrestricted Density Functional Theory (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 215-220 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Density functional calculations ; Vinylcyclopropane-cyclopentene rearrangement ; [1,3]-Sigmatropic shift ; Biradical-like transition structure ; Substituent effects ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The effect of donor substitution by the hydroxy group and of acceptor substitution by the cyano group on the activation energies of the vinylcyclopropane-cyclopentene rearrangement was calculated by the spin-restricted RB3LYP/6-31G* method for reactant structures and by the spin-unrestricted UB3LYP/6-31G* method for transition structures. The activation energies of the rearrangement of hydroxy- and cyano-substituted vinylcyclopropanes are very similar for substitution in the same position. In agreement with earlier findings the substituent effects on the activation energies are closely connected with the radical stabilizing properties of the substituents. As indicated by singlet/triplet splitting energies, the transition structures are essentially biradicaloid. In spite of spin pairing in the transition structure the substituent effects on bond lengths and on stabilization energies are very similar to those of the free radicals corresponding to the two radical substructures. Thus, the transition structures may be considered, in good approximation, as structures consisting of two weakly interacting radicals.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98349_s.pdf or from the author.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 138
    Digitale Medien
    Digitale Medien
    Syntheses and Reactions of 1-Amino-2,2-dialkylcyclopropane-1-carbonitriles and -carboxamides - Potential Precursors of ACC Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 239-250 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Cyclopropanes ; Rearrangements ; Cyanohydrins ; Schiff bases ; Small ring systems ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The direct cyclization of 2-amino-4-chloro-3,3-dimethylbutanenitrile with potassium tert-butoxide in THF afforded 1-amino-2,2-dimethylcyclopropane-1-carbonitrile and a dimerization product. Various new cis- and trans-1-(tert-butylamino)-2-benzyl-2-methylcyclopropane-carbonitriles and© the corresponding cyclopropanecarboxamides have been synthesized, with focus on the isolation of the pure stereoisomeric cyclopropanecarboxamides. The relative configuration of the stereoisomers was established by X-ray crystallographic analysis of one of the model compounds. A new route to the latter functionalized cyclopropanes was developed by reaction of 1-methoxycyclopropylamines with potassium cyanide. Some remarkable rearrangements of 1-aminocyclopropane-1-carbonitriles into azetidine and oxazine derivatives via Favorskii-derived intermediates are reported. Various aspects of the chemistry of geminally functionalized cyclopropanes are discussed.
    Zusätzliches Material: 1 Ill.
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  • 139
    Digitale Medien
    Digitale Medien
    Regio- and Stereoselective Synthesis of Vinylallenes by 1,5-(SN′′)-Substitution of Enyne Acetates and Oxiranes with Organocuprates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 267-275 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Vinylallenes ; Organocuprates ; Substitution ; Stereoselective synthesis ; Copper catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Enyne acetates 2, 4, 6, and 8, as well as enyne oxiranes 10, with different substitution patterns react with organocuprates regioselectively under 1,5-(SN2′′)-substitution to provide vinylallenes 11 and 12. With lithium dimethylcuprate, reduced vinylallenes originating from a (formal) transfer of a hydride ion to the substrate are formed in some cases. The products are usually obtained as mixtures of (E/Z)isomers; however, pure (E)-vinylallenes are formed occasionally. The 1,5-substitutions can also be carried out with catalytic amounts of copper reagents. The reaction of chiral enyne acetate (S)-2a with tBu2CuLi · LiCN proceeds enantioselectively, so that this transformation constitutes a new case of remote stereocontrol.
    Zusätzliches Material: 1 Tab.
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  • 140
    Digitale Medien
    Digitale Medien
    Reactions of the Hydrofluoroborate Salts of Open-Chain Analogues of Reissert Compounds with Some α,β-Ethylenic Esters (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 297-303 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Nitrogen heterocycles ; Open-chain analogue of Reissert compound ; Hydrofluoroborate salts ; α,β-Ethylenic esters ; 1,3-Dipolar cycloaddition ; Azomethine ylide ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The reaction of the hydrofluoroborate salt of an open-chain analogue of a Reissert compound with some α,β-ethylenic esters does not give a [4 + 2] cycloadduct, as previously described in the case of ethyl acrylate. The reaction starts with a 1,3-dipolar cycloaddition of a münchnone imine 5c, d. The [3 + 2] cycloadducts 13 evolve via a rearrangement-condensation sequence to give a substituted 2-pyridone derivative 18 or 19. The proposed mechanism has been verified by the isolation and structural X-ray analysis of some compounds of the reaction sequence.
    Zusätzliches Material: 5 Ill.
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  • 141
    Digitale Medien
    Digitale Medien
    EPC-Synthesis of β-Amino Acid Derivatives through Lithiated Hydropyrimidines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 335-360 
    Details
    ISSN: 1434-193X
    Schlagwort(e): 2-tert-Butylhydropyrimidinones ; 3-Aminocarboxylic acid derivatives ; Cyclic imino esters ; Lithium enaminates ; Alkylations ; β-Amino acids ; Asymmetric synthesis ; Kinetic resolution ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Racemic and enantiopure 2-tert-butyltetrahydropyrimidinones (from pivalaldehyde and 3-aminocarboxylic acids) are converted to Alloc-, Boc-, and Z-protected cyclic imino esters (7-10, Schemes 2-4). These are deprotonated to Li enaminates (K, L). Reactions with electrophiles (prim., sec. alkyl, allyl, benzyl, propargyl halides, aldehydes, imines, enoates) give good yields and are highly diastereoselective (products 11-42, Schemes 5-10). A two-step cleavage (removal of protecting group and hydrolysis) under very mild conditions converts the heterocyclic products to α-branched β-amino acid methyl esters (43-61, Schemes 11-13). The structure of the products is determined by NMR spectroscopy (Figure 1), by chemical correlation (Scheme 14), and by X-ray analysis (Figure 2, 3, 7, Table 1). A structure of the Li enaminates is proposed (Figure 4). Mechanistic models are derived for the reactions occurring with formation of two stereogenic centers with relative topicity like (Figures 5, 6).
    Zusätzliches Material: 7 Ill.
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  • 142
    Digitale Medien
    Digitale Medien
    A Unified Synthetic Strategy for the Indolopyridine Alkaloid Group (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 373-378 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Alkaloids ; Cross-coupling ; N-Heterocycles ; Palladium ; Synthesis design ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Thermal or acetyl chloride induced cyclization of bromoenamide 10 affords the pentacyclic derivative 12 with high yield and regioselectivity. From this common synthetic intermediate, palladium-catalyzed reactions allow the total synthesis of indolopyridine alkaloids 1-6.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98332_s.pdf or from the author.
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  • 143
    Digitale Medien
    Digitale Medien
    Conformational Preferences of Peptides Containing Reverse-Turn Mimetic Bicyclic Lactams: Inverse γ-Turns versus Type-II′ β-Turns - Insights into β-Hairpin Stability (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 389-400 
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    ISSN: 1434-193X
    Schlagwort(e): Reverse-turn mimics ; γ-Turns ; β-Turns ; β-Hairpins ; NMR spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The solid-phase synthesis and characterization of a series of peptides (3-9), containing reverse-turn mimetic bicyclic lactams (1a, 1b), was reported in the preceding paper. The bicyclic lactams (1a, 1b) possess high structural similarity to the two central residues of a β-turn. The conformational preferences of the constrained peptides have been investigated by NMR spectroscopy and IR spectroscopy. Our experimental results have been complemented by computer modelling studies and show that the constrained peptides (3-9) form an inverse γ-turn or a type-II′ β-turn through intramolecular hydrogen bonding, depending on the nature of the reverse-turn mimic. In N-acetylated tetrapeptide mimics incorporating the two different bicyclic lactams (a series and b series), H5 is available for either a γ-turn (7-membered ring with the carbonyl group of the bicyclic lactam) or a β-turn (10-membered ring with the carbonyl group of residue 2), as shown in Figures 7 and 9. The a series incorporating the (5,7)-bicyclic lactam predominantly induces the γ-turn conformation, while the b series incorporating the (5,6)-bicyclic lactam can promote either a γ-turn or a β-turn conformation, with the β-turn usually being preferred and with varying degrees of β-hairpin formation.
    Zusätzliches Material: 10 Ill.
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  • 144
    Digitale Medien
    Digitale Medien
    Deprotonation of Oxazolinyloxiranes: Formation of Substituted Acyloxiranes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 409-417 
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    ISSN: 1434-193X
    Schlagwort(e): Deprotonation ; Oxiranyloxazolines ; Oxazolinyloxiranyllithium compounds ; Oxazolidines ; Acyloxiranes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Deprotonation of oxazolinyloxiranes 1a, 1h, and 1k with sBuLi/TMEDA at -100 °C in Et2O furnishes oxazolinyloxiranyllithium compounds[1]1b, 1i, and 1l which are stable at low temperature and can be trapped with electrophiles to give substituted oxiranes 1c-1g and 1j. The reaction of 1b with aldehydes produced diastereomers syn (2a-d) and anti (3a-d). Oxiranyllithium 1i from trans-1-(4,4-dimethyl-2-oxazolinyl)-2-p-tolylepoxyethane (1h) was found to be configurationally stable while oxiranyllithium 1l, generated from the cis isomer 1k, was not. Oxazolinylepoxides 1d, 1j, and 1m could be deblocked to acyloxiranes 5a-e through oxazolidines 4a-e.
    Zusätzliches Material: 2 Ill.
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  • 145
    Digitale Medien
    Digitale Medien
    N-Substituted 1-Aminoindoles from Electrogenerated N-Substituted 2-(ortho-Nitrosophenyl)ethylamines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 419-430 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Electrochemistry ; Electrosynthesis ; Nitrosobenzenes ; Nitrogen heterocycles ; 1-Aminoindoles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -An electrochemical methodology offering efficient access to N-alkyl- and N-aryl-substituted 1-aminoindoles has been developed. N-Substituted 2-(ortho-nitrosophenyl)ethylamines, electrogenerated in a “redox” flow cell, undergo intramolecular cyclization to hydrocinnoline-type intermediates. Under slightly basic conditions, these undergo spontaneous ring-contraction to produce the N-substituted heterocycles in good yields. The reactions have been studied in slightly acidic and slightly basic aqueous alcoholic media.
    Zusätzliches Material: 11 Ill.
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  • 146
    Digitale Medien
    Digitale Medien
    Synthesis of Enantiopure β- and γ-Amino Alcohols from Homochiral α- and β-Aminoacylsilanes as Stable Synthetic Equivalents of α- and β-Amino Aldehydes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 437-445 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Aminoacylsilanes ; Amino aldehydes ; Amino alcohols ; Allylation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -A practical route is described for the synthesis of enantiopure β- and γ-amino alcohols with two stereocenters, starting from homochiral α- (1 and 5) and β- (13 and 16) -aminoacylsilanes, and involving stereoselective addition of allylmetal compounds and subsequent stereospecific protiodesilylation of the adducts. The degree of diastereoselectivity achieved in the nucleophilic addition step depends on both the nitrogen-protecting group and the reagents used. Diastereomeric excess (de) values equal to or higher than 98% were obtained in the TiCl4-promoted allylation of the N-Pht-aminoacylsilanes 1 and 13 and of the N-Ts-aminoacylsilane 5 with allyltrimethylsilane. Lower de values were obtained in the Sc(OTf)3-catalyzed allylation of 5 with tetraallyltin and in the additions of both allyltrimethylsilane and tetraallyltin to the N-Ts-β-aminoacylsilane 16. Protiodesilylation of the adducts, leading to the β- and γ-amino alcohols, was accomplished with TBAF, except in the case of the adducts obtained from 5. For these, a preliminary removal of the tosyl group was necessary, which was accomplished with simultaneous desilylation by treatment with Na in liquid ammonia.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98342_s.pdf or from the author.
    Zusätzliches Material: 1 Tab.
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  • 147
    Digitale Medien
    Digitale Medien
    Diastereoselective Intramolecular meta Photocycloaddition of Side-Chain-Substituted 5-(2-Methoxyphenyl)pent-1-enes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 463-470 
    Details
    ISSN: 1434-193X
    Schlagwort(e): meta Photocycloaddition ; Photochemistry ; Steric hindrance ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Irradiation of a series of 5-(2-methoxyphenyl)pent-1-enes substituted with a hydroxy or trimethylsilyloxy group at the α-, β-, or γ-position of the side-chain yields in all cases meta photocycloadducts, in which the configuration at the substituted carbon atom is mainly endo. This indicates that the diastereoselectivity originates from minimization of steric interactions between the side-chain substituent and the ortho-methoxy group at the arene unit. Hydrogen bonding does not seem to be involved. The introduction of the side-chain substituents also influences the regioselectivity of the addition: The linear to angular adduct ratios are significantly increased compared to the case of the parent compound.
    Zusätzliches Material: 3 Tab.
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  • 148
    Digitale Medien
    Digitale Medien
    5-Aza-7-deaza-2′-deoxyguanosine: Oligonucleotide Duplexes with Novel Base Pairs, Parallel Chain Orientation and Protonation Sites in the Core of a Double Helix (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 485-496 
    Details
    ISSN: 1434-193X
    Schlagwort(e): 5-Aza-7-deaza-2′-deoxyguanosine ; Oligonucleotides ; Parallel DNA ; Protonated base pairs ; Tm values ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Oligonucleotides containing 5-aza-7-deaza-2′-deoxyguanosine (1) were synthesized. Solid-phase synthesis was performed with the phosphonate 15 or the phosphoramidite 5. The amino-unprotected phosphonate 4 was also employed. Hybridization studies of oligonucleotides containing 1 resulted in new base pairs leading to duplexes with parallel (ps) or antiparallel (aps) chain orientation. Among those with parallel chains a stable “purine-purine” base pair was observed between 5-aza-7-deazaguanine and guanine or 7-deazaguanine. Antiparallel stranded duplexes are formed when 5-aza-7-deazaguanine pairs with cytosine. This base pair has only two hydrogen bonds under neutral conditions but is stabilized by a third one in acidic medium. A new base pair is also detected between the base of 1 and isoguanine (neutral medium).
    Zusätzliches Material: 1 Ill.
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  • 149
    Digitale Medien
    Digitale Medien
    Polar and Steric Substituent Effects in 5-exo-trig Cyclizations of 1-Aryl-4-penten-1-oxyl Radicals (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 523-523 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -By mistake wrong concentrations were given in the footnote of Table 1 and in the Discussion. Instead of c0 = 1.2 M read c0 = 0.12 M if 2-naphthalenethiol was used as hydrogen donor and instead of c0 = 1.8 M read c0 = 0.18 M if Bu3SnH was used to trap photoproducts. In Table 2 relative rate constants of radical 2d refer to radical 2e and vice versa as correctly stated in the Discussion. In the Experimental Section (Iodocyclization) read 2.25 g (8.86 mmol) of iodine instead of 2.25 g (1.10 mmol) of iodine.
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  • 150
    Digitale Medien
    Digitale Medien
    Arylboron Compounds as Acid Catalysts in Organic Synthetic Transformations (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 527-538 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Tris(pentafluorophenyl)borane ; Diarylborinic acid ; Arylboronic acid ; Chiral arylboron catalyst ; Lewis acid ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Arylboron compounds, ArnB(OH)3-n (n = 1-3), bearing electron-withdrawing aromatic groups such as triarylboranes, diarylborinic acids, and arylboronic acids represent a new class of air-stable and water-tolerant Lewis acid or Brønsted acid catalysts in organic synthesis. In particular, while tris(pentafluorophenyl)borane has primarily been used as a co-catalyst in metallocene-mediated olefin polymerization, its potential as a Lewis acid catalyst for organic transformation is now much more extensive. Diarylborinic acids and arylboronic acids have shown themselves to be powerful tools in the design of chiral boron catalysts. This article provides a comprehensive summary of the organic transformations catalyzed by arylboron compounds as acids.
    Zusätzliches Material: 2 Ill.
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  • 151
    Digitale Medien
    Digitale Medien
    2D-NMR-Guided Constitutional Analysis of Organic Compounds Employing the Computer Program COCON[#] (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 573-577 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Structure elucidation ; Constitutional analysis ; Natural products ; HMBC ; Computational chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The computer program COCON is introduced as a tool for the comprehensive structure elucidation of unknown organic compounds. In particular, structural proposals made on the basis of the molecular formula and of 2D-NMR experiments can be analyzed for the existence of alternative constitutions being in agreement with the same data set. The computational speed grounds on the evaluation of ambiguous long-range connectivity information during the process of structure generation. The data set experimentally obtained for the marine natural product oroidin (1) was selected, because proton-poor compounds usually cause uncertainties in NMR-based structure determinations. The calculation results encourage to move from the experience-based analysis of NMR chemical shifts or of MS fragmentations to the automated evaluation of routinely available connectivity information.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98241_s.pdf or from the author.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 152
    Digitale Medien
    Digitale Medien
    3,5-Dimesityl-1,2,4-oxadiphosphole - Synthesis and Reactivity of a Novel Heterocycle (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 587-595 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Phosphaalkenes ; Heterodiphospholes ; Cycloadditions ; Phosphaalkyne cyclooligomers ; Phosphorus-carbon cage compounds ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The first synthesis of a 1,2,4-oxadiphosphole 6 has been achieved by vacuum thermolysis of mesitylphosphaalkene 5. The novel heterocycle 6 exhibits an enormous potential for cycloaddition reactions, which predominantly proceed selectively at low temperatures. Compound 6 undergoes addition with two equivalents of phosphaalkynes 10 by a [4+2] cycloaddition/homo Diels-Alder reaction sequence to form novel oxatetraphosphadeltacyclenes 12 and 13. Tetrachloro-o-benzoquinone (14) undergoes a selective [4+1] cycloaddition with 12 and 13 leading to the spirocyclic products 15 and 16 containing λ5-phosphorus atoms. Treatment of the oxadiphosphole 6 with dimethyl acetylenedicarboxylate (17) provides the first access to a 1,2-oxaphosphole 18, which is formed after an initial [4+2] cycloaddition followed by a retro Diels-Alder reaction. An unexpected reaction of 6 is observed with tri-tert-butylazete (20) furnishing a new polycyclic system (→ 21).
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 153
    Digitale Medien
    Digitale Medien
    Synthesis of 1β-Methylcarbapenem Antibiotic Precursors by Cyclization Using π-Allylpalladium Complexes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 621-626 
    Details
    ISSN: 1434-193X
    Schlagwort(e): 1β-Methylcarbapenems ; Palladium ; Ruthenium ; Catalysis ; Cyclizations ; Stereoselective hydrogenation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -An efficient diastereoselective multi-step synthesis of bicyclic 1β-methylcarbapenem antibiotic precursors has been developed, starting from the commercially available 4-acetoxyazetidin-2-one 4. Chiral ruthenium catalysts are used in the hydrogenation step to control the β-stereochemistry at the 1-position, and a π-allylpalladium ring-closure strategy is used to form the functionalized carbapenem skeleton.
    Zusätzliches Material: 1 Tab.
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  • 154
    Digitale Medien
    Digitale Medien
    Oligo-2,6-naphthylenevinylenes - New Building Blocks for the Preparation of Photoluminescent Polymeric Materials (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 643-651 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Oligomers ; Synthesis design ; Substituent effects ; Luminescence ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Synthetic strategies towards appropriate symmetric and unsymmetric functionalization of the naphthalene ring are presented. By means of Knoevenagel and Wittig condensation reactions new fluorescent, differently functionalized oligo(2,6-naphthylenevinylene)s have been synthesized, the presence of terminal aldehyde or bromine substitution opening the way to the incorporation of the fluorescent trimers in a variety of polymeric materials. The effect of substituting the phenylene ring by the more bulky dialkoxynaphthalene system in arylenevinylene-type materials is studied from the structural point of view and the possibility to tune the emission color and the electron affinity through the introduction of naphthylenevinylene and cyano-substituted naphthylenevinylene units is also investigated.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 155
    Digitale Medien
    Digitale Medien
    New Type of Skipped Oligoaziridines: Synthesis of New Fatty AcidDerivatives Containing Aziridine Functions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 661-664 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Aziridines ; N-Heterocycles ; Fatty acids ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The first successful preparation of the aziridines methyl cis-9,10;cis-12,13-diepiminooctadecanoate (3) derived from linoleic acid, and methyl cis-9,10;cis-12,13;cis-15,16-triepiminooctadecanoate (6) derived from linolenic acid, is reported. Remarkably, the bis- and trisaziridine were obtained in a reaction sequence that consists of only two steps, using technically pure methyl esters of epoxidized sunflower and linseed oil. The conversion of methyl 9,10;12,13-diepoxyoctadecanoate (1), with sodium azide and ammonium chloride in ethanol in the presence of water, yielded the new diazidodihydroxy compound methyl 9(10),12(13)-diazido-10(9),13(12)-dihydroxyoctadecanoate (2) in the first step. 2 was obtained as a regioisomeric mixture. The reaction of 2 with triphenylphosphane led to the bisaziridine 3. The analogous conversion of methyl 9,10;12,13;15,16-triepoxyoctadecanoate (4), via the new triazidotrihydroxy compound methyl 9(10),12(13),15(16)-triazido-10(9),13(12),16(15)-trihydroxyoctadecanoate (5), afforded trisaziridine 6.
    Zusätzliches Material: 1 Tab.
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  • 156
    Digitale Medien
    Digitale Medien
    Novel Ligands for the Separation of Trivalent Lanthanides and Actinides - Tetrakis(phosphane sulfide) and -(phosphinic acid) Cavitands (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 665-674 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Cavitands ; Nuclear waste ; Actinide/lanthanide separation ; Solvent extraction ; Sulfur atoms ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Cavitands with phosphane sulfide moieties 4 and 8a,b were prepared in good yields from their phosphane oxide analogues, as more stable alternatives for the dithiophosphinic acids used at present. The cavitands 7a and 7b with flexible butoxyphosphane oxide ligating sites are more efficient than cavitand 3 having rigid methylphosphane oxide groups as was studied with EuIII picrate extractions. Due to the absence of an ionic functionality in the phosphane sulfides 4 and 8a,b AmIII and EuIII are not extracted, not even in the presence of synergents (e.g. TBP, TOPO, HDNNS). Cavitand 10 with phosphinic acid groups efficiently extracts EuIII in 1:1 or 2:1 complexes, depending on the metal-to-ligand concentration ratio (extraction constants Kex1 = 3.9·10-5M2 and Kex2 = 1.9·102M, respectively). Furthermore, in the case of 10 EuIII is preferentially extracted over AmIII with a separation factor SEu/Am up to 5.
    Zusätzliches Material: 5 Ill.
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  • 157
    Digitale Medien
    Digitale Medien
    Preparation of 2,3,5-Tri-O-benzyl-4-thio-L-arabino-furanosides and the Corresponding 4′-Thionucleoside Analogues (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 691-696 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Carbohydrates ; 4-Thiofuranosides ; Nucleosides ; Reaction mechanisms ; NOE measurements ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabino-furanose (9) has been prepared from D-xylose via the 1,4-dithio-L-arabino-furanoside 8. The crucial step of the reaction, i.e. the intramolecular cyclization of the open-chain dithioacetal 5, has been achieved in a yield of 90% by applying tetrabutylammonium iodide as promoter. Reaction of 9 with bis(trimethylsilyl)uracil or -thymine led to the benzyl derivatives 12 and 13 from which the deprotected 4′-thionucleoside analogues 14 and 15 have been prepared by debenzylation with boron tribromide.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 158
    Digitale Medien
    Digitale Medien
    100 Years of Baeyer-Villiger Oxidations (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 737-750 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Baeyer-Villiger oxidation ; Ketones ; Monopersulfate ; Peracids ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -In the present review, we report the discovery of the formation of esters and lactones by oxidation of ketones with a peroxide derivative, namely the Baeyer-Villiger reaction. This reaction was first reported by Adolf von Baeyer and Victor Villiger a century ago in 1899, just one year after the oxidant they used (KHSO5) has been described. Furthermore, Baeyer and Villiger established the composition of this new inorganic peroxide and showed that its instability was the reason of a controversy between several European chemists between 1878 and 1893. For the first 50 years the mechanism of the Baeyer-Villiger reaction was a matter of debate. A side product, 1,2,4,5-tetraoxocyclohexane, was ruled out as an intermediate in the ester formation by Dilthey. Criegee postulated a nucleophilic attack of the oxidant on the carbonyl group. This mechanism was confirmed by von E. Doering by a labeling experiment with [18O]benzophenone. The rearrangement step occurs with retention of the stereochemistry at the migrating center. The competitive migration and the rate-determining step are also discussed in this review.
    Zusätzliches Material: 4 Ill.
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  • 159
    Digitale Medien
    Digitale Medien
    Transferase Activity of a β-Glycosidase from Thermus thermophilus: Specificities and Limits - Application to the Synthesis of β-[1→3]-Disaccharides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 757-763 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Transglycosylation ; Glycosidases ; Thermus thermophilus ; Carbohydrates ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The aim of this paper is to test the ability of a β-glycosidase from Thermus thermophilus to catalyse transglycosylation reactions in the presence of nitrophenyl glycosides as donors and other monosaccharides as acceptors. Our results show that this enzyme is able to induce such reactions either with nitrophenylgalactosides, -glucosides and -fucosides. With the two former donors, the autocondensation of the donor, which thus acts also as an acceptor, is faster than the transglycosylation with other acceptors. Furthermore, as the regioselectivity of the reactions is mainly of the β-[1→3] type, good yields are obtained for the synthesis of 2-nitrophenyl-β-D-galactopyranosyl-[1→3]-β-D-galactopyranoside and 2-nitrophenyl-β-D-glucopyranosyl-[1→3]-β-D-glucopyranoside. Conversely, in the presence of p-nitrophenylfucoside, the autocondensation is very limited, and with methyl-α-D-galactoside as an acceptor, the regioselectivity is mainly of the β-[1→6]-type resulting in the synthesis of methyl-β-D-fucopyranosyl-[1→6]-α-D-galactopyranoside.
    Zusätzliches Material: 7 Ill.
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  • 160
    Digitale Medien
    Digitale Medien
    Reduction of Acetylenic Compounds to (E)-Olefins by Alkali Metals - An Investigation of the Scope (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 775-779 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Monoynes ; Polyynes ; Alkali metals ; Liquid NH3 ; Hexamethylphosphoric triamide ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Efficient procedures have been developed for the stereospecific reduction by alkali metals of disubstituted acetylenes with long carbon chains. Acetylenes containing two or more (isolated) triple bonds are reduced considerably more easily than are monoynes.
    Zusätzliches Material: 1 Tab.
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  • 161
    Digitale Medien
    Digitale Medien
    Synthesis of Enantiopure o-Hydroxybenzylamines by Stereoselective Reduction of 2-Imidoylphenols: Application in the Catalytic Enantioselective Addition of Diethylzinc to Aldehydes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 805-811 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Aminophenols /Asymmetric synthesis ; C-C coupling ; Reductions ; Conformation analysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Enantiopure o-hydroxybenzylamines 2a-i were synthesized by diastereoselective reduction of the 2-imidoylphenols (R)-1a-i. Conformational analysis enabled the assignment of the absolute configurations of compounds 2a-i. The accessible o-hydroxybenzylamine (R,R)-2h serves as an effective catalyst precursor for highly enantioselective addition of diethylzinc to aliphatic and aromatic aldehydes. This pathway represents a practical and operationally very simple methodology for the enantioselective synthesis of both the enantiomers of secondary alcohols 7a-f.
    Zusätzliches Material: 4 Ill.
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  • 162
    Digitale Medien
    Digitale Medien
    Cyclialkylation of Arylalkyl Epoxides with Solid Acid Catalysts (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 837-846 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Friedel-Crafts reaction ; Hydroxyalkylation ; Aromatics ; Epoxides ; Zeolites ; Clays ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Solid acids, such as zeolites and clays, catalyse the intramolecular hydroxyalkylation (cyclialkylation) of several arylalkyl epoxides in moderate to excellent conversions and selectivities. The use of solid acids in these cyclialkylations provides a cleaner, better alternative to conventional Lewis and Brønsted acids, enabling a more facile workup of reaction mixtures and, in several cases, better selectivities.
    Zusätzliches Material: 3 Ill.
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  • 163
    Digitale Medien
    Digitale Medien
    Phosphorylating Power of Red Phosphorus towards Aldehydes in Basic and in Acidic Media (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 861-868 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Red phosphorus ; Phosphane PH3 ; Phosphorylations ; Ultrasound irradiation ; Redox chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The reactivity of red phosphorus towards aldehydes was investigated under basic and acidic media. It was demonstrated that the real phosphorylating agent involved in the reaction was phosphane (PH3) in basic media, and hypophosphorous acid (H3PO2) in acidic media. A convenient one-pot synthesis of (α-hydroxyalkyl)phosphinic acids from red phosphorus and aldehydes in basic media was realized under sonication. The same reaction under acidic media in the presence of hydriodic acid led to the corresponding phosphonic acids. The (α-hydroxyalkyl)phosphinic acids were readily prepared under sonication from hypophosphorous acid and aldehydes in the presence of catalytic amounts of hydrochloric acid. The mechanism of the addition reaction of PH3 to benzaldehyde was elucidated and shows the complexity of the reaction as a function of the experimental conditions.
    Zusätzliches Material: 1 Tab.
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  • 164
    Digitale Medien
    Digitale Medien
    A New Approach to Erythrinanes through Pummerer-Type Cyclization (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 909-915 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Erythrina alkaloids ; Nitrogen heterocycles ; Nitro aldol reaction ; Michael addition ; Pummerer reaction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -A successful new strategy for the synthesis of erythrinanes is reported. (Nitromethyl)arene derivative 16 was condensed with aldehyde 17 to give nitro aldol 19. After removal of the hydroxy group, the subunits 26a,b, containing the erythrinane rings A and D, were formed by intramolecular Michael addition. Reduction of the nitro function, followed by cyclization of the resulting amino group with the appended acetate group afforded the bicyclic lactams 29a,b, bearing an angular aryl group. Two-carbon elongation at the nitrogen atoms of 29a and 29b by means of hetero Michael addition of methyl phenyl sulfoxide, followed by Pummerer-type cyclization, gave cis- and trans-11-phenylthioerythrinan-8-ones 35a and 35b, respectively. Reductive desulfurization at C-11 furnished the desired erythrinan-8-ones 39a and 39b in 8 steps from 16.
    Zusätzliches Material: 1 Ill.
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  • 165
    Digitale Medien
    Digitale Medien
    Synthesis, X-ray Structure Analysis and Topochemical Photopolymerization of Substituted 1,6-Bis(2,5-dimethoxyphenyl)hexa-2,4-diynes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 917-922 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Crystal engineering ; Diynes ; Photochemistry ; Solid-state chemistry ; Polymers ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The 1,6-bis(2,5-dimethoxyphenyl)hexa-2,4-diynes 4a-c were obtained from the corresponding 2,5-dimethoxybenzenes 1 by bromination followed by a copper-catalyzed Grignard reaction with 3-bromoprop-1-yne. Catalyzed coupling of the resulting 3-(2,5-dimethoxyphenyl)prop-1-ynes 3 under Hay conditions gave the hexa-2,4-diynes 4a-c in good yields. The molecular structures of the diynes 4a and 4b were determined by X-ray diffraction analysis. In each crystal structure, an unusual 1,6-synperiplanar conformation of the hexa-2,4-diyne unit is observed, with the 1,6-diphenyl substituents arranged in a coplanar orientation. According to the crystal structure data obtained, irradiation of diynes 4a and 4b afforded the deeply-colored, highly-ordered polymers 5a and 5b under topochemical control. Oxidation of 4a and 4b with cerium(IV) ammonium nitrate gave the corresponding 1,6-bis(2,5-dimethoxyphenyl)hexa-2,4-diyne-1,6-diones 6a and 6b.
    Zusätzliches Material: 5 Ill.
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  • 166
    Digitale Medien
    Digitale Medien
    Synthesis of Acyclic Carba-Nucleoside Phosphonates, Structural Analogues to Natural Deoxyribonucleotides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 931-936 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Nucleosides ; Phosphonates ; Nucleophilic additions ; C-C coupling ; Reduction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Acyclic carba-nucleoside phosphonates, modelled on natural deoxyribonucleotides have been prepared starting from DNA nucleobases and tert-butyl acrylate. The products obtained from a Michael-type reaction were elongated to β-oxo esters that were first reduced to β-hydroxy esters and then transformed into protected β-hydroxy aldehydes. Wittig-Horner-Emmons reaction with the anion of tetraisopropyl methylenebisphosphonate gave, after deprotection, the desired 4-hydroxy-6-purinyl- or -6-pyrimidinyl-1-hexenylphosphonic acids. A dimer, potential precursor of acyclic polynucleotides (APN), homomorphous with DNA, was also prepared.
    Materialart: Digitale Medien
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  • 167
    Digitale Medien
    Digitale Medien
    Electrochemically Induced N-Alkylation of Pyrroles (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 955-958 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Tetraethylammonium peroxydicarbonate ; Tetraethylammonium carbonate ; N-alkylated pyrroles ; Electrochemistry ; Electrogenerated bases ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Electrochemically generated tetraethylammonium peroxydicarbonate (TEAPC) and tetraethylammonium carbonate (TEAC) react under very mild conditions with pyrroles affording, after addition of a suitable alkylating agent, the corresponding N-alkylated pyrroles in high yields. C-Alkylated pyrroles have not been isolated in any case reported.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 168
    Digitale Medien
    Digitale Medien
    Simple Synthesis of (±)-Stigmolone (8-Hydroxy-2,5,8-trimethyl-4-nonanone), the Pheromone of Stigmatella aurantiaca (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 979-980 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Ketones ; Myxobacterium ; Pheromones ; Stigmatellaaurantiaca ; Stigmolone ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The racemic myxobacterial pheromone (±)-1 (stigmolone), which induces the formation of the fruiting body of Stigmatellaaurantiaca, was synthesized from methyl isobutyl ketone (2) in 48% overall yield in four steps
    Materialart: Digitale Medien
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  • 169
    Digitale Medien
    Digitale Medien
    Photochemical Hydrogen Migration in Methylanthronylidenes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1005-1009 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Hydrogen migration ; Anthronylidene ; Quinone methide ; Matrix isolation ; Photochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The photochemistry of 4-methyl-9,10-diazoanthrone (7a) and 1,4-dimethyl-9,10-diazoanthrone (7b) was investigated in argon matrices at 10 K. Visible-light irradiation results in the formation of the anthronylidenes 5a and b, respectively, which were identified by oxygen trapping, by comparison of the IR and UV/Vis spectra with that of the parent anthronylidene 6, and by comparison of the IR spectrum with that calculated by DFT methods. The carbenes 5 are thermally stable under the conditions of matrix isolation; however, irradiation with visible or UV light results in the rearrangement to the quinone methides 10a and b.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 170
    Digitale Medien
    Digitale Medien
    Metallated 2-Alkenyl Sulfoximines in Asymmetric Synthesis: Regio- and Stereoselective Synthesis of Highly Substituted Oxabicyclic Ethers and Studies Towards the Total Syntheses of the Euglobals G1 and G2 and Arenaran A (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1011-1031 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Sulfoximines ; Oxabicyclic ethers ; Asymmetric synthesis ; Euglobal ; Arenaran ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -2-Cyclopentenyl- and 2-cyclohexenylmethyl sulfoximines can be converted into angular carbon-functionalised, highly substituted, isomerically pure (ds ≥ 98%) 2-oxabicyclo[3.3.0]octanes and 2-oxabicyclo[3.4.0]nonanes in high yields by a convenient one-pot sequence. Molecular frameworks such as these can be found in many biologically active natural products. In addition to the methodological work, we report on studies towards the total synthesis of the euglobals G1 and G2 and arenaran A.
    Zusätzliches Material: 1 Tab.
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  • 171
    Digitale Medien
    Digitale Medien
    On the Behavior of 5,8-Bis(trimethylsilyl)cycloocta-1,3,6-triene in Cycloaddition Reactions and Subsequent Chemistry (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1041-1050 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Phosphaalkynes ; Cycloadditions ; Polycycles ; Cage compounds ; λ3-Phosphinines ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Phosphaalkynes 2 and electron-deficient alkynes 11 readily react in a [4 + 2] cycloaddition process with 5,8-bis(trimethylsilyl)cycloocta-1,3,6-triene (8) in its bicyclic form 10 to furnish regioselectively the tricyclodecadienes 12 and 13, respectively. The phosphorus-containing compounds 12 exhibit structural features which make them suitable for homo-Diels-Alder reactions with electron-deficient acetylenes. A single crystal structure analysis of the homo-Diels-Alder adduct 14b confirmed the structure and relative configuration of the phophatricyclodecadienes 12. In solution the tricyclodecadienes 13 are prone to facile cycloreversion yielding the phthalic esters 15 and the cyclobutene 16. The latter is rapidly converted into the corresponding 1,3-butadiene 18, which can be trapped in a Diels-Alder/phospha-ene/Diels-Alder tandem reaction sequence by phosphaalkyne 2a. The phosphatricyclodecadiene 12 is thermally more stable; loss of cyclobutene 16 only occurs under FVP conditions to afford the λ3-phosphinine 22.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 172
    Digitale Medien
    Digitale Medien
    Totally Regio- and Stereoselective P-O-to-P-C Rearrangement in the Synthesis of Chiral P-(o-Hydroxyaryl)diazaphospholidine P-Oxides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1099-1105 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Asymmetric synthesis ; Chiral synthons ; P-(o-Hydroxyaryl)diazaphospholidine P-oxides ; Rearrangements ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The totally regio- and stereoselective P-O-to-P-C rearrangement in the synthesis of various chiral P-(o-hydroxyaryl)diazaphospholidine P-oxides has been investigated. This reaction proceeds with excellent yields ranging from 72 to 92%, total retention of configuration at the phosphorus atom, and complete regioselectivity. An exception was found with naphthyl derivatives, which gave mixtures of two regioisomers. In all cases, the products generated have been unambiguously characterized by 1H-, 13C-, and 31P-NMR spectroscopy as well as by X-ray-diffraction analysis.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 173
    Digitale Medien
    Digitale Medien
    Palladium-Catalyzed Cyclocarbonylation of o-Ethynylphenols and Vinyl Triflates To Form 3-Alkylidene-2-coumaranones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1137-1141 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Cyclocarbonylation ; Alkynes ; Catalysis ; Palladium ; Vinyl triflates ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -o-Ethynylphenols react with vinyl triflates, in the presence of tetrakis(triphenylphosphane)palladium(0) and under carbon monoxide, to form 3-alkylidene-2-coumaranones in good yield.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 174
    Digitale Medien
    Digitale Medien
    S-Linked Thiomimetics of Phytoalexin-Elicitor-Active, Branched Oligosaccharides, Their Synthesis, Protein-Binding Ability and Phytoalexin-Inducing Activity (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1143-1152 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Sulfur-linked thiooligosaccharides ; Oligosaccharin thio analogs ; Phytoalexin elicitor thio analogs ; Soybean glucan-binding assays ; Structure-activity relationships ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The sulfur-linked pentathiohexasaccharide 3I,3IV-di-β-D-glucopyranosylthiogentiotetraose (12) has been prepared by a convergent approach involving the reaction of 1,2,4-tri-O-acetyl-6-deoxy-6-iodo-3-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-3-thio-β-D-glucopyranose (10) with the sodium salt of 2,3,4-tri-O-acetyl-6-S-[2,4-di-O-acetyl-3,6-di-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-3,6-dithio-β-D-glucopyranosyl]-1,6-dithio-β-D-glucopyranose (4). A further reaction, involving the sodium salt of the peracetylated β-1-thio derivative of 12 with 1,2,3,4-tetra-O-acetyl-6-deoxy-6-iodo-β-D-glucopyranose (26), afforded the homologous sulfur-linked hexathioheptasaccharide 3II,3V-di-β-D-glucopyranosylthiogentiopentaose (28). Related sulfur-linked positional isomers 3II,3IV-di-D-β-glucopyranosylthiogentiotetraose (34) and 3III,3V-di-β-D-glucopyranosylthiogentiopentaose (39) have been prepared using analogous synthetic strategies. Thus, SN2 displacement of the iodine atom in 10 by the sodium salt of 2,4-di-O-acetyl-3,6-di-S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-1,3,6-trithio-β-D-glucopyranose afforded a tetrathiopentasaccharide, which resulted in the pentathiohexasaccharide 34 by a sequence of reactions involving the 1-thioglycose 32 in reaction with 26. The hexathioheptasaccharide 39 was obtained conveniently by the reaction of 26 with the acetylated 1-thio-6I, 3II, 6II, 3IV, 6IV-pentathio derivative 37, followed by deacylation. The four isomeric pentathiohexa- and hexathioheptasaccharides 12,34 and 28,39, respectively, were all found to be active in eliciting phytoalexin accumulation in soybean cotyledon tissue and in binding to a glucan-binding protein of soybean, although to a lesser extent than the corresponding O-oligosaccharides, the alternate thiohexa- and thioheptasaccharides 12,28 being more active as compared to the geminally branched isomers 34,39.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
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  • 175
    Digitale Medien
    Digitale Medien
    Flash Vacuum Thermolysis of Acenaphtho[1,2-a]acenaphthylene, Fluoranthene, Benzo[k]- and Benzo[j]fluoranthene - Homolytic Scission of Carbon-Carbon Single Bonds of Internally Fused Cyclopenta Moieties at T ≥ 1100 °C (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1191-1200 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Pyrolysis ; Ring contraction-ring expansion ; Rearrangements ; Homolytic scission ; IGLOIII//6-31G ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Flash vacuum thermolysis (FVT, 1000 °C ≥ T ≥ 1200 °C) of acenaphtho[1,2-a]acenaphthylene (3, C22H12) gave the C22H12 cyclopenta-fused polycyclic aromatic hydrocarbon (CP-PAH) acenaphtho[1,2-e]acenaphthylene (4), cyclopenta[cd]perylene (5) and cyclopenta[def]benzo[hi]chrysene (6). Whereas the formation of 4 is explained by a ring contraction/ring expansion rearrangement of 3, the identification of 5 and 6 suggests that 3 also undergoes homolytic scission of a five-membered ring's Carbon-Carbon single bond furnishing the transient diradical intermediate 7. Ring closure of 7to form 8 after rotation around the Carbon-Carbon single bond of the intact five-membered ring followed by hydrogen shifts will give 6. The latter can rearrange subsequently into 5by ring contraction/ring expansion. The structural assignment of 4 and 5 was supported by independent FVT of 6,12-bis(1-chloroethenyl)chrysene (14) and 3-(1-chloroethenyl)perylene (23), respectively. FVT of 14 (900-1200 °C) gave in a consecutive process 6,12-bis(ethynyl)chrysene (15), 9-ethynylbenz[j]acephenanthrylene (16) and bis(cyclopenta[hi,qr])chrysene (17). Although at T ≥ 900 °C 17 selectively rearranges into 4 by ring contraction/ring expansion, at 1200 °C the latter is converted into 5 presumably via a diradical intermediate obtained by homolytic scission of a single Carbon-Carbon bond of a five-membered ring. FVT of 23 gave in situ 3-ethynylperylene (25), which at 1000 °C is nearly quantitatively converted into 5. The propensity of internal cyclopenta moieties to undergo homolytic scission of a five-membered ring′s Carbon-Carbon single bond was corroborated by independent FVT of benzo[k]- (11) and benzo[j]fluoranthene (12). Previously unknown thermal pathways to important (CP)-PAH combustion effluents are disclosed at T ≥ 1000 °C.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 176
    Digitale Medien
    Digitale Medien
    Chemical Reactions in the Axle of Rotaxanes - Steric Hindrance by the Wheel (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1233-1238 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Electrophilic additions ; Bromine addition to double bonds ; Hydrogenation of double bonds ; Rotaxanes ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Here we report on the possibility of using rotaxane wheels as noncovalent protecting groups which significantly decrease the activity of functional groups in the central part of the axle. The amide-linked rotaxanes 5aand 5b, each containing a C=C double bond in their axle, have been synthesised. The catalytic hydrogenation of these two rotaxanes proceeds slower than those of the corresponding free axle compounds 6a and 6b, indicating steric hindrance of the C=C double bond by the wheel of the rotaxane in each case. Nontheless, the rotaxane 9with an aliphatic (succinic acid) middle region in its axle can be prepared in this manner. Dehydrobromination of the axle in the rotaxane 15yields the rotaxane 16 with a C≡C triple bond located in the centre of the axle.
    Zusätzliches Material: 1 Tab.
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  • 177
    Digitale Medien
    Digitale Medien
    The Cubane Cage - A Sensitive Probe for Assessing Substituent Effects on a Four-Membered Ring, Part II (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1253-1257 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Cage compounds ; Cubanes ; Donor-acceptor systems ; Solid-state structures ; Substituent effects ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The crystal structures of methyl 4-methoxycubane-1-carboxylate (1), 1-acetamido-4-fluorocubane (2), methyl 4-acetoxycubane-1-carboxylate (3), 1,4-difluorocubane (4), 1,4-dichlorocubane (5), and N,N-diisopropylcubane-1,4-dicarboxamide (6) have been investigated by means of X-ray diffraction analysis. Fluorine and chlorine substituents cause a shortening of the vicinal bonds, as is seen in the 4-halocubane-1-carboxylates. The cage bonds vicinal to the ester substituent, with a favorable orientation with regard to the π-acceptor influence of this group become longer than the CH-CH bonds. Furthermore, the influence on bond length with respect to the orientation of this group relative to bonds within the cubane skeleton has been investigated experimentally. The effect of the methoxy group has also been found to depend on the orientation. The cage bond antiperiplanar to the methyl group is shortened, while the cage bonds in gauche orientation to this group are lengthened. As seen in the case of the halogen-substituted derivatives, the bonds bearing the acetoxy substituent are shortened due to the σ-acceptor property of this group. Ab initio calculations on compounds 1, 2, 4, and 5 performed at the 6-31G* level confirm the experimental results.
    Zusätzliches Material: 3 Ill.
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  • 178
    Digitale Medien
    Digitale Medien
    Template-Directed Synthesis of a Rotacatenane (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1295-1302 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Catenanes ; Mechanically interlocked molecules ; Molecular recognition ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -A [2]catenane, able to bind π-electron-rich guests inside the cavity of one of its two macrocyclic components has been designed and synthesized using supramolecular assistance. This recognition motif has been exploited to template the formation of a so-called rotacatenane - i.e., a molecule composed of a dumbbell-shaped component threaded through the cavity of one of the two mechanically interlocked macrocyclic components of a [2]catenane. The structure of this [2]catenane, as well as that of a model [2]catenane, have been characterized unequivocally by single-crystal X-ray analyses. Furthermore, some of the co-conformational changes associated with these mechanically interlocked molecules in solution have been probed by variable-temperature 1H-NMR spectroscopy.
    Zusätzliches Material: 10 Ill.
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  • 179
    Digitale Medien
    Digitale Medien
    Diastereoselective Addition of Radicals to Chiral 1,3-Dioxin-4-ones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1057-1073 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Free radicals ; Stereoselective addition ; Chiral 1,3-dioxin-4-ones ; Photoreactions ; Spirocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Intermolecular addition of radicals to the 1,3-dioxin-4-ones 1a,b and 2a,b with (-)-menthone incorporated as chiral auxiliary in 2-position were investigated. Photochemically generated radicals from 1,3-dioxolane, oxolane, and 2-propanol were added with high facial selectivity from the more exposed a-side. Intramolecular addition of 1,3-dioxolan-2-yl radicals to chiral dioxinones proceeded less efficiently and with lower selectivity also from the a-side. Nevertheless, it was possible to form the new spirocyclic compounds 22-27. The 1,3-dioxin-4-ones 32a,b possessing an unsaturated side chain were attacked by radicals at the terminal double bond. In the case of irradiation of 32b in 1,3-dioxolane a cyclization followed the intermolecular addition of a 1,3-dioxolan-2-yl radical and the dispiro compound 36 was formed. However, the formation of dispiro compound 40 required two reaction steps starting with irradiation of 32b and bromotrichloromethane. The achiral 1,3-dioxin-4-one 44 possessing an unsaturated side chain at C-2 was attacked by 1,3-dioxolan-2-yl radicals preferentially at C-6.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 180
    Digitale Medien
    Digitale Medien
    Enantioselective Synthesis of the Chromane Moiety of Vitamin E (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1075-1084 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Asymmetric synthesis ; Atropisomerism ; Bis(hydroxylation) ; Conformational analysis ; Palladium ; Vitamin E ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Several new approaches for the enantioselective synthesis of the chromane moiety of vitamin E are described. Sonogashira coupling of 3a with the alkyne 4 and subsequent elimination gave 6, which was bis(hydroxylated) in 93% yield and with 85% ee. Recrystallization gave enantiopure 7a, which was hydrogenated and transformed into the vitamin E precursor 11. The bis(hydroxylation) of 18 and 21 to give 9 and 22, respectively, was less than satisfactory, proceeding with ee values of 28% and 18%. In contrast, stereoselective allylation of ketone 15 followed by removal of the protecting group or ozonolysis of the allyl moiety furnished the allyl alcohol 26 and the aldehyde 27, respectively, in almost enantiopure form, which again could be used as precursors for vitamin E. Partial hydrogenation of 5a gave the alkene 32a and that of 28 the alkene 30b, both of which show interesting atropisomerism.
    Zusätzliches Material: 3 Tab.
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  • 181
    Digitale Medien
    Digitale Medien
    Crystalline Hosts Based on the Assembly of Anthracene and Bulky Alcoholic Groups - Host Synthesis, Complex Formation, and X-ray Crystal Structures of Several Inclusion Compounds (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1115-1125 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Clathrate hosts ; Clathrates ; Crystalline inclusion compounds ; Clathrate structures ; Host-guest chemistry ; Anthracene derivatives ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -A series of new clathrate host molecules (1-10) containing two diarylhydroxymethyl groups attached to different positions (1,5 or 1,8) of a basic anthracene construction unit have been synthesized. Their clathrate formation properties with a variety of organic guests, including amines, alcohols, ketones, and other dipolar aprotic compounds or aromatic hydrocarbons are reported (143 examples of clathrates). The inclusion properties and the clathrate stoichiometries depend in a systematic manner on the structure of the host molecules. The crystal structures of six selected clathrates of different classes of compound have been determined by X-ray diffraction.
    Zusätzliches Material: 6 Ill.
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  • 182
    Digitale Medien
    Digitale Medien
    A Novel and Efficient Route towards α-GalNAc-Ser and α-GalNAc-Thr Building Blocks for Glycopeptide Synthesis (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1167-1171 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Carbohydrates ; Glycals, nitro ; Michael additions ; Glycosylations ; Glycosides, galactosamine ; Reduction, nitro group ; Glycopeptides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Michael addition of serine and threonine derivatives 4a-4c to 3,4,6-tri-O-benzyl-2-nitro-D-galactal (1) afforded the corresponding 2-deoxy-2-nitro-α-D-galactopyranosides 5a-5c in good yield and stereoselectivity. 2-deoxy-2-nitroglycosides 5a and 5b were reduced to the 2-acetamido compounds by platinized Raney nickel T4. Manipulation of the protecting groups afforded known N-Fmoc-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-galactopyranosyl)-L-serine (8a) and -threonine (8b), valuable building blocks for O-glycopeptide synthesis.
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  • 183
    Digitale Medien
    Digitale Medien
    Syntheses of Batzelline A, Batzeline B, Isobatzelline A, and Isobatzelline B (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1173-1183 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Marine alkaloids ; Pyrroloquinoline ; Total synthesis ; Heterocycles ; Alkaloids ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Batzellines A and B (1a, b) and isobatzellines A and B (2a, b) are 1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline-containing marine alkaloids characterized by the presence of a methylthio substituent at C-2 of the tricyclic system. We describe here the total synthesis of these natural compounds following the synthetic strategy that we have used previously for the synthesis of damirones A and B, batzelline C, isobatzelline C, discorhabdin C, and makaluvamines A, B, C, and D. The introduction of the methylthio group by electrophilic substitution of a pyrrolo[4,3,2-de]quinoline, appropriately substituted and in a suitable oxidation state, is the key step in the success of these syntheses.
    Zusätzliches Material: 2 Ill.
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  • 184
    Digitale Medien
    Digitale Medien
    Intramolecular Copper- and Rhodium-Mediated Carbenoid Reactions of α-(Propargyloxy)silyl-α-diazoacetates (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1213-1221 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Diazo compounds ; Carbenes ; Carbenoids ; Silicon ; Heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Copper(I) triflate catalyzes the transformation of α-[(2-alkynyl)oxy]silyl-α-diazoacetates 1a-g into 1,2-bis(2,5-dihydro-1,2-oxasilol-4-yl)ethenes 2 and/or 2H-1,2-oxasilines 3. With rhodium(II) perfluorobutyrate as catalyst, 1a-e furnish only 3 but no 2. Bicyclic 2-methoxyfurans 6 are formed when 1a,c,e (containing terminal alkyne functions) are treated with catalytic amounts of copper(I) chloride. The experimental observations are explained in terms of metal-mediated intramolecular cyclopropenation and subsequent metal-assisted ring-opening of the strained bicyclic cyclopropene leading to vinylcarbene-metal complexes. An unusual autoxidation of 2H-1,2-oxasilines 3a,c,e is also described.
    Zusätzliches Material: 1 Ill.
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  • 185
    Digitale Medien
    Digitale Medien
    Syntheses of Cyclobutane Derivatives: Total Synthesis of (+) and (-) Enantiomers of the Oleander Scale Aspidiotus nerii Sex Pheromone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1201-1211 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Pheromones ; Aspidiotus nerii ; Sex attractant ; Cyclobutane ; Enantiomeric purity ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Synthesis of both enantiomers of the Aspidiotus nerii sex pheromone and their diastereomers has been achieved using, as a key step, an intramolecular ester enolate alkylation reaction for the formation of the cyclobutane ring with a good control of the relative configurations of the asymmetric centers. Stereoselective synthesis of a number of other trisubstituted cyclobutane derivatives also proves the versatility of the methodology used for the synthesis of the Aspidiotus nerii sex pheromone.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 186
    Digitale Medien
    Digitale Medien
    Formation of Chiral N-Oxides from 2-Azabicyclo[3.3.0]octanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1249-1252 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Amino alcohols ; Amine N-oxides ; Asymmetric synthesis ; Hydrogen bonds ; Structure determination ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -Enantiopure 2-azabicyclo[3.3.0]octanes 1a-d and ent-1e were oxidized with mCPBA to provide either diastereomeric pairs of N-oxides (2a/3a and 2b/3b) or diastereomerically pure compounds (2c,d and ent-2e). The structure of compounds 2a and ent-2e was confirmed by an X-ray study. The factors that affect the oxidation process are discussed.
    Zusätzliches Material: 2 Ill.
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  • 187
    Digitale Medien
    Digitale Medien
    Synthesis, Fluorescence Properties, and Head-to-Tail Regioselectivity in the Photodimerization of a Donor-Acceptor-Substituted Anthracene (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1595-1600 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Photochemistry ; Anthracenes ; Fluorescence spectroscopy ; Cycloaddition reactions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The novel 2,6-donor-acceptor-substituted anthracene, namely 6-methoxy-2-anthracene carboxylic acid (7), was synthesized. The emission of this compound exhibits significant solvatochromism. The fluorescence band position and intensity are also remarkably sensitive to H+. Irradiation of the anthracene 7 in solution yields the syn and anti head-to-tail dimers exclusively. A synergistic electronic effect between the donor and acceptor substituents is proposed to operate on the photophysical and photochemical properties of anthracene 7.
    Zusätzliches Material: 2 Ill.
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  • 188
    Digitale Medien
    Digitale Medien
    Spectroscopic and Theoretical Investigations of Monocyclic Dioximes and Dimethoximes with Six-, Eight-, and Ten-Membered Rings (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1601-1609 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Photoelectron spectroscopy ; Conformation analysis ; Ab initio calculations ; Through-space interactions ; NMR spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The dioximes 4-6 and the dimethoximes 7-9, which contain the functional groups in opposite positions of a six-, eight-, or ten-membered ring, were synthesized. Their conformational properties and transannular interactions were investigated by spectroscopic (PE, 13C NMR) and theoretical (MMX, AM1, ab initio HF, and B3LYP) methods. While the cyclooctane derivatives 5 and 8 have conformations favourable for through-space interactions of the π(C=N) orbitals, in the other compounds no such interactions can be ascertained. Through-space orbital interactions in the molecules with an eight-membered ring lead to a splitting of the π(C=N) MOs of 0.4 eV.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 189
    Digitale Medien
    Digitale Medien
    Spectroscopic and Theoretical Investigations of Bicyclic Dioximes and Dimethoximes with Eight-Membered Rings (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1611-1617 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Photoelectron spectroscopy ; Conformation analysis ; Ab initio calculations ; Through-space interactions ; NMR spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The bicyclic dioximes 4-6 and dimethoximes 7-9, which contain the functional groups in opposite positions of bridged eight-membered rings, were synthesized. Their conformational properties and transannular interactions were investigated by spectroscopic (PE, 13C NMR) and theoretical (MMX, AM1, ab initio HF, and B3LYP) methods. While in the 3,7-disubstituted bicyclo[3.3.1]nonane derivatives 5 and 8 the eight-membered ring has a CC conformation favourable for through-space interactions of the π(C=N) orbitals, in the bicyclo[3.3.0]octane derivatives 4 and 7 as well as the 2,6-disubstituted bicyclo[3.3.1]nonanes 6 and 9 the functional groups are in geometric orientations that are unfavourable for such interactions. Through-space orbital interactions in the molecules with favourable conformations lead to a splitting of the π(C=N) MOs of 0.4-0.6 eV.
    Zusätzliches Material: 7 Ill.
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  • 190
    Digitale Medien
    Digitale Medien
    Diastereomers Composed of Two Planar-Chiral Subunits: Bis([2.2]paracyclophan-4-yl)methane and Analogues (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1653-1663 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Planar chirality ; Cyclophanes ; Configuration determination ; NMR spectroscopy ; Diastereomers ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of compounds Q2Z was prepared, where Q = [2.2]paracyclophan-4-yl and Z = C(=O) (4), CH2 (5), SiMe2 (6), S (7), P(=O)OMe (8), and C(=O)C(=O) (9). Because of the planar chirality of Q, these compounds occur as meso- (m) and chiral (c) diastereomers, which were formed in equal amounts. They were separated in the cases of 4-7 and enriched in the case of 9 (diastereomeric ratio ca. 7:3). Compound 8 possesses a pseudoasymmetric phosphorus centre and occurs as one chiral (8c) and two meso diastereomers (8m1, 8m2), all three of which were isolated separately. The configurations of 5m/5c, 6m/6c, and 8c were directly determined by NMR spectroscopy, that of 4m/4c indirectly by reducing the separated compounds to 5m and 5c, respectively, and that of 7m by X-ray diffraction. The favoured conformations of 4-8 were studied by molecular mechanics computations by using the MM3(94) program. An attempt was made to rationalize some chemical shift differences between diastereomers on the basis of the conformers predicted.
    Zusätzliches Material: 3 Ill.
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  • 191
    Digitale Medien
    Digitale Medien
    Synthesis and Experimental Electron Density of Bis(heterocyclic) Azines: The Case of 6,6′-Bis(chloromethyl)-2,2′-bipyrazine (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1427-1440 
    Details
    ISSN: 1434-193X
    Schlagwort(e): 2,2′-Bipyrazine reactivity ; Experimental electron density distribution ; High-resolution X-ray diffraction ; Electron density topology ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The synthesis and reactivity of mono- and bis(chloromethyl)-2,2′-bipyrazines toward nucleophiles are reported. The reactivity of the bipyrazine ring is explained in terms of allylic substitution and rearrangement mechanisms. A new family of monofunctionalized bipyrazine derivatives as molecular building blocks for supermolecules has been obtained, opening access to unsymmetrical ligands. The low-temperature crystallographic structure and the experimental electron density distribution of 6,6′-bis(chloromethyl)-2,2′-bipyrazine have been determined on the basis of high-resolution X-ray diffraction data. The electron density of the molecule has been accurately analyzed using the topological properties of its gradient and Laplacian features. The reactivity of these bidentate molecules in metal complexation is related to the shape of the atomic basins and may be explained in terms of a key/lock-type interaction. The results are compared with corresponding data for 2,2′-dimethyl-6,6′-diphenyl-4,4′-bipyrimidine.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98532_s.pdf or from the author.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 192
    Digitale Medien
    Digitale Medien
    Steric Effects on the Proton-Transfer Equilibria of Ketones, Sulfoxides, and Phenols (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1507-1515 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Ketones ; Sulfoxides ; Phenols ; Steric hindrance ; Acidity ; Basicity ; NMR spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The proton-transfer equilibrium of several bases and acids, including some sterically hindered ketones, sulfoxides, and phenols, has been investigated by means of the determination of the thermodynamics of the equilibrium, NMR 13C relaxation measurements, and quantum chemical calculations. The analysis of such data yields information about the steric effects on basicity or acidity and about the underlying reasons for the anomalous behavior of species having a sterically hindered basic or acidic site. Thus, it is demonstrated that the anomalously low basicity of two sterically hindered ketones (tBu2CO and PhCOtBu) is enthalpic in origin and stems from steric hindrance to the solvation of their protonated forms. No such effect is found for analogous sulfoxides, whereas phenols display a more complex behavior.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/1999/99105_s.pdf or from the author.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 193
    Digitale Medien
    Digitale Medien
    Reaction of Diphenyldiazomethane with N-Methyloxy- and N-Ethyloxycarbonyl-N-(2,2,2-trichloroethylidene)amines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1541-1544 
    Details
    ISSN: 1434-193X
    Schlagwort(e): 1,3-Dipolar cycloadditions ; Diphenyldiazomethane ; N-Alkyloxycarbonyl-N-(2,2,2-trichloroethylidene)-amines ; Δ3-1,3,4-Triazoline ; Aziridines ; 2-Azadiene ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of the title imines with diphenyldiazomethane gives a Δ3-1,3,4-triazoline, which leads, after loss of dinitrogen, to a transient azomethine ylide. Subsequent elimination of ethyl or methyl chloroformate gives the unexpected 1,1-diphenyl-4,4-dichloro-2-aza-1,3-butadiene.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 194
    Digitale Medien
    Digitale Medien
    Synthesis and Mesogenic Properties of Porphyrin Octaesters (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1527-1539 
    Details
    ISSN: 1434-193X
    Schlagwort(e): 3,4-Disubstituted pyrroles ; Porphyrin octaesters ; Liquid crystals ; π-π interactions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new and efficient method of preparing 3,4-pyrrolediacetic esters 3 is reported, together with their conversion, according to the Lindsey procedure, to a series of octa- and dodeca-substituted porphyrins. This procedure, which consists of a palladium-catalysed oxidative alkoxycarbonylation of N-substituted dipropargylamine derivatives 1, works nicely for n-alkyl alcohols in the range C1 to C14. The thermotropic behaviour of this series of porphyrins (28 compounds) has been investigated using polarization microscopy, DSC, X-ray diffraction, and miscibility tests. The planarity of the macrocyclic core constitutes the major structural requirement for mesophase formation. The mesophase temperature range is controlled by the length of the side chains through the melting point and by the strength of π-π interactions among the cores through the clearing point. The same set of rules governing porphyrin packing in the solid state can be employed to predict mesophase formation and organization in porphyrin octaesters
    Zusätzliches Material: 4 Ill.
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  • 195
    Digitale Medien
    Digitale Medien
    The Electrocyclic Reactions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1921-1924 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Cyclizations ; Electrocyclic reactions ; Solvent effects ; Salt effect ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rate constants of the electrocyclic ring closure of (1Z,3Z,5E)-1,2,6-triphenylhexa-1,3,5-triene (1) and of the ring opening of dimethyl 3,4-dimethyl-1,2-diphenylcyclobutene-cis-3,4-dicarboxylate (3) were determined in 15 and 16 solvents, respectively. The ring closure of 1 shows, in spite of theoretical predictions, neither solvent nor salt effects. For the ring opening of 3, small solvent and salt effects were found, suggesting the possibility of observing small acceleration due to specific solute-solvent or salt interactions.
    Zusätzliches Material: 1 Ill.
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  • 196
    Digitale Medien
    Digitale Medien
    Radical Cyclizations - Synthesis of γ-Lycorane (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1925-1933 
    Details
    ISSN: 1434-193X
    Schlagwort(e): γ-Lycorane ; Radicals ; Cyclizations ; Natural products ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (±)-γ-Lycorane has been synthesized in ten steps from piperonylic alcohol. Two radical reactions were used successively to build the D and B rings. A formal synthesis of (+)-γ-lycorane was achieved via an optically active unsaturated aldehyde intermediate.
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  • 197
    Digitale Medien
    Digitale Medien
    Enantioselective Catalysis in Fluorinated Media - Synthesis and Properties of Chiral Perfluoroalkylated (Salen)manganese Complexes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1947-1955 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Biphasic catalysis ; Epoxidations ; Fluorinated compounds ; Manganese ; Salen ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Chiral (salen)manganese complexes, which are selectively soluble in perfluorocarbons, were synthesized and tested as epoxidation catalysts in fluorous-organic two-phase systems. The immiscibility of the perfluorocarbons with regular organic solvents allowed a quick and effective separation of the catalyst from the products. These unprecedented perfluoroalkylated salen complexes were found to be efficient and chemoselective catalysts in the presence of several oxygen donors, but enantioselectivities were generally poor. An interesting exception to this behaviour was observed in the asymmetric epoxidation of indene that provides indene oxide with 70-92% enantiomeric excess.
    Zusätzliches Material: 1 Ill.
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  • 198
    Digitale Medien
    Digitale Medien
    Palladium-Catalysed Synthesis of Dibenzo[de,g]quinolines. A Novel Approach to the B-Ring System of Aporphine-Related Heterocycles (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1957-1961 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Aporphines ; Nitrogen heterocycles ; Palladium ; Homogeneous catalysis ; Dibenzo[de,g]quinolines ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dibenzo[de,g]quinolines 5were formed by the palladium-catalysed heteroannulation of disubstituted alkynes and 1-iodo-10-(dimethylamino)phenanthrene (3c). Symmetric alkynes led to high levels of regioselectivity. These reactions constitute a new synthesis of the B-ring system of aporphine heterocycles.
    Zusätzliches Material: 1 Ill.
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  • 199
    Digitale Medien
    Digitale Medien
    A Variation of Titanium-Induced Carbonyl Coupling - Synthesis and Conformations of Terfluorenyl (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1979-1984 
    Details
    ISSN: 1434-193X
    Schlagwort(e): McMurry reaction ; C-C coupling ; Low-valent titanium ; Reductive “trimerization” ; Semiempirical calculations ; Overcrowding ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of fluorenone (4) with a low-valent titanium reagent generated from TiCl4 and Zn in THF in the presence of pyridine gave terfluorenyl (6) in 71% yield, bifluorenylidene (2), the conventional McMurry reaction product, in 2% yield, and additional reduction products. The reductive “trimerization” was rationalized in terms of an attack of the intermediate fluorenone dianion on bifluorenylidene. The molecular structure of a single crystal of 6 indicated an approximately C2 conformation, with a slightly twisted central ring, and two equally folded side moieties with dihedral angles of 58.1° and 58.0° between the central and side five-membered rings. The AM1 and PM3 calculations showed C2 global minima, similar to the conformation in the crystal. The calculated Cs transition state conformations were found to be 21.3 (AM1) and 19.9 (PM3) kcal/mol higher in energy than the global C2 minima. A 2D-NMR NOESY experiment on 6 supported the C2 (+sc,+sc) or C2 (-sc,-sc) conformation in solution.
    Zusätzliches Material: 3 Ill.
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  • 200
    Digitale Medien
    Digitale Medien
    Asymmetric Synthesis Employing a Chiral 5-Methoxy-1,4-oxazin-2-one Derivative: Preparation of Enantiomerically Pure α-Quaternary α-Amino Acids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1967-1978 
    Details
    ISSN: 1434-193X
    Schlagwort(e): 1,4-Oxazines ; Asymmetric synthesis ; Amino acids ; Glycine derivatives ; Aminocyclopropanecarboxylic acid derivatives ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new asymmetric synthesis of disubstituted α-amino acids is presented. This synthesis is based on the chiral 5-methoxy-1,4-oxazin-2-one derivative 5 relying on the α-hydroxy acid 1 as a chiral auxiliary. Alkylation reactions of the glycine equivalent 5 are performed by deprotonation with sec-butyllithium and subsequent reaction with alkyl halides, yielding the monoalkylated compounds 13 and 14. A second alkylation step of the lithium enolates of 13 and 14 leads to the α,α-disubstituted compounds 17. Both steps proceed with good yields and excellent stereoselectivities (up to 99% de). From the major diastereomers 17c-d the corresponding α-amino acids 19c-d are obtained enantiomerically pure upon hydrolytic cleavage with aqueous sodium hydroxide. Alkylation of the enolate ion of 5 with epichlorohydrines as bifunctional electrophiles provides the cyclopropyl derivatives 20a-b. Direct hydrolysis or oxidation of 20a-b, followed by reductive amination and hydrolysis leads to the substituted 1-aminocyclopropanecarboxylic acids 21a-b and 24a-b.
    Zusätzliches Material: 2 Tab.
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