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  • 1990-1994  (1.004)
  • 1965-1969
  • 1860-1869
  • 1991  (1.004)
  • Organic Chemistry  (822)
  • Biochemistry  (158)
  • Insulin
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Materialart
Erscheinungszeitraum
  • 1990-1994  (1.004)
  • 1965-1969
  • 1860-1869
Jahr
Schlagwörter
  • 1
    Digitale Medien
    Digitale Medien
    Effect of hyperkalemia on insulin secretion (1991)
    Springer
    Cellular and molecular life sciences 47 (1991), S. 270-272 
    Details
    ISSN: 1420-9071
    Schlagwort(e): Insulin ; potassium ; hyperkalemia ; portal vein ; glucose
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The effect of hyperkalemia on insulin secretion remains undefined. We evaluated portal and peripheral insulin levels in anesthetized dogs after infusions of KCl. The mean maximal increase in peripheral plasma potassium at infusion rates of 0.2 mEq/kg/h was 0.68±0.20 mEq/l. There were no significant increases in either portal or peripheral insulin levels. In contrast, in six dogs whose plasma potassium concentration increased in each case by more than 2.0 mEq/l (infusion rate of 0.5 mEq/kg/h), portal insulin levels increased fivefold (p〈0.05). We conclude that only marked increases in plasma potassium concentration stimulate pancreatic insulin secretion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01958157
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  • 2
    Digitale Medien
    Digitale Medien
    Serum levels of glucose, insulin, and C-peptide during long-term D-ribose administration in man (1991)
    Springer
    Journal of molecular medicine 69 (1991), S. 31-36 
    Details
    ISSN: 1432-1440
    Schlagwort(e): (D-)ribose ; Glucose ; Insulin ; C-peptide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary D-ribose was given orally and/or intravenously to nine healthy subjects at doses ranging from 83.3 to 222.2 mg/kg per hour for at least four hours. The serum ribose level increased in a dose-dependent manner to maximum concentrations of 75 to 85 mg/dl. The serum glucose level decreased after the beginning of continuous ribose administration and was reduced as long as ribose was being administered. The oral or intravenous administration of 166.7 mg/kg per hour of ribose resulted in a 25% decrease in serum glucose. Higher intravenous doses of ribose did not provoke a further decrease in serum glucose concentration. Oral administration of 166.7 mg/kg per hour led to an increase in serum insulin concentrations from a mean of 8.4 (range 6.4–11.5) to 10.4 (range 6.3–15.4) μU/ml (p〈0.05). In contrast, intravenous administration did not change serum insulin concentrations significantly. The serum c-peptide concentration remained unchanged regardless of treatment. We conclude that the variations in plasma insulin concentrations do not account for the observed decrease in mean serum glucose concentrations accompanying D-ribose administration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01649054
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  • 3
    Digitale Medien
    Digitale Medien
    Different aetiologies of Type 2 (non-insulin-dependent) diabetes mellitus in obese and non-obese subjects (1991)
    Springer
    Diabetologia 34 (1991), S. 483-487 
    Details
    ISSN: 1432-0428
    Schlagwort(e): Insulin ; glucose ; obesity ; glucose disposal ; insulin secretion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Insulin responses to intravenous glucose infusion and glucose utilization during hyperinsulinaemic euglycaemic clamp were determined in a large homogeneous group of 65-year-old male subjects. Twenty-eight had untreated Type 2 (non-insulin-dependent) diabetes mellitus and the remaining 44 control subjects had a normal glucose tolerance. Diabetic patients with abdominal obesity displayed peripheral insulin resistance in combination with defective insulin secretion, whereas non-obese diabetic patients showed only a secretory defect. Thus, Type 2 diabetes in obese and non-obese elderly male subjects may take two forms where the cause of hyperglycaemia differs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00403284
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  • 4
    Digitale Medien
    Digitale Medien
    No glucotoxicity after 53 hours of 6.0 mmol/l hyperglycaemia in normal man (1991)
    Springer
    Diabetologia 34 (1991), S. 570-575 
    Details
    ISSN: 1432-0428
    Schlagwort(e): Insulin ; glucose ; insulin resistance ; man ; glucotoxicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In vitro and in vivo studies have suggested that metabolic deterioration can be induced by hyperglycaemia per se. The effect of 53 h of 2.2 mg glucose · kg ideal body weight−1· min−1 was examined in four normal male subjects. This produced overnight hyperglycaemia of 6.0 mmol/l on the two nights of the study compared with 4.7 mmol/l on the control night (p〈0.05). In response there was a sustained, two-fold increase in basal plasma insulin (p〈0.005) and C-peptide (p〈0.05) levels. After two days of hyperglycaemia an increased Beta-cell response was demonstrated in response to an additional glucose infusion stimulus (estimated Beta-cell function median of 84% on the control day to 100% after two days glucose infusion). Plasma insulin and C-peptide responses to a 10.0 mmol/l hyperglycaemic clamp increased over the two days of the study (insulin from median 48 mU/l to 73 mU/l and C-peptide from median 2.0 pmol/ml to 2.6 pmol/ml). Glucose tolerance to the additional glucose infusion stimulus improved, suggesting that the increased insulin response during hyperglycaemia was enhancing peripheral glucose uptake. The calculated peripheral insulin sensitivity was unchanged during the hyperglycaemic clamp. Thus, in response to the two days of basal hyperglycaemia, both the basal and stimulated Beta-cell responses were enhanced and there was no evidence for ‘glucose toxicity’ to the Beta-cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00400275
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  • 5
    Digitale Medien
    Digitale Medien
    Receptor-recycling model of clearance and distribution of insulin in the perfused mouse liver (1991)
    Springer
    Diabetologia 34 (1991), S. 613-621 
    Details
    ISSN: 1432-0428
    Schlagwort(e): Insulin ; hepatic clearance ; receptor recycling ; receptor-mediated endocytosis ; physiological model ; mouse liver perfusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary After perfusion of mouse livers with A14-125I-insulin for designated intervals, an acid-wash technique was employed to separately measure the surface-bound (Xs) and intracellular (Xi) A14-125I-insulin, as well as intracellular degradation products (Xdeg) of labelled insulin. From the perfusate concentrations (Cp) of A14-125I-insulin, the apparent intrinsic hepatic clearance of labelled insulin at a high dose (0.2 nmol/l) was shown to be 60% smaller than that at a low dose (0.018 nmol/l), indicating that the cellular uptake of insulin is remarkably nonlinear at the concentration range examined. From the time courses of Cp, Xs, Xi and Xdeg, the hepatic insulin disposition was shown to be largely accounted for by the receptor-mediated endocytosis. The observed data at the low dose were analysed to estimate biochemical parameters, (i.e., total receptor number, endocytotic rate constant and intracellular degradation rate constant) according to “receptor-recycling” and “non-receptor-recycling” models, using a computer-aided optimization procedure. The “receptor-recycling” model could not only adequately explain the Cp, Xs, Xi and Xdeg at the low dose, but also predict the Cp at the high dose. On the other hand, a “non-receptor-recycling” model, in which recycling of receptors was not assumed, could also explain the observed data at the low dose, but failed to predict the Cp at the high dose, indicating that the receptor recycling process is necessary to explain the hepatic insulin clearance at high insulin concentrations, at which hepatic insulin clearance should be limited by the rate of receptor recycling. However, the applicability of our model might be limited within the physiologic insulin concentrations, because of the negative co-operativity of insulin-receptor interaction and a high-capacity, non-degradative and more rapidly recycling pathway for receptors that may occur at high concentrations of insulin. In conclusion, we have developed a mathematical model of hepatic insulin clearance and distribution under physiological conditions, including receptor binding, receptor-mediated endocytosis and receptor recycling, which has been so far demonstrated using isolated hepatocytes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00400989
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  • 6
    Digitale Medien
    Digitale Medien
    Time-related, cross-sectional and prospective follow-up of pancreatic endocrine function after pancreas allograft transplantation in Type 1 (insulin-dependent) diabetic patients (1991)
    Springer
    Diabetologia 34 (1991), S. S57 
    Details
    ISSN: 1432-0428
    Schlagwort(e): Insulin ; C-peptide ; Glucagon ; Pancreas ; Transplantation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary It has been established that successful pancreas transplantation in Type 1 (insulin-dependent) diabetic patients results in normal but exaggerated phasic glucose-induced insulin secretion, normal intravenous glucose disappearance rates, improved glucose recovery from insulin-induced hypoglycaemia, improved glucagon secretion during insulin-induced hypoglycaemia, but no alterations in pancreatic polypeptide responses to hypoglycaemia. However, previous reports have not segregated the data in terms of the length of time following successful transplantation and very little prospective data collected over time in individual patients has been published. This article reports that in general there are no significant differences in the level of improvement when comparing responses as early as three months post-operatively up to as long as two years post-operatively when examining the data cross-sectionally in patients who have successfully maintained their allografts. Moreover, this remarkable constancy in pancreatic islet function is also seen in a smaller group of patients who have been examined prospectively at various intervals post-operatively. It is concluded that successful pancreas transplantation results in remarkable improvements in Alpha and Beta cell but not PP cell function that are maintained for at least one to two years.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00587621
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  • 7
    Digitale Medien
    Digitale Medien
    In vivo metabolic action of insulin-like growth factor I in adult rats (1991)
    Springer
    Diabetologia 34 (1991), S. 144-149 
    Details
    ISSN: 1432-0428
    Schlagwort(e): Insulin ; insulin-like growth factor I ; euglycaemic clamping ; glucose metabolism ; lipogenesis ; glycogenesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The acute metabolic actions of insulin-like growth factor I were studied in anaesthetized adult rats and its potency was compared to that of insulin. Following an i. v. bolus injection of insulin-like growth factor I a dose-dependent decrease of blood glucose and serum non-esterified fatty acid concentrations was noted with a potency of about 2% that of insulin. Stimulation of total body glucose disposal during euglycaemic clamping required ∼ 50times higher insulin-like growth factor I serum concentrations to achieve an identical half-maximal response. A similar difference in potency was observed for the stimulatory action on 2-de-oxyglucose uptake and on glycogen formation in skeletal muscle. Lipogenesis in epididymal fat pads was increased dose-dependently by both hormones requiring approximately 30 times higher half-maximally effective serum concentrations of insulin-like growth factor I. These data demonstrate that insulin-like growth factor I exerted acute insulin-like metabolic actions in vivo with low potency. These effects were probably mediated via insulin receptors. A preferential stimulation of glucose metabolism in skeletal muscle was not observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00418267
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  • 8
    Digitale Medien
    Digitale Medien
    Ontogenesis of insulin processing in fetal rat hepatocytes (1991)
    Springer
    Diabetologia 34 (1991), S. 868-876 
    Details
    ISSN: 1432-0428
    Schlagwort(e): Insulin ; fetal rat hepatocytes ; glycogen ; endocytosis ; degradation ; retroendocytosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary We studied insulin processing and hepatic glycogenesis in cultured hepatocytes isolated from rat fetuses of 17, 19, and 21 days of gestation. Steady-state insulin binding increased by 250% between days 17 and 19, from 145±8 to 361±52 fmol/mg protein, and by an additional 40% (405±69 fmol/mg protein) by 21 days of gestation. At 37°C, 125I-insulin was rapidly (t1/2〈5 min) internalized by hepatocytes at all three ages, reaching maximal levels (63–76% of the total cell-associated radioactivity) by 15 min. 125I-labelled degradation products appeared rapidly (t1/2〈15 min) within the cells. Yet, the majority (68–77%) of the intracellular radioactivity consisted of intact 125I-insulin, even after 4 h at 37°C. Hepatocytes pre-loaded with 125I-insulin and then acid-stripped of surface-bound radioactivity, rapidly released both intact 125I-insulin (retroendocytosis) and its radiolabelled degradation products. While intact insulin was initially released more rapidly (t1/2〈6 min), and reached a plateau after 15–30 min, the degradation products continued to accumulate in the medium for at least 4 h. Methylamine inhibited intracellular 125I-insulin degradation at all three gestational ages and also blocked insulin-stimulated glycogenesis in 19- and 21-day hepatocytes, without altering basal glycogen synthesis. Insulin-stimulated glycogenesis was not induced in 17-day fetal rat hepatocytes in control or methylamine-treated cultures. We conclude that both degradative and retroendocytotic pathways for processing insulin are present in fetal rat hepatocytes by 17 days of gestation. Further, insulin-receptor processing was functionally related to the glycogenic action of insulin in responsive 19- and 21-day fetal rat hepatocytes
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00400194
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  • 9
    Digitale Medien
    Digitale Medien
    Binding and biological effects of insulin, insulin analogues and insulin-like growth factors in rat aortic smooth muscle cells. Comparison of maximal growth promoting activities (1991)
    Springer
    Diabetologia 34 (1991), S. 307-313 
    Details
    ISSN: 1432-0428
    Schlagwort(e): Insulin ; insulin analogues ; insulin-like growth factors ; proliferation ; vascular smooth muscle cells
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Binding and growth promoting effects of insulin, insulin analogues modified in the B chain, proinsulin, insulin-like growth factor-I and -II were studied in cultured rat aortic smooth muscle cells. Specific binding of125I-insulin was 0.9±0.2% of total 125I-insulin added, and the IC50-value was estimated to 8.9 pmol/1. The insulin analogue B10 Asp tended to be more potent than insulin in displacing 125I-insulin, B28 Asp was equipotent, B9 Asp/B27 Glu was approximately 100 times less potent and insulin-like growth factor-I more than 1000 times less potent than insulin. Specific binding of 125I-insulin-like growth factor-I after 4 h incubation at 10 °C was five times higher than the specific binding of insulin (4.4±0.4% of total 125I-insulin-like growth factor-I added), and the IC50-value was 0.3 nmol/l. Insulin was approximately 500 times less potent than insulin-like growth factor-I in displacing 125I-insulin-like growth factor-I. The insulin analogue B10 Asp was slightly more potent and analogue B28 Asp was equipotent with insulin. Analogue B9 Asp/B27 Glu was ten times less potent and proinsulin was more than ten times less potent than insulin. The order of potency was similar for 3H-thymidine incorporation into DNA: insulin-like growth factor-I 〉 B10 Asp 〉 insulin-like growth factor-II 〉 insulin 〉 B28 Asp 〉 B9 Asp/B27 Glu 〉 proinsulin. The maximal effect of insulin-like growth factor-I on 3H-thymidine incorporation was 71±16% higher than the maximal effect of insulin. The maximal effect of insulin-like growth factor-II was at least as high as the effect of insulin-like growth factor-I. Furthermore, the maximal effect of B10 Asp was 62±10% higher than the maximal effect of insulin. Insulin-like growth factor-I and B10 Asp tended to increase cell number more than insulin. In conclusion, this study shows that insulin analogues interact with different potencies with receptors for insulin and insulin-like growth factor-I in vascular smooth muscle cells and that insulin-like growth factors and the insulin analogue B10 Asp have more pronounced growth effects than insulin. Substitution of the amino acid Asp for His at position B10 in insulin makes the molecule more similar to insulin-like growth factor-I, chemically and probably also biologically.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00405001
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  • 10
    Digitale Medien
    Digitale Medien
    Reduced secretion of gastric inhibitory polypeptide in turner patients with impaired glucose tolerance (1991)
    Springer
    European journal of pediatrics 150 (1991), S. 339-342 
    Details
    ISSN: 1432-1076
    Schlagwort(e): Glucose tolerance ; Turner syndrome ; Insulin ; GIP
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract There is a well documented increase in the incidence of abnormal glucose tolerance in patients with Turner syndrome. To elucidate the pathophysiology of this phenomenon, we studied the serum concentrations of gastric inhibitory polypeptide (GIP) — as probably the most important hormonal factor of the entero-insular axis — in relation to impaired glucose tolerance in this syndrome. Oral glucose tolerance tests were performed in 12 Turner patients with simultaneous determination of plasma glucose, insulin and GIP. An impaired glucose tolerance (iGT) was found in four patients with a chronological age between 12.3 and 14.9 years. These patients were compared with found Turner patients of similar age and weight and a normal glucose tolerance (nGT). The highest insulin level occurred 90 min after stimulation in the patients with iGT compared to 30 min in the nGT group. Interestingly, the total areas under the insulin curves were not different. Stimulated plasma GIP concentrations and the areas under the GIP curves wer significantly lower in iGT compared to nGT patients. A disturbed entero-insular axis might contribute to the delayed — rather than diminished — release of insulin in patients with Turner syndrome and impaired glucose tolerance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01955936
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  • 11
    Digitale Medien
    Digitale Medien
    Extrapancreatic insulin effect of glibenclamide (1991)
    Springer
    European journal of clinical pharmacology 40 (1991), S. 379-381 
    Details
    ISSN: 1432-1041
    Schlagwort(e): Insulin ; glibenclamide ; C-peptide ; insulin catabolism ; diabetes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Medizin
    Notizen: Summary In eight patients with uncomplicated non insulin dependent diabetes mellitus, serum insulin levels, serum C-peptide levels and blood glucose levels were measured before and after oral administration of glibenclamide 0.1 mg/kg body weight and a test meal, or after a test meal alone. The rise in serum insulin levels persisted longer after glibenclamide. The initial rise in serum insulin was of the same magnitude in both situations, as was the rise in serum C-peptide levels during the entire 5 h study. It is concluded that glibenclamide is able to maintain a more protonged increase in serum insulin levels by inhibiting the degradation of insulin in the vascular endothelial cells of the liver. The inhibition contributes to the blood glucose lowering effect of glibenclamide.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00265847
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  • 12
    Digitale Medien
    Digitale Medien
    Risks of jet injection of insulin in children (1991)
    Springer
    European journal of pediatrics 150 (1991), S. 554-556 
    Details
    ISSN: 1432-1076
    Schlagwort(e): Diabetes ; Insulin ; Therapy ; Child
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The aim of our study was to assess whether a non-invasive insulin injector could improve the metabolic control of ten diabetic children complaining of painful injections with syringe and needle. The cumulative study period amounted to 1347 days. Whereas a non-significant rise in insulin needs was observed (from 0.98±0.03 to 1.03±0.06 units/kg per day, mean ± sem), mean HbA1c value remained unchanged (8.9%±0.4% vs 9.0%±0.5%). Jet injections were felt as less painful than those using syringe and needle (nine out of ten cases). This advantage was hampered by side-effects in eight out of ten cases such as episodes of glycoketonuria (six out of ten cases) leading to hospitalization in three patients. Other side-effects included inability to adjust injection pressure (four out of ten cases) and technical failure requiring an exchange of injector in five cases. The four children with most serious problems were significantly younger (P=0.009) than other subjects. In conclusion, this type of injector should be discouraged in young diabetic children. For older children and adolescents, it may be an alternative to syringe and needle provided repeated detailed information and tight medical supervision is available.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02072205
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  • 13
    Digitale Medien
    Digitale Medien
    Effects of insulin and somatostatin on the growth and the colony formation of two human pancreatic cancer cell lines (1991)
    Springer
    Journal of cancer research and clinical oncology 117 (1991), S. 416-420 
    Details
    ISSN: 1432-1335
    Schlagwort(e): Pancreas cancer ; Insulin ; Somatostatin ; Growth ; Colony formation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The effects of insulin and somatostatin on the growth and the colony formation of two human pancreatic cancer cell lines, BxPC-3 and SOJ-6, were studied. The BxPC-3 cell line (American Type Culture Collection no. CRL 1687) was derived from a moderately differentiated pancreatic adenocarcinoma. The SOJ-6 cell line is a subclone of SOJ that was initiated from ascites of a well-differentiated pancreatic adenocarcinoma. Both cell lines express fetoacinar pancreatic antigen, an antigen that might be associated with early transformation stages. However, these lines have different proliferation and tumoral powers. SOJ-6 cells showed an almost twofold higher division rate over BxPC-3 cells when cultured in RPMI-1640 medium containing 10% fetal bovine serum. The tumorigenic degree of SOJ-6 cells, as assessed by tumor growth in nude mice, was about three times greater than that of BxPC-3. The in vitro growth of BxPC-3 cells was significantly promoted by insulin, and was slightly inhibited by somatostatin, whereas the growth of SOJ-6 cells was not influenced by these hormones. Using a clonogenic assay in soft agar, the average ratio of colony numbers formed by SOJ-6 and BxPC-3 was about 10/1, indicating a good correlation between the colony formation and tumorigenic degree in vivo. In this test, the number of colonies formed by BxPC-3 cells was increased about twofold in insulin-supplemented medium. On the other hand, somatostatin inhibited the colony formation by a factor of four to six. However, no hormonal modulation of the colony formation of SOJ-6 cells was observed. Our data show that pancreatic cancer cell lines respond differently to pancreatic hormones, and suggest that this may be correlated to a tumour stage or a tumour type.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01612760
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  • 14
    Digitale Medien
    Digitale Medien
    Linear prediction enhancement of 2D heteronuclear correlated spectra of proteins (1991)
    Springer
    Journal of biomolecular NMR 1 (1991), S. 237-246 
    Details
    ISSN: 1573-5001
    Schlagwort(e): Linear prediction ; Heteronuclear correlation ; 2D NMR spectra ; Protein ; Insulin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Summary Linear prediction has been used to extrapolate the t1 domain of natural abundance1H−13C correlated two-dimensional (2D) FIDs of insulin. The FIDs were obtained by two different heteronuclear correlation experiments, one that utilizes heteronuclear multiple-quantum coherence during t1, and one that utilizes13C single-quantum coherence. It is shown that the enhancement of the resolution and sensitivity in the F1 dimension of the Fourier transform spectrum that results from the linear prediction extrapolation allows the t1 domain to be confined to a relatively short time period where the signal intensity is at maximum. In particular, it is found that the enhancement thus obtained is sufficiently good to allow an observation of the difference between the F1 line widths in the single-quantum and double-quantum coherence spectra.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01875517
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  • 15
    Digitale Medien
    Digitale Medien
    Effect of sulphonylurea on glucose-stimulated insulin secretion in healthy and non-insulin dependent diabetic subjects: a dose-response study (1991)
    Springer
    Acta diabetologica 28 (1991), S. 162-168 
    Details
    ISSN: 1432-5233
    Schlagwort(e): Insulin ; C-peptide ; Glucose ; Glipizide ; Non-insulin-dependent diabetes mellitus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The effect of a rapid-acting sulphonylurea, glipizide, on the dose-response relationship between the β-cell response (insulin and C-peptide secretion) and the ambient plasma glucose concentration was examined in 12 healthy and 6 non-insulin-dependent diabetic subjects. The subjects participated in two sets of experiments which were performed in random order: (A) four hyperglycaemic clamp studies, during which the plasma glucose concentration was raised for 120 min by 1 (only in healthy subjects), 3, 7, and 17 mmol/l; and (B) the same four hyperglycaemic clamp studies preceded by ingestion of 5 mg glipizide. All subjects participated in a further study, in which glipizide was ingested and the plasma glucose concentration was maintained at the basal level. In control subjects in the absence of glipizide, the firstphase plasma insulin response (0–10 min) increased progressively with increasing plasma glucose concentration up to 10 mmol/l, above which it tended to plateau. Glipizide augmented the first-phase insulin response without changing the slope of the regression line relating plasma insulin to glucose concentrations. The second-phase plasma insulin response (20–120 min) increased linearly with increasing hyperglycaemia (r=0.997). Glipizide alone increased the plasma insulin response by 180 pmol/l. A similar increase in plasma insulin response following glipizide was observed at each hyperglycaemic step, indicating that glipizide did not affect the sensitivity of the β-cell to glucose. First-phase insulin secretion was reduced in the type 2 (non-insulin-dependent) diabetic patients, and was not influenced by glipizide. The dose-response curve relating second-phase insulin secretion to the ambient plasma glucose concentration was significantly (P〈0.001) flatter in the diabetic patients than in the control subjects. Glipizide alone increased the plasma insulin response by 60 pmol/l without changing the slope of the dose-response curve. It is concluded that, in both type 2 diabetic patients and healthy subjects: (A) sulphonylurea augments glucose-stimulated second-phase insulin secretion without changing the sensitivity of the β-cell to glucose; (B) first-phase insulin secretion is reduced in non-insulin-dependent diabetic patients with fasting hyperglycaemia and is not influenced by sulphonylurea.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00579720
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  • 16
    Digitale Medien
    Digitale Medien
    Immunohistochemical colocalization of insulin, aromatic L-amino acid decarboxylase and dopamine beta-hydroxylase in islet B cells of chicken pancreas (1991)
    Springer
    Cell & tissue research 263 (1991), S. 131-136 
    Details
    ISSN: 1432-0878
    Schlagwort(e): B cells ; Insulin ; Catecholamine ; synthesizing enzymes ; Immunohistochemistry ; Chicken
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The identity of the monoamine which produces a very weak formaldehyde-induced fluorescence in some pancreatic islet cells was studied by fluorescence microscopy and immunohistochemistry either on the same tissue section or on serial tissue sections of tissue from male chickens. Pancreatic islet cells showing this very weak formaldehyde-induced fluorescence react immunohistochemically with antisera directed against insulin, aromatic L-amino acid decarboxylase and dopamine beta-hydroxylase and therefore appear to be islet B cells producing insulin and noradrenaline.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00318408
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  • 17
    Digitale Medien
    Digitale Medien
    The endocrine pancreas of glucagon-and somatostatin-immunized rabbits (1991)
    Springer
    Cell & tissue research 265 (1991), S. 261-273 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Endocrine pancreas ; Immunization ; Insulin ; Glucagon ; Somatostatin ; Electron microscopy ; Rabbit (Chinchilla, Ch: b Ch)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary An active or passive immunization against hormones and the subsequent neutralization of hormones by circulating antibodies is a valuable tool for the identification of hormonal action. To recognize presumed local (autocrine, paracrine) effects exerted by pancreatic hormones, the endocrine pancreas of rabbits was investigated electron-microscopically after long-term immunization against glucagon or somatostatin. Glucagon immunization resulted in hyperplasia and hypertrophy of glucagon- (A-) cells and in their increased metabolic activities: They showed prominent nucleoli, increased amounts of endoplasmic reticulum, Golgi areas, and mitochondria. These changes were paralleled by alterations in secretion granules (increased size, decreased hormonal content), increased numbers of lysosomes (crinophagic bodies), and an increment of the filamentous system. Basically, these findings point to an autocrine regulation of A-cells. Following somatostatin immunization, somatostatin- (D-) cells were hyperplastic but unchanged in their metabolic state. Instead, insulin-(B-) cells and A-cells exhibited equivalents of increased cellular activities (parameters, see above). This stimulation most probably is caused by cancelled paracrine (inhibitory) effects of somatostatin. The changes observed after both immunizations were differently expressed in morphologically heterogeneous islet types (size, angioarchitecture, cellular composition, microtopology of the various cell types). It is concluded, therefore, that the regulation of islets is not uniform. Autocrine and paracrine effects exerted by islet hormones are of different significance in individual islets, or they interfere differently with other regulatory signals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00398074
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  • 18
    Digitale Medien
    Digitale Medien
    Effects of carbohydrate type on postprandial blood pressure, neuroendocrine and gastrointestinal hormone changes in the elderly (1991)
    Springer
    Clinical autonomic research 1 (1991), S. 219-224 
    Details
    ISSN: 1619-1560
    Schlagwort(e): Postprandial hypotension ; Elderly ; Carbohydrate ; Neurotensin ; Catecholamines ; Insulin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Previous studies have demonstrated that blood pressure falls postprandially in fit elderly subjects, the greatest changes occurring after meals with a high carbohydrate content. To evaluate the influence of the type of carbohydrate on postprandial blood pressure, the effects of equivalent energy content (2.4 MJ) high complex (starch) and high simple (monosaccharide) carbohydrate meals were studied in seven healthy elderly subjects. Blood pressure, heart rate, autonomic function, plasma catecholamines, insulin and neurotensin levels were measured pre- and postprandially. Greater falls in supine and erect systolic blood pressure occurred after the high simple than the high complex carbohydrate meal (p 〈 0.05). No differences were found in supine or erect diastolic blood pressure, heart rate or in any of the biochemical parameters measured between the meal types. It is concluded that a simple carbohydrate meal results in a greater postprandial fall in blood pressure than an equivalent energy complex carbohydrate meal in the elderly, although the mechanisms for these changes are unknown.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01824990
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  • 19
    Digitale Medien
    Digitale Medien
    Glucoregulatory hormones in man at high altitude (1991)
    Springer
    European journal of applied physiology 62 (1991), S. 286-291 
    Details
    ISSN: 1439-6327
    Schlagwort(e): High altitude ; Cortisol ; Insulin ; Growth hormone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Concentrations of glucose, lactic acid, free fatty acid (FFA), insulin, cortisol and growth hormone (GH) in the blood were monitored in 15 euglycaemic men (sojourners, SJ) at sea level (SL) and while at altitudes of 3500 m and 5080 m, in acclimatised low landers (ALL) and in high altitude natives (HAN). In SJ, blood glucose and insulin concentrations showed a significant increase on the 3rd and 7th day after arrival at high altitude (HA), thereafter returning to sea level values and remaining the same during the entire period of their stay at 3500 m. Subsequently, on arrival at higher altitude (5080 m) the glucose concentrations again showed an increase over the preceding values and returned to SL values on day 41 while at 5080 m. A significant increase in cortisol concentrations was seen on day 3 after arrival at HA and the increased levels were maintained until day 21 at 3500 m. The cortisol concentrations on day 30 after arrival at 5080 m came down to SL values and remained unchanged thereafter. No appreciable change in GH and FFA was seen during the sojourn at HA. On the other hand, blood lactic acid concentration decreased significantly. There was no difference between the fasting glucose concentrations in ALL at 3500 m and in HAN at 3500 m and 4200 m compared to values of SJ at SL, whereas ALL at 4200 m had higher glucose values. Concentrations of plasma insulin and GH in ALL and HAN were higher than the values of SJ at SL, whereas cortisol values did not show any difference. These observations indicated that at HA the glucose values were high for the insulin concentration observed and might have been due to increased secretion of GH by the pituitary gland.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00571554
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  • 20
    Digitale Medien
    Digitale Medien
    Training effects of cross-country skiing and running on maximal aerobic cycle performance and on blood lipids (1991)
    Springer
    European journal of applied physiology 62 (1991), S. 400-404 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Endurance conditioning ; Aerobic fitness ; Lipoproteins ; Insulin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Two experiments were carried out to compare the cardiorespiratory and metabolic effects of cross-country skiing and running training during two successive winters. Forty-year-old men were randomly assigned into skiing (n = 15 in study 1,n = 16 in study 2), running (n = 16 in study 1 andn = 16 in study 2) and control (n = 17 in study 1 andn = 16 in study 2) groups. Three subjects dropped out of the programme. The training lasted 9–10 weeks with 40-min exercise sessions three times each week. The training intensity was controlled at 75%–85% of the maximal oxygen consumption (VO2max) using portable heart rate metres and the mean heart rate was 156–157 beats·min−1 in the training groups. In the pooled data of the two studies the mean increase in theVO2max (in ml·min−1·kg−1) on a cycle ergometer was 17% for the skiing group, 13% for the running group and 2% for the control group. The increase inVO2max was highly significant in the combined exercise group compared to the control group but did not differ significantly between the skiing and running groups. The fasting serum concentrations of lipoproteins and insulin did not change significantly in any of the groups. These results suggested that training by cross-country skiing and running of the same duration and intensity at each session for 9–10 weeks improved equally the cardiorespiratory fitness of untrained middle-aged men.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00626610
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  • 21
    Digitale Medien
    Digitale Medien
    Effects of supramaximal exercise on blood glucose levels during a subsequent exercise (1991)
    Springer
    European journal of applied physiology 63 (1991), S. 48-51 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Insulin ; Hyperglycemia ; Hyperinsulinemia ; Human subjects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The purpose of the present investigation was to examine the effects of hyperglycoemia induced by supramaximal exercise on blood glucose homeostasis during submaximal exercise following immediately after. Six men were subjected to three experimental situations; in two of these situations, 3 min of high-intensity exercise (corresponding to 112, SD 1%VO2 max) was immediately followed by either a 60-min period of submaximal exercise (68, SD 2%VO2 max) or a 60-min resting period. In the third situation, subjects performed a 63-min period of submaximal exercise only. There were no significant differences between the heurt rates, oxygen uptakes, and respiratory exchange ratios during the two submaximal exercise bouts (〉 15 min) whether or not preceded by supramaximal exercise. The supramaximal exercise was associated within 10 min of the start increases (P〈0.05) in blood glucose, insulin, and lactate concentrations. This hyperglycemia was more pronounced when subjects continued to exercise submaximally than when they rested (at 7.5 min;P〈0.05). There was a more rapid return to normal exercise blood glucose and insulin values during submaximal exercise compared with rest. The data show that the hyperinsulinemia following supramaximal exercise is corrected in between 10–30 min during submaximal exercise following immediately, suggesting that this exercise combination does not lead to premature hypoglycemia.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00760800
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  • 22
    Digitale Medien
    Digitale Medien
    Thermogenic effect of adrenaline: interaction with insulin (1991)
    Springer
    European journal of applied physiology 63 (1991), S. 417-423 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Energy expenditure ; Thermogenesis ; Epinephrine ; Insulin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The contribution of insulin (3.6 pmol sd kg body mass−1·min−1 to adrenaline-induced (0.164 nmol · kg fat free mass−1·min−1) thermogenesis was studied in ten postabsorptive healthy volunteers using two sequential protocols. Variables considered were oxygen consumption as well as carbon dioxide production, heart rate, blood pressure, plasma concentrations of glucose, insulin, glycerol, free fatty acids,β-HO-butyrate and lactate. Adrenaline increased plasma concentrations of glucose, glycerol, free fatty acids, andβ-HO-butyrate, and heart rate and metabolic rate during normo-insulinaemia [61.3 (SEM 6.6) pmol·−1]. Similar effects were observed during hyperinsulinaemia [167.9 (SEM 18.7) pmol·−1], but the effect of adrenaline on oxygen consumption was reduced. On average, metabolic rate increased by 12.9% during normo-insulinaemia and by 8.9% during hyperinsulinaemia. We concluded that relative hyperinsulinaemia resulted in decreased adrenaline-induced thermogenesis and therefore increased whole body anabolism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00868072
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  • 23
    Digitale Medien
    Digitale Medien
    Effects of muscarinic blockade on the thermic effect of oral or intravenous carbohydrate (1991)
    Springer
    European journal of applied physiology 63 (1991), S. 242-249 
    Details
    ISSN: 1439-6327
    Schlagwort(e): Atropine ; Glucose ; Fructose ; Dietary thermogenesis ; Insulin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Muscarinic blockade by atropine has been shown to decrease the thermic effect of a mixed meal, but not of intravenous glucose. To further delineate the mechanisms involved in the atropine-induced inhibition of thermogenesis after a meal, plasma substrate and hormone concentrations, energy expenditure (EE) and substrate oxidation rates were measured before and during a continuous glucose infusion (44.4 μmol·kg−1·min−1) with or without atropine. After 2 h of glucose infusion, a 20-g oral fructose load was administered while the glucose infusion was continued. Plasma insulin concentrations attained a plateau at 596 (SEM 100) pmol·l−1 after 120 min of glucose infusion and were not affected by muscarinic blockade; plasma glucose concentrations peaked at 13.3 (SEM 0.5) mmol·l−1 at 90 min and decreased progressively thereafter; no difference was observed with or without atropine. Plasma free fatty acid and glucagon concentrations, with or without atropine, were both decreased to 201 (SEM 18) μmol·l−1 and 74 (SEM 4) ng·l−1, respectively, after 2 h of glucose infusion, and were not further suppressed after oral fructose. Carbohydrate oxidation rates (CHOox) increased to 20.8 (SEM 1.4) μmol·kg−1·min−1 and lipid oxidation rates (Lox) decreased to 1.5 (SEM 0.3) μmol·kg−1·min−1 between 90 and 120 min after the beginning of glucose infusion and were not affected by atropine. Glucose-induced thermogenesis was similar with [6.5% (SEM 1.4%) of basal EE] or without [6.0% (SEM 1.0%), NS) muscarinic blockade during the 30 min preceding fructose ingestion. During the second half-hour after fructose ingestion, atropine infusion inhibited markedly the stimulation of CHOox [+2.8 (SEM 1.0) μmol·kg−1·min−1 vs +6.9 (SEM 1.0) μmol·kg−1·min−1, saline, P〈0.02] and the suppression of Lox [−0.8 (SEM 0.2) μmol·kg−1·min−1 vs −1.4 (SEM 0.2) μmol·kg−1·min−1, saline, P〈0.05]. Carbohydrate-induced thermogenesis during the second half-hour after fructose ingestion, increased to 13.0% (SEM 2.0%) without atropine and was suppressed to 7.7% (SEM 1.9%) (P〈 0.05, vs saline) with atropine. It was concluded that muscarinic blockade suppressed the increase of thermogenesis observed after oral fructose, but not during intravenous glucose infusion and that this suppression occurred independently of alterations of plasma insulin concentrations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00233855
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  • 24
    Digitale Medien
    Digitale Medien
    Bioreductive activation of quinones: A mixed blessing (1991)
    Springer
    Pharmacy world & science 13 (1991), S. 123-126 
    Details
    ISSN: 1573-739X
    Schlagwort(e): Alkylation ; Antineoplastic agents ; Biochemistry ; Cytotoxicity ; Oxidation-reduction ; Quinones
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Quinones can be metabolized by various routes: substitution or reductive addition with nucleophilic compounds (mainly glutathione and protein thiol groups), one-electron reduction (mainly by NADPH: cytochrome P-450 reductase) and two-electron reduction (by D,T-diaphorase). During reduction semiquinone radicals and hydroquinones are formed, which can transfer electrons to molecular oxygen, resulting in the formation of reactive oxygen intermediates and back-formation of the parent quinone (redox cycling). Reaction of semiquinones and reactive oxygen intermediates with DNA and other macromolecules can lead to acute cytotoxicity and/or to mutagenicity and carcinogenicity. The enhanced DNA-alkylating properties of certain hydroquinones are exploited in the bioreductive alkylating quinones. Acute cytotoxicity of quinones appears to be related to glutathione depletion and to interaction with mitochondria and subsequent disturbance of cellular energy homoeostasis and calcium homoeostasis. These effects can to a certain extent be predicted from the electron-withdrawing and electron-donating effects of the substituents on the quinone nucleus of the molecule. Prediction of cytostatic potential remains much more complicated, because reduction of the quinones and the reactivity of the reduction products with DNA are modulated by the prevailing oxygen tension and by the prevalence of reducing enzymes in tumour cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01981528
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  • 25
    Digitale Medien
    Digitale Medien
    Effects of ossein-hydroxyapatite compound on ewe bone remodeling: Biochemical and histomorphometric study (1991)
    Springer
    Clinical rheumatology 10 (1991), S. 269-273 
    Details
    ISSN: 1434-9949
    Schlagwort(e): Ossein-Hydroxyapatite Compound ; Bone Remodeling ; Biochemistry ; Histomorphometry ; Ewe
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Ossein-hydroxyapatite compound (OHC) is a protein-mineral complex derived from bovine bone. Its effects on bone remodeling were studied in old ewes which have seasonal variations in bone remodeling. Seven animals received 200 mg OHC/kg b.w./day for 90 days from July to September. The control group consisted of 7 untreated animals followed for the same period of time. OHC was administered through a fistula into the fourth stomach. A significant decrease of bone histomorphometric parameter values was noted in controls at the end of the experiment, due to seasonal variations: the cancellous eroded perimeter decreased by 45%, the osteoblastic perimeter by 60% and the bone formation rate at the cell level by 20%. In contrast, in the treated-group, these parameters tended to increase or did not change. In conclusion, counteracting the significant seasonal reduction of bone remodeling in ewes, OHC seems able to stimulate directly or indirectly bone metabolism, especially when osteoblast activity is reduced and may partly prevent the seasonal reduction of bone turnover.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02208688
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  • 26
    Digitale Medien
    Digitale Medien
    A New General Synthesis of 2,2-Dialkyl-2,3-dihydro-4H-pyran-4-ones and Their Application for the in situ Preparation of Electron-Rich Dienes in Carbonyl-Alkyne Exchange Reactions with AcetylenesPresented in part at the autumn meeting of the Swiss Chemical Society in Bern on October 20, 1989. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 27-46 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The substituted 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones of type II and III have been prepared by acid-catalyzed cyclization of the corresponding substituted acetylenic ketones I in good to excellent yields (Scheme 1). These 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones II and III have been used for the in situ preparation of highly reactive dienes of type IV-VI (Scheme 2) in carbonyl-alkyne exchange reactions with electron-poor alkynes VII to yield the highly substituted aromatic compounds VIII and IX. These reactions proceed in good yields and with excellent degree of regioselectivity. Aryl-substituted 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones III (R1 = Ar) subsequently yield highly substituted biaryls. Reaction mechanisms are presented for the formation of the 2,2-dialkyl-2,3-dihydro-4H-pyran-4-ones as well as for the carbonyl-alkyne exchange reactions with electron-poor acetylenes.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740106
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  • 27
    Digitale Medien
    Digitale Medien
    Structural and Luminescence Study of the 3:2 Complex between Europium Nitrate and the B Isomer of Dicyclohexyl-18-crown-6Part 40 of the series ‘Complexes of Lanthanoid Salts with Macrocyclic Ligands’; Part 39 [1]. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 65-78 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal and molecular structure of bis[dinitrato-(2,4,8,15,18,21-hexaoxatricyclo[20.4.0.09,14]hexacosane)europium(III)]pentakis(nitrato)europiate(III) [Eu(NO3)2LB]2([Eu(NO3)5]), has been determined at 170 K from single-crystal X-ray diffraction. The complex crystallizes in the monoclinic space group P21/n (ITC No. 14): a = 16.338(3) Å, b = 15.704(3) Å, c = 24.474(4) Å, β = 97.73(1)°, Z = 4. The structure was refined to a final R value of 0.058 (Rw = 0.060). The asymmetric unit contains three independent ions lying on general positions: [Eu(NO3)5]2- and two distinct [Eu(NO3)2LB]+ cations with the macrocyclic ligand in the cis-anti-cis conformation (B-isomer). The EuIIIions are 10-coordinate with the following mean bond lengths: Eu-O(nitrate) = 2.48(2) Å in the anion and 2.45(2) Å in the two cations, Eu-O(ether) = 2.56(8) and 2.55(5) Å. Small but significant differences are observed between the two complex cations, especially with respect to the positions of the cyclohexyl substituent. A conformational analysis performed on the six O-atoms of the complex cations confirms the predictions of a simple model. The metal ion sites of the complex have been probed by high-resolution excitation and emission spectra at 296 and 77 K. The 5D0←7F0 excitation spectrum displays two main bands along with several other minor components. A detailed analysis of the corresponding and selectively excited emission spectra leads to the observation of three types of spectra corresponding to the three crystallographically different EuIII ions. Moreover, three minor sites are identified, one anionic and two cationic, with a population equal to ca. 10% of the population of the main sites. We interpret this finding as reflecting the presence of molecules with slightly different conformations.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740109
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  • 28
    Digitale Medien
    Digitale Medien
    Asymmetric Diels-Alder Cycloadditions with C2-Symmetrical Chiral Carbamoylnitroso Dienophiles (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 103-109 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The C2-symmetrical chiral pyrrolidines 2 and 3 are of opposite helicity. The corresponding N-acylnitroso dienophiles 6 and 7 react in good yield with cyclohexadiene, leading thereby with excellent diastereoisomeric excess to the expected Diels-Alder cycloadducts (see Scheme). The [2.2.2] bicyclic moieties of the major diastereoisomers 9 and 11 proved to be of opposite configuration, as expected. Their configuration is best explained by assuming the acylnitroso dienophile to be in the s-cis conformation in the transition state, the approach of the diene being endo (see Fig.).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740112
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  • 29
    Digitale Medien
    Digitale Medien
    2,3- and 4,5-Secodopa, the Biosynthetic Intermediates Generated from L-Dopa by an Enzyme System Extracted from the Fly Agaric, Amanita muscaria L., and Their Spontaneous Conversion to Muscaflavin and Betalamic Acid, Respectively, and Betalains (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 124-140 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An enzyme is extracted from the red peel of Amanita muscaria which cleaves the C(2)-C(3) and the C(4)-C(5) bond of the aromatic ring of L-dopa (1) to form a mixture of 4,5-secodopa (= salt of 6-amino-2-hydroxy-4-(2′-oxoethylidene)hept-2-enedioic acid; 2) and 2,3-secodopa ( = salt of 7-amino-5-formyl-2-hydroxyocta-2,4-dienedioic acid; 3), two hitherto hypothetical biosynthetic intermediates (see Scheme). Though isolation of these products has not been possible, structural evidence is inferred from reaction products, kinetics, and spectroscopical characteristics in comparison with known compounds. Secodopas 2 and 3 are characterized in dilute solution by HPLC and UV/VIS spectroscopy (anions; λmax 424 and 414 nm, resp., ∊420 = 25500; on acidification, shift to 380 and 372 nm, resp.). They cyclize without enzyme catalysis, optimally at pH 4.5-5; 3 produces muscaflavin (5) and 2 betalamic acid (4). The products arc identified by direct comparison with authentic samples in HPLC, by 1H-NMR of 5, and by condensation of 4 with L-proline to form the well known betalain indicaxanthin (7). The enzymatic conversion of L-dopa (1) via 2 to betalamic acid (4; (S)) and its condensation with L-proline leads to pure natural indicaxanthin (7; (2S,115)); correspondingly, the enzymatic conversion of D-dopa to (R)-betalamic acid and its condensation with L-proline produces isoindicaxanthin ((2S,11R)) which is unknown in nature. Particularly relevant is the fact that the same enzyme cleaves pyrocatechol to produce a solution of the enolate form of the known 2-hydroxy-6-oxohexa-2,4-dienoate (secopyrocatechol; 9; see Fig. 5). Dissociation constants of the corresponding enolic functions in the cleavage products are determined by spectrometric titration and compared to those of known systems.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740115
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  • 30
    Digitale Medien
    Digitale Medien
    Photochemical Reactions of Tetrahydroquinoxalin-2(1H)-ones and Related Compound (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 225-231 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Photochemical behaviors of the pyrazinone derivatives 5,6,7,8-tetrahydroquinoxalin-2(1H)-ones 1a-c and 1,5,6,7,8,9-hexahydro-2H-cyclohepta[b]pyrazin-2-one 1d were investigated. Dye-sensitized photo-oxygenation of 1a-c gave the 1:1 adducts 5a-c of the corresponding 3,8a-epidioxy-3,5,6,7,8,8a-hexahydroquinoxalin-2(1H)-one 4 and H2O, whereas 1d gave 3,9a-epidioxy-1,3,5,6,7,8,9,9a-octahydro-2H-cyclohepta[b]pyrazin-2-one 4d (Scheme 2). The different kind of products was interpreted as being the result of the ring strain and steric hindrance of endoperoxides produced from 1a-d with singlet oxygen. Irradiation of 1a-b in the presence of alkenes gave tricyclic azetidine derivatives 9 by [2 + 2] cycloaddition of the C=N bond of 1 to the alkene.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740122
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  • 31
    Digitale Medien
    Digitale Medien
    Analogues of Sialic Acids as Potential Sialidase Inhibitors. Synthesis of C6 and C7 Analogues of N-Acetyl-6-amino-2,6-dideoxyneuraminic Acid (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 343-369 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The piperidines 12-18, piperidmose analogues of Neu5Ac (1) with a shortened side chain, were synthesized from N-acetyl-D-glucosamine via the azidoalkene 32 and tested as inhibitors of Vibrio cholerae sialidase. Deoxygenation at C(4) of the uronate 22, obtained from the known D-GlcNAc derivative 20, was effected by β-elimination (→ 23), exchange of the AcO at C(3) with a (t-Bu)Me2SiO group and hydrogenation (→ 26; Scheme 1). Chain extension of 26 by reaction with Me3SiCH2MgCl gave the D-ido-dihydroxysilane 28, which was transformed into the unsaturated L-xylo-mesylate 29 and further into the L-lyxo-alcohol 30, the mesylate 31, and the L-xylo-azide 32. The derivatives 29-31 prefer a sickle zig-zag and 32 mainly an extended zig-zag conformation (Fig. 2). The piperidinecarboxylate 15 was obtained from 32 by ozonolysis (→ 33), intramolecular reductive animation (→ 34), and deprotection, while reductive animation of 34 with glycolaldehyde (→ 35) and deprotection gave 16 (Scheme 2). An intramolecular azide-olefin cycloaddition of 32 yielded exclusively the fused dihydrotriazole 36, while the lactone 39 did not cyclize (Scheme 3). Treatment of 36 with AcOH (→ 37) followed by hydrolysis (→ 38) and deprotection led to the amino acid 18. To prepare the (hydroxymethyl)piperidinecarboxylates 12 and 17, 32 was first dihydroxylated (Scheme 4). The L-gluco-diol 40 was obtained as the major product, in agreement with Kishi's rule. Silylation of 40 (→ 42), oxidation with periodinane (→ 44), and reductive animation gave the L-gluco-piperidine 45. It was, on the one hand, deprotected to the amino acid 12 and, on the other hand, N-phenylated (→ 46) and deprotected to 17. While 45 and 12 adopt a 2C5 conformation, the analogous N-Ph derivatives 46 and 17 adopt a 5C2 and a B3,6 conformation, respectively, on account of the allylic 1,3-strain. The conformational effects of this 1,3-strain are also evident in the carbamate 47, obtained from 45 (Scheme 5), and in the C(2)-epimerized bicyclic ether 48, which was formed upon treatment of 47 with (diethylamino)sulfur trifluoride (DAST). Fluorination of 40 with DAST (→ 49) followed by treatment with AcOH led to the D-ido-fluorohydrin 50. Oxidation of 50 (→ 51) followed by a Staudinger reaction and reduction with NaBH3CN afforded the (fluoromethyl)piperidine 52, while reductive amination of 51 with H2/Pd led to the methylpiperidine 55, which was similarly obtained from the keto tosylate 54 and from the dihydrotriazole 36. Deprotection of 52 and 55 gave the amino acids 13 and 14, respectively. The aniline 17 does not inhibit V. cholerae sialidase; the piperidines 12-16 and 18 are weak inhibitors, evidencing the importance of an intact 1,2,3-trihydroxypropyl side chain.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740214
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  • 32
    Digitale Medien
    Digitale Medien
    Synthese von Monomorin I, einem Spurpheromon der Pharao-Ameise (Monomorium pharaonis) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 438-444 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis of Monomorin I, a Trail Pheromone of the Pharao Ant (Monomorium pharaonis)Katalytic hydrogenation of the 4-nitroalkanone 5 yielded the cis-pyrrolidine ester 6 (Scheme). The preparation of 5 was accomplished by ethanolysis of the nitrocyclohexanone derivative 4. Iodination at C(α) of 6, followed by cyclization, gave a nearly 5:6 mixture of the two C(5)-epimers 10/9 of octahydroindolizine. Epimerisation of the undesired 10 to 9 and subsequent transformation of the latter gave racemic monomorine I (1; 34% yield from 5).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740221
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  • 33
    Digitale Medien
    Digitale Medien
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740301
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  • 34
    Digitale Medien
    Digitale Medien
    Structure cristalline d'une thiazolorifamycine: rifamycine P (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 326-330 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Crystal Structure of a Thiazolorifamycine: Rifamycine PThe crystal structure of a natural thiazolorifamycin, rifamycin P, as an adduct with EtOH and H2O, has been determined by X-ray crystallography by a combination of direct methods and Patterson techniques. Block-diagonal least-squares refinement using 5996 independent reflections and 1475 parameters led to an R factor of 0.092 (two independent molecules of rifamycin P). The middle part of the ansa chain, essential for activity against the bacterial DNA-dependent RNA polymerase (DDRP) resembles that of active rifamycins. The four OH groups lie on the same side of the molecule and are almost in the same plane. Interatomic distances between the O-atoms agree well with a spatial model derived from X-ray studies, performed on semisynthetic active rifamycins.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740211
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  • 35
    Digitale Medien
    Digitale Medien
    Synthesis of 4-{{[(Isopropyloxy)methylphosphoryloxy]imino}methyl}-1-methylpyridinium Iodide and Its Characterisation (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 331-335 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oximes are used in the therapy of organophosphate poisoning. They form an interaction product with the organophosphate which is claimed to be more toxic than the organophosphate itself. We have synthesized one of these compounds which would be formed by the reaction of pyridine-4-carbaldehyde oxime methiodide with sarin (GB). Thus, reaction of oxime 1 with sarin chloridate (2), yielded 4-{{[(isopropyloxy)methylphosphoryloxy]-imino}methyl}-1-methylpyridinium iodide (4) which was characterized by NMR spectroscopy and X-ray crystallography.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740212
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  • 36
    Digitale Medien
    Digitale Medien
    Transformations in the Isoxazole Series: Synthesis of Substituted 2-AminothiazolesDedicated to Prof. Dr. Oskar Jeger (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 531-542 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Substitued N-(isoxazol-4-yl)thioureas 1 undergo a transformation in the presence of hexacarbonylmolybdenum and acid to yield functionalized thiazoles 3 in a one-pot reaction. In a few cases, 1,4,5-trisubstituted dihydroimidazolethiones 4 are also isolated as side products. Mechanistic considerations are outlined and scope and limitations of this new methodology discussed.
    Zusätzliches Material: 6 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740309
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  • 37
    Digitale Medien
    Digitale Medien
    Biosynthesis of the Spermine Alkaloid Aphelandrine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 565-571 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Aphelandrine (1) is shown to be biosynthesized in the root cells of Aphelandra tetragona (VAHL) NEES from labelled putrescine (4), spermidine (5), and cinnamic acid (3). Whether spermine (6) and the (p-hydroxycinnamoyl)spermidine 8 are precursors of 1 is uncertain, since the latter is hydrolysed to a large extent before incorporation, and the former is metabolized to 4 and 5. Methionine (7) is the source of the 3-aminopropyl unit of 5 and 6.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740313
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  • 38
    Digitale Medien
    Digitale Medien
    Glycosylidene Carbenes. Part 3. Synthesis of SpirocyclopropanesPresented at the ‘XVIth International Carbohydrate Symposium’, Yokohama, Japan, 12th-17th August 1990, Abstr. PL-05. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 585-593 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Thermolysis of the glycosylidene-derived O-benzylated diazirine 1 in the presence of N-phenylmaleimide (2), acrylonitrile (3), dimethyl fumarate (4), or dimethyl maleate (5) led in good yields to mixtures of the spirocyclopropanes 6/7, 8-11, 12/13, and 12/13/16/17. The diastereoselectivity depends upon the alkene. The cycloaddition of 1 to 5 is not diastereospecific, in keeping with previous results. Deprotection of 12, 13, 16, and 17 yielded the tetrols 14,15, 18, and 19, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740316
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  • 39
    Digitale Medien
    Digitale Medien
    Lithium-Salt Effects in Peptide Synthesis. Part II. Improvement of Degree of Resin Swelling and of Efficiency of Coupling in Solid-Phase Synthesis (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 628-643 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The course of solid-phase peptide-coupling reactions as well as the swelling properties of a peptide-resin are influenced by the addition of inorganic salts (LiCl, LiBr, LiClO4, KSCN). Used as additives, these salts can (i) improve coupling yields (e.g., for Fmoc-(Ala)5-Phe-resin → Fmoc-(AIa)6-Phe-resin in DMF/CH2Cl2 1:1 from 89.4 to 97.1% (for polyethylene oxide) on polystyrene (= PEO-PS) resin) or from 77.5 to 93.8% (for poly-(N,N′-dimethylacrylamide) on ‘Kieselgur’ (=PDMAA-KG) resin) without and with 0.4M LiCl, respectively), (ii) increase resin swelling (e.g. for Fmoc-(Ala)5-Phe-(polystyrene resin) from 2.42- to 5.73-fold in 1-methylpyrrolidin-2-one (=NMP) without and with LiCl, (respectively), and (iii) change coupling rates. Example;; of coupling reactions and swelling behaviour (degree and rate) in different solvents (DMF, DMF/CH2Cl2 1:1, THF, NMP, N,N-dimethylpropyleneurea (= DMPU) with and without salts) using different resins (polystyrene (PS); PEO-PS, and PDMAA-KG) and an improved analysis of alanine oligomers up to Ala12-Phe by HPLC and FAB-MS are reported.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740320
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  • 40
    Digitale Medien
    Digitale Medien
    On the Methyl-Transfer Reaction in Crystalline Methyl 2-(Methylthio)benzenesulfonate: a Thermally Induced Non-Topochemical Solid-State Reaction (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 662-669 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rearrangement of methyl 2-(methylthio)benzenesulfonate (1) to the zwitterionic 2-(dimethyl-sulfonium)benzenesulfonate (2) is known to proceed in solution by intermolecular Me transfers. The same rearrangement has been observed to occur in crystalline 1, but the crystal structure shows that the molecular packing is not conducive to intermolecular Me transfer. The reaction has been carried out with mixed crystals composed of 1 and deuteriomethylated (D6)-l. By fast-atom-bombardment mass spectroscopy, it has been shown that the product consists of a 1:2:1 mixture of the non-, tri-, and hexadeuterated species, the mixture expected, if the solid-state reaction proceeds by intermolecular Me transfers. From this result, together with the slower rates of conversion in the single crystal compared with the melt, it can be concluded that the reaction must occur not topochemically but rather at defects such as microcavities, surfaces, and other irregularities in the ordered crystal arrangement.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740323
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  • 41
    Digitale Medien
    Digitale Medien
    Syntheses and Crystal Structures of 4,5-Dihydro-2-(2′-hydroxyphenyl)oxazole-Containing Metal Complexes (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 717-726 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the complexes 3 of various metals ligated to chiral 4,5-dihydro-2-(2′-oxidophenyl-ϰO)oxazoles-ϰN is described (Scheme). Three of them, i.e. 3a, 3e, and 3f containing CuII, ZnII and NiII, respectively, were analyzed by X-ray diffraction studies. A series of CuII complexes (6a-d) with differently substituted dihydrooxazoles have been synthesized.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740405
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  • 42
    Digitale Medien
    Digitale Medien
    1-(2′-Deoxy-β-D-xylofuranosyl)thymine Building Blocks for Solid-Phase Synthesis and Properties of Oligo(2′-Deoxyxylonucleotides) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 748-760 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1-(2′-Deoxy-β-D-threo-pentofuranosyl)thymine (= 1-(2′-deoxy-β-D-xylofuranosyl)thymine; xTd; 2) was converted into its phosphonate 3b as well as its 2-cyanoethyl phosphoramidite 3c. Both compounds were used for solid-phase synthesis of d[(xT)12-T] (5), representing the first DNA fragment build up from 3′-5′-linked 2′-deoxy--β-D-xylonucleosides. Moreover, xTd was introduced into the innermost part of the self-complementary dodecamer d(G-T-A-G-A-A-xT-xT-C-T-A-C)2 (9). The CD spectrum of d[(xT)12-T] (5) exhibits reversed Cotton effects compared to d(T12) (6; see Fig. 1), implying a left-handed single strand. With d(A12) (7) it could be hybridized to form a propably Left-handed double strand d(A12) · d[(xT)12-T] (7·5) which was confirmed by melting experiments in combination with temperature-dependent CD spectroscopy. While 5 was hydrolyzed by snake-venom phosphodiesterase, it was resistant towards calf-spleen phosphodiesterase. The modified, self-complementary duplex 9 was hydrolyzed completely by snake-venom phosphodiesterase, at a twelvefold slower rate compared to unmodified 8; calf-spleen phosphodiesterase hydrolyzed 9 only partially.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740408
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  • 43
    Digitale Medien
    Digitale Medien
    Conformational Analysis of Marine Polyhalogenated β-Chamigrenes Through Temperature-Dependent NMR SpectraPresented in part by G.G. at both CISCI 90, S. Benedetto del Tronto, 30 September-5 October 1990, and the Congresso Nazionale di Risonanze Magnetiche, Pisa, 22-24 October 1990. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 774-786 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Temperature-dependent 1H- and 13C-NMR spectra reveal that polyhalogenated marine β-chamigrenes or synthetic derivatives thereof which are trans-diequatorially, substituted at C(8) and C(9), such as rogiolol ((-)-2), obtusol ((+)-3), and their acetates (+)-1 and (-)-4, undergo slow ring-A chair-chair inversion. Conformational equilibria and kinetics are investigated with the aid of synthetic model compounds and molecular-mechanics calculations. Thus, steric repulsions between Brax-C(2) and Heq-C(7) are seen to disfavour thermodynamically conformers 1b, 2b, 3b, and 4b, which can only be detected through cross-saturation transfer, while additional steric repulsions between Meax-C(1) and OHax-C(3) make conformer 8b of obtusol epimer so scarcely populated that it can not be detected. In agreement, with (+)-9 and (+)-10, which have a trigonal C(2), two conformers can be directly observed by NMR. The kinetic barriers, which are seen to arise mainly from steric repulsions between Hax-C(14) and the axial H or halogen atoms at C(8) and C(10), are calculated and discussed with respect to well documented exocycliemethylidene-substituted cyclohexane(ene) systems. This helps to rationalize why in rogiolol acetate ((+)-1) ring B is unusually inert towards Zn/Et2O/AcOH which causes bromohydrine-group elimination from ring A.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740411
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  • 44
    Digitale Medien
    Digitale Medien
    Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3,6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotin-5,5′-diol), ein neues Carotinoid aus Paprika (Capsicum annuum) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 819-824 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3.6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-5,5′-diol), a Novel Carotenoid from Red Paprika (Capsicum annuum)From red paprika (Capsicum annuum var. longum nigrum) cycloviolaxanthin was isolated as a minor carotenoid and, based on spectral data, assigned the symmetrical structure 8.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740416
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  • 45
    Digitale Medien
    Digitale Medien
    Studies Directed Towards the Biosynthesis of the C7N Unit of Rifamycin B: A New Synthesis of Quinic Acid from Shikimic Acid (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 807-818 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of quinic acid (4) via epoxide 13, starting from shikimic acid (5), is described (Scheme 1). Treatment of 13 with thiophenol yielded not only 17, but also the γ-lactones 18 and 19 as result of migration of silyl groups within a cis- and trans-diol system. The conversion provides a direct stereoselective epoxidation of a shikimic-acid derivative as well as an alternative pathway for the preparation of 4. A shorter approach via the disilylated epoxide 22 was unsuccessful because the γ-lactone 25 was obtained in place of the desired α-hydroxy ester 24 (Scheme 2).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740415
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  • 46
    Digitale Medien
    Digitale Medien
    Nucleotides. Part XXXVIPart XXXV:[1]. Syntheses and biological characterization of phosphorothioate analogues of (3′-5′)adenylate trimer (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 892-898 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The four protected diastereoisomcrs 7a/7b and 8a/8b P-thioadenylyl-(3′-5′)-P-thioadenylyI-(3′-5′)-adenosine were synthesized, separated, and deblocked to the free oligonucleotides (Scheme). Biochemical characterization of these (3′-5′)phosphorothioate analogues of adenyiate trimer indicate that these compounds, and the corresponding 5′-monophosphates, neither bind to nor activate RNase L, and are considered to be valuable control compounds in screening experiments.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740420
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  • 47
    Digitale Medien
    Digitale Medien
    Double-Diamond Inclusion Compounds of 2,6-Dimethylydeneadamantane-1,3,5,7-tetracarboxylic Acid (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 825-877 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal structures of four inclusion compounds of 2,6-dimethylideneadamantane-1,3,5,7-tetracarboxylic acid (4) are described, which involve the following guest species: (a) a mixture of 4-methylpent-3-en-2-one, 2,6-dimethylhepta-2,5-dien-4-one, and mesitylene (condensation products of acetone); (b) mesitylene; (c) a mixture of 4-methylpent-3-en-2-one and mesitylene; (d) (tert-butyl)benzene. In all four cases, the host architectures consist of two interpenetrating super-diamond networks built up by the tetra-acid molecules via pairwise H-bonds between the tetrahedrally directed COOH groups. In the first three cases (tetragonal crystal symmetry), the two diamond-like host lattices interpenetrate symmetrically, in the fourth case (monoclinic) asymmetrically. This asymmetry is brought about by the increased steric bulk of the (tert-butyl)benzene guest molecules. Attempts to enforce an inclusion compound of 4 with a single, extremely hollow diamond-like host lattice by offering still bulkier guest molecules have as yet not been met with success. The generally very high propensity of 4 to form inclusion compounds was envisaged and designed beforehand by appropriate evaluation and modulation of the crystal structure of the parent adamantane-1,3,5,7-tetracarboxylic acid, which represents a fivefold diamond-like self-inclusion compound. Crystals of the free, uncomplexed 4 appear to be extremely unstable and could so far not be obtained. On the other hand, from aqueous solution a very stable monohydrate of 4 may be crystallized (4-H2O), which was also subjected to X-ray analysis. The (triclinic) crystal structure of 4·H2O involves an interesting dichotomy inasmuch its pattern of H-bonding may be rationalized either in terms of a double, cross-linked super-zincblende (sphalerite) architecture, or as a system of porous, puckered 4-connected sheets, which interpenetrate each other pairwise and are cross-linked by the H2O molecules. Various structure and (space group) symmetry characteristics of the supramolecular solid-state complexes reported here are highlighted by pointing out analogies with comparable structures retrieved from the literature.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740417
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  • 48
    Digitale Medien
    Digitale Medien
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740501
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  • 49
    Digitale Medien
    Digitale Medien
    Novel Antifungal Tetracyclic Compounds from Bauhinia rufescens LAM.Presented in part at the Meeting of the Swiss Chemical Society, Bern, 19th October 1990. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 791-799 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: As the root bark CH2Cl2 extract of Bauhinia rufescens showed antifungal activity in a bioassay with the plant pathogenic fungus Cladosporium cucumerinum, a phytochemical investigation was undertaken on material collected in Niger. Activity-guided fractionation of this extract, using different preparative chromatographic methods, allowed the isolation of the four new antifungal tetracyclic compounds 1-4. Their structures were established by 1H- and 13C-NMR data, and single-crystal X-ray analyses were used to confirm the structures of 1 and 3. The isolated compounds seem to be biogenetically related to a stilbene.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740413
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  • 50
    Digitale Medien
    Digitale Medien
    Versatile Stereoselective Synthesis of Completely Protected Trifunctional α-Methylated α-Amino Acids Starting from Alanine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 800-806 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new route to completely protected α-methylated α-amino acids starting from alanine is described (see Scheme). These derivatives, which are obtained via base-catalyzed opening of the oxazolidinones (2S,4R)- and (2R,4S)-2, can be directly employed in peptide synthesis. The synthesis of both enantiomers of Z-protected α-methylaspartic acid β-(tert-butyl)ester (O4-(tert-butyl) hydrogen 2-methylaspartates (R) or (S)-4a), α-methyl-glutamic acid γ-(tert-butyl) ester (O5-(tert-butyl) hydrogen 2-methylglutamate (R)- or (S)-4b), and of Nε-bis-Boc-protected α-methyllysine (N6,N6-bis[(tert-butyloxy)carbonyl]-2-methyllysine (R)- or (S)-4c) is described in full detail.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740414
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  • 51
    Digitale Medien
    Digitale Medien
    Nucleotides. Part XXXVPart XXXV:[1]. Synthesis of 3′-deoxyadenylyl-(2′-5′)-3′-deoxyadenyIyl-(2′-ω)-9-(ω-hydroxyalkyl)adenines (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 887-891 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Via the phosphotriester approach, new structural analogs of (2′-5′)oligoadenyiates, namely 3′-deoxyadenylyl-(2′-5′)-3′-dcoxyadenylyl-(2′-ω)-9-(ω-hydroxyalkyl)adenines 18-21, have been synthesized (see Scheme) which should preserve biological activity and show higher stability towards phosphodiesterases. The newly synthesized oligonucleotides 18-21 have been characterized by 1H-NMR spectra, TLC, and HPLC analysis.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740419
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  • 52
    Digitale Medien
    Digitale Medien
    Mitteilungen (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 905-906 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740423
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  • 53
    Digitale Medien
    Digitale Medien
    [5-Leucin]enkephalin-Related Glycoconjugates: Structurally Novel Agents Effective against HIV-1 (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 951-955 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of [Leu5]enkephalin-related glycoconjugates with an ester-, ether-, or amide-type linkage were synthesized and evaluated for antiviral activity against HIV-1 in a cell-culture system using peripheral blood lymphocytes. All tested glycoconjugates exhibited a certain antiviral activity which was significantly higher than the activity of the parent peptide compound itself. These results indicate that synthetic glycoconjugates of opioid peptides are good candidates for the development of anti-HIV agents.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740505
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  • 54
    Digitale Medien
    Digitale Medien
    Synthesis, Isolation, and Full Spectroscopic Characterization of Eleven (Z)-Isomers of (3R,3′R)-Zeaxanthin (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 969-982 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Developmental efforts to improve the yield of the chemical synthesis of (3R,3′R)-zeaxanthin resulted in the isolation, partly by chromatography from reaction mixtures, and full spectroscopic characterization by 1H-NMR, UV/VIS, and CD spectrosocpy of eleven (Z/E)-isomers of zeaxanthin: (7Z)-, (9Z), (13Z)-, (15Z)-, (7Z,7′Z)-, (9Z,9′Z)- (7Z,9Z,7Z)-, (7Z,11Z,7′Z)-, (9Z,13Z,9′Z)-, (7Z,9Z,7′Z,9′Z)-, and (7Z,9Z,11Z,7′Z,9′Z)-zeaxanthin. Five of these isomers were obtained by specific synthesis, namely the (7Z)-, (7Z,7′Z)-, (9Z,9′Z)-, (7Z,9Z,7′Z)-, and (7Z,9Z,7′Z-9Z)-isomers.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740507
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  • 55
    Digitale Medien
    Digitale Medien
    Ringerweiterung von 1,2-Thiazol-3(2H)-on-1,1-dioxiden und 3-Amino-2H-azirinen zu 4H-1,2,5-Thiadiazocin-6-on-1,1-dioxiden (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1002-1010 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ring Enlargement of 1,2-Thiazol-3(2H)-one-1,1-dioxides and 3-Amino-2H-azirines to 4H-1,2,5-Thiadiazocin-6-one-1,1-dioxidesReaction of 3-amino-2H-azirines 2 with the 1,1-dioxides 4 and 7 of 1,2-thiazol-3(2H)-ones and 1,2-thiazoli-din-3-ones, respectively, in i-PrOH at room temperature leads to 4H-1,2,5-thiadiazocin-6(5H)-one-1,1-dioxides 5 (Scheme 2, Table) and the corresponding 7,8-dihydro derivatives 8 (Scheme 4), respectively. The structure of some of the new 8-membered heterocycles as well as the structure of the minor by-product 6 (Scheme 3) have been established by X-ray crystallography (Chapt. 4). The proposed reaction mechanism for the ring expansion to 5 and 8 (Scheme 2) is in accordance with previously published results of reactions of 2 and NH-acidic heterocycles and is further supported by the results of the reaction of 4a and the (1-15N)-labelled aminoazirine 2a*.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740511
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  • 56
    Digitale Medien
    Digitale Medien
    Zur Oxidation von 1,2-Thiazolen: Ein einfacher Zugang zu 1,2-Thiazol-3(2H)-on-1,1-dioxidenHerrn Prof. Dr. Siegfried Hauptmann zum 60. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1059-1070 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oxidation of 1,2-Thiazoles; A Convenient Approach to 1,2-Thiazol-3(2H)-one 1,1-DioxidesThe 1,2-thiazoles obtained from 3-chloroalk-2-enals and ammonium thiocyanate (7 → 9, Scheme 1) are easily transformed to 1,2-thiazol-3(2H)-one 1,1-dioxidcs 10 on treatment with H2O2 in AcOH at 80°. Hydrogenation of 10 in AcOH yields the corresponding saturated 1,2-thiazolidin-3-one 1,1-dioxides 16 (Scheme 3). Cycloalka[c]-1,2-thiazoles 18 are prepared from 2-[(thiocyanato)methyliden]cycloalkan-1-ones and ammonia (Scheme 4). Surprisingly, oxidation of 18a with H2O2 in AcOH yields the tricyclic oxaziridine 19.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740515
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  • 57
    Digitale Medien
    Digitale Medien
    Zur Synthese von Derivaten des Pyrido[1,2-a]azepinsProf. Horst Prinzbach zum 60. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1095-1101 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: On the Synthesis of Derivatives of Pyrido[1,2-a]lazepineThe conjugated pyridinium ylides of type 4 undergo 8π -electrocyclisation affording the heterobicyclic allenes 5 which, in the presence of H2O and H2O2, are subsequently transformed into the substituted pyrido[1,2-a]-azepinones 6, a novel heterocyclic system. The chemical behaviour of 6a,b is dominated by cleavage of the lactam bond and subsequent reaction to pyridinc and isoquinoline derivatives, respectively; e.g. reaction of 6a, b with 4,5-dihydro-4-methyl-3H-1,2,4-triazole-3,5-dione affords the cycloadducts 11 and 12 almost quantitatively. The successful transformation of 6b into 15 is described, the latter being the first representative of the presently unknown, potentially antiaromatic pyrido[1,2-a]azepine (1).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740519
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  • 58
    Digitale Medien
    Digitale Medien
    Mitteilungen (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1156-1156 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740525
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  • 59
    Digitale Medien
    Digitale Medien
    Regioselectivity, Stereoselectivity, and Isotopically Sensitive Branching in the Fe(I)-Mediated Dehydrogenation of Octane-1,8-diol in the Gas PhaseDedicated to Prof. Jürgen Sauer on the occasion of his 60th birthday (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1127-1134 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Regio- and stereospecific labeling experiments are conducted to unravel the mechanistic features of the Fe+-induced dehydrogenation of octane-1,8-diol in the gas phase. With regard to the regioselectivity, ca. 20% of molecular hydrogen originates from the C(3)/C(4) or the equivalent C(5)/C(6) positions. The remaining 80% are, provided by the C(4)/C(5) methylene units. The steps, preceding the reductive elimination of hydrogen, are irreversible, and the overall reaction follows a 1,2-elimination mode. The loss of HD from C(3)/C(4) is associated with a kinetic isotope effect KH2/KHD = 1.68. Formation of D2 from the positions C(4)/C(5) has an isotope effect of KH2/KD2 = 4.7; this figure is slightly dependent on the configuration at C(4)/C(5). Most interesting is the finding that the configuration at C(4)/C(5) in [4,5-D2]octane-1,8-diol, i.e. 5c vs. 5d, plays a pivotal role in the dehydrogenation of the central C(4)/C(5) part. This unexpected and unprecedented result is explained in terms of conformational analysis. A staggered-like conformation serves as a precursor to generate a trans-fused bicyclic intermediate 6. It is this very intermediate from which most of the molecular hydrogen is eliminated. Of minor importance is the as-fused chelate 7, which is formed from an eclipsed-like conformation of the octane-1,8-diol/Fe+ complex. The contribution of 6 and 7 to the product formation is controlled by the relative configuration at the labeled positions C(4)/C(5). For the D,L-form 5c, we estimate a ratio of ca. 9:1 for the contribution of 6 vs. 7; due to an isotope effect, this ratio drops to 1:85:1 for the meso-form 5d. This finding constitutes the first example for the existence of isotopically sensitive branching (‘metabolic switching’) in gas-phase organometallic chemistry.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740522
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  • 60
    Digitale Medien
    Digitale Medien
    Crystal Structures of the Lanthanum(III), Europium(III), and Terbium(III) Cryptates of Tris(bipyridine) Macrobicyclic Ligands (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1163-1170 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal structures of the LaIII, EuIII, and TbIII complexes of macrobicyclic [bpy.bpy.bpy] ligands, [La3+ ⊂ 1]3 Cl- ( = 3-La), [Tb3+ ⊂ 1]3 Cl- ( = 3-Tb), and [Eu3+ ⊂ 2]3 C1- ( = 3-Eu), have been determined. They confirm the cryptate nature of these species, the cations being bound to the eight N-sites of the ligand. The macrobicycle presents two open faces, thus allowing additional coordination of two species, Cl- ions or H2O molecules, to the bound cations. These data provide structural support for the photophysical studies of the luminescent properties of the EuIII and TbIII cryptates, which indicated residual coordination of H2O molecules.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740603
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  • 61
    Digitale Medien
    Digitale Medien
    Biphenyltetrols and Dibenzofuranones from Oxidative Coupling of Resorcinols with 4-Alkylpyrocatechols: New Ciues to the Mechanism of Insect Cuticle Sclerotization (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1205-1212 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oxidation of 4-alkylpyrocatechols 2 by means of an insect diphenoloxidase (laccase) or K3 [Fe(CN)6] yields, in the presence of resorcinols 1 (R2 = H), complex mixtures of products from which biphenyltetrols 3 (R3 = H) and dibenzofuranones 5 and 6 were isolated. It is suggested that similar homo-coupling products are formed from pyrocatechols 2b and 2c in insects during cuticle sclerotization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740607
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  • 62
    Digitale Medien
    Digitale Medien
    Quantitative Formation in Water of [Ru(CO)(H2O)5]2+ from Hexaaquaruthenium(II) and Carbon Monoxide (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1236-1238 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: High-pressure 17O- and 13C-NMR show that [Ru(H2O)6]2+ reacts quantitatively with carbon monoxide (50 bar) in water to form [Ru(CO)(H2O)5]2+.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740611
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  • 63
    Digitale Medien
    Digitale Medien
    Synthese von ‘Push-Pull’-Oligoacetylenen24. Miteilung über Aminoacryl-Derivate. 23. Mitteilung: [1]Kurzmitteilung: [2] (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1264-1272 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis of ‘Push-Pull’-OligoAcetylenes‘Push-pull’ triacetylenes 11a, b, c, as well as ‘push-pull’ tetraacetylene 13b have been prepared by reaction of the corresponding trichloroene(oligoinyl)amines 9 and 10 with 2 mol-equiv. of BuLi followed by acylation. The sequences (Schemes 3 and 4) are very simple and straightforward, they could in principle be applied to the synthesis of ‘push-pull’ pentaAcetylenes 15 and hexaacetylenes 17 (Scheme 5). Main limitations are the moderate yields as well as the low thermal stability of push-pull oligoacetylenes.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740614
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  • 64
    Digitale Medien
    Digitale Medien
    Metabolic products of microorganisms. Part 262Part 261: [1].. The absolute configuration of sphydrofuran, a widespread metabolite from streptomycetes (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1281-1286 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Sphydrofuran (1) was isolated from the culture filtrate of Streptomyces sp. (strain Gö 28 and Tü 3616) by chemical screening methods. Metabolite 1 is an anomeric and ring-chain tautomeric mixture and could easily be transformed into the stable furan derivative 2 under acidic conditions. The constitution and relative configuration of 1 was established by X-ray crystallography of its 8-O-methyl derivative 3a. The absolute configuration at C(4) of 1 and thus of the whole molecule (3R,4S,5S) could be determined starting from 2 using the Helmchen method.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740617
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  • 65
    Digitale Medien
    Digitale Medien
    Structure and reactivity of xanthocorrinoids. Part VPart IV, [1].. Formation of trans-diol derivatives of 5,6-dihydrocobyrinic acid from xanthocorrinoids under acidic conditions (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1287-1295 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: On treatment with H2SO4/MeOH, epimerization of hexamethyl cis-5,6-dihydroxycobyrinate c,8-lactam (3) takes place quantitatively at C(6), yielding the corresponding trans-diol 4. The corresponding lactone 7, whose structure has been established by X-ray analysis, is obtained from xanthocorrinoids 5 and 6 under similar conditions.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740618
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  • 66
    Digitale Medien
    Digitale Medien
    Alternative Strategies for the Fmoc Solid-Phase Synthesis of O4-Phospho-L-tyrosine-Containing Peptides (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1314-1328 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A number of biologically relevant O4-phospho-L-tyrosine-containing peptides have been synthesized by either the global phosphorylation of the side-chain-unprotected L-tyrosine moiety in presynthesized resin-bound peptides or alternatively by the incorporation of suitably protected O4-phospho-L-tyrosine building blocks in the continuous-flow method of Fmoc solid-phase peptide synthesis. Different phosphate-protecting groups have been applied.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740621
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  • 67
    Digitale Medien
    Digitale Medien
    Stereoselektive Synthese von Pyrrolizidin-Alkaloiden aus NitroalkanonenHerrn Professor Dr. C. H. Eugster zurn 70. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1352-1361 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Stereoselective Synthesis von Pyrrolizidin Alkaloids from NitroalkanonesReduction of 5-nitropentadecane-2,8-dione (11), synthesized by a Michael reaction from nitromethane, methyl vinyl ketone, and dec-1-en-3-one, gave, depending on the conditions, two epimeric 3-heptyl-2,3,5,6,7,7a-hexahydro-5-methyl-1H-pyrrolizines as the main products: Catalytic hydrogenation (Pd/C) afforded the expected 7aα-hydro epimer 1b with cis-orieted H-atoms at C(3), C(5), and C(7a). NaBH3CN/NH4OAc reduction of the nitrodione 11 yielded all four diastereoisomers with the 7aβ-hydro epimer 1a as the predominant component; 1a is a pheromone of the cryptic thief ant Solenopsis sp. The N-atom of the pyrrolizidine ring stems from NH4OAc exclusively as shown by reduction of 11 with NaBH3CN/(15N)H4OAc.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740624
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  • 68
    Digitale Medien
    Digitale Medien
    Glycosylidene Carbenes. Part 4. Synthesis of Spirocyclopropanes from Acetamidoglycosylidene-Derived Diazirines (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1362-1372 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the first glycosylidene-derived 2-acetamido-2-deoxydiazirine 4 from N-acetylglucosamine 6 is described. Thus, 6 was transformed into the 3-O-mesylglucopyranoside 9 by glycosidation with allyl alcohol, benzylidenation, and mesylation (Scheme 2). Solvolysis of 9 gave the allopyranoside 10 which, upon benzylation and glycoside cleavage, yielded the hemiacetals 12. Using our established method (via the lactone oxime 14 and the diaziridines 16), 12 gave the diazirine 4. Thermolysis of this diazirine in the presence of i-PrOH gave the dihydro-1,3-oxazole 5 (Scheme 1); in the presence of acrylonitrile, the four diastereoisomeric spirocyclopropanes 17-20 and the acetamidoallal 21 were obtained and separated by prep. HPLC (Scheme 3). Assignment of the configuration of 17-20 is based on NOE measurements and on the effect of diamagnetic anisotropy of the CN group. The ratio of the four cyclopropanes, which is in keeping with earlier results, is rationalized.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740625
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  • 69
    Digitale Medien
    Digitale Medien
    Mammalian alkaloids: Synthesis and O-methylation of (S)- and (R)-3′-hydroxycoclaurine and their N-methylated analogues with S-adenosyl-L-[methyl-14C]methionine in presence of mammalian catechol O-methyltransferase (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1399-1411 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: O-Methylation of the optically active 3′-hydroxycoclaurines 3a and 3b and of the N-methylated analogs 5a,b with S-adenosyl-L-[methyl-14C]methionine in presence of mammalian COMT was investigated in vitro. The N-unsubstituted (1S)- and (1R )-isomers 3a and 3b, respectively, afforded almost equal amounts of the corresponding N-norreticuline 4 and N-nororientaline 19, besides two unknown by-products (see Fig. and Table 1). The N-methylated (1S)-isoquinoline 5a, on the other hand, afforded largely (S)-orientaline ((S)-19), while an almost equal mixture of (R)-reticuline (6b) and (R)-orientaline ((R)-19) was obtained from the (1R)-enantiomer 5b. The isoquinolines 3a,b and 5a,b were prepared by a Bischler-Napieralski cyclization yielding O-benzyl-protected isoquinoline 10 (Scheme 1). The optical resolution of 10 was accomplished with 2′-bromotartranilic acid. The N-methylated isoquinolines were prepared by N-formylation of 10a,b and reduction of the formamides 13a,b with diborane (→ 14a,b). Deblocking of the benzyl-ether moieties of 10a,b and 14a,b was accomplished by catalytic hydrogenation in presence of HCl, affording directly 3a,b·HCl and 5a,b·HCl, respectively.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740704
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  • 70
    Digitale Medien
    Digitale Medien
    A Novel, Degraded Polyketidic Lactone, Leptosphaerolide, and Its Likely Diketone Precursor, Leptosphaerodione. Isolation from Cultures of the Marine Ascomycete Leptosphaeria oraemaris (LINDER)Presented in part by A. G. at the ‘Giornate di chimica delle Sostanze Naturali’ meeting, Maratea (Potenza), on June 3, 1991. (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1445-1450 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Acetone extraction of cultures of the marine ascomycete Leptosphaeria oraemaris (LINDER) on cornmeal disk gave the novel polyketide derivative leptosphaerolide ( = (+)-7-[(1E)-l,3-dimethylpent-1-enyl]-10-hydroxy-3-methoxybenzo[1,2-b:5,4-c′]dipyran-2(9H)-one; (4+)-8) besides the o-dihydroquinone 3-[(1E)-1,3-dimethylpent-1-euyl]-8,10-dihydroxy-7-methoxy-8-(2-oxopropyl)-1H-naphtho[2,3-c]pyran-9(8H)-one (1) as a 10:9 mixture of epimers. retro-Aldol reaction of 1 gave leptosphaerodione ( = (-)-3-[(1E)-1,3-dimethylpent-1-enyl]-10-hydroxy-7-methoxy-1H-naphtho[2,3-c]pyran-8,9(8H)-dione; (-)-6) which was also present in small amounts in the extracts and which gave 1 on reaction with acetone. It is thus likely that 1 is an artefact of the extraction by acetone. Biogenetically (+)-8 might derive from (-)-6 via an unusual oxidation with loss of CO2.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740707
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  • 71
    Digitale Medien
    Digitale Medien
    1,2-Stereoinduction in Radical Reactions: Stereoselective Synthesis of 2-Alkyl-3-hydroxybutanoates (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1600-1607 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Radical addition to 2-cyclohexyl-5-methylidene-6-methyl-1,3-dioxan-4-one (2) affords stereoselectively 5,6-trans-products trans-3. The size of the radical has no influence on the selectivity. These trans-acetals are converted into threo-3-hydroxy-butanoates 4. Methyl 2-methylidene-3-[(tert-butyl)diphenylsilyloxy]butanoate (5), treated under the same conditions, leads mainly to the erythro-isomer of 4 after deprotection. An influence of the steric bulkyness of the radical is observed. The stereochemical course of the reactions is discussed.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740722
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  • 72
    Digitale Medien
    Digitale Medien
    Gas-Phase Chemistry of Ti+ to Zn+ with Butyl Isothiocyanate (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1609-1621 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using a complete set of 2H-labeled isotopomers, the gas-phase reactions of Ti+ to Zn+ with butyl isothio-cyanate are studied. The main product for most of the metal ions is MHNCS+ formed by an ion/dipole mechanism. Exceptions are Cr+, which yields significant amounts of H2 and H2S loss, Mn+, which is the only ion that does not form MHNCS+ at all but produces mainly C2H4 and C3H6, and Zn+, which predominantly reacts by charge transfer.
    Zusätzliches Material: 6 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740802
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  • 73
    Digitale Medien
    Digitale Medien
    1,3-Oxathiolan-Synthese: Spirocyclische 1,3-Oxathiolane aus der Lewis-Säure-katalysierten Umsetzung von cyclischen Trithiocarbonaten und OxiranenHerrn Professor Dr. C. H. Eugster zum 70. Geburtstag gewidmet (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1500-1510 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1,3-Oxathiolanc Synthesis: Spirocyclic 1,3-Oxathiolanes from the Lewis-Acid-Catalyzed Reaction of Cyclic Trithiocarbonates and OxiranesThe cyclic trithiocarbonates 1.3-dithiolane-2-thione (4) and 1,3-dithiole-2-thione (9) in 1,2-dichloroethane and MeCN, respectively, react with alkyl- and phenyl-substituted oxiranes 2 in the presence of Lewis acids to give 1-oxa-4,6,9-trithiaspiro[4.4]nonanes 5 and 6 (Scheme 2) and 1-oxa-4,6,9-trithiaspiro[4.4]non-7-enes 10 and 11 (Scheme 3), respectively. The reactions proceed regioselectively yielding 2-alkyl (5, 10) and 3-phenyl derivatives (6, 11) as the main products. From the reaction of 4 and 2-phenyloxirane (2e) with TiCl4, 2-phenyl-1,4,6,9-tetrathia-spiro[4.4]nonane (7) is isolated as a minor product. The molecular structures of 5a, 6e, and 7 are established by X-ray crystallography.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740714
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  • 74
    Digitale Medien
    Digitale Medien
    2D-NMR ConformationaL Studies of ChiraL Functionalized Ferrocenylphosphine Ligands for the Gold(I)-Catalyzed Aldol Reaction (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1533-1543 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformations in solution of six selected chiral 1,1′-bis (diphenylphosphino)ferrocenyl ligands bearing functionalized side chains, the diastercoisomers 4 and 5 and 6-9, have been elucidated by 2D-NMR methods (COSY, TOCSY, NOESY, and 1H,31P and 1H,13C correlations). The possible relationship between the preferred conformation and the stereoselectivity observed in the gold(I)-catalyzed asymmetric aldol condensation in the presence of these ligands is discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740717
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  • 75
    Digitale Medien
    Digitale Medien
    Crystal Structure and ESR Study of a Bimetallic Copper/Iron Crown Ether Inclusion Complex (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1591-1599 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Bimetallic inclusion complexes have been synthesized by a secondary coordination interaction between the guest complex [Fe(η5-C5H5)(CO)2(NH3)][PF6] and copper(II) complex 1a or nickel(II) complex lb containing crown-ether hosts. The X-ray crystal-structure analysis established that the Cu,Fe inclusion complex 2 crystallize as a centrosymmetric dimer with a Cu—Cu separation of 3.73 Å and a novel out-of-plane Cu—N interaction. The magnetic parameters for 2 were obtained by ESR and ENDOR spectroscopy. ESR susceptibility measurements down to 6 K exclude the presence of any antiferromagnetic coupling interaction between the CuIIcenters of the dimer.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740721
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  • 76
    Digitale Medien
    Digitale Medien
    Synthesis of Aristotelia-type alkaloids. Part VIIIPart VII: [1].. Synthesis of (±)-aristolasicone (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1636-1642 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The revised structure of the indole alkaloid aristolasicone (2) was confirmed through a convergent total synthesis of the racemic form of this metabolite. The key step involves a one-pot condensation/cyclization reaction between 1-(4-methoxyphenylsulfonyl)-1H-indole-2-acetaldehyde (9) and (±)-trans-5-(2,6-difluorobenzyloxy)-p-menth-l-en-8-amine ((±)-7). The resulting allohobartine derivative (±)-13, obtained in 84% yield, was deprotected and oxidized to (±)-alloscrratenone ((±)-15) which cyclized smoothly to the target molecule (±)-2 upon exposure to BF3 · Et2O.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740804
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  • 77
    Digitale Medien
    Digitale Medien
    From 1-(Silyloxy)Butadiene to 4-Amino-4-Deoxy-DL-Erythrose and to 1-Amino-1-Deoxy-DL-Erythritol Derivatives via Hetero-Diels-Alder Reactions with Acylnitroso Dienophiles (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1653-1670 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Acylnitroso dienophiles 4 reacted instantly with 1-(silyloxy)butadiene 5α and led in good yield to the regioisomeric cycloadducts 6 (major) and 7 (minor; Scheme 2, Table 1). cis-Hydroxylation of these primary cycloadducts with OsO4 (catalyst) occurred stereospecifically and in high yield (→8 and 9, resp.; Scheme 2). It was followed by reductive ring cleavage to give either 1-amino-1-deoxy-DL-erythritol or 4-amino-4-deoxy-DL-erythrose derivatives 10 and 14, respectively, depending on the nature of the reducing agent (Schemes 3 and 4).
    Zusätzliches Material: 7 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740806
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  • 78
    Digitale Medien
    Digitale Medien
    Cuprous complexes and dioxygen. Part 11Part 10: [1].. Concomitant one- and two-electron reduction of O2 by the Cuaq+ ion (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1679-1688 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The autoxidation of CuI in aqueous MeCN has been studied using a Clark oxygen electrode in the presence and absence of Cu11. The reaction is inhibited by Cu11 in the pH range of 0.5 to 5.0, reaching a lower limiting value at the highest concentrations. The reaction order changes from 1 to 2 with respect to CuI under the influence of Cu2+ ion. Detailed kinetics analysis of a total of 275 measurements has shown that an unstable primary adduct CuO+2 decomoses to give .O2- or HO2., depnding on pH, and also reacts directly with a second Cu+ ion, avoiding one-electrton reduction of O2 by this path. Reaction of HO2. is faster with CuI than with Cu11 by a factor of 20, and single-electron transfer within CuO+2 to Cu2+ and .O2- predominates over reaction with a second copper ion for [CuItot] 〈 2. 10-3M in the absence of Cu2+. The most likely value for the reaction of .O2- with CuI is 5.3 · 108 M-1S-1, but even this high rate constant is at the limit of significance. All secondary reactions followinfg the initial formation of CuO+2 are shown to be very fast, a fact that should be properly considered in the discussion of mechanisms of copper-catalyzed oxidations and oxygenations.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740808
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  • 79
    Digitale Medien
    Digitale Medien
    A Molecular-Mechanics Analysis of Complexes of the Sexidentate Macrocycles cis- and trans-6,13-Dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1834-1842 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular-mechanics calculations of the sexidentate coordinated complexes of the pendant arm macrocyclic hexaamines trans- (L1) and cis-6,13-dimethyl-3,4,8,11-tetraazacyclotetradecane-6,13-diamine (L2) reveal that the trans-isomer shows a preference toward small metal ions, whereas the L2 may coordinate a wider range of metal ions without significant intramolecular strain. Conformational disorder in previously reported crystal structures of complexes of L1 is interpreted, and predictions for some, as yet, unknown complexes of L2 are made.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740826
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  • 80
    Digitale Medien
    Digitale Medien
    3-Deazaguanine N7- and N9-(2′-Deoxy-β-D-ribofuranosides): Building Blocks for Solid-Phase Synthesis and Incorporation into Oligodeoxyribonucleotides (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1790-1800 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oligonucleotides continuing 3-deaza-2′-deoxyguanosine (I) or its N7-regioisomer 2 were prepared by solid-phase synthesis using P111 chemistry. Protection of 1 or 2 with N,N V-dimethylformamide diethyl acetal followed by 4,4′-dimethoxytritylation afforded imidazo[4,5-c]pyridines 10b and 11b, respectively. The latter were converted into the 3′-phosphonates 10c or lie, respectively; the cyanoethyl N,N-diisopropylphosphoramidite 10d was also prepared. The oligonucleotide building blocks were employed in automated solid-phase synthesis. 1 he self-complementary oligomers 13, 15, and 17 were prepared and characterized by enzymatic hydrolysis with snake-venom phosphodiesterase followed by alkaline phosphatase. There CD spectra exhibited the general structure of a B-DNA.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740821
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  • 81
    Digitale Medien
    Digitale Medien
    Steric Effects on Reaction Rates. Part XII. Force-Field Calculations for the Solvolysis of Cyclobutyl and Tricyclyl Derivatives (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1808-1816 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Force-field parameters have been developed for the molecular-mechanics calculation of tertiary carbenium ions with tricyclane structure, for tertiary cyclobutyl and cubyl cations. The cyclobutyl parameters are also applicable to tertiary 7-norbornyl cations. Satisfactory plots are obtained for correlation of the rates of solvolysis with the differences in steric energies between carbenium ions and the corresponding bromides.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740823
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  • 82
    Digitale Medien
    Digitale Medien
    Imidazole-Analogues of 6-Epicastanospermine and of 3,7a-Diepialexine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 934-940 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The chiral bicyclic imidazol derivatives 7 and 8 were obtained from D-glucose derivative 9 by a sequence of selective protection/deprotection and intramolecular SN2 reactions. Triols 7 and 8 are analogues of 6-epica-stanospermine (4) and of 3,7a-diepialexine (6), respectively, and are potential glycosidase inhibitors. However, their anti-HIV activity proved to be only marginal.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740503
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  • 83
    Digitale Medien
    Digitale Medien
    Ionization Behavior and Ionization-Dependent Conformation of Raclopride, a Dopamine D2 Receptor Antagonist (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 956-968 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Raclopride, an antipsychotic 6-methoxysalicylamide (= 2-hydroxy-6-methoxybenzamide) derivative, was shown by titrimetry and UV-pholometry to exist in zwitterionic form at physiological pH. Calculations revealed that the neutral and zwitterionic forms differ considerably in their conformational behavior, the latter form being energetically favored by an intramolecular phenolate-ammonium ionic bond. These findings indicate that raciopride and other halogenated 6-melhoxysalicylamides with a highly acidic phenolic group may not resemble other ortho-methoxybenzamides in their stereoelectronic structure and mode of binding to the dopamine D2 receptor.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740506
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  • 84
    Digitale Medien
    Digitale Medien
    Synthesis and Structure of the Copper(II) Complex of a Chiral Bis(dihydrooxazole) Ligand (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1-6 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The bridged bis(dihydrooxazole) compound (-)-2 and its silylated derivative (-)-3 have been synthesised as building blocks for chiral ligands. The complex of (-)-3 with CuII has been obtained, and its crystal structure has been determined. The CuII ion is bound to two deprotonated ligands in a twisted tetracoordinated geometry.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740103
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  • 85
    Digitale Medien
    Digitale Medien
    Generation and Trapping of Cyclopropenes from 2-Alkoxy-1,1-dichlorocyclopropanes (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 55-64 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In presence of crown ether, 2-alkoxy-1,1-dichlorocyclopropanes react with t-BuOK/THF preferentially via ring opening to 2-chloroalk-2-en-1-ones and alkynones or to chlorocyclopropenes. The latter may be intercepted with 1,3-diphenylisobenzofuran, but in the absence of trapping agent, the rearrangement to vinylcarbenes does not occur.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740108
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  • 86
    Digitale Medien
    Digitale Medien
    1H-Phenalen-1-one: Photophysical Properties and Singlet-Oxygen Production (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 79-90 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The efficiency of aromatic ketones as singlet-oxygen (1O2(1Δg)) sensitizers can vary considerably with the electronic configuration of their lowest triplet state and the solvent used. Near-infrared measurements of tie luminescence of singlet oxygen have shown that the quantum yield of singlet-oxygen production (ΦΔ) by 1H-phenalen-1-one (1) is close to unity in both polar (ΦΔ = 0.97±0.03 in methanol) and non-polar solvents (ΦΔ = 0.93±0.04 in benzene). Analysis of the absorption spectra of the ground state and phosphorescence measurements show that the lowest singlet and triplet states have dominant π, π* electronic configurations. The quantum yield of intersystem crossing (ΦISC) of 1, determined by laser flash photolysis (partial-saturation method), is equal to unity. In comparison with other aromatic ketones, these parameters are important for the discussion of the surprisingly high ΦISC of 1 and the efficient energy transfer from its triplet state to molecular oxygen. The 1H-phenalen-1-one (1), being one of the most efficient singlet-oxygen sensitizers in both polar and non-polar media, could be used as a reference sensitizer, in particular in the area of relatively high energies of excitation.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740110
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  • 87
    Digitale Medien
    Digitale Medien
    Neurotoxic Sesquiterpenoids from the Yellow Star Thistle Centaurea solstitialis L. (Asteraceae) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 117-123 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ingestion of yellow star thistle (Centaurea solstitialis L.) by horses produces parkinsonism due to nigro-pallidal degeneration. The toxin responsible has not been identified so far. A CH2Cl2 extract from the aerial parts of C. solstitialis exhibited significant neurotoxicity against primary neuronal cultures of foetal rat brain. Activity-guided fractionation yielded the known sesquiterpene lactones solstitialin A (1), 13-0-acetylsolstitialin A (3), cynaropicrin (4), and the hitherto unknown 3-O-acetylsolstitialin A (2). In the bioassay with rat foetal full cell culture, 3 and 4 were toxic in a concentration-dependent manner and may be responsible for the ability of the plant to cause neurodegenerative changes in the brain of horses.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740114
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  • 88
    Digitale Medien
    Digitale Medien
    1-Methoxycarbonyl-substituiertes 2,3-Dihydropyridin-4(1H)-on (= Methyl-1,2,3,4-tetrahydro-4-oxopyridin-1-carboxylat) als Chromophor für die photochemische [2 + 2]-Cycloaddition (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 163-178 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1-Methoxycarbonyl-Substituted 2,3-Dihydropyridin-4(1H)-one(= Methyl 1,2,3,4-Tetrahydro-4-oxopyridine-1-carboxylate) as Chromophore for Photochemical [2 + 2]-CycloadditionsWith olefins having an electron-acceptor as well as with olefins having an electron-donor substituent, 1-methoxycarbonyl-substituted dihydropyridinone 12 undergoes [2 + 2] cycloaddition in good preparative yields. The photochemical cycloaddition is highly regioselective. For preparative purposes, the ring junction can be equilibrated to the thermodynamically more stable cis-junction. Only the ‘endo’/‘exo’ selectivity at the C-atom bearing the olefin substituent cannot be controlled. The photodimerization of 12 is the only side reaction. Using a slight excess of the olefin, the photodimerization can be suppressed. The protecting group at the N-atom of the dihydropyridinone can be varied in order to introduce an internal sensitizer, as shown with 1-acyl-substituted compound 29, which underwent the cycloaddition process even with sunlight.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740118
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  • 89
    Digitale Medien
    Digitale Medien
    C2-Symmetric 4,4′,5,5′-Tetrahydrobi(oxazoles) and 4,4′,5,5′-Tetrahydro-2,2′-methylenebis[oxazoles] as Chiral Ligands for Enantioselective Catalysis Preliminary Communication (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 232-240 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of a series of enantiomerically pure, C2-symmetric 4,4′,5,5′-tetrahydro-2,2′-methylenebis[oxazoles] and 4,4′,5,5′-tetrahydro-2,2′-bi(oxazoles) is reported. Copper complexes with anionic tetrahydromethylenebis[oxazole] ligands are efficient catalysts for the enantioselective cyclopropane formation from olefins and diazo compounds (up to 96% ee in the reaction of styrene with menthyl diazoacetate). Tetrahydrobi(oxazole)iridium(I) complexes were found to catalyze transfer hydrogenations of aryl alkyl ketones with i-PrOH (up to 91% ee). Tetrahydrobi(oxazole)palladium complexes can be used as enantioselective catalysts for allylic nucleophilic substitution (up to 77% ee in the reaction of PhCH=CHCH(OAc)Ph with NaHC(COOMe)2).
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740123
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  • 90
    Digitale Medien
    Digitale Medien
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740201
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  • 91
    Digitale Medien
    Digitale Medien
    Electronic and Conformational Effects on the Lipophilicity of Isomers and Analogs of the Neurotoxin 1-Methyl-4-phenylpyridinium (MPP+) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 290-296 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A number of isomers and analogs of the neurotoxin 1-methyl-4-phenylpyridinium (MPP+) were examined for their lipophilic behavior. Their partition coefficients in the 1-octanol/H2O system were measured by centrifugal partition chromatography (CPC), which, being much faster and markedly more precise than the classical shake-flask method, proved a very promising alternative for assessing lipophilicity. A smaller-than-expected lipophilicity was shown by the ortho-isomer of MPP+ (M2PP+) and is explained in terms of electronic effects and rigidity, as revealed by UV and NMR spectroscopy, and conformational analysis. Implications of lipophilicity in modulating the in vivo dopaminergic neurotoxicity of the examined compounds are also discussed.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740205
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  • 92
    Digitale Medien
    Digitale Medien
    On the Regioselectivity Control in the Palladium-Catalyzed Hydro-alkoxycarbonylation of α,β-Unsaturated Esters (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 323-325 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The regioselectivity of the hydro-alkoxycarbonylation of methyl acrylate, methacrylate, and crotonate catalyzed by [PdCl2L2] complexes (L = phosphine ligands) can be largely controlled by variation of the ligands. PPh3, promotes preferential carbonylation at the α-position, whereas with [(2,2-dimethyl-1,3-dioxolane-4,5-diyl)bis-(methylene)]bis[diphenylphosphine] as ligand, the β-position is overwhelmingly carbonylated.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740210
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  • 93
    Digitale Medien
    Digitale Medien
    The Synthesis of Boronolide (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 336-342 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Racemic boronolide (1) is prepared in six steps in 4.4% overall yield from acrolein dimer 6 and 1-(trimethyl-silyl)hex-1-yne (8). The latter, by hydromagnesiation, is condensed with 6 to give the corresponding threo-allylic alcohol 13 (Scheme 2). Conversion of 13 to the erythro-allylic alcohol 5 (Scheme 3), bis-hydroxylation, and acetylation afford 1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740213
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  • 94
    Digitale Medien
    Digitale Medien
    C-Alkylation of Peptides through Polylithiated and LiCl-Solvated Derivatives Containing Sarcosine Li-Enolate Units (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 197-224 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The tripeptide and hexapeptide derivatives Boc-Gly-Sar-MeLeu-OH (5b), Boc-Ala-Sar-Sar-OH (6b), Boc-Ala-Sar-MeLeu-OH (7b), and Boc-Abu-Sar-MeLeu-Val-MeLeu-Ala-OH (12b) can be poly-deprotonated (tri- and pentalithio derivatives K and P, respectively), and thus C-alkylated on sarcosine (Sar) moieties with MeI and allyl or PhCH2Br. The polylithiated species are solubilized in THF, and their reactivity modified by excess base (lithium diisopropylamide (LDA)), by added LiCl, and/or the cosolvent N,N′-dimethylpropyleneurea (DMPU). Optimization of the reaction conditions for methylation in the cases of 7b (Table 3) and 12b (Scheme 8) gave products in which the Sar residue of the educt has been transformed into a Me-D-Ala unit in yields of 80 (9c/8c) and 67% (14c/13c), respectively, and with a diastereoselectivity of ca. 4:1. Less selective methylations and benzylations were observed with the tripeptides 5b and 6b containing only one stereogenic center; also, excess base and alkyl halide may lead to double alkylations in those latter two cases (Tables 1 and 2). No epimerization of stereogenic centers was detected under the strong-base conditions. The analysis of the products was accomplished by a combination of NMR and FAB-MS spectroscopy, as well as by hydrolysis to the parent amino acids, subsequent formation of derivatives with isopropyl isocyanate, and GC analysis on the chiral column Chirasil-Val®.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740121
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  • 95
    Digitale Medien
    Digitale Medien
    Quantitative Structure-Affinity Relationships of Dopamine D2 Receptor Antagonists: A Comparison between Orthopramides and 6-Methoxysalicylamides (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 241-254 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A large series of orthopramides (= 2-methoxybenzamides), 6-methoxysalicylamides, and 2,6-dimethoxy-benzamides were examined for their affinity to the dopamine D2 receptor. The binding data were correlated with physicochemical parameters and 13C-NMR chemical shifts using the cross-validated partial least-squares method and multiple linear regression analysis. The results quantitate the influence of electronic factors and lipophilicity to D2 receptor binding. They also show that the N-[(1-ethylpyrroIidin-2-yl)methyl] and N-(1-benzylpiperidin-4-yl) side-chains affect the mode of binding of these compounds.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740202
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  • 96
    Digitale Medien
    Digitale Medien
    The Synthesis of 3-Acyl-2,3-dihydro-2,2-dimethyl-1,3-thiazoles (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 297-303 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Acylation of 2,5-dihydro-2,2-dimethyl-1,3-thiazoles leads to 3-acyl-2,3-dihydro-2,2-dimethyl-1,3-thiazoles as potential starting materials for the total synthesis of racemic cephalosporins.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740206
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  • 97
    Digitale Medien
    Digitale Medien
    Stereoselective Synthesis of Indazole 2′-Deoxy-β-D-ribonucleosides: Glycosylation of the Nucleobase Anion (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 315-322 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The glycosylation of indazolyl anions derived from 4a, b with 2-deoxy-3,5-bis-O-(4-methylbenzoyl)-α-D-erythro-pentofuranosyl chloride (5) is described. The reaction was Stereoselective - exclusive β-D-anomer formation - but regioisomeric N1- and N2-(2′-deoxy-β-D-ribofuranosides) (i.e. 6a and 7a, resp., and 6b and 7b, resp.) were formed in about equal amounts. They were deprotected to yield 8a, b and 9a, b. Compound 1, related to 2′-deoxyadenosine (3), and its regioisomer 2 were obtained from 8b and 9b, respectively, by catalytic hydrogenation. The anomeric configuration as well as the position of glycosylation were determined by 1D NOE-difference spectroscopy. The first protonation site of 1 and 2 was found to be the NH2 group. The N-glycosylic bond of 1H-indazole N1-(2′-deoxyribofuranosides) is more stable than that of the parent purine nucleosides. Compound 1 is no substrate for adenosine deaminase.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740209
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  • 98
    Digitale Medien
    Digitale Medien
    Enantioselective Synthesis of Both Enantiomers of a Isoproterenol Analogue and of Di-O-pivaloylepinephrine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 390-396 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An asymmetric synthesis of the analogue 4a of isoproterenol and of di-o-pyvaloylepinephrine 3 which provides both enantiomers in optically pure state is reported. The key step of the method is the highly diastereo-selective reduction (using DIBAL or DIBAL/ZnCl2) of a β-ketosulfoxide 7 which leads, as desired, to the (S)- or the (R)-configuration at C(1) (Schemes 4 and 5).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740216
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  • 99
    Digitale Medien
    Digitale Medien
    Über die Reaktion einiger 2H-Pyran-2-on-Derivate mit primären Aminen (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 407-416 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: On the Reaction of Some 2H-Pyran-2-one Derivatives with Primary AminesThe versatile reactivity of 6-unsubstituted 2H-pyran-2-ones towards aliphatic and aromatic amines has been studied. It was found that the result of the reaction depends not only on the substitution of 2H-pyran-2-ones and on the structure of amines, but also on the stoichiometric ratio of reacting compounds.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740218
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  • 100
    Digitale Medien
    Digitale Medien
    A New Synthesis of (2S,3R,4R)-2-(Hydroxymethyl)pyrrolidine-3,4-diol (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 445-450 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The title compound 6 was synthesized from 2,3,5-tri-O-benzyl-D-arabinofuranose (7) in three steps and 48% overall yield. Moreover, it was shown, in the case of γ-hydroxy amide 9, that the Mitsunobu reaction is not suitable for the preparation of γ-lactams, because O-alkylation is predominant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740222
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