Expedient Diels-Alder assembly of 4-aryl-4-phenylsulfonyl cyclohexanones

The efficient preparation of 4-aryl-4-phenylsulfonyl cyclohexanones, containing a quaternary sulfone-bearing carbon centre, is described. Their synthesis proceeds in 38-78% overall yield by way of three steps: (i) sulfinate alkylation; (ii) methylenation; and (iii) regioselective Diels-Alder condensation with 2-trimethylsiloxybutadiene. The scope and limitations of the one-pot Mannich-type methylenation described were examined.     

Molekül- und Kristallstruktur des 1,4-Bis[tris(tetrahydrofuran)lithium]-octaphenyltetrasilans

Molecular and Crystal Structure of 1,4-Bis[tris(tetrahydrofuran)lithium]-octaphenyltetrasilane 1,4-Dilithium-octaphenyltetrasilane prepared from octaphenyl-cyclo-tetrasilane and lithium in tetrahydrofuran (THF) [4], can be isolated from tetrahydrofuran/n-pentane as an adduct with six molecules of tetrahydrofuran per formula unit. The orange-red compound crystallizes in the triclinic space group P1 {a = 1159.6(3); b = 1268.4(2); c = 1367.8(3) pm; α = 92,23(2)° β = 113.79(2)° γ = 111.62(2)° at ?5 ± 3°C; Z = 1}. An x-ray structure determination (R_w = 0.046) shows the existence of a centrosymmetric molecule with an extended planar Li? Si₄? Li unit; either lithium atom is bound to silicon and to the oxygen atoms of three molecules of tetrahydrofuran. Characteristic bond lengths and angles are: Li? Si 271; Si? Si 241 and 243; Si? C 190 to 192 pm; Li? Si? Si 126°; Si? Si? Si 127°. ²⁹Si and ⁷Li n.m.r. measurements at low temperatures indicate the presence of three different adducts.     

Functional organization of the outer membrane of escherichia coli: phage and colicin receptors as components of iron uptake systems.

The functional interaction of outer membrane proteins of E. coli can be studied using phage and colicin receptors which are essential components of penetration systems. The uptake of ferric iron in the form of the ferrichrome complex requires the ton A and ton B functions in the outer membrane of E. coli. The ton A gene product is the receptor protein for phage T5 and is required together with the ton B function by the phages T1 and ?80 to infect cells and by colicin M and the antibiotic albomycin, a structural analogue of ferrichrome, to kill cells. The ton B function is necessary for the uptake of ferric iron complexed by citrate. Iron complexed by enterochelin is only transported in the presence of the ton B and feu functions. Cells which have lost the feu function are resistant to the colicins B, I or V while ton B mutants are resistant to all 3 colicins. The interaction of the ton A, ton B, and feu functions apparently permits quite different "substrates" to overcome the permeability barrier of the outer membrane. It was shown for ferrichrome dependent iron uptake that the complexing agent was not altered and could be used repeatedly. Only very low amounts of 3H-labeled ferrichrome were found in the cell. It is possible that the iron is mobilized in the membrane and that desferri-ferrichrome is released into the medium without having entered the cytoplasm. Growth on ferrichrome as the sole iron source was used to select revertants of T5 resistant ton A mutants. All revertants exhibited wild-type properties with the exception of partial revertants. In these 4 strains, as in the ton A mutants, the ton A protein was not detectable by SDS polyacrylamide gel electrophoreses of outer membranes. Albomycin resistant mutants were selected and shown to fall into 5 categories: 1) ton A; 2) ton B mutants; 3) mutants with no iron transport defects and normal ton A/ton B functions, which might be target site mutants; 4) mutants which were deficient in ferrichrome-mediated iron uptake but had normal ton A/ton B functions. We tentatively consider that the defect might be located in the active transport system of the cytoplasmic membrane; 5) a variety of mutants with the following general properties: most of them were resistant to colicin M, transported iron poorly, and, like ton B mutants, contained additional proteins in the outer membrane. The outer membrane protein patterns of wild-type and ton B mutant strains were compared by slab gel electrophoresis in an attempt to identify a ton B protein. It was observed that under most growth conditions, ton B mutants overproduced 3 proteins of molecular weights 74,000-83,000. In extracted, iron-deficient medium, both the wild-type and ton B mutant strains had similar large amounts of these proteins in their outer membranes. The appearance of these proteins was suppressed by excess iron in both wild-type and mutant. From this evidence it is apparent that the proteins appear as a response to low intracellular iron rather than being controlled by the ton B gene...     

Novel binding of beryllium to dicarboxyimidazole-based model compounds and polymers

The ligand 4,5-dicarboxyimidazole (H(2)DCI) and its methyl derivative 1-methyl-4,5-dicarboxyimidazole (H(2)MDCI) have been shown to bind to Be(II) forming a zwitterionic species that has been structurally characterized. A new dicarboxyimidazole-based polymer has been prepared and its Be-binding properties have been studied using NMR ((1)H and (9)Be) and fluorescence spectroscopy; it represents a rare example of beryllium binding to a polymer. Models of the mononuclear and polymeric Be(II)-binding sites have been studied using density functional theory (DFT), and the (9)Be NMR chemical shifts of these model materials have been calculated for the purpose of direct comparison to experimentally observed values. Differences in the binding modes of the mononuclear and polymeric species are discussed.     

Quantification of polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) in the picogram/liter range in water of the river Elbe

Sampling and determination of dissolved and particlebound PCBs and HCB in the river Elbe are described. A new filtration/adsorption unit for sampling of dissolved lipophilic contaminants was developed. The detection limit for dissolved PCBs and HCB was 5 pg/l. The data show that more than 98% of the PCBs and of HCB in the water of the river Elbe are particle-bound.     

Nuclear analogs of β-lactam antibiotics. 7. The synthesis of 3-thia- and 3-aza-1-dethiaceph-1-em esters

The total synthesis of a 3-thia- and a 3-aza-1-dethiacepham ($\text{9}$ and $\text{16}$) are described. Neither compound possessed antibacterial activity $\text{vs}$$\text{B}$. $\text{subtilis}$. An unsaturated analog, a 3-aza-1-dethiaceph-1-em exhibited weak antibacterial activity.     

Synthese,IR-Spektrum und Kristallstruktur von N,N'-Bis(trimethylsilyl)benzamidinium-tetrachloroferrat(III)

Synthesis, IR Spectrum, and Crystal Structure of N,N'-Bis(trimethylsilyl)benzamidinium Tetrachloroferrate(III) The title compound [C₆H₅? C(NHSiMe₃)₂][FeCl₄] is obtained by the reaction of FeCl₃ with N,N,N'-tris(trimethylsilyl)benzamidine in the presence of tetrahydrofurane, forming yellow, moisture sensitive crystals. The compound is characterized by its IR spectrum as well as by an X-ray structure determination. Space group P2₁/n, Z = 8, 5974 independent observed reflexions, R = 0.066. The lattice dimensions are at ?70°C: a = 2110.7, b = 1109.5, c = 2120.4 pm; β = 111.17º. The compound forms ion pairs, in which the H atoms of the amidinium cation are coordinated with one chlorine ligand of the FeCl₄^? ion in a chelating manner.     

Disruption of DNA repair processes by carcinogenic metal compounds

Based on pronounced enhancing effects in combination with other DNA-damaging agents the potentials of Ni(II), Cd(II) and As(III) to interfere with DNA repair processes in HeLa cells was investigated. With respect to oxidative DNA damage, Ni(II) and Cd(II) induced DNA strand breaks starting at concentrations of 250 μM and 5 μM, respectively. The induction of oxidative DNA base modifications like 8-hydroxyguanine was restricted to the cytotoxic concentration of 750 μM Ni(II) and not observed after treatment with Cd(II). In contrast, the removal of oxidative DNA base modifications was inhibited at concentrations as low as 50 μM Ni(II) and 0.5 μM Cd(II). Regarding nucleotide excision repair, Ni(II) and Cd(II) disturbed the DNA-protein interactions involved in the damage recognition step when applying HeLa nuclear protein extracts and a UV-damaged oligonucleotide, while As(III) inhibited the actual incision event. In the case of Ni(II) and Cd(II), this effect was reversible by the addition of Mg(II) and Zn(II), respectively. Furthermore, Cd(II) inactivated the isolated bacterial Fpg protein, most likely by the displacement of Zn(II) from its zinc finger structure. Since DNA is continuously damaged by exogenous and endogenous sources, an impaired repair capacity might well account for the carcinogenic action of the metal compounds. Received: 30 July 1997 / Revised: 6 October 1997 / Accepted: 10 October 1997     

EVIDENCE FOR THE EXISTENCE OF MEMBRANE-ASSOCIATED PHYTOCHROME IN THE CELL

Abstract Comparative fluorescence and photochemical studies of phytochrome in etiolated seedlings of maize and in soluble and membrane-containing fractions isolated from them were camed out. The membrane fractions prepared in the absence of Mg²⁺ from etiolated coleoptiles contained 13% of total photoreversible phytochrome, which was readily solubilized by mild detergents. Its molecular size was indistinguishable from soluble phytochrome and equal to nondegraded maize phytochrome. Low-temperature fluorescence studies with intact tissue found that the position of the emission maximum at 85 K (λ_max) and the extent of the phototransformation of the red-absorbing form (Pr) into the first stable photoproduct, lumi-R, at 85 K (γ₁), varied in different parts of etiolated seedlings: λ_max and γ₁ reached their maximum values in the tips of coleoptiles and roots, 686 nm and 0.30–0.40, whereas the lowest values, 682 nm and ca 0.05, were observed in the root base. These parameters correlated well with those obtained for the pigment in the soluble and membrane-containing fractions: 684 and 680 nm, and 0.33 and 0.06, respectively. The extent of the Pr phototransformation into the far red-absorbing form (Pfr) (γ₂) did not differ much: values of 0.80–0.85 and 0.70–0.75 correlated with the high and low values of γ₁. These variations of the parameters were interpreted in agreement with our previous observations in terms of two phytochrome A species whose relative concentrations vary depending on the experimental conditions—the longer wavelength bulk light-labile species with high γ₁ (Pr″), and the shorter wavelength minor light-stable species with low γ₁ (Pr″). Close similarity between Pr’and the soluble phytochrome and between Pr″ and the membrane-bound phytochrome points to the possible origin of the native Pr’and PrPrime; species, thus providing evidence for the existence of membrane-bound pigment in the cell.     

Absolutberechnung der Normalfrequenzen des Hydrogendifluoridions

Zusammenfassung Mit Hilfe eines einfachen quantenmechanischen Näherungsansatzes wird versucht, Bindungsabstände und Normalfrequenzen des Hydrogendifluoridions sowie des entsprechenden deuterierten Ions zu berechnen. Hierbei wird die Elektronenwechselwirkung der beiden Fluoridionen untereinander durch einen der Statistik entlehnten Ausdruck berücksichtigt. Die Methode liefert für die Abstände gute, für die Normalfrequenzen durchaus befriedigende Ergebnisse.

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On the basis of a quantum mechanical treatment the bond distances and the normal frequences of the hydrogen difluoride ion and its deuterated analogue are calculated. The electronic interaction of the two fluoride ions is approximated by a statistical calculation. The results are in fairly good agreement with the experimental values.

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Résumé Sur la base d'un traitement quantique simple, le calcul des distances de liaison et des fréquences normales est tenté pour l'ion de bifluorure d'hydrogène et son analogue deutéré. L'intéraction électronique des deux ions fluorures est approximée au moyen d'un calcul statistique. Les résultats sont en très bon accord avec les valeurs expérimentales.

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Der Deutschen Forschungsgemeinschaft danken wir für die Gewährung eines Stipendiums an Karl Hensen.