Konformationsanalyse von Gallenfarbstoffen mit Hilfe von Kraftfeldrechnungen

A force field constructed for bile pigments and parametrized on partial structures of bile pigments was used to calculate the minimum energy geometries of diastereomeric bilatrienes-abc. In addition the relative energies of these isomers were deduced and the energies of interconversion between the mirror images of the more or less helical (Z,Z,Z)-syn, syn, syn-form were calculated for various paths.

     

Synthese von 3-Dimethylamino-3a,4,5,7a-tetrahydro-1H-iso-indol-1-onen durch intramolekulare Diels-Alder-Reaktion

Synthesis of 3-Dimethylamino-3a,4,5, 7a-tetrahydro-1H-isoindol-1-ones by Intramolecular Diels-Alder Reaction Thermolysis of N²-acylamidines, the acyl group of which derives from an α,β,γ,δ-unsaturated carboxylic acid ( 2, 5 – 7 ), yields 3-dimethylamino-3a,4,5,7a-tetrahydro-1H-isoindol-1-ones ( 3,8 – 10 , Schemes 1 and 3) in 63–78%. Only the thermodynamically controlled cis-fused ring system is formed. The starting materials are readily available by the reaction of 3-dimethylamino2H-azirines ( 1 and 4 ) and carboxylic acid chlorides.     

α-Eliminierungsreaktionen an di-t-butyl(trichlorgermyl)phosphin: Ein weg zu phosphinogermylenen und triorganophosphin-dichlorogermylen-komplexen

The complex PtClMe(2,2′-bipy)(MeO₂CCCCO₂Me) decomposes to PtClMe(2,2′bipy) and MeO₂ CCCCO₂ Me by a complex mechanism involving preliminary ionisation of the chloride ligand, but the dissociation of CF₃CCCF₃ from PtlMe(2,2′-bipy)(CF₃CCCF₃) takes place without ionisation of iodide.     

On the nature of “soluble” hypericin inHypericum species

Summary The two red and two violet soluble pigments ofHypericum species were isolated by means of extraction, chromatography, and counter-current droplet chromatography. In contrast to authentic hypericin, they are soluble in common organic solvents and even in water. Using NMR experiments it was deduced that hypericin, pseudohypericin, protohypericin, and protopseudohypericin are present in the plant as their rapidly interconverting 3- and 4-phenolate ions. From AAS the main counter-ion of these phenolates was derived to be potassium. The potassium and N-ethyl-N,N-diisopropylammonium salts of hypericin were synthesizcd for comparison. A preparative procedure to isolate hypericin and pseudohypericin from plant material was developed.

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Zur Natur des löslichen Hypericins inHypericum-Arten

Zusammenfassung Die zwei roten und zwei violetten löslichen Pigmente ausHypericum Arten wurde durch Extraktion, Chromatographie und Tropfen-Gegenstromchromatographie isoliert. Im Gegensatz zu authentischem Hypericin sind diese in organischen Lösungsmitteln und sogar in Wasser löslich. Aus NMR-Experimenten wurde abgeleitet, daß Hypericin, Pseudohypericin, Protohypericin und Protopseudohypericin in diesen Pflanzen als deren rasch interkonvertierende 3- und 4-Phenolationen vorliegen. Durch AAS wurde gefunden, daß diese Phenolationen Kalium als Gegenion aufweisen. Das Kalium- und N-Ethyl-N,N-diisopropylammonium-Salz des Hypericins wurden zu Vergleichszwecken dargestellt. Ein präparatives Verfahren zur Isolierung von Hypericin und Pseudohypericin aus Pflanzenmaterial wurde entwickelt.

     

The Beginnings of Organic Photochemistry

Although sunlight induced photochemistry must have occurred on the planet Earth for billions of years, the chemical changes caused by light have attracted systematic scientific scrutiny only relatively recently. How did scientists first conceive the idea that the interaction of materials with light could not only cause physical phenomena, but could also alter their chemical nature? When sunlight began to be employed as a heat source for distillation, the eventual discovery of photochemical reactions was assured. One can envision three types of changes that would have aroused the curiosity of laboratory chemists: color changes; the evolution of gas bubbles (oxygen in photosynthesis); and the precipitation of a photoproduct less soluble than its precursor. Less predictable was the observation that sunlight caused crystalline santonin to burst because it is converted into a product with a different crystal lattice. In the course of the eighteenth and nineteenth centuries a variety of photochemical reactions, some observed by chance, others uncovered in carefully planned studies, ultimately led to a major systematic investigation that established photochemistry as a viable branch of chemistry.     

Fluorocarbonyl trifluoromethanesulfonate, FC(O)OSO2CF3: structure and conformational properties in the gaseous and condensed phases

Pure fluorocarbonyl trifluoromethanesulfonate, FC(O)OSO(2)CF(3), is prepared in about 70% yield by the ambient-temperature reaction between FC(O)SCl and AgCF(3)SO(3). The geometric structure and conformational properties of the gaseous molecule have been studied by gas electron diffraction (GED), vibrational spectroscopy [IR(gas), IR(matrix), and Raman(liquid)] and quantum chemical calculations (HF, MP2, and B3LYP with 6-311G basis sets); in addition, the solid-state structure has been determined by X-ray crystallography. FC(O)OSO(2)CF(3) exists in the gas phase as a mixture of trans [FC(O) group trans with respect to the CF(3) group] and gauche conformers with the trans form prevailing [67(8)% from GED and 59(5)% from IR(matrix) measurements]. In both conformers the C=O bond of the FC(O) group is oriented synperiplanar with respect to the S-O single bond. The experimental free energy difference between the two forms, DeltaG degrees = 0.49(13) kcal mol(-1) (GED) and 0.22(12) kcal mol(-1) (IR), is slightly smaller than the calculated value (0.74-0.94 kcal mol(-1)). The crystalline solid at 150 K [monoclinic, P2(1)/c, a = 10.983(1) A, b = 6.4613(6) A, c = 8.8508(8) A, beta = 104.786(2) degrees ] consists exclusively of the trans conformer.     

Ultra-Thin Gold Cluster Films by Langmuir–Blodgett-Techniques

The extraordinary electronic properties of the full-shell cluster Au₅₅(PPh₃)₁₂Cl₆ and its ligand modified derivatives make them one of the most attractive building blocks in future nanoelectronics. The reason is the ability to act as a single electron switch or transistor at room temperature. As a consequence of this knowledge, further developments to organize these quantum dots in two dimensions are necessary. In this study, the Langmuir–Blodgett (LB) technique has been applied to generate extended two-dimensionally organized arrangements of Au₅₅(PPh₃)₁₂Cl₆, Au₅₅[(cyclopentyl)₇Si₈O₁₂(CH₂)₃SH]₁₂Cl₆ and of Au₅₅(PhSH) _x Cl₆. Film formation was performed by spreading dichloromethane or pentane solutions of the clusters onto the water surface in a LB trough, followed by compression by means of a film balance. From the π-A isotherms exact cluster dimensions could be calculated from monolayers, except for Au₅₅[(cyclopentyl)₇Si₈O₁₂(CH₂)₃SH]₁₂Cl₆, the size of which resulted as too small. The reason is to be seen in the formation cluster double layers. Brewster angle microscopy (BAM) investigations of the thin films on the water surface, atomic force microscopy (AFM) and transmission electron microscopy (TEM) studies of transferred films clearly demonstrated formation of densely packed monolayers and of double layers, respectively. These extended mono- and double layers are now available for electric investigations and the construction of layered systems. Those works are in progress. Dedicated to Professor Ilya Moiseev on the occasion of his 75th birthday.     

9,12-Dibenzothiazolylhypericin and 10,11-Dibenzothiazolyl-10,11-didemethylhypericin: Photochemical Properties of Hypericin Derivatives Depending on the Substitution Site

Summary. Investigating the properties of similar but regioselectively differently substituted hypericin derivatives, 9,12-dibenzothiazolylhypericin was synthesized and compared with the recently prepared 10,11-analogue. A significant difference in the ability to generate singlet oxygen and/or reactive oxygen species and different absorption spectra of these two derivatives were observed.     

Characterization of the early stage aminoshikimate pathway in the formation of 3-amino-5-hydroxybenzoic acid: the RifN protein specifically converts kanosamine into kanosamine 6-phosphate

The biosynthesis of 3-amino-5-hydroxybenzoic acid (AHBA), precursor of the ansamycin and mitomycin antibiotics, proceeds by the aminoshikimate pathway from 3,4-dideoxy-4-amino-D-arabino-heptulosonic acid 7-phosphate (aminoDAHP). Identification of RifN, product of one of three genes from the rifamycin biosynthetic gene cluster known to be essential for aminoDAHP formation, as a specific kanosamine (3-deoxy-3-amino-D-glucose) 6-kinase establishes kanosamine and its 6-phosphate as specific intermediates in AHBA formation. This suggests a hypothetical reaction sequence for aminoDAHP formation, and thus for the early steps of AHBA biosynthesis, starting from UDP-D-glucose and introducing the nitrogen by oxidation and transamination at C-3.     

Beiträge zur Chemie der Pyrrolpigmente, 28. Mitt.: Die thermische Stabilität der geometrischen Isomeren von Bilatrienen-abc

In the equilibrium between the two diastereomeric (Z, Z, Z) and (E, Z, Z) forms of aetiobiliverdine-IV- the former is preferred by about 20kJ/mol. For the thermal isomerization a barrier of 108kJ/mol has to be surmounted—as measured for the latter isomer. A value of 12.4 for the logarithm of the preexponential factor leads to a polar singlet mechanism, which was deduced previously for pyrromethenones and arylmethylenepyrrolinones, but a much more positive activation entropy for the verdinoid system indicates a pronounced delocalisation of charge over the entire conjugated system in the corresponding transition state.

27. Mitt.:H. Falk, K. Grubmayr undF. Neufingerl, Mh. Chem.110, 1027 (1979).