Preparation and Properties of Novel Cationically Active Oligo-p-Methoxystyryl-Silica Composites

Abstract

The preparation of cationically active oligo-p-methoxystyrene-silica composites by cationic interfacial polymerization is described. In addition to the effective preparation of the interfacial initiator, p-methoxybenzylium-hydrogen sulfate-silica, and p-methoxybenzylium-trifluoroacetate-silica, a procedure to yield new kinds of composites is reported. The outstanding properties of the “living” oligo-p-methoxy-styryl-hydrogen sulfate-silica is demonstrated by means of zeta potential measurements, solid-state ¹³C-NMR spectroscopy, UV/Vis spectroscopy, and electron scanning microscopy.     

Optically active imidazole N-oxides derived from l-prolinamine1

Starting with (S)-1-benzylprolinamine and α-hydroxyimino ketones, enantiomerically pure bisheterocyclic imidazole N-oxides bearing the (S)-configured N-benzyl(pyrrolidin-2-yl)methyl residue were prepared. These N-oxides reacted with 2,2,4,4-tetramethylcyclobutane-1,3-dithione to give the corresponding optically active imidazole-2-thione derivatives via a sulfur transfer reaction. Reduction of the N-oxides with Raney-nickel led to deoxygenation, whereas catalytic hydrogenation (Pd/C) in ethanol occurred with simultaneous deoxygenation and debenzylation, leading to optically active 1-(pyrrolidin-2-yl)methyl-1H-imidazoles. Alkylation of the prepared imidazole N-oxides and their respective imidazoles with butyl and hexyl bromide and subsequent anion exchange gave optically active N-alkoxy- and N-alkylimidazolium tetrafluoroborates, respectively, with the properties of ‘room temperature ionic liquids’.     

Sensitive detection of hydroxymethylcytosine levels in normal and neoplastic cells and tissues

A new sensitive analytical method using capillary electrophoresis with laser induced fluorescence (CE‐LIF) was applied for the simultaneous detection of DNA methylation and hydroxymethylation levels in human cancers of different origin. DNA hydroxymethylation, measured as 5‐hydroxymethylcytosine (5hmC) levels, was decreased in gliomas with mutation in the isocitrate dehydrogenase 1 (IDH1) gene when compared to IDH1‐wildtype gliomas. Independent from IDH1 mutation, 5hmC levels were decreased in lung carcinomas when compared to normal lung tissue. Reduced DNA hydroxymethylation was also observed upon dedifferentiation in cultured murine embryonic fibroblasts. Our data show that reduced DNA hydroxymethylation is related to cellular dedifferentiation and can be detected in various types of cancers, independent from the IDH1 mutation status. Quantitative determination of altered 5hmC levels may therefore have potential as a biomarker linked to cellular differentiation and tumorigenesis.     

Freezing and Hydrate Formation in Aqueous Sodium Perchlorate Solutions

The determination of the phase diagram of the binary system sodium perchlorate – water is reported. Beside the eutectic point, two polymorph crystal structures of sodium perchlorate dihydrate were determined. The two crystal structures are discussed, compared to each other and to other known sodiumhalide dihydrate crystal structures. The two polymorphs of the perchlorate dihydrate represent the two variants of connected octahedra in the layer structure found for sodium halide dihydrates.     

The Effect of Oxygen on Conversion in the Organic Peroxide-initiated High-Pressure Polymerization of Ethylene

To initiate the high-pressure polymerization of ethylene, oxygen is used together with organic peroxides in a number of tubular reactor processes. Since molecular oxygen is capable of promoting or inhibiting radical polymerization, depending on the reaction conditions chosen, controlled experiments were carried out to clarify these aspects of high pressure ethylene polymerization. In continuous polymerization tests carried out at 1700 bar and temperatures between 110 and 320°C, conversions were determined with tert-amyl perneodecanoate and di-tert-butyl peroxide initiation in the presence of various quantities of oxygen. Batch tests using a photo-initiator together with oxygen were also carried out. A comparison with polymerizations under conditions of careful elimination of oxygen shows no effect on the peroxide-initiated polymerization up to temperatures of 160 to 170°C. Although oxygen is an initiator at higher temperatures, the conversions obtained from the simultaneous addition of controlled quantities of oxygen and organic peroxides is lower than that obtained by adding together the conversions from the separate polymerizations.     

Synthesis and Biological Activity of 7,8,9‐Trideoxy‐ and 7R DesTHP‐Peloruside A

The stereoselective syntheses of 7,8,9‐trideoxypeloruside A ( 4 ) and a monocyclic peloruside A analogue lacking the entire tetrahydropyran moiety ( 3 ) are described. The syntheses proceeded through the PMB‐ether of an ω‐hydroxy β‐keto aldehyde as a common intermediate which was elaborated into a pair of diastereomeric 1,3‐syn and ‐anti diols by stereoselective Duthaler–Hafner allylations and subsequent 1,3‐syn or anti reduction. One of these isomers was further converted into a tetrahydropyran derivative in a high‐yielding Prins reaction, to provide the precursor for bicyclic analogue 4 . Downstream steps for both syntheses included the substrate‐controlled addition of a vinyl lithium intermediate to an aldehyde, thus connecting the peloruside side chain to C15 (C13) of the macrocyclic core structure in a fully stereoselective fashion. In the case of monocyclic 3 macrocyclization was based on ring‐closing olefin metathesis (RCM), while bicyclic 4 was cyclized through Yamaguchi‐type macrolactonization. The macrolactonization step was surprisingly difficult and was accompanied by extensive cyclic dimer formation. Peloruside A analogues 3 and 4 inhibited the proliferation of human cancer cell lines in vitro with micromolar and sub‐micromolar IC₅₀ values, respectively. The higher potency of 4 highlights the importance of the bicyclic core structure of peloruside A for nM biological activity.     

Small‐Peptide‐Based Organogel Kit: Towards the Development of Multicomponent Self‐Sorting Organogels

The results presented here highlight the extremely useful nature of ultra‐short peptides as building blocks in the development of smart multicomponent supramolecular devices. A facile bottom‐up strategy for the synthesis of a small library of stimuli‐responsive smart organogelators has been proposed based on the predictive self‐assembly of ultra‐short peptides. More importantly, the narcissistic self‐sorting of the gelators has been evaluated as a simple method for the efficient co‐assembly of a donor–acceptor dual‐component gel, allowing the investigation of possible future applications of similar systems in the development of a supramolecular photo‐conversion device. Interestingly, it was observed that the self‐organization of the components can lead to highly ordered systems in which discrimination between compatible and non‐compatible building blocks directs the effective organization of the chromophores and gives rise to the formation of an excited‐state complex with exciplex‐like emission. The current report may prove important in the development of organogel‐based multicomponent smart devices.     

Synthesis and supramolecular properties of trimethylene-bridged clips

The novel trimethylene-bridged clips 3 and 4 have been synthesized by using repetitive stereoselective Diels-Alder reactions of the benzo- and naphthobismethylenenorbornenes 8 and 19 as dienes and norbornadiene 9 as bisdienophile, and subsequent dehydrogenation of the primary cyclobisadducts 10 and 20 by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Clips 3 and 4 serve as receptors for a variety of electron-deficient neutral and cationic aromatic substrates, comparable to the molecular tweezers 1 and 2. The thermodynamic parameters of the complex formation, K(a) and DeltaG, were determined by (1)H NMR titration experiments and, in the case of the highly stable complex TCNB 32@4, by the use of isothermal titration microcalorimetry. The finding that clip 4 forms more stable complexes than 3 can be explained by the larger van der Waals contact surfaces of the naphthalene sidewalls in 4 compared to the corresponding benzene systems in 3. In the complexes with 4 as receptor, the plane of each aromatic substrate molecule is calculated to be oriented almost parallel to the naphthalene sidewalls. However, in the complexes of tweezers 2, the substrate is usually oriented parallel to the central naphthalene spacer unit. Due to the more open topology of 4, most complexes were calculated to consist of two or more equilibrating noncovalent conformers.     

On the synthesis of hypericin by oxidative trimethylemodin anthrone and emodin anthrone dimerization: Isohypericin

Summary The base catalyzed oxidative dimerization of emodin anthrone exclusively yields hypericin. However, on oxidative dimerization of trimethylemodinanthrone a mixture of hexamethylhypericin and hexamethylisohypericin was obtained. Chromatographic separation of the hexabenzoyl derivatives was achieved, and by saponification about equal amounts of hypericin and isohypericrin were produced. Isohypericin could be characterized for the first time by its spectroscopic data and its protonation and deprotonationpK _a andpK _a ^* values.

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Zur Synthese von Hypericin durch oxidative Dimerisierung von Trimethylemodinanthron und Emodinanthron: Isohypericin

Zusammenfassung Die basenkatalysierte oxidative Dimerisierung von Emodinanthron liefert ausschließlich Hypericin. Oxidative Dimerisierung von Trimethylemodinanthron ergibt jedoch ein Gemisch von Hexamethylhypericin und Hexamethylisohypericin. Die Hexabenzoylderivate wurden chromatographisch getrennt, und Hypericin und Isohypericin konnten aus diesen Derivaten durch Verseifung freigesetzt werden. Isohypercin konnte erstmals durch seine spektroskopischen Daten und seine Protonierungs- und Deprotonierungs-pK _aundpK _a ^* -Werte charakterisiert werden.