Gabel, Detlef
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Gabel, Detlef
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Gabel, Detlef
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Gabel, Detlev
Gabel, D.
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Item-typ:Veröffentlichung, Synthesis of iron sulfur clusters as models for primordial life(2013-02-28); ; ; The synthesis of a lipid-bound ligand of the [4Fe4S] hydrogenase model complex is described. The ligand, after reaction to the final hydrogenase complex, can be incorporated into liposomes, which serve as models for cell membranes and allow research on primitive bio-systems. The crucial synthetic steps were the choice of nucleophile for substitution of tribromo-trifluorobenzene and the choice of a benzoyl group instead of a methoxymethyl group as protecting group.Dissertation317 125 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Dodecahydro-closo-dodecaboratderivate für die Anwendung in der nichtlinearen Optik(2009-05-25); ; ; Previously investigated and calculated properties of the dodecahydro-closo-dodecaborate(2-) derivatives predict a high probability that they are applicable for nonlinear optical materials for compounds in which the B12-cluster acts as a donor and is connected via a Pi-conjugated system to an acceptor substituent. For this reason it was of interest to prepare new dodecaborate containing nonlinear optical molecules.Palladium catalyzed coupling reactions were carried out and new coupling products could be achieved, which could serve as intermediates for further reactions. Alkynyl derivatives of the dodecaborate are described, [B12H11C6H4CCH](2-),[B12H11CCPh](2-), [B12H11CCSi(CH3)3](2-)and the resulting ethynyl derivative. Also coupling-products with double bonds could be achieved([B12H11C6H4CCH2](2-)). [B12H11C6H4CCH](2-) was able to be connected via Sonogashira coupling to acceptor containing molecules, 1-bromo-4-nitrobenzene, trans-2,3,4,5,6-pentafluoro-4'-bromostilben, and 1-(4-bromophenyl)-2-phenyl-o-carborane. The resulting compounds (16, 18, 22) might have nonlinear optical properties. The advantage of the compound which contains the dodecaborate and the o-carborane is a high transparency in the region above 400 nm. Dodecaborates should be also connected via an amino group to an acceptor substituted aromatic compound, to increase the donor properties of the amino group by the cluster and to prevent a centrosymmetric crystallization.The nucleophilic aromatic substitution with [B12H11NH2](2-) on aromatic systems with electron withdrawing substituents, such as 4-nitrophthalonitrile, which results in two different products (33, 34), and 1-chloro-2,4-dinitrobenzene (32), was successful. In the case of the dinitrophenyl derivative 32 single crystals for X-ray analysis could be obtained. Another possibility for a boron-nitrogen-aryl linkage is the reaction of TBA2B12H12 with arylamines, such as aniline and N,N-dimethylaniline, which results in the expected arylammonium derivatives (35, 36) of the cluster.Mass spectral analyses helped to explain the as yet unknown mechanistic pathway: in the case of N,N-dimethylaniline, and 4-(dimethylamino)pyridine, Hofmann elimination of the tetrabutylammonium ion at high temperatures takes place, initiated by the abstraction of a hydride from the cluster. The structure of the N,N-dimethylaniline derivative could be elucidated by X-ray analysis. In the case of aniline and 4-aminopyridine (the latter is described by Koch and Preetz (1997b)), the formed hydride reacts with a proton of the amino group to form dihydrogen. The nucleophilic attack at the electropositive boron atom occurs by the amino nitrogen. This could also be the mechanisms of the reactions resulting in a linkage to nitrogen (Koch and Preetz 1997a and 1997b), or carbon (Preetz and von Bismarck 1991). Overnight reaction of aniline and TBA2B12H12 leads to dodecaborate derivatives, substituted with one up to three aniline moieties. Interestingly, hydroamination products of these compounds with butene could be observed.Dissertation258 146 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Cellular and subcellular localization of mercaptoundecahydro-closo-dodecaborate (2-) (BSH) in human glioblastoma multiforme(2001-07-03); ; ; The cellular and subcellular distribution of mercaptoundecahydro-closo-dodecaborate (BSH) were investigated in glioblastoma multiforme tissue sections of seven patients, whom having received BSH prior to surgery. To achieve this, several microscopic techniques were used. Direct detection of boron was performed by x-ray photoelectron emission spectromicroscopy (X-PEEM), electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI). For visualization of BSH in light-, fluorescence microscopy and transmission electron microscopy (TEM) antibodies against BSH were used.These microscopic techniques show that BSH is associated with the cell membrane as well as with the chromatin in the nucleus. With use of specific antibodies against different tumor specific epi-topes, BSH could be found predominantly (approx. 90 %) in the cytoplasm of GFAP-positive cells of all but two patients. The latter were significantly younger (33 and 38 years versus to 46-71 (mean 60) years). Based on the expression of EGFR and p53, the tumors of five patients could be characterized as primary or secondary glioblastoma. Although the tissue regions of EGFR and p53 overexpression do not seem to correspond with the regions of high BSH incidence, muta-tions during tumor development could be the reason for the distinct accumulation of BSH. No direct correlation between BSH uptake and expression of CD44, vWF, laminin and Ki-67 has been observed.By x-ray photoelectron emission spectromicroscopy boron was found in a reduced chemical state (with respect to boron in BSH). The reduced boron species was found in tissue in the same general areas, which stained positive for BSH in light microscopy. The present work presents for the first time evidence that a proportion of the BSH injected into the patient could have been bound or metabolized in vivo.Dissertation318 139 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Triggered release of liposome contents by the divalent anion B12H11SH(2-): Biochemical studiesBSH is one of the two boron compounds in use in BNCT. Triggered release of liposome contents by BSH has been achieved. We used liposomes of different compositions as a model for studying the interaction of BSH with cell membranes. The interaction of BSH with cationic liposomes of different compositions was investigated. Zeta potential and size measurements of the liposomes in absence and presence of BSH indicated a firm binding of BSH with the headgroups of these liposomes. Beside exploiting the liposomes as model for cell membranes, there is also great interest in liposomes as drug carriers. To have a pronounced therapeutic effect, the release of the drug from the liposomes should be as complete as possible. Because of this, developing tools for triggering release of agents encapsulated inside the aqueous compartment of the liposomes is an important factor in the liposome drug delivery systems.We studied the interaction of BSH with neutral liposomes prepared either from DMPC or DPPC lipids and proved that they released their contents under the influence of BSH within minutes.Dissertation259 105 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Chromatographische Untersuchung der Wechselwirkung von Arzneimitteln und Borclusterverbindungen mit Lipidmembranen(2012-09-26); ; ; Immobilized liposome chromatography (ILC) was utilized to investigate the interaction of drugs, chemicals and dodecaborate cluster compounds with liposomes. Dodecaborate cluster compounds were found to interact with hydrophilic column materials (Superdex 200, Sepharose 4B, Sephadex G50 and Sephadex G100). Silica gel showed no or very weak interaction with dodecaborate cluster compounds, and the modified silica gel was used to investigate the interation of dodecaborate cluster compounds with lipid membranes.Dissertation256 119 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Synthesis of boron-cluster containing amino acids and preparation of their polymers(2006-04-26); ; ; The first aim of this work was to prepare water soluble [B12H12]2- containing amino acids. This task was reached by using the ability of dodecaborate derivatives such as ammonio-undecahydro-closo-dodecaborate BNH3, hydroxo-undecahydro-closo-dodecaborate BOH and S-(2-cyanoethyl)-thio-undecahydro-closo-dodecaborate(2-)CE-BSH to undergo alkylation reactions. With this idea we used halogen substituted monoalkylated educts such as:- 4-Bromobutylacetamidodiethylmalonate. Alkylation reactions with BOH 4 and CE-BSH were made with high yield (93%) for CE-BSH and with moderate yield (53%) for BOH. Alkylation of BNH3 gave a mixture of mono- and dialkyl-substituted products. Separation of this mixture could not be achieved.- Chloroacetone. Alkylation of CE-BSH and BOH with chloroacetone was carried out with quantitative yields. We showed the ability of these ketones formed to give appropriate hydantoins.- (2S)-2-[(Tert-butoxycarbonyl)amino]-3-(p-tolylsulfonyl-oxy)propionate. It was shown that alkylation of CE-BSH with tosylated serine is possible.All alkylated derivatives were hydrolyzed in 6M NaOH to yield free amino acids. The solubility of synthesized amino acids depends of the cation. Cs increases solubility in water.In vitro toxicity tests were carried out with two amino acids having different number of carbons and two different heteroatoms between cluster and side chain. Toxicity test was done with V 79 Chinese hamster cells. For amino acid 13a LD50 was 5.7 mM and for 16a LD50 was 5.0 mM. According to these results, we can say that addition of an amino acid group to, e.g. the BSH cage, does not change the toxicity.For the second task of this work - synthesis of D,L-polypeptides - the ring-opening polymerization method was chosen. We showed the ability of the synthesized dodecaborate-containing amino acids to form N-carboxy anhydride by phosgenation. Polymerization was carried out with two initiators: n-butylamine and dansyl amine. It was shown that the initiator did not interact to the polymer structure, but act as a catalyst in the AM mechanism. The determination of the molecular weight of the synthesized polymers (number of monomers) failed, however.All synthesized compounds were identified by 1H-, 13C-, 11B-NMR, mass spectrometry, IR spectra. In the course of the characterization of [B12H12]2- containing compounds we found that the [B12H11]- ion is easily formed in ESI-MS. The origin of the peak at m/z 141 was found and proven in a MS/MS experiment. The MS/MS experiment of peak at m/z 141 showed of the following processes proceeding:- Hydroxylation - Addition of H2 - Exchange of D to HDissertation337 156 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Borierte Chromophore für die nichtlineare Optik und Untersuchungen zur Oligomerisierung borreicher Phosphoramidite für die Anwendung gegen Krebs(2003-09-11); ; ; One part of this thesis was the synthesis of chromophoric compounds, which stands a good chance of being used as materials for nonlinear optics. Based on ammonium-undecahydro-closo-dodecaborate requirements for the synthesis of a target compound could be established. The process leading to this target compound so far could not be achieved due to failure to synthesize one internal compound. The reasons for this failure and several alternatives for the preparation of the internal compound were discussed in detail.Another part of this thesis was the synthesis of building blocks based on mercapto-undecahydro-closo-dodecaborate, which were to be oligomerized using the phosphite-triester approach. A sequence for the use in Boron Neutron Capture Therapy was desirable, which consists of these monomers. Four building blocks based on the double charged dodecaborate thus far unknown in the literature were synthesized and characterized. The use of one boronated building block in a standard sequence and the following cleavage of the oligomer by concentrated ammonia revealed that the new monomer in fact marks a point of cleavage in the sequence. However, the successful coupling of the boronated building block before cleavage of the oligomer was underpinned by UV-VIS-spectroscopic detection of coupling yields. The repetition of the experiment under milder cleavage conditions should led to higher mass numbers than before. Therefore investigation in cleavage conditions was expanded systemati-cally. The best results in a comparative study were achieved with ethanolamine (Polushin et al., 1994). The detected values from MALDI-TOF were very close (M 11) to that of the calculated mass of the oligomer. An important disadvantage seemed to be a decomposition of the oligomer, because an unusually high number of signals could be found. Because of that further alternative methods such as usage of photolabile linkers (Greenberg et al., 1994) have been taken into consideration.Dissertation229 302 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Synthese von mehrfach geladenen closo-Dodecaborat-Derivaten und borhaltigen Lipiden(2013-12-04); ; ; The boron neutron capture therapy (BNCT) opens a fascinatingly perspective for cancer treatment. Non toxic or low toxic boron-containing compounds are used in BNCT. Therefore, the first part of the work is the synthesis of amphiphilic boron compounds. In particular, neutral and singly positively charged lipid-like compounds were synthesized. The second part of this work is the synthesis of a six negatively charged fluorescent boron compound.Dissertation264 152 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Dodecaboratclusterhaltige Membranen für Brennstoffzellen(2014-07-02); ; ; In this work it was to be shown whether dodecaborate cluster-containing polymers can have possible applications as polymer electrolyte membranes in fuel cells. There are two possibilities to prepare membranes containing dodecahydro-closo-dodecaborate (2-). On the one hand by polymerization of boron cluster-containing monomers to linear, branched or cross-linked polymers. Or on the other hand by substitution of existing membranes such as Nafion with the B12-cluster. It was possible to synthesize a variety of monomers with a [B12H11]2- moiety, which some could be polymerized successfully. Radical homo-, co- and photo polymerizations were not successful with boron cluster monomers. Only the photo polymerization of the acrylic acid derivative in the NMR experiment was successful, which might be due to the used Spot Lamps. Cationic polymerizations were also not successful. Also hydrosilylations were no suitable polymerizations for boron cluster-containing monomers. Polycondensation reactions with B12H11 monomers were promising. The reaction of dihydroxybenzylammonioundecahydro-closo-dodecaborate with decafluorobiphenyl showed no starting material in the MS, instead it shows a triply negatively charged peak with a yet unknown structure. With the ring-opening metathesis polymerization bis-norbornene derivatives of the dodecaborate cluster could not be polymerized. However, the mono norbornene derivatives of B12H12(2-) formed insoluble swelling polymers in the homo- and copolymerization with dicyclopentadiene and Grubbs 2nd Generation catalysts. Another method to produce a boron cluster-containing polymer is the substitution of Nafion with the boron cluster. From the obtained polymers, films can be produced, which, however, have no better thermal stability than the pure Nafion membrane. However, investigations whether they are suitable as a membrane material must still be carried out.Dissertation265 98 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Synthese von N-Carboranoylamido-Derivaten der Sialinsäure und der Glucose(2007-04-13); ; ; Aim of the work was the development of a highly potent inhibitor of Myelin-associated glycoprotein(MAG)also called siglec-4a protein. MAG inhibits neurite outgrowth from neurons of the injured central nervous system (CNS). Gangliosides with terminal sialic acid (Sia) groups are known in literature as functional binding partners for MAG. The inhibition of this binding by synthetic Sia-derivatives might benefit the regeneration of the injured CNS. Inhibitor was to be synthesized through connection of closo-carboranyl carboxylic acid chloride with the 9-amino-group of 9-amino-5-N-acetylneuraminic acid glycosides. The glucose derivative glucosamine was used as a model compound to study reaction details. The synthesis of the desired N-carboranoylamido derivative of glucose was successful. During the attempt to synthesize an N-carboranoylamido derivative of Sia a degradation of the closo-carborane C2B10-cage to the nido-carborane C2B9-structure was observed. The new synthesized water soluble Sia-derivative nido-carboranoylamido-Neu5Ac2Bn was used in a hapten-inhibition assay. It is a potent inhibitor of soluble Fc-MAG-chimeras.Dissertation251 138