Spektroskopische Untersuchungen an organometallischen Verbindungen

Es wird gezeigt, daß in den IR-Spektren von Aromaten-metall-carbonylen zu jeder C -O-Valenz-frequenz eine langwellige Bande so zugeordnet werden kann, daß die Summen aller „Schwingungspaare“ für eine Verbindung jeweils ungefähr gleich groß sind. Diese langwelligen Absorptionen werden empirisch M - C-Valenzschwingungen zugewiesen. Auf Grund dieser Zuordnungen lassen sich Aromaten-metall-carbonyle vergleichend betrachten.

Experimental and predicted crystal structures of Pigment Red 168 and other dihalogenated anthanthrones

The crystal structures of 4,10-dibromo-anthanthrone (Pigment Red 168; 4,10-dibromo-dibenzo[def,mno]chrysene-6,12-dione), 4,10-dichloro- and 4,10-diiodo-anthanthrone have been determined by single-crystal X-ray analyses. The dibromo and diiodo derivatives crystallize inP21/c,Z= 2, the dichloro derivative in P\bar 1,Z= 1. The molecular structures are almost identical and the unit-cell parameters show some similarities for all three compounds, but the crystal structures are neither isotypic to another nor to the unsubstituted anthanthrone, which crystallizes inP21/c,Z= 8. In order to explain why the four anthanthrone derivatives have four different crystal structures, lattice-energy minimizations were performed using anisotropic atom–atom model potentials as well as using the semi-classical density sums (SCDS-Pixel) approach. The calculations showed the crystal structures of the dichloro and the diiodo derivatives to be the most stable ones for the corresponding compound; whereas for dibromo-anthanthrone the calculations suggest that the dichloro and diiodo structure types should be more stable than the experimentally observed structure. An experimental search for new polymorphs of dibromo-anthanthrone was carried out, but the experiments were hampered by the remarkable insolubility of the compound. A metastable nanocrystalline second polymorph of the dibromo derivative does exist, but it is not isostructural to the dichloro or diiodo compound. In order to determine the crystal structure of this phase, crystal structure predictions were performed in various space groups, using anisotropic atom–atom potentials. For all low-energy structures, X-ray powder patterns were calculated and compared with the experimental diagram, which consisted of a few broad lines only. It turned out that the crystallinity of this phase was not sufficient to determine which of the calculated structures corresponds to the actual structure of this nanocrystalline polymorph.

The crystal structure of CaSiO3-walstromite, a special isomorph of wollastonite-II

The crystal structure of CaSiO3-walstromite has been solved and refined by a data set collected in situ from an inclusion in a diamond single crystal (1135 observed reflections, MoKα , Nonius CAD4, R = 3.46). The crystal structure is almost identical to that of walstromite (Ca2BaSi3O9). The replacement of Ba2+ by Ca2+ causes no significant structural changes (ring silicate; according to F. Liebau: dreier single rings). The structural differences to wollastonite-II (Ca3Si3O9) are also relatively small: The Ca positions are almost the same, but the axial Si3O9-ring is isomorphously replaced by the same ring with the inverse axiality. This constitutes a new principle of isomorphous replacement. Based on density functional theory the equation of state has been predicted. This allows us to estimate the remaining pressure of the investigated CaSiO3 inclusion in the diamond to be ≈3 GPa.

Structures of six industrial benzimidazolone pigments from laboratory powder diffraction data

The crystal structures of six industrially produced benzimidazolone pigments [Pigment Orange 36 (beta phase), Pigment Orange 62, Pigment Yellow 151, Pigment Yellow 154 (alpha phase), Pigment Yellow 181 (beta phase) and Pigment Yellow 194] were determined from laboratory X-ray powder diffraction data by means of real-space methods using the programs DASH and MRIA, respectively. Subsequent Rietveld refinements were carried out with TOPAS. The crystal phases correspond to those produced industrially. Additionally, the crystal structures of the non-commercial compound 'BIRZIL' (a chloro derivative of Pigment Yellow 194) and of a dimethylsulfoxide solvate of Pigment Yellow 154 were determined by single-crystal structure analyses. All eight crystal structures are different; the six industrial pigments even exhibit five different hydrogen-bond topologies. Apparently, the good application properties of the benzimidazolone pigments are not the result of one specific hydrogen-bonding pattern, but are the result of a combination of efficient molecular packing and strong intermolecular hydrogen bonds.

4-(4-Chlorophenyl)-3-(4-phenylpent-4-enyloxy)-1,3-thiazole-2(3H)-thione

The title compound, C(20)H(18)ClNOS(2), is a thiazole-derived thiohydroxamic acid O-ester. The value of Z' is 3 and the asymmetric unit comprises three molecules of identical helicity along the N-O bond. Two of these show an anti and the third a syn arrangement of substituents attached in positions 3 and 4 to the 1,3-thiazole nucleus.

Ustilipids, acylated beta-D-mannopyranosyl D-erythritols from Ustilago maydis and Geotrichum candidum

Ustilago species produce an extracellular oil that shows activity in various pharmaceutical assays. We isolated several complexes of this heterogeneous glycolipid from cultures of Ustilago maydis DSM 11494 and Geotrichum candidum ST 002515, and determined the chemical structures of these new compounds, termed ustilipids, on the basis of NMR experiments, mass spectra, and fatty acid analyses. They all possess a 4-O-beta-D-mannopyranosyl D-erythritol basic framework, the configuration of which was confirmed, after initial solvolysis, by a single-crystal X-ray structure analysis. All the investigated ustilipids and related compounds are similarly constructed: the three hydroxy groups of the erythritol side chain are free in all cases, whereas the hydroxy groups of the mannose residue are for the most part acylated. Medium-chain fatty acids have for the first time been detected as components of glycolipids produced by Ustilaginales. While the 2-hydroxy group of the mannose residue is esterified with a C2-C8 carboxylate side chain, the 3-hydroxy group is in all cases esterified by a longer, C12-C20 fatty acid residue. The oxygen functionalities at the 4 and 6 positions are either acetylated or present as free hydroxy groups. Ustilipids antagonize dopamine D3 receptors in micromolar quantities; other members of this class of compounds have been found to possess an inhibitory action on the neurotensin receptor. The hemolytic activity of ustilipids is low.

Synthesis and Extraction Behaviour of Calix[4]arenes Partially Substituted at the Wide Rim by Carbamoylmethylphosphine Oxide (CMPO) Functions

Tetraethers of calix[4]arenes fixed in the cone conformation and substituted at their wide rim by one to three CMPO residues and hydrogen atoms or t-butyl moieties in the remaining position(s) were synthesized. Liquid/liquid extraction studies of selected lanthanides and actinides were undertaken with these calix[4]arenes, including also a linear trimer, in order to obtain a better understanding for the extraction properties of the corresponding calix[4]arene substituted by four CMPO functions. The structure of the 1,3-di-CMPO derivative was confirmed by single crystal X-ray analysis.

Synthesis and activity of novel and selective I(Ks)-channel blockers

Since the discovery of the I(Ks)-potassium channel as the slowly activating component of the delayed rectifier current (I(k)) in cardiac tissue, the search for blockers of this current has been intense. During the screening of K(ATP)-channel openers of the chromanol type we found that chromanol 293B was able to block I(Ks). Chromanol 293B is a sulfonamide analogue of the K(ATP)-channel openers but had no activity on this target. Experiments were initiated to improve the activity and properties based on this lead compound. As a screening model we used Xenopus oocytes injected with human minK (KCNE1). Variations of the aromatic substituent and the sulfonamide group were prepared, and their activity was evaluated. We found that the greatest influence on activity was found in the aromatic substituents. The most active compounds were alkoxy substituted. We chose HMR1556 ((3R, 4S)-(+)-N-[-3-hydroxy-2,2-dimethyl-6-(4,4,4-trifluorobutoxy)chroman-4-yl]-N-methyl-ethanesulfonamide) 10a for development as an antiarrhythmic drug. The absolute configuration, resulting from an X-ray single-crystal structure analysis, was determined.

Resorcarenes in the boat conformation as building blocks for hydrogen-bonded assemblies including two ammonium cations

Crystal structures are reported for various co-crystals of rccc-resorcarenes with triethylammonium chloride. Usually, two molecules of a C2v-symmetric tetraester 2 in the boat conformation are linked through four hydrogen-bonded chloride anions to give dimeric assemblies. Two of the chloride anions may be replaced by four hydrogen-bonded ethanol molecules in an otherwise similar structure. These assemblies, which consist of six or eight components, posses voluminous, negatively charged chambers in which two triethylammionium cations, 3+, are included as guests by strong electrostatic and hydrogen-bonding interactions. The host-guest N-H...Cl hydrogen bonds were clearly detected at 173 K. These are the first examples of hydrogen-bonded, solid-state capsules trapping two ions of the same charge in close proximity. In the 1:2 complex with 3+ Cl-, the molecule of the parent resorcarene 1 also adopts a boat conformation whose cavity is considerably extended by four hydrogen-bonded chloride anions. The pocket formed in this way again includes two 3+ ions as a result of electrostatic and hydrogen bonding host-guest interactions. All these structures show that the boat conformers of resorcarenes can be used as a novel motif for the construction of hydrogen-bonded assemblies capable of molecular inclusion and encapsulation.

The chemical structure of mumbaistatin, a novel glucose-6-phosphate translocase inhibitor produced by Streptomyces sp. DSM 11641

The characterization of the structure of mumbaistatin (1), an effective inhibitor of the glucose-6-phosphatase system (EC 3.1.3.9), is reported. Isolation of mumbaistatin from cultures of Streptomyces sp. DSM 11641 was achieved by anion-exchange and reversed-phase chromatography. The acid-labile inhibitor was methylated for the structure determination. Single-crystal X-ray structure analysis of a triply methylated dehydration product, C31H24O11, revealed the structure of an aromatic dispirodiketal (2), a compound containing a previously undescribed ring system. Extensive 2D-NMR experiments with mumbaistatin and with the methylation products showed that mumbaistatin itself possesses the hydroxydiketodicarboxylic acid structure 1, C28H20O12, which, in the presence of acid or upon activation through methyl ester formation, undergoes self-condensation with loss of water to the dispirodiketal form (2). Mumbaistatin is an anthraquinone derivative, whose open-chain diketo form acts as a specific and powerful inhibitor of glucose-6-phosphate translocase: IC50=5 nM. The activity towards the same enzyme of the cyclized dispirodiketal derivatives is roughly one thousand times lower.

Kodaistatins, novel inhibitors of glucose-6-phosphate translocase T1 from Aspergillus terreus thom DSM 11247. Isolation and structural elucidation

Two novel compounds, kodaistatin A, C35H34O11, molecular weight 630, and kodaistatin C, C35H34O12, molecular weight 646, have been isolated from cultures of Aspergillus terreus Thom DSM 11247 by solid-phase extraction, size-exclusion chromatography, and various preparative HPLC steps. The use of a range of 2D NMR measurements, in particular 13C-13C correlation measurements, has led to the clarification of the structure of kodaistatin A. Kodaistatin C is a hydroxylated derivative of kodaistatin A. Both natural products contain hydroxylated aspulvinones and identical highly substituted polyketide units. An X-ray single crystal structure analysis of aspulvinon E demonstrated the z-configuration at the central double bond. The kodaistatins are effective inhibitors of the glucose-6-phosphate translocase component of the glucose-6-phosphatase system (EC 3.1.3.9), an enzyme system which is important for the control of blood glucose levels. The IC50 is 80 nM for kodaistatin A and 130 nM for kodaistatin C.

Guest-Controlled Formation of a Hydrogen-Bonded Molecular Capsule

The dimerization of the self-complementary resorcarene tetraesters is triggered by the entrapment of a tropylium cation in the pi-basic cavity. Eight intermolecular OH small middle dot small middle dot small middle dotOC hydrogen bonds together with host-guest interactions such as charge transfer and C-H small middle dot small middle dot small middle dotpi bonding are responsible for the high stability of this assembly (see picture). Hereby neither the host-guest interaction nor the interaction of two resorcarene molecules through hydrogen bonds is sufficient by itself to form the complex.

Aurantimycins, new depsipeptide antibiotics from Streptomyces aurantiacus IMET 43917. Production, isolation, structure elucidation, and biological activity

Aurantimycins A (1), B (2) and C (3) were isolated from the mycelium of Streptomyces aurantiacus JA 4570 as new representatives of the azinothricin group of hexadepsipeptide antibiotics. Their structures were settled by X-ray diffraction analysis of crystalline aurantimycin A (1), high field homo- and heteronuclear 2D NMR experiments, high-resolution mass spectrometry and amino acid analysis. Aurantimycins are characterized by a new side chain containing fourteen carbon atoms. They display strong activity against Gram-positive bacteria and cytotoxic effects against L-929 mouse fibroblast cells.

Resolution, absolute stereochemistry, and enantioselective activity of nomifensine and hexahydro-1H-indeno[1,2-b]pyridines

Nomifensine and three selected compounds from the series of H4a,H5-trans,H4a,H9b-cis-2,3,4,4a,5,9b-hexahydro-1H-in deno[1,2-b]pyridines have been resolved into their enantiomers. All compounds exhibit pronounced enantioselective activity with respect to their inhibition of tetrabenazine-induced ptosis and potentiation of yohimbine toxicity. Nomifensine exhibits the same preference for one enantiomer with respect to dopamine and norepinephrine reuptake, whereas in the indeno[1,2-b]pyridine series in vitro experiments do not discriminate between the optical antipodes. The absolute stereochemistry of the pharmacologically active enantiomers in both series was determined by X-ray analyses and comparative CD spectra. For biological activity the diphenylmethane is an essential structure feature in both series. Its absolute configuration proved to be 4S for nomifensine and 5S for indenopyridines. The similar pharmacological profile of the two chemical entities is therefore reflected in an identical configuration of this pharmacologically important molecular part.