Zur Stereochemie der Vitamin D3-Epoxide Röntgenstrukturanalyse einer 5,6-7,8-Diepoxidverbindung

Epoxidation of vitamin D₃ with benzonitrile ¦H₂O₂¦ KHCO₃ (Payne's reagent) yields exclusively the 5,6-mono-oxirane2. Further epoxidation with the same reagent gives the 5,6-7,8-bisepoxide3 a. Its stereochemistry and therefore the stereochemistry of2 was established by single crystal X-ray analysis of thep-Brbenzoate3b. Thereby for the first time a directive effect of a homoallylic hydroxyl group during thePayne-epoxidation was established.

Herrn Prof.Mihailovic (Universität Belgrad) mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Is the Conventional Interpretation of the Anisotropic Effects of CC Double Bonds and Aromatic Rings in NMR Spectra in Terms of the π‐Electron Shielding/Deshielding Contributions Correct?

Based on the nucleus‐independent chemical shift (NICS) concept, isotropic magnetic shielding values have been computed along the three Cartesian axes for ethene, cyclobutadiene, benzene, naphthalene, and benzocyclobutadiene, starting from the molecular/ring center up to 10 Å away. These through‐space NMR spectroscopic shielding (TSNMRS) values, which reflect the anisotropic effects, have been broken down into contributions from localized‐ and canonical molecular orbitals (LMOs and CMOs); these contributions revealed that the proton NMR spectroscopic chemical shifts of nuclei that are spatially close to the C?C double bond or the aromatic ring should not be explained in terms of the conventionally accepted π‐electron shielding/deshielding effects. In fact, these effects followed the predictions only for the antiaromatic cyclobutadiene ring.     

Simultaneous determination of capecitabine and its metabolite 5-fluorouracil by column switching and liquid chromatographic/tandem mass spectrometry

A liquid chromatographic/tandem mass spectrometric method was developed and validated for the quantitation of capecitabine and its metabolite 5-fluorouracil in human plasma. The simultaneous determination of both analytes was achieved by a column switching method using a trapping column and two analytical columns with different stationary phases. Isocratic elution was used for the separation of capecitabine on a C18 column whereas 5-fluorouracil was separated using gradient elution on an non-polar carbon phase. The calibration curves were linear for both compounds with a correlation factor (R2) > 0.9993 for 5-fluorouracil and >0.9942 for capecitabine. The assay was validated in the concentration range 5.00-1000 ng ml(-1) for both compounds. The intra-day precision was better than 10% for 5-fluorouracil and better than 11% for capecitabine whereas the inter-day precision was better than 8% for 5-fluorouracil and better than 14% for capecitabine.     

Improved STR typing of telogen hair root and hair shaft DNA

Today the STR typing of telogen hair and hair shafts is regarded as a challenge. The small DNA quantity in the hair is highly degraded. Another problem are PCR inhibitors in the hair. In particular hair pigments, the melanins, are known to inhibit PCR. Hairs are exposed to sunlight and partly to chemical oxidation processes, which make them even more difficult to analyze. To increase the chances of a correct typing of hair, the small amount of DNA must be successfully isolated and the inhibitors have to be removed or neutralized. Furthermore, miniSTR typing improves the analysis of stains with degraded DNA like it is the case with hair. We introduce a nonorganic extraction method and in addition a miniSTR concept which is promising in typing stains with little and degraded DNA, especially hairs. The miniSTR concept including five database STRs (SE33, VWA, TH01, FGA, D3S1358) and the gender typing system Amelogenin was optimized for the amplification of hair DNA. Compared to commercial STR kits, this approach resulted in considerably higher success rates.     

The structure of amorphous sulfur

The λ‐transition of elemental sulfur occurring at about 159°C has long been associated with the conversion of cyclic S₈ rings (c‐S₈) to amorphous polymer (a‐S) via a ring opening polymerization. Here we demonstrate, with the use of both density functional and Hartree‐Fock quantum mechanical calculations, the existence of an energetically accessible, locally stable, hypervalent state of S that can form branch sites in the polymer. The significance of this finding is that the λ‐transition is best described as a gelation transition. The geometry of the tetravalent S atom is trigonal bipyramidal, with a lone pair occupying one of the three equatorial sites; it lies in a local energy minimum about 31 kcal/mol above the normal divalent state, and so is accessible both thermally and photochemically. Because the branched structure is formed endothermically, Le Chatelier's principle confirms that a percolation network can form on heating the element. The reactions that form branched structures are reversible, implying that the gel is fluxional. It decomposes at higher temperatures as chain scission competes with branching. The hypervalent structure provides an essential insight into the chemistry of elemental sulfur.     

Kristallstruktur von Na3(NH4)12[Mo57Fe6(NO)6O174(OH)3(H2O)24]·76H2O,einer Verbindung mit einem ungewöhnlichen Clusteranion

Summary The X-ray crystal structure of the compound Na₃(NH₄)₁₂[Mo₅₇Fe₆(NO)₆O₁₇₄(OH)₃(H₂O)₂₄]·76H₂O (3) [P6₃/mmc;a=2380.6(5),c=2763.4(7),Z=2], the giant cluster anion of which has the shape of a doughnut, shows remarkable details: The cluster [{Fe(H₂O)₂}₆{Mo(-H₂O)₂(-OH)Mo}₃{ Mo₁₅(MoNO) ₂ ³⁺ O₅₈(H₂O)₂}₃]^15– can be described as being composed of three transferable {Mo₁₇} ligands bridged by cationic centers and contains a novel nanodimensional central cavity.

     

Einfache Trithio- und Perthiocarbonatokomplexe mit interessanter Koordinationschemie: [E(CS3)2]2− (E = Sn,Zn, Cd), [E(CS3)3]3− (E = As,Sb, Bi,Co), {Cu(CS3)−}∞ und [Zn(CS4)2]2−

Simple Trithio- and Perthiocarbonato Complexes with Interesting Bond Properties: [E(CS₃)₂]^2? (E = Sn, Zn, Cd), [E(CS₃)₃]^3? (E = As, Sb, Bi, Co), {Cu(CS₃)^?}_∞ and [Zn(CS₄)₂]^2? By reactions of potassium trithiocarbonate ( 1 ) with solutions of zinc(II)- acetylacetonate, cadmium(II)-chloride, tin(II)-chloride, arsenic(III)-sulfide (suspension), antimony(III)-chloride, bismuth(III)-chloride and copper(II)-chloride in dimethyl sulfoxide, as well as of trisodium hexanitrito cobaltate(III) in water, and the precipitation of the complexes with an aqueous solution of tetraphenylphosphonium chloride the compounds (PPh₄)₂[Zn(CS₃)₂] ( 2 ), (PPh₄)₂[Cd(CS₃)₂] ( 3 ), (PPh₄)₂[Sn(CS₃)₂] ( 4 ), (PPh₄)₃[As(CS₃)₃] ( 5 ), (PPh₄)₃[Sb(CS₃)₃] ( 6 ), (PPh₄)₃[Bi(CS₃)₃] ( 7 ), (PPh₄)₃[Co(CS₃)₃] ( 8 ) and (PPh₄)Cu(CS₃) ( 9 ) have been isolated. (PPh₄)₂[Zn(CS₄)₂] · CH₃NO₂ ( 10 ) has been prepared by heating a solution of 2 in nitromethane to 60--70°C in presence of air. The reaction of 1 in dimethyl sulfoxide with an aqueous tetraphenylphosphonium chloride solution in presence of oxygen leads to (PPh₄)₂[C₂S₆] ( 11 ). The compounds have been characterized by spectroscopical studies (IR, Raman, UV/Vis, ¹¹³Cd/⁵⁹Co-NMR), magnetic susceptibility measurements, powder diffractometry, elemental analyses and single crystal X-ray structure analysis ( 4 – 7 , 10 and 11 ). The difficult growing of single crystals has been reported in detail. For crystal data see Inhaltsübersicht.     

Platinum complexes of oxopurines: cis‐bis(theophyllinato‐N7)bis(triphenylphosphine)platinum(II) and cis‐chloro(theobrominato‐N1)bis(triphenylphosphine)platinum(II) ethanol hemisolvate

The syntheses and structures of two mixed‐ligand complexes of platinum(II) with deprotonated oxopurine bases and tri­phenyl­phosphine are reported, namely the theophyllinate complex cis‐bis(1,2,3,6‐tetra­hydro‐1,3‐di­methyl­purine‐2,6‐dionato‐κN⁷)­bis(tri­phenyl­phosphine‐κP)­platinum(II), [Pt(C₇H₇N₄O₂)₂(C₁₈H₁₅P)₂], (I), and the theobrominate complex cis‐chloro(1,2,3,6‐tetrahydro‐3,7‐dimethylpurine‐2,6‐dionato‐κN¹)­bis(tri­phenyl­phosphine‐κP)­platinum(II) ethanol hemisolvate, [PtCl(C₇H₇N₄O₂)(C₁₈H₁₅P)₂]·0.5C₂H₅OH, (II). In (I), the coordination geometry of Pt is square planar, formed by the two coordinating N atoms of the theophyl­linate anions in a cis arrangement and two P atoms from the tri­phenyl­phosphine groups. In (II), there are two crystallographically independent mol­ecules. They both exhibit a square‐planar coordination geometry around Pt involving one Cl atom, the coordinating N atom of the theobrominate anion and two P atoms from the tri­phenyl­phosphine groups. The two tri­phenyl­phosphine groups are arranged in a cis configuration in both structures. The heterocyclic rings are rotated with respect to the coordination plane of the metal by 82.99 (8) and 88.09 (8)° in complex (I), and by 85.91 (16) and 88.14 (18)° in complex (II). Both structures are stabilized by intramolecular stacking interactions involving the purine rings and the phenyl rings of adjacent tri­phenyl­phosphine moieties.     

Technical Procedures for the Syntheses of Carotenoids and Related Compounds from 6-Oxo-isophorone: Syntheses of (3R,3′R)-Zeaxanthin. Part I

Starting from the readily available, optically active (4R)-4-hydroxy-2,2,6-trimethylcyclohexanone ( 1 ), a new technical synthesis of (3R,3′R)-zeaxanthin is described. According to a 2(C₉ + C₆) + C₁₀ = C₄₀ construction scheme, the ketone 1 was first transformed with (E)-3-methylpent-2-en-4-yn-1-ol ( 5 ) into a C₁₅-intermediate which, by a three-step sequence, could be converted into the known olefinic C₁₅-Wittig salt 4 . Optimized conditions for the final Wittig reaction of 4 with the C₁₀-dialdehyde 3 are discussed. Based on 1 , the overall yield of the entire technical process is ca. 40%.     

Solution- and bound-state conformational study of N,N',N"-triacetyl chitotriose and other analogous potential inhibitors of hevamine: application of trNOESY and STD NMR spectroscopy

The solution-state conformations of N,N',N"-triacetyl chitotriose (1) and other potential chitinase inhibitors 2-4 were studied using a combination of NMR spectroscopy (NOESY) and molecular mechanics calculations. Determination solely of the global energy minimum conformation was found to be insufficient for an agreement with the NMR results. An appropriate consistency between the NMR experimental data and theoretical calculations was only reached by assessing the structures as population-weighted average conformers based on Boltzmann distributions derived from the calculated relative energies. Analogies, but also particular differences, between the synthetic compounds 2-4 and the naturally-occurring N,N',N"-triacetyl chitotriose were found. Furthermore, the conformation of compounds 1 and 2 when bound to hevamine was also studied using transferred NOESY experiments and the binding process was found to impart a level of conformational restriction on the ligands. The preferred conformation as determined for 1 in the bound state to hevamine belonged to one of the conformational families found for the compound when free in solution, although full characterisation of the bound-state conformations was impeded due to severe signal overlap. Saturation transfer difference NMR experiments were also employed to analyse the binding epitopes of the bound compounds. We thus determined that it is mainly the acetyl amido groups of the trisaccharide and the heterocyclic moiety which are in close contact with hevamine.