Syntheses and Properties of Two Heterocyclically Substituted Hypericin Derivatives: 10,11-Dibenzothiazolyl-10,11-didemethylhypericin and 10,11-Dibenzoxazolyl-10,11-didemethylhypericin

Summary. The syntheses of the two heterocyclically substituted title hypericin derivatives were achieved starting either from 6-benzothiazolyl-tri-O-methyl-6-demethylemodin or 6-benzoxazolyl-tri-O-methyl-6-demethylemodin. The use of microwave assisted synthesis for the preparation of these anthraquinone synthons and the chemical as well as photochemical properties of the corresponding unique hypericin derivatives, which might constitute new photodynamic therapy agents, are reported. The tautomeric and stereochemical aspects of these hypericin derivatives were investigated by means of semiempirical calculations (AM1).     

Square-planar coordinated polyanions of palladium, platinum, and gold stannaborate [SnB11H11]2- coordination chemistry

The tetrasubstituted polyanions of platinum, palladium, and gold [M(SnB(11)H(11))(4)](x-) (x=6, M=Pd, Pt; x=5, M=Au) have been prepared and characterized by single-crystal X-ray diffraction, elemental analysis, IR, Raman, (11)B, and (119)Sn heteronuclear NMR spectroscopy. In the case of the platinum derivative [Bu(3)MeN](6)[Pt(SnB(11)H(11))(4)] (2) (119)Sn M?ssbauer spectroscopy has been carried out. The isolated salts are stable towards moisture and air and the complexes 2 and 3 were treated with 1,3-bis(diphenylphosphino)propane (dppp) to give the respective substitution products [Bu(3)MeN](2)[(dppp)M(SnB(11)H(11))(2)] (M=Pd, Pt).     

A Convenient Regiospecific Synthesis of New Conjugated Tetrazole Derivatives via the Reaction of Dienones with the Tetrachlorosilane-Sodium Azide Reagent and their NMR Structural Assignment

Several new 1-aryl-, aralkyl-, and heteroaryl-5-(4-phenylbuta-1,3-dienyl)tetrazole derivatives and annulated tetrazole derivatives were efficiently and regiospecifically prepared in nearly quantitative yield via a facile one step reaction of dienones with a combination of tetrachlorosilane and sodium azide in acetonitrile under mild conditions. A complete structure assignment of three representative examples of the tetrazoles was achieved by advanced 2D NMR measurements including COSY, TOCSY, HSQC, HMBC, NOESY, and ROESY experiments.     

Neue Fluropalladate(II)

New Fluoropalladates(II) Single crystal investigations on \documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{*{20}c} {[6][4]} \\ {{\rm CsPdPdF}_{\rm 5} } \\ \end{array} $\end{document} (orange brown) demonstrate the close structural relationship to the CsAgFeF₆ – and CsNiNiF₆-type, respectively. One half of the Pd²⁺ ions is surrounded octahedrally, whereas the other half, because of the “absence” of one F^?, is coordinated planar quadratically. CsPd₂F₅ crystallizes orthorhombic (Imma – D, No. 74; Z = 4) with a = 6.53₃, b = 7.86₂, c = 10.79 Å (four circle diffractometer data). From Guinier data are isotypic CsMgPdF₅ (yellow, a = 6.603(2), b = 7.415(2), c = 10.548(3) Å), CsZnPdF₅ (beige, a = 6.576(1), b = 7,483(2), c = 10.645(2) Å), CsNiPdF₅ (yellow, a = 6.499(1), b = 7.504(2), c = 10.575(3) Å) and CsCoPdF₅ (brown, a = 6.527(1), b = 7.553(1), c = 10.659(2) Å). Besides of CsPd₂F₅ there exist compounds of the composition Me₃PdF₅ on the alkali-rich side of the system MeF/PdF₂. Single crystal investigations for Rb₃PdF₃ (yellow, P4/mbm–D, No. 127; Z = 2) led to a = 7.46₇, c = 6.49₇ Å (four circle diffractometer data). Isotypic are (single crystal data) Cs₃PdF₅ (yellow, a = 7.84₈, c = 6.68₈ Å) and Rb₂CsPdF₅ (yellow, ordered distribution of the alkali ions, a = 7.57₅, c = 6.44₅ Å).     

Reaction of 1,4-pentadiyne with diethylaminotrimethylstannane

The reaction between 1,4-pentadiyne and diethylaminotrimethylstannane leads predominantly to (E)-2-diethylamino-4-trimethylstannyl-2,4-pentaenyne (with either a 1/1 or 1/2 mol ratio of 1,4-pentadiyne and diethylaminotrimethylstannane). With 1/2 stoicheiometry 1,1,5-tris(trimethylstannyl)penta-1,2-dien-4-yne is formed as a minor product. ¹³C and ¹¹⁹Sn NMR data are reported.     

A quantum-chemical study of dinitrogen reduction at mononuclear iron-sulfur complexes with hints to the mechanism of nitrogenase

The mechanism of biological dinitrogen reduction is still unsolved, and the structure of the biological reaction center, the FeMo cofactor with its seven iron atoms bridged by sulfur atoms, is too complicated for direct attack by current sophisticated quantum chemical methods. Therefore, iron-sulfur complexes with biologically compatible ligands are utilized as models for studying particular features of the reduction process: coordination energetics, thermodynamic stability of intermediates, relative stability of isomers of N2H2, end-on versus side-on binding of N2, and the role of states of different multiplicity at a single iron center. From the thermodynamical point of view, the crucial steps are dinitrogen binding and reduction to diazene, while especially the reduction of hydrazine to ammonia is not affected by the transition metal complex, because the complex-free reduction reaction is equally favored. Moreover, the abstraction of coordinated ammonia can be easily achieved and the complex is recovered for the next reduction cycle. Our results are discussed in the light of studies on various model systems in order to identify common features and to arrive at conclusions which are of importance for the biological mechanism.     

1H detection in MAS solid-state NMR spectroscopy of biomacromolecules employing pulsed field gradients for residual solvent suppression

In this communication, we demonstrate the feasibility of 1H detection in MAS solid-state NMR for a microcrystalline, uniformly 2H,15N-labeled sample of a SH3 domain of chicken alpha-spectrin, using pulsed field gradients for suppression of water magnetization. Today, B0 gradients are employed routinely in solution-state NMR for coherence order selection and solvent suppression. We suggest to use gradients to purge water magnetization which cannot be suppressed using conventional water suppression schemes. The achievable gain in sensitivity for 1H detection is in the order of 5 compared to the 15N detected version of the experiment (at a MAS rotation frequency of 13.5 kHz). We expect that this labeling concept which achieves high sensitivity due to 1H detection, in combination with the possibility to measure long range 1H-1H distances as we have shown previously, to be a useful tool for the determination of protein structures in the solid state.     

Chemie von α-Aminonitrilen 22. Mitteilung Regioselektive Synthese und Kristallstruktur von Uroporphyrinogen-(Typ I)-octanitril

Chemistry of α-Aminonitriles. Regioselective Synthesis and Crystal Structure of Uroporphyrinogen (Type I) Octanitrile A regioselective synthesis of uroporphyrinogen-octanitrile (type I) based on the strategy of multiple use of (dimethylmethylidene)ammonium iodide for stepwise regioselective functionalization of the pyrrole nucleus is described. This uroporphyrinogen derivative is remarkably stable and beautifully crystallizes in space group P1 with one molecule per unit cell. The crystal structure of the compound shows interesting conformational characteristics which are interpreted to be caused by subtle stereoelectronic effects. The English Footnotes to Schemes 1-3 and Figs. 1-12 provide an extension of this summary.     

Carbon-carbon bond formation between alkylated alkenes and acrylic ester via 2-methoxyalkyl radicals

Methoxymercuration/demercuration reactions of alkenes 10 in $\text{10}$ in the presence of acrylic ester yield products $\text{11}$ in a carbon-carbon bond formation reaction.     

An Efficient Synthesis of <Emphasis Type="Italic">O</Emphasis>-Methyl Protected Emodin Aldehyde and Emodin Nitrile

Summary. An efficient synthesis of tri-O-methylemodin aldehyde was achieved via bromination of tri-O-methylemodin utilizing N-bromosuccinimide yielding the monobromo and dibromo derivatives. Sommelet reaction of the monobromomethyl derivative as well as hydrolysis of the dibromomethyl analog with aqueous silver nitrate afforded the protected aldehyde in good yield. Accordingly, both bromo derivatives can be used even when they are obtained as a mixture of the bromination reaction, which could not be controlled easily to yield the bromo products selectively. From the aldehyde the tri-O-methylemodin nitrile was prepared in a one-pot reaction using hydroxylamine-O-sulfonic acid.Received February 18, 2003; accepted March 3, 2003 Published online June 2, 2003