Steroide und Sexualhormone. 260. Mitteilung. Limonoide Bitterstoffe V. Untersuchungen zur Stereochemie der C(8)-Alkylierung von 7-Oxo-13,17-secosteroiden

On the Stereochemistry of the C(8)-Alkylation of 7-Oxo-13,17-secosteroids It is shown that the title compounds, e.g. 10 , can be alkylated with methyl iodide under strongly basic conditions to afford 8α-methylated products, e.g. 11 (Scheme 1). The configuration was assigned by ¹³C-NMR.-spectroscopy, CD. measurements, and finally proved by a X-ray crystallographic structure analysis.     

Notizen zur Synthese von 2-Aminophenylsulfonen

Syntheses of some Alkyl, Cycloalkyl and Aryl 2-Aminophenyl Sulfones Syntheses of the alkyl, cycloalkyl and aryl 2-aminophenyl sulfones 10 were achieved by oxidation of the corresponding 2-nitrophenyl sulfides 7 to the 2-nitrophenyl sulfones 9 followed by ethanolic Béchamp-reduction. The sulfides 7 in turn were obtained either by reactions of 2-nitro-thiophenol ( 8 ) with the appropriate alkyl and cycloalkyl halides or of 2-chloro-nitrobenzene ( 5 ) with the relevant thiols. Condensation of 2-nitrobenzenesulfinic acid ( 3 ) with bromoacetic acid in aqueous alkaline solution led - presumably via 2-nitrophenylsulfonylacetic acid ( 4 ) - to methyl 2 nitrophenyl sulfone ( 1 ), reduction of which gave 2-aminophenyl methyl sulfone ( 2 ). Treatment of 2-aminothiophenol ( 11 ) with t-butyl alcohol in aqueous sulfuric acid gave 2-aminophenyl t-butyl sulfide ( 12 ), which was acetylated to o-t-butylthio-acetanilide ( 13 ). Oxidation of the latter to o-t-butylsulfonyl-acetanilide ( 14 ) followed by hydrolysis led to 2-aminophenyl t-butyl sulfone ( 15 ).     

Herstellung der reinen,bicyclischen Olefine Bicyclo[4.2.1]non-2-en,Bicyclo[4.2.1]non-3-en und Bicyclo[4.2.1]non-7-en

Synthesis of the pure, bicyclic olefines Bicyclo[4.2.1]non-2-ene, Bicyclo[4.2.1]non-3-ene and Bicyclo[4.2.1]non-7-ene The synthesis of the olefines bicyclo[4.2.1]non-2-ene ( 3 ), bicyclo[4.2.1]non-3-ene ( 4 ) and bicyclo[4.2.1]non-7-ene ( 5 ) of high ‘certified’ purity from one common precursor ( 7 ) is described.     

Quantitative Rietveld texture analysis of CaSiO(3) perovskite deformed in a diamond anvil cell

The Rietveld method is used to extract quantitative texture information from a single synchrotron diffraction image of a CaSiO(3) perovskite sample deformed in axial compression in a diamond anvil cell. The image used for analysis was taken in radial geometry at 49?GPa and room temperature. We obtain a preferred orientation of {100} lattice planes oriented perpendicular to the compression direction and this is compatible with [Formula: see text] slip.     

Die Reaktion von 1-Halogeno-1-Lithiocyclopropanen mit CuCl2: Konkurrenz zwischen ‘Carben-Dimerisierung’ und oxidativer Kupplung

The Reaction of 1-Halogeno-1-lithiocyclopropanes with CuCl₂: Competition between ‘Carbene Dimerization’ and Oxidative Coupling The 1-chloro-1-lithiocyclopropanes 2a – d react at low temperature with CuCl₂ to give diastereoisomeric mixtures of oxidative-coupling products 5a – d and of ‘carbene dimers’ 6a–d . The relative amount of 5a – d increases with CuCl₂ concentration and reaction time. Diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoisomers are difficult. The conformational behavior of 1,1′-dichloro-1,1′-bi(cyclopropyls) 5c and 5d is discussed. Contrary to 2a – d , 1-bromo-1-lithiocyclopropanes normally react with CuCl₂ to give ‘carbene dimers’ 6 and no coupling products 5 . So far the only exception is 1-bromo-1-lithio-2-phenylcyclopropane 2e which in the presence of CuCl₂ gives some percents of coupling products 5e besides carbene dimers 6b as main products. An X-ray structure analysis of the predominant diastereoisomer 5e was performed.     

The Structure of Pyroergotamine

The molecular structure of pyroergotamine has been determined by single-crystal X-ray diffraction analysis to be the pyruvoyldiketopiperazine 1 . The diketopiperazine ring exists in a folded or boat conformation, with a dihedral angle of 40° between the two almost planar peptide units. The R-group of the phenylalanine residue occupies a quasi-axial position of the diketopiperazine ring, while that of the proline residue is in a quasi-equatorial position. Puzzling spectroscopic and chemical properties of the compound can be rationalised in terms of crowding within the molecule.     

New cyclopeptides from Trichoderma polysporum (Link ex Pers.) Rifai: cyclosporins B, D and E (author's transl)

New Cyclopeptides from Trichoderma polysporum (LINK EX PERS .) RIFAI : Cyclosporins B, D and E Cyclosporins represent a new group of biologically active metabolites produced by Trichoderma polysporum (LINK EX PERS .) RIFAI and other fungi imperfecti. The structures of the main components, cyclosporins A ( 1 ) and C( 3 ) have been determined as neutral cyclic oligopeptides composed of 11 amino acids, among them a new C₉-amino acid [2–4]. In addition, three minor metabolites, cyclosporins B, D and E, have now been isolated and characterized. Chemical investigation, spectroscopic evidence and X-ray analysis led to the structural formulae of cyclosporins B (2) and D (4) . Both compounds have the same sequence of amino acids as cyclosporin A (1) , with the exception of L -α-aminobutyric acid, replaced in cyclosporin B (2) by L -alanine and in cyclosporin D (4) by L -valine, respectively. Cyclosporins undergo a characteristic intramolecular N,O-acyl migration to furnish the corresponding basic isocompounds. The antifungal activities of cyclosporins are reported.     

Electrochemical Properties of Hydroxyphenazine-Coated Electrodes

Glassy carbon and gold electrodes were coated with 1-hydroxyphenazine, and the electrochemical properties of these electrodes were tested using them as a rotating disc electrode to reduce Ru (bipy)₃³⁺, Fe³⁺, quinoxaline, O₂, and to oxidize Eu²⁺. The fixed redox couple can be reversibly reduced and oxidized, and acts as an intermediate medium for the electron transfer. For example the Ru(bipy)₃³⁺ (E_1/2= 1010 mV vs. SCE. (saturated calomel electrode) on a glassy carbon electrode in 1M H₂SO₄) is only reduced at 50 mV, whereas the oxidation of Eu²⁺ (E_1/2= ?460 mV vs. SCE. on a Hg-electrode in 1M HCl) takes place at ? 100 mV. The heterogeneous rate constant depends on the second order reaction between the attached coating and the redox couple in solution. Depending on this rate constant, selectivity of the electrode is observed.     

(Strept)avidin as host for biotinylated coordination complexes: stability, chiral discrimination, and cooperativity

Incorporation of a biotinylated ruthenium tris(bipyridine) [Ru(bpy)(2)(Biot-bpy)](2+) (1) in either avidin or streptavidin-(strept)avidin-can be conveniently followed by circular dichroism spectroscopy. To determine the stepwise association constants, cooperativity, and chiral discrimination properties, diastereopure (Lambda and Delta)-1 species were synthesized and incorporated in tetrameric (strept)avidin to afford (Delta-[Ru(bpy)(2)(Biot-bpy)](2+))(x)() subsetavidin, (Lambda-[Ru(bpy)(2)(Biot-bpy)](2+))(x)() subsetavidin, (Delta-[Ru(bpy)(2)(Biot-bpy)](2+))(x)() subsetstreptavidin, and (Lambda-[Ru(bpy)(2)(Biot-bpy)](2+))(x)() subsetstreptavidin (x = 1-4) For these four systems, the overall stability constants are log beta(4) = 28.6, 30.3, 36.2, and 36.4, respectively. Critical analysis of the CD titrations data suggests a strong cooperativity between the first and the second binding event (x = 1, 2) and a pronounced difference in affinity between avidin and streptavidin for the dicationic guest 1 as well as modest enantiodiscrimination properties with avidin as host.