An investigation by the NMR method of the structure of the alkaloid sophorine fromSophora alopecuroides

A new base — sophorine, with mp 59–60°C, [] _D ²³ -18.9° (c 0.98; ethanol) — has been isolated from the epigeal part of the plantSophora alopecuroides L. Its IR spectrum and the nature of its mass spectrometric composition have permitted sophorine to be assigned to the quinolizidine alkaloids. The¹³C NMR spectrum has shown the presence of 19 carbon atoms. The analysis of several of the carbon signals has confirmed the results of IR and mass spectroscopy. Additional details of the structure of sophorine have been obtained from its PMR spectrum.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 604–608, September–October, 1981.     

The structure of the alkaloid nitraramine fromNitraria schoberi

The spatial structure of the alkaloid nitraramine has been determined by x-ray structural analysis. This has shown that it has the structure of 2,1-epoxy-1,3-propanoperhydrobenzo [3,2-d]-1,8-naphthyridine. Its reactivity has been studied.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 692–698, September–October, 1985.     

First synthesis of enantiomerically pure (1S,2S)- and (1R,2R)-1,2-diaminocyclobutanecarboxylic acid–ornithine derivative–, from racemic 2-aminocyclobutanone

An easy and efficient one-pot reaction from readily available 2-(N-Cbz) aminocyclobutanone selectively gave, by means of an asymmetric Strecker synthesis in the presence of a chiral benzylic amine, the thermodynamic 1,2-diamino nitriles. Basic hydrolysis, cleavage of the benzylic group and acidic hydrolysis of the resulting trans-1,2-diaminocyclobutanecarbonitrile gave, in a four-step sequence from the ketone, (1S,2S)- or (1R,2R)-1,2-diaminocyclobutanecarboxylic acid, ornithine derivatives. The absolute configuration has been established by X-ray analysis of the corresponding trans-diamino amide.     

Lithiation–alkylation of polystyrene occurs only on the ring

When polystyrene is treated with an organolithium reagent, the hydrogen on the para carbon is removed and this position may be alkylated with e.g., iodomethane or chlorotrimethylsilane. The metalation occurs directly at this position and does not involve metalation at the benzylic carbon with resonance distribution of the charge to the ring. The reaction of cumene with butyllithium also occurs by direct ring metalation and it is shown that these results are consistent with both the kinetic and the thermodynamic acidity of the hydrocarbons. © 1997 John Wiley & Sons, Inc.     

A short, practical synthesis of the ant venom alkaloid, three (3R,5S,8aS)-3-alkyl-5-methylindolizidines

A short, practical and diastereoselective method for preparing the ant venom alkaloid, three (3R,5S,8aS)-3-alkyl-5-methylindolizidines (1–3), has been developed. The stereoselective intramolecular amidomercuration of the N-alkenylurethane 4 followed by oxidative demercuration provides the piperidine alcohol cis-6 as a major product. Thereafter, oxidation of cis-6 followed by the Horner-Emmons elongation of the ring appendages affords the enones 8, 10, and 11, which are stereoselectively converted into 1, 2, and 3, respectively, by catalytic hydrogenation.     

Dynamic mechanical investigations on drawn samples of isotactic polypropylene/EPM–Rubber blend

The physical behavior of isotropic and oriented samples of an isotactic polypropylene (iPP)/ethylene–propylene–copolymer (EPM) reactor blend was studied by performance of dynamic mechanical measurements over a wide temperature range (DMTA). The influence of thermal history and drawing procedure was examined. The results showed that with increasing draw ratio the uniaxial elastic modulus of the material was considerably enhanced, whereas the intensity and strength of the amorphous relaxations of both components were reduced. At a certain draw ratio, the glass transtions of iPP and EPM phenomenologically merged and appeared as a single relaxation. The crystalline relaxation of iPP emerged with increased draw ratio at higher temperatures and was better seperated and easier to detect. The effects observed were attributed to the orientation of the crystallites in a fibrillar structure and to the restricted molecular mobility in amorphous regions. Measurements by differential scanning calorimetry (DSC) and x-ray diffraction of several drawn samples were performed to determine the effects of drawing on the melting behavior and the crystal orientation in the semicrystalline polymer. For comparison, some results of analogous studies on neat isotactic PP are presented and discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1439–1448, 1997     

The failure of the Lennard–Jones n,m intermolecular potentials to represent some common gases

It is shown that none of the Lennard–Jones n,m intermolecular potentials can represent any of the gases, neon, argon, krypton, xenon, nitrogen, oxygen, hydrogen, methane, ethane, and propane. In particular, the second and third virial coefficients B^* and C^*, and , computed for these potentials cannot describe the experimental behavior of B, C, and V_T. This is demonstrated by their inability to match the temperature dependence of the dimensionless variable, , thus failing to satisfy a necessary condition for representing the PVT behavior of these gases.     

A new cyclopeptide alkaloid from the bark of waltheria douradinha

Waltherine-C (5), a novel 14-membered cyclopeptide alkaloid has been isolated, together with four known cyclopeptide alkaloids, waltherine-A (1) and -B (2), scutianine-B (3) and adouetine-Y' (4), from the bark of Waltheria douradinha (Sterculiaceae) from Rio Grande do Sul, Brazil. The structure and NMR assignments of this new alkaloid were determined by 1D and 2D NMR techniques. The stereochemistry of the ring amino acid residue and the N,N-dimethyl amino acid side-chain has been assigned by gas chromatography employing modified cyclodextrins as chiral stationary phases.     

Further investigations on the thermophysical properties of gamma-irradiated urania-doped orthoferrites

(Y_1.85?U_0.15) FeO₃ orthoferrite was carefully prepared using the solid-state high temperature ceramic and sintering technique. On this orthoferrite, numerous measurements have been undertaken before and after 1.24 Mrad γ-absorbed dose, namely X-ray diffraction (XRD), DC-electrical conductivity versus temperature, UV/Vis. absorption, IR absorption, Mössbauer effect (ME) and EPR. In the present work the results obtained were explained, interpreted and discussed in details on the basis of lattice structure of the new perovskite investigated and the interaction of γ-radiation with the orthoferrite lattice.     

Further studies on the rotational barriers of Carbamates. An NMR and DFT analysis of the solvent effect for Cyclohexyl N,N-dimethylcarbamate

The solvent effect on the Gibbs energy of activation for rotation around the (C=O)–N bond in cyclohexyl N,N-dimethylcarbamate was investigated by dynamic NMR spectroscopy and density-functional theory at the B3LYP/6-311+G^** level. The experimental barriers were about 15 kcal mol⁻¹ with no appreciable variation when the solvent polarity was changed. A reaction field model was applied to theoretically mediate the solvent effect and the results were comparable to the experimental data. An analysis, based on the Onsager solvation theory, showed that the solvent effect on rotational barriers can be understood employing the total molecular dipole moment, the difference between the dipole moments of the ground and the transition state structures, or both, as appropriate.     

Coordination networks constructed with supramolecular synthon RX–CCAgn (n = 4, 5; RX = halophenyl)

Eight new silver(I) double salts: AgL¹·2AgCF₃COO (1), AgL¹·3AgNO₃ (2), 2AgL²·5AgCF₃COO·2CH₃CN·H₂O (3), 4AgL³·6AgCF₃COO·5CH₃CN (4), 4AgL⁴·6AgCF₃COO·5CH₃CN (5), 2AgL⁵·4AgCF₃COO·NC(CH₂)₄CN (6), 2AgL⁵·4AgCF₃COO·2CH₃CN (7) and AgL⁶·2CF₂(CF₂COOAg)₂·2CH₃CN (8) (L¹ = 4-iodophenylethynide; L² = 3,4-dichlorophenylethynide; L³ = 3-chlorophenylethynide; L⁴ = 3-bromophenylethynide; L⁵ = 2-chlorophenylethynide; L⁶ = 2-fluorophenylethynide) have been synthesised and characterized by X-ray crystallography. All compounds contain the silver–halophenylethynide supramolecular synthon R_X−CCAg_n (n = 4, 5). In particular, the three-dimensional supramolecular structures in 1 and 2 are stabilized by strong AgI interactions, while that in 3 is consolidated by both AgCl and van der Waals type FCl interactions. In isomorphous compounds 4 and 5, the presence of respective FCl or FBr contact contributes to the stability of the network. The silver aggregates in 6, 7 and 8 are stabilized by AgCl or AgF interactions between the ortho-halo substituent and the Ag_n basket.     

Sculponins A–C, three new 6,7-seco-ent-kauranoids from Isodon sculponeatus

Three new 6,7-seco-ent-kauranoids (1–3) were isolated and structures were elucidated from Isodon sculponeatus. Diterpenoids 1–3 possessing multicyclic skeletons formed via oxygen atoms are all unprecedented among ent-kauranes. Compound 1 displayed significant cytotoxic activity against K562, A549, and HepG2 human tumor cell lines, with IC₅₀ values of 1.4, 2.3, and 2.0 μM, respectively, equal to the positive control. Plausible pathways for the biosynthesis of 1 and 2 from one related diterpenoid were also postulated.     

An ab initio study on the vibrational and electronic spectra of the molybdenum–sulfur clusters with Mo2OnS4−n(n=0–4) core

Using the ab initio method, the vibrational and electronic spectra of binuclear molybdenum clusters which contain Mo₂O_nS_4−n(n=0–4) core were investigated. The main absorption bands in the IR spectra of these clusters are assigned and compared with each other, especially for the case of the trans isomers. The electronic spectra were studied by performing the CIS calculations. The ground state and the first excited state of the clusters were discussed by using the natural bond orbital method. It is shown that the band corresponding to the longest wavelength can be assigned to three kinds of transition types. Two transitions, σ(Mo–Mo)→π*(Mo–X_t)(X=S,O) and σ(Mo–Mo)→σ*(Mo–Mo), can be seen in most cases.