Reactions of Molecules with Two Equivalent Functional Groups. 5. Anomalous Reactivity of 1,10-Cyclooctadecanedione. Crystal and Molecular Structures of cis,cis-1,10-Diphenyl-1,10-cyclooctadiene and the Stereoisomers of 1,10-Diphenyl-1,10-cyclooctadecanediol(1)

The reaction of the title diketone (3) with phenyl Grignard produces (with rate constant k(1)) the conjugate base (6-M) of 10-hydroxy-10-phenylcyclooctadecanone (6), which is subsequently converted (with rate constant k(2)) to the conjugate base of the title diol, as a mixture of the cis (7, 55%) and trans (8, 45%) isomers. The ratio k(2)/k(1), 2.2 +/- 0.4, indicates that the carbonyl group in 6-M is 4.4 times as reactive as each carbonyl in 3. Competition experiments further demonstrate that the relative rates (per carbonyl) for addition of phenylmagnesium bromide to 3, 10-methylenecyclooctadecanone (11), and cyclopentadecanone (12) are 1.0:0.60:1.92. Possible reasons for this order of reactivity are discussed. Diols 7 and 8 undergo facile double dehydration to form the title diene 13, which is predicted by molecular mechanics calculations to be the most stable of the four possible symmetrical diene isomers. The structures of 7, 8, and 13 were secured by single-crystal X-ray studies.     

Nanostructure investigations with the analytical transmission electron microscope

Concerning the conventional TEM-imaging as well as the analytical procedures the capabilities are pointed out: electron diffraction, energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS). The possibilities of investigation of both nanocrystalline materials and multilayers are discussed, accompanied by examples of current investigations: At alloys, produced by intense milling, at single nanocrystals the imaging by diffraction contrast was successful, the analysis has failed because of the sample thickness. By means of energy spectroscopic imaging multilayers from Fe-SiB/NbCu and Fe/Cr as well as Al₂O₃/TiN have been characterized. Received: 15 July 1997 / Revised: 16 February 1998 / Accepted: 21 February 1998     

Rapid synthesis of 2,5‐disubtituted 1,3,4‐thiadiazoles under microwave irradiation

The one pot, three‐components condensation of aromatic aldehydes, hydrazine and sulfur in ethanol under microwave irradiation provided symmetrically 3,5‐disubstituted 1,3,4‐thiadiazoles in high yields and good purity. This reaction must be conducted under pressure of hydrogen sulfide produced in‐situ. The structure of the compounds was confirmed by ¹H, ¹³C NMR, MS and elemental analysis.     

Rapid analysis of triterpenic acids by liquid chromatography using porous graphitic carbon and evaporative light scattering detection

An original system which uses Porous Graphitic Carbon as support and a mixture of organic solvents as mobile phase is proposed for the analysis of triterpenic acids by liquid chromatography. The separation of betulinic acid, ursolic acid, oleanolic acid, and 18alpha- and 18beta-glycyrrhetinic acids was carried out within a short time and monitored by evaporative light scattering detection as universal detection method. Molecular modelling studies show that the main contribution to the selectivity comes from the electrostatic interaction characterised by the dipole moment of the products.     

On xenon molecule excited state lifetimes

Time-resolved excitation spectra of xenon vapor in the 150 nm region are analysed in terms of four main fluorescence lifetimes corresponding to decays of four stable excited electronic states of the Xe dimer. The two shortest decay times, ≈ 2 ns and ≈ 60 ns, are assigned to the direct radiative relaxation of the two lowest excited ungerade states, (¹Σ⁺_u)0⁺_u and (³Σ⁺_u))1 u respectively. The two longest decay times, ≈ 150 ns and ≈ 500 ns, must correspond to the overall depopulation rates of the two lowest excited gerade states, (³Σ⁺_g)1g and (¹Σ⁺_g)0⁺_g, decaying into the gerade ground state by cascading down through the intermediate ungerade states.     

Isolement de l'acide 3-amino 12-methyl tetradecanoique et de l'acide 3-amino 12-methyl tridecanoique a partir de l'iturine,antibiotique de Bacillus subtilis

lturin, a peptide antibiotic from Bacillus subtilis, was separated into three iturins: A, B, C by thin-layer chromatography. Iturin A, which has an antifungal activity, contains Asp, Glu, Tyr, Ser, Pro in a molar ratio 3:1:1:1:1 and a lipid moiety AL. The latter was shown to be a mixture of C₁₄ (40%) and C₁₅, (60%) amino-acids. The structure of these was determined by combined gas chromatography-mass spectrometry of the N-acetylmethyl esters. Strong peaks at m/e = 144 and m/e = 102 indicate a β-amino group. Identification of acetone and methylethylketone after chromic acid oxidation indicates an iso and anteiso structure. After comparison of the natural amino-acids with synthetic 3-amino pentadecanoic acid it is concluded that the lipid AL is a mixture of 3-amino 12- methyltetradecanoic acid and 3-amino 12-methyltridecanoic acid.     

Cyclen based bis-macrocyclic ligands as phosphates receptors. A potentiometric and NMR study

The host-guest interaction between orthophosphate, pyrophosphate and triphosphate anions and four cyclen based bis-macrocycles ligands possessing ortho-(BOC), meta-(BMC), para-xylenyl (BPC) or 2,6-pyridinyl (BPyC) linker was investigated by potentiometric measurements and NMR spectroscopy. Each ligand gave protonated species in aqueous solution that further formed ternary complexes after binding with anions; these complexes were analyzed as a result of hydrogen bond formation and Coulombic attraction between the organic host and the inorganic guest. The equilibrium constants for all the detected species are reported and the selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed the importance of the distance between the two cyclen cores and underlined, especially for the triphosphate species, the contribution of the nitrogen atom of the pyridinyl spacer as a supplementary anchoring point in acidic medium.     

Synthesis of Novel Nucleic Acid Mimics via the Stereoselective Intermolecular Radical Coupling of 3'-Iodo Nucleosides and Formaldoximes(1)

A highly convergent free radical coupling of alkyl iodides and oximes, mediated by bis(trimethylstannyl) benzopinacolate (8), has been utilized to prepare a series of dimeric nucleosides as mimics of natural nucleic acids. The systematic optimization of the reaction conditions allowed for the single-step conversion of the appropriate iodides and oximes into the 2'-deoxy dimers 9 in moderate to excellent yields. For example, the reaction of 3'-deoxy-3'-iodo-5'-(triphenylmethyl)thymidine (6a) with 3'-O-(tert-butyldiphenylsilyl)-5'-O-(methyleneimino)thymidine (7a) in the presence of 8 in degassed benzene gave an 81% yield of 3'-de(oxyphosphinico)-3'-(methyleneimino)-5'-O-(triphenylmethyl)thymidylyl-(3'-->5')-3'-O-(tert-butyldiphenylsilyl)thymidine (9a). Similarly prepared were dimers containing both pyrimidine (thymine, 5-methylcytosine) and purine (adenine, guanine) bases. The reaction was highly stereoselective, giving only a single dimeric species having the ribo-configuration of the newly introduced C-3'-branched methylene moiety. Also prepared were dimers 16, incorporating 2'-O-methyl ribonucleosides in both halves of the dimer. This required the synthesis of 3'-deoxy-3'-iodo-2'-O-methyl nucleosides 12 as well as 2'-O-methyl-5'-O-methyleneimino nucleosides 15. For example, 5'-O-(tert-butyldiphenylsilyl)-3'-deoxy-3'-iodo-2'-O-methyl-5-methyluridine (12e) was prepared in 80% yield by displacement of the corresponding triflate with Bu(4)NI. Also prepared were the suitably protected 3'-deoxy-3'-iodo adenosine and guanosine derivatives. Compounds 15 were prepared in high yield by a regioselective Mitsunobu reaction to give the corresponding 5'-O-phthalimido nucleosides 13, which were subsequently converted to the requisite oximes 15. In the 2'-O-methyl series, the pinacolate coupling reaction proceeded with efficiency equal to that observed for the 2'-deoxy series 9, but with slightly less stereoselectivity, giving predominantly the C-3'ribo products 16, contaminated with 5-25% of the epimeric material. Mixed base dimers containing both pyrimidine and purine bases at all possible positions, including purine-purine dimers were prepared. The hydroxylamine or methyleneimino (MI) backbone of several representative dimers so prepared was converted via methylation to give the corresponding methylenemethylimino (MMI)-linked compounds, which are novel phosphate surrogates for use in antisense oligonucleotides.     

Novel estradiol derivatives labeled with Ru,W, and Co complexes. Influence on hormone-receptor affinity of several organometallic groups at the 17 alpha position

In order to elucidate the extent to which recognition of the estrogen receptor is influenced by addition of an organometallic substituent at the 17 alpha position, modification of 17 beta-estradiol at this position was carried out by using the organometallic groups -C identical to C(eta 5-C5H4)RuCp, CH2-(eta 5-C5H4)RuCp, -C identical to C-(eta 5-C5H4)-W(CO)3(Me), -(C identical to CCHO)Co2(CO)6, and -(C identical to CCH2OH)Co2(CO)6. The relative binding affinity (RBA) values for estradiol receptor alpha showed that recognition was good (RBA between 20 and 13.5%) when the organometallic moiety was attached at the end of a rigid alkyne spacer. However, the affinity of the modified hormone for the receptor was severely reduced (RBA = 1%) for a substituent such as -CH2-(eta 5-C5H4)RuCP, in which the spacer is reduced to a single flexible sp3 carbon atom, allowing the organometallic moiety greater freedom of movement around the attachment point. The RBA values found were in agreement with results obtained from a molecular-modeling study in which 5, an organometallic hormone with a rigid spacer, or 7, a molecule with a flexible spacer, was inserted into the cavity of the recently characterized Ligand-Binding Domain of estrogen receptor alpha.     

Acidité dans le nitrométhane: III. Détermination électrochimique de la basicité du nitrométhane — Corrélation Dn/Eo(Hs+/H2/

The use of the complex acid HAlCl₄ (HCl+AlCl₃) permits the detemrination of the standard potential of the hydrogen electrode in nitromethane. The result (E₀(H_s⁺/H₂)=0.5 V vs. Fc/Fc⁺, Fc=ferrocene) shows that nitromethane is very weakly basic. This measurement is confirmed by showing that the standard potential of the hydrogen electrode in various solvents is linked to Gutmann's donor numbers of these solvents. The E₀(H_s⁺/H₂) value obtained in nitromethane belongs to the correlation line.