Biosynthesis of kinamycin D. incorporation of [1,2-13C] acetate and of [2-2H3,1-13C]acetate

Results from the incorporation of [1,2-¹³C₂]- and [2-²H₃,1-¹³C]acetates into kinamycin D. indicate the involvement of only unsymmetrical intermediates; the identity of some of these are suggested.     

Distortions in trihapto-allyls induced by electronic asymmetry: A comparison of the structures of (η5-C5H5)Mo(CO)2(η3-C3H5) and (η5-C5H5)Mo(NO(I)(η3-C3H5)

The electronic asymmetry induced by replacing two carbonyls by a nitrosyl and iodide ligand causes severe distortion in the allyl moiety. The allyl group in the nitrosyl complex is bound in a sigma-pi mode rather than the symmetrical mode found in the dicarbonyl. This change in ground state structure alters the exo—endo conformer interconversion mechanism from a rotation of the allyl in the dicarbonyl to a sigma-pi interconversion in the nitrosyl iodide.     

Biosynthesis of psilotin from [2′,3′-13C2,1′-14C,4-3H]phenylalanine studied with 13C-NMR

The 6-phenyl-dihydro-α-pyrone moiety of psilotin is formed from [2′,3′-¹³C₂,1′-¹⁴C,-4-³H]phenylalanine in the plant $\text{Psilotum}$$\text{nudum}$ with retention of all the isotopes.     

Vibrational spectra and internal rotation barriers of cyclopentadienyl germanium trihalides: (C5H5)GeCl3, (C5H5)GeBr3 and (C5H5)GeI3

IR and Raman spectra of gaseous and solid CpGeX₃ species (Cp  C₅H₅ and X = Cl, Br, I) are reported. The results are compared with those obtained previously for CpTiCl₃. Internal rotation barriers and thermodynamic functions are reported.     

New route to (3RS) (5R) (5-2H)- and (3RS) (5S) (5-2H)-mevalonolactones

The synthesis of mevalonolactone stereospecifically labeled at carbon 5 is described combining chemical reactions with an enzymatic reduction step.     

Internally coordinated organozinc-transition metal compounds. Crystal structure of (CH3)2N(CH2)3ZnW(ν-C5H5)(CO)3

The stabilities of simple and internally coordinated organozinc-transition metal compounds towards disproportionation have been investigated by the microwave titration technique. Simple alkyl- and aryl-derivatives disproportionate to such an extent as to preclude isolation. Internal coordination was found to stabilize the asymmetric compounds, and several derivatives containing the dimethylaminopropyl group were isolated. The crystal structure of one of them, Me₂N(CH₂)₃-ZnW(Cp)(CO)₃, was determined by a single-crystal X-ray study. The crystals are orthorhombic, space group P2₁2₁2₁, with four molecular units in a cell with parameters a 8.406(1), b 12.179(2) and c 16.642(2) Å. The structure was solved by standard Patterson and Fourier techniques. The refinement, with anisotropic temperature factors for the two heavy atoms, converged at R_F = 0.092 (R_wF = 0.089) for 1536 observed reflections with I>2.5σ(I). The molecule consists of a central tungsten atom, surrounded in a tetragonal pyramidal fashion by a cyclopentadienyl group in the apical position and three carbon monoxyde molecules and a zinc atom occupying the basal positions. The zinc atom is three-coordinate, being surrounded by the tungsten atom and the chelating dimethylaminopropyl group; there is, however, a short intermolecular contact between zinc and a carbonyl oxygen atom at 2.61(3) Å.     

Kondensierte Phosphate (NaPO3-Na5P3O10)

Ohne Zusammenfassung     

钼铁混合金属原子簇化合物[(η5-C5H5)4Mo4Fe2(μ3-S)5(CO)5]的合成和结构

(η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5 have been prepared from (η~5-C_5H_5)_2Mo_2(CO)_6 and Fe_8S_2(CO)_9 under toluene reflux for 14.5 hrs.The crystal and molecular structures of (η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5 were studied by X-ray structure analysis. The Crystallographic data are as follows: monoclinic, space group P2_1/n, unit cell: a=1.0589(4), b=1.7260(4), c=1.8963(4) nm, β=101.44(2)°, V=3.3967 nm, D_c=2.06 gcm~(-3) for Z=4, X-ray data were obtained over the range of 2°<2θ<50° via the ω-2θ scan mode with MoKα radiation on an Enraf-Nonius CAD4 diffractometer. The structure was solved by direct method (MULTAN) and refined by full matrix least-squares techniques for 3993 reflections with I>2σ(I), The final R=0.081. Figure 1 illustrates the configuration of the molecule (η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5, composing of a cubane-like (FeMo_3S_4) core and a trigonal pyramid (MoFe_2S) core, which linked by sharing Fe(1) atom.     

Neutron scattering study of the reorientational motions in Cr(CO)3(η6C6H6) and Mn(CO)3(η5C5H5)

Incoherent quasi-eleastic neutron scattering experiments: using different resolutions and a wide Q range, have been performed on polycrystalline samples of Cr(CO)₃(η⁶C₆H₆) and Mn(CO)₃(η⁵C₅H₅) in the 280–320 K temperature range. It is shown that aromatic rings are involved into a reorientational process characterized by an activation energy of ≈ 16 kJ mol^?1 and by correlation times of the order of 2 × 10^?11 s and 5 × 10^?11 s at 300 K for C₆H₆ and C₅H₅ rings respectively. Experimental elastic incoherent structure factors are in agreement with the 2π/6 and 2π/5 jump models and the fitted spectra confirm these models. From a comparison with heat-capacity results we conclude that M(CO)₃ groups are fixed during the reorientational process. Finally a comparison with literature data is presented.     

A new synthesis of (R)- and (S)-2-2H-amino acids,including (R)- and (S)-2-2H1-glycine via stereochemically inert Co(III) complexes

Chemical synthesis of deuterated optically active 2-²H-amino acids via chiral complexes [Co(3-X-Sal-(S)-2-¹H-aa)₂]Na, where X is H, Me; aa is valine, norvaline, tyrosine, methionine, alanine and glycine; Sal is salicylaldehyde, is described.The technique includes preparation of a mixture of XXX and Δ diastereomeric complexes of [Co(3-X-Sal-(S)-2-¹H-aa)₂]Na which are separated on Al₂O₃.Then under the action of NaOD in D₂O the 2-¹H of the amino acid moiety is exchanged by deuterium, the resulting mixture of deuterated diastereomers is again separated on Al₂O₃, and optically active 2-²H aa are isolated after electrochemical reduction of pure deuterated diasteroisomers. S and R-2-²H₁glycines are obtained by stereospecific ¹H-²H exchange of glycine moiety in XXX and Δ [Co(3-Mesal-gly)₂]Na.     

Synthesis of [1-15N,2-13C]-labeled difloxacin

Abstract  

The synthesis of [1-¹⁵N,2-¹³C]-difloxacin, an arylfluoroquinolone antibacterial agent, is reported. As a crucial initial step, the starting materials ethyl 2,4,5-trifluorobenzoylacetate, [formyl-¹³C]-triethyl orthoformate, and [¹⁵N]-4-fluoroaniline were reacted to ethyl [¹⁵N,3-¹³C]-3-(4-fluoroanilino)-2-(2,4,5-trifluorobenzoyl)acrylate. After cyclization and ester cleavage, the resulting intermediate was reacted with 1-methylpiperazine to [1-¹⁵N,2-¹³C]-1-(4-fluorophenyl)-6-fluoro-7-(4-methyl-1-piperazinyl)-1,4-dihydro-4-oxoquinoline-3-carboxylate, i.e., [1-¹⁵N,2-¹³C]-difloxacin. The overall yield was 62% based on the non-labeled and 43% based on the labeled starting materials (both used in 1.4 molar excess). The product was identified by ¹H-, ¹³C-, and ¹⁵N-NMR spectroscopy and by cochromatography (TLC, HPLC) with an authentic reference; its purity (HPLC) was above 98%. Prior to synthesis of [1-¹⁵N,2-¹³C]-difloxacin, non-labeled difloxacin was synthesized in order to optimize procedures and to identify and characterize all intermediates.     

The synthesis and decarbonylation of (η5-C5H5)Mo(Co)2(COCH3)E(C6H5)3, where E is arsenic or antimony

The synthesis of the title compounds by reaction of (η⁵-C₅H₅)Mo(CO)₃CH₃ with excess As(C₆H₅)₃ or Sb(C₆H₅)₃ in CH₃CN is described. Thermal decarbonylation results in the preferential ejection of As(C₆H₅)₃ or Sb(C₆H₅)₃ from the new acetyl complexes, which accounts for the failure of previous attempts to synthesise the acetyl complexes. Photolytic decarbonylations lead to new-alkyl complexes (η⁵-C₅H₅)Mo(CO)₂(CH₃)E(C₆H₅)₃. IR and NMR data for the new complexes are tabulated.     

Antimonypentafluoroorthotellurates: Sb(OTeF5)3, Sb(OTeF5)5 and salts of Sb(OTeF5)6−

Antimony(III)pentafluoroorthotellurate has been synthesized from SbF₃ and B(OTeF₅)₃. Contrary to a previous report it is a low melting, sublimable solid (mp = 28°, bp (0.1 torr) = 68°, ¹⁹F - NMR: AB₄ spinsystem δ (A) = ?42.7, δ (B) = ?38.1, J (AB) = 186 Hz). It reacts with F₂, Cl₂ and Br₂ to give SbF₂(OTeF₅)₃, SbCl₄⁺Sb(OTeF₅)₆^? and SbBr₄⁺ Sb(OTeF₅)₆^? respectively. Interaction of Xe(OTeF₅)₂ and Sb(OTeF₅)₃ yields Sb(OTeF₅)₅, which is unstable at room temperature. Salts containing the new anion Sb(OTeF₅)₆^? have been synthesized either from Sb(OTeF₅)₅ and a corresponding pentafluoroorthotellurate e.g. Sb(OTeF₅)₅ + NMe₄⁺ OTeF₅^? = NMe₄⁺ Sb(OTeF₅)₆^?, or from SbCl₄ Sb(OTeF₅)₆^? and an appropriate chloride SbCl₄⁺ Sb(OTeF₅)₆^? + NOCl = SbCl₅ + NO⁺ Sb(OTeF₅)₆^?, or oxidatively, using a mixture of Xe(OTeF₅)₂ and Sb(OTeF₅)₅, e.g. C₆F₆ + $\text{1}\text{2}$ Xe(OTeF₅)₂ + Sb(OTeF₅)₅ = C₆F₆⁺ Sb(OTeF₅)₆^? + $\text{1}\text{2}$ Xe.