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51.
Zhu L Ostash B Rix U Nur-E-Alam M Mayers A Luzhetskyy A Mendez C Salas JA Bechthold A Fedorenko V Rohr J 《The Journal of organic chemistry》2005,70(2):631-638
The angucycline antibiotic family of the landomycins displays potent antitumor activity. To elucidate early post polyketide synthase (PKS) tailoring steps of the landomycin E biosynthetic pathway in Streptomyces globisporus 1912, the mutant S. globisporus M12 was prepared through gene replacement experiment of lndM2. It encodes an enzyme with putative oxygenase and reductase domains, according to sequencing of the gene and its counterpart lanM2 from S. cyanogenus S136 landomycin A biosynthetic gene cluster. The isolation of the novel shunt products 11-hydroxytetrangomycin and 4-hydroxytetrangomycin along with the well-known angucyclines tetrangomycin and tetrangulol from the culture of S. globisporus M12 provides evidence for the involvement of lndM2 in the early biosynthetic pathway of the landomycins, in particular in the formation of the alicyclic 6-hydroxy function of the landomycin aglycon. We therefore propose LndM2 to be responsible for both hydroxylation of the 6-position and its subsequent reduction. These reactions are necessary before the glycosylation reactions can occur. The results are in agreement with the originally published structure of landomycin but do not support the recently suggested revised structure. 相似文献
52.
53.
The generation of thiirenes in the thermal and photochemical nitrogen elimination of 1,2,3-thiadiazoles is discussed in relation to oxirene formation. Isotope labelling experiments were performed with 4-phenyl-[4-13C]-1,2,3-thiadiazole ( 7 ) as the substrate. 相似文献
54.
Burlakov VV Arndt P Baumann W Spannenberg A Rosenthal U Parameswaran P Jemmis ED 《Chemical communications (Cambridge, England)》2004,(18):2074-2075
The 2,5-dititanabicyclo[2.2.0]hex-1(4)-ene (bis-titanocene-mu-(Z)-1,2,3-butatriene complex)3 is formed starting from [Cp2Ti(eta2-Me3SiC2SiMe3)] by in situ generated titanocene and 1,4-dichlorobut-2-yne via the 1-titanacyclobut-3-yne (2). 相似文献
55.
New experimental time-of-flight distributions are reported for Li+-N2 and Li2-CO at two center-of-mass energies of about 8 and 16 eV and large scattering angles θlab ? 120°. The Li+-N2 spectra show two widely spaced maxima, whereas the Li+-CO spectra show two and sometimes three maxima. The results are consistent with the model of rotational rainbows, and have also been analyzed in terms of an impulsive model involving collisions with the individual atoms of the molecules with energy-dependent masses. Classical trajectories for a simple model potential reveal only small contributions from vibrational excitation. 相似文献
56.
Uwe Klingebiel Dieter Bentmann Anton Meller 《Monatshefte für Chemie / Chemical Monthly》1978,109(5):1067-1073
Aminofluorosilanes react with lithiated amines undergoing LiF-elimination and substitution (1). The acyclic silicon-nitrogen-compound2 is isolated in the reaction with a difluorosilane after renewed lithiation.2 is cyclisated in the reaction with butyllithium by butane- and LiF-elimination (3). Aminofluorosilanes with bulky (4) or mesomeric stabilized (5) ligands form stable lithioaminofluorosilanes, which react with fluorosilanes giving substitution products (6, 7).6 and7 react with the lithium salt oftert-butylamin in a molar ratio of 12 to give8 and9 by intramolecular cyclisation.—The mass,1H and19F nmr spectra of the compounds are reported. 相似文献
57.
al-Ktaifani MM Bauer W Bergsträsser U Breit B Francis MD Heinemann FW Hitchcock PB Mack A Nixon JF Pritzkow H Regitz M Zeller M Zenneck U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(11):2622-2633
Several independent synthetic routes are described leading to the formation of a novel unsaturated tetracyclic phosphorus carbon cage compound tBu4C4P6 (1), which undergoes a light-induced valence isomerization to produce the first hexaphosphapentaprismane cage tBu4C4P6 (2). A second unsaturated isomer tBu4C4P6 (9) of 1 and the bis-[W(CO)5] complex 13 of 1 are stable towards similar isomerization reactions. Another starting material for the synthesis of the hexaphosphapentaprismane cage tBu4C4P6 (2) is the trimeric mercury complex [(tBu4C4P6)Hg]3 (11), which undergoes elimination of mercury to afford the title compound 2. Single-crystal X-ray structural determinations have been carried out on compounds 1, 2, 9, 11, and 13. 相似文献
58.
Indium(III) chloride forms in water with potassium 1,2‐dithiooxalate (dto) and potassium 1,2‐dithiosquarate (dtsq) stable coordination compounds. Due to the higher bridging ability of the 1,2‐dithiooxalate ligand in all cases only thiooxalate bridged binuclear complexes were found. From 1,2‐dithioquadratate with an identical donor atom set mononuclear trischelates could be isolated. Five crystalline complexes, (BzlMe3N)4[(dto)2In(dto)In(dto)2] ( 1 ), (BzlPh3P)4[(dto)2In(dto)In(dto)2] ( 2 ), (BzlMe3N)3[In(dtsq)3] ( 3 ), (Bu4N)3[In(dtsq)3] ( 4 ) and (Ph4P)[In(dtsq)2(DMF)2] ( 5 ), have been isolated and characterized by X‐ray analyses. Due to the type of the complex and the cations involved these compounds crystallize in different space groups with the following parameters: 1 , monoclinic in P21/c with a = 14.4035(5) Å, b = 10.8141(5) Å, c = 23.3698(9) Å, β = 124.664(2)°, and Z = 2; 2 , triclinic in P with a = 11.3872(7) Å, b = 13.6669(9) Å, c = 17.4296(10) Å, α = 88.883(5)°, β = 96.763(1)°, γ = 74.587(5)°, and Z = 1; 3 , hexagonal in R3 with a = 20.6501(16) Å, b = 20.6501(16) Å, c = 19.0706(13) Å and Z = 6; 4 , monoclinic in P21/c with a = 22.7650(15) Å, b = 20.4656(10) Å, c = 14.4770(9) Å, β = 101.095(5)°, and Z = 4; 5 , triclinic in P with a = 9.2227(6) Å, b = 15.3876(9) Å, c = 15.5298(9) Å, α = 110.526(1)°, β = 100.138(1)°, γ = 101.003(1)°, and Z = 2. 相似文献
59.
In this work a novel graphical method is applied to the presentation of intercomparison results. This is demonstrated with
the results of a recent intercomparison in measuring the 137Cs, 40K, and 90Sr activity concentration in milk powder. The “PomPlot”, an intuitive graphical method, is used for producing a summary overview
of the participants’ results of a common measurand. The “PomPlot” displays (relative) deviations of individual results from
the reference value on the horizontal axis and (relative) uncertainties on the vertical axis. 相似文献
60.