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31.
Hofmann C Boll R Heitmann B Hauser G Dürr C Frerich A Weitnauer G Glaser SJ Bechthold A 《Chemistry & biology》2005,12(10):1137-1143
The oligosaccharide antibiotic avilamycin A is composed of a polyketide-derived dichloroisoeverninic acid moiety attached to a heptasaccharide chain consisting of six hexoses and one unusual pentose moiety. We describe the generation of mutant strains of the avilamycin producer defective in different sugar biosynthetic genes. Inactivation of two genes (aviD and aviE2) resulted in the breakdown of the avilamycin biosynthesis. In contrast, avilamycin production was not influenced in an aviP mutant. Inactivation of aviGT4 resulted in a mutant that accumulated a novel avilamycin derivative lacking the terminal eurekanate residue. Finally, AviE2 was expressed in Escherichia coli and the gene product was characterized biochemically. AviE2 was shown to convert UDP-D-glucuronic acid to UDP-D-xylose, indicating that the pentose residue of avilamycin A is derived from D-glucose and not from D-ribose. Here we report a UDP-D-glucuronic acid decarboxylase in actinomycetes. 相似文献
32.
Dieter Seebach Thomas Weller Gerd Protschuk Albert K. Beck Marvin S. Hoekstra 《Helvetica chimica acta》1981,64(3):716-735
Preparation of 1,3-Diketones and of Nitro-diketones by (1:1)-Acylation of Lithium Enolates with Acyl Chlorides Slow addition of precooled solutions of lithium enolates in THF (Fig. 1) to solutions of equimolar amounts of acyl chlorides in the same solvent at temperatures between ? 80 and ? 100° furnishes 1, 3-diketones in acceptable to good yields (Tables 1?3). Even 3-nitropropionyl and 4-nitrobutyryl chloride can be employed for the (1:1)-acylation of enolates to give the synthetically useful 5- and 6-nitro-1, 3-diketones 13 and 25 , respectively. The scope and the limitations of this method of preparing 1, 3-diketones are given and are compared with alternative methods. 相似文献
33.
Ernst Bayer Gerd Wahl und Heinz Günther Witsch 《Fresenius' Journal of Analytical Chemistry》1961,181(1):384-390
Zusammenfassung Es werden zwei neue, sehr selektive Trennflüssigkeiten, Äthylenglykol-bis(propionitril)-äther und Glycerin-tri(propionitril)-äther, angegeben. Die Trennflüssigkeiten sind so selektiv wie ,-Bis(propionitril)-äther, erlauben aber höhere Arbeitstemperaturen von 140° bzw. 170°C. An Säulen kleinen Querschnittes wird die präparative Trennung größerer Mengen unter Ausnutzung der Selektivität dieser Trennflüssigkeiten aufgezeigt.Die Trennwirksamkeit und die Belastbarkeit von Säulen verschiedenen Durchmessers zwischen 1–10 cm wird angegeben. Die Trennwirksamkeit liegt in der gleichen Größenordnung wie die der analytischen Säulen. Die Belastbarkeit steigt proportional dem Querschnitt an.I. Mitteilung: E. Bayer u. H. G. Witsch, diese Z. 170, 278 (1959). 相似文献
34.
Gerhard Hamprecht Karl-Heinz Knig Gerd Stubenrauch 《Angewandte Chemie (International ed. in English)》1981,20(2):151-164
Due to their bifunctional character, alkylsulfamoyl chlorides are versatile units for the synthesis of heterocycles, polar sulfamates, and sulfonamides. In the last decade, synthetic methods of general preparative use have been developed, by means of which amine hydrochlorides, isocyanates, aziridines or tertiary alcohols can be reacted with suitable sulfuric acid derivatives to give novel, variously substituted alkylsulfamoyl chlorides. These compounds can subsequently be converted either to previously unobtainable N-alkoxyalkyl-N-alkylsulfamoyl chlorides or to novel heterocycles of the type 1H-2,1,3-benzothiadiazin-4-one-2,2-dioxide, 2H-1,2,6-thiadia-zin-3-one-1,1-dioxide and 2H-1,2,4,6-thiatriazin-5-one-1,1-dioxide; these compounds are examples of interesting models which illustrate the relation between the structure and the action of the compound, and in some cases lead to highly selective, ecologically unobjectionable herbicides. On the other hand, the alkylsulfamoyl chlorides themselves can be N-acylated to give further 3- to 5-atom bifunctional synthesis units, with which novel heterocyclic syntheses can be carried out. Further uses of the alkylsulfamoyl chlorides include the preparation of biologically active sulfamates, and cycloaddition reactions of N-sulfonylamines prepared in situ. 相似文献
35.
Privat E Melvin T Mérola F Schweizer G Prodhomme S Asseline U Vigny P 《Photochemistry and photobiology》2002,75(3):201-210
The fluorescence properties of thiazole orange, linked via a (1) hydrophobic alkyl or a (2) hydrophilic ethylene glycol chain to the central internucleotidic phosphate group of a pentadeca-2'-deoxyriboadenylate (dA15), are evaluated. Linkage at the phosphate group yields two stereoisomers, S-isomer of the phosphorus chiral center (Sp) and R-isomer of the phosphorus chiral center (Rp); these are studied separately. The character of the linkage chain and the chirality of the internucleotidic phosphate linkage site influence the fluorescent properties of these thiazole orange-oligonucleotide conjugates (TO-probes). Quantum yields of fluorescence (phifl) of between 0.04 and 0.07 were determined for the single-stranded conjugates. The fluorescence yield increased by up to five times upon hybridization with the complementary sequence (d5'[CACT15CAC3']); (phifl values of between 0.06-0.35 were determined for the double-stranded conjugates. The phifl value (0.17) of thiazole orange, 1-(N,N'-trimethylaminopropyl)-4-[3-methyl-2,3-dihydro-(benzo-1,3-thiazole)-2-methylidene]-quinolinium iodide (TO-Pro 1) in the presence of the oligonucleotide duplex (TO-Pro 1: dA15.d5'[CACT15CAC3'] (1:1)) is much less than that for some of the hybrids of the conjugates. Our studies, using steady-state and time-resolved fluorescence experiments, show that a number of discrete fluorescent association species between the thiazole orange and the helix are formed. Time-resolved studies on the four double-stranded TO-probes revealed that the fluorescent oligonucleotide-thiazole orange complexes are common, only the distribution of the species varies with the character of the chain and the chirality at the internucleotidic phosphate site. Those TO-probes in which the isomeric structure of the phosphate-chain linkage is Rp, and therefore such that the fluorophore is directed toward the minor groove, have higher phifl values than the Sp isomer. Of the systems studied, thiazole orange linked by an alkyl chain to the internucleotidic phosphate (Rp isomer) has the highest phifl and the greatest fraction of the longest-lived fluorescent thiazole orange species (in the hybrid form). 相似文献
36.
Low-Temperature Synthesis of Oxyhalides, YOX (X = Cl, Br, I), as the Source of Impurity in the Preparation of Trihalides, YX3, via the Ammonium Halide Route. Analogy of YOCl and YSCl Ammonium halides, NH4X (X = Cl, Br, I), react with Y2O3 and Y2S3, respectively, at temperatures as low as 230=C (X = Cl), 280=C (Br), and 360=C (I) (molar ratio 12:1) to yield (NH4)3YX6, NH3, and H2O (H2S). The choice of smaller ratios than 12:1 (for example 2:1) results in the formation of oxyhalides, YOX, via the reaction of (NH4)3YX6 with surplus Y2O3. This reaction is therefore the actual source of impurity of rare-earth trihalides in their preparation via the ammonium halide routes. 相似文献
37.
Ternary Rare-Earth Halides of the A2MX5 Type (A = K, In, NH4, Rb, Cs; X = Cl, Br, I) Ternary rare-earth (=M) chlorides, bromides, and iodides In2MCl5, (NH4)2MCl5, Rb2MCl5, Cs2MCl5, CsRbMCl5, K2MBr5, Rb2MBr5, K2MI5, and Rb2MI5 have been synthesized. Single crystals of In2PrCl5, Rb2PrCl5, K2PrBr5, and K2PrI5 were grown and the structures refined. The other halides were characterized by x-ray powder patterns. They are isotypic either with K2PrCl5(orthorhombic, Pnma, Z = 4, hexagonal arrangement of chains of edge-connected polyhedra [PrX7]) or with Cs2DyCl5 (orthorhombic, Pbnm, Z = 4, hexagonal arrangement of cis-corner-connected octahedra [DyCl6]) which may be discriminated in structure field diagrams. The thermal expansion was investigated für Cs2LuCl5 and Rb2PrX5 (X = Cl, Br, I). 相似文献
38.
Jan Cocquyt Ulf Olsson Gerd Olofsson Paul Van der Meeren 《Colloid and polymer science》2005,283(12):1376-1381
Two endothermic transitions, at 36°C and 44°C, were observed with differential scanning calorimetry (DSC) upon heating dioctadecyldimethylammonium
bromide vesicle dispersions that were equilibrated below 15°C while in samples kept at 25°C there was only the transition
at 44°C, which was shown to be the gel to liquid–crystalline transition by 1H-NMR measurements. The transition at 36°C was reversed in an exothermic transition around 13°C upon cooling. The slowness
of this transition at ambient temperatures suggests that the presence of the transition at 36°C in a DSC upscan depends strongly
on the sample history. 相似文献
39.
Trimethylsilyl Derivatives of Vb Elements. VII. Crystal Structures of Lithium Bis(trimethylsilyl)bismuthide · DME and of Tetrakis(trimethylsilyl)dibismuthane as well as Some Comments on the Crystal Structure of Bis(4-methoxyphenyl)ditellane Colourless lithium bis(trimethylsilyl)bismuthide · DME 1 1,2-Dimethoxyethan (DME); Tetrahydrofuran (THF) 1 and green, metallic lustrous tetrakis(trimethylsilyl)dibismuthane 2 crystallize isotopic to their antimony homologues [1, 2]. As it is shown by crystal structure determinations { 1 : ?90°C; I 4 2d; a = 1017,3(4); c = 3738,0(26) pm; Z = 8; R w = 0,065; 2 : + 20°C; P2 1 /c; a = 680,9(4); b = 1704,8(13); c = 1197,9 (10) pm; β = 119,46(6)°; Z = 2; R w = 0,084} both compounds form chains which in the case of bismuthide 1 are built up as screws of alternating bismuth and lithium atoms; bonding further to two trimethylsilyl groups or to the chelating DME ligand both atoms gain coordination number 4 {Li? Bi 292(3); Bi? Si 263.3(14) pm; Bi? Li? Bi 132(1); Li? Bi? Li 148(1); φ(Li? Bi? Li? Bi) 83°}. In the case of dibismuthane 2 the centrosymmetric molecules are strung, their Bi-Bi groups forming nearly linear zigzag chains with shortened intermolecular contact distances {Bi-Bi 303.5(3); Bi …? Bi 380.4(3); Bi? Si 268 pm; Bi? Bi …? Bi 169; Bi? Bi? Si 97.4(5) and 92.0(5)°}. Structure and properties of 2 are compared with those of similar compounds; the crystal structure of brown, green metallic lustrous bis(4-methoxyphenyl)ditellane 5 already published by Ludlow and McCarthy[3] is reinvestigated with respect to very short intermolecular Te…?Te contacts. 相似文献
40.
Gerd Meyer 《无机化学与普通化学杂志》1981,478(7):39-51
Indium Sesquichloride, In2Cl3: a Pseudobinary, Mixed-valence Indium(I) Hexachloroindate(III) Colorless In2Cl3, obtained by reduction of InCl3 with metallic In, according to In[InIIICl6] a pseudobinary, mixed-valence indium(I) hexachloroindate(III), crystallizes orthorhombic (Pnma, Z = 32) with a = 1261.4(3), b = 2523.8(5), c = 1456.2(2) pm (Guinier-Simon data), Vm(In2Cl3) = 87.3 cm3 × mol?1. InIII occupies octahedral holes separated from each other (d?(InIII? Cl) = 251 pm). Coordination numbers of 7 to 11 are observed for InI (d?(InI? Cl) = 329–359 pm). In2Cl3 is isotypic with α-Tl2Cl3. 相似文献